= Higher cylinder powers available (customized)

Table 1. Currently available monofocal Toric Intraocular lenses

#### **2.1 IOL material**

268 Astigmatism – Optics, Physiology and Management

^ = Same IOL model under different name; \* = Highest cylinder powers are custom made; # = Higher cylinder powers available (customized)

Table 1. Currently available monofocal Toric Intraocular lenses

The IOL biomaterial is of great influence on the postoperative rotation of the IOL. Older toric IOL models such as the STAAR toric IOL (STAAR Surgical Company, Monrovia, California) and the MicroSil toric IOL (HumanOptics, Erlangen, Germany) were made of silicone materials and showed relatively high postoperative misalignment rates and often required surgical realignment. As visible in Table 1, currently available toric IOLs are usually made of acrylic material.

After implantation of the toric IOL in the capsular bag, the anterior and posterior capsules fuse with the IOL which prevents IOL rotation. Therefore, strong IOL adhesion to the capsular bag is thought to prevent IOL rotation. Several in vitro studies have examined the interactions between different IOL materials and the capsular bag. Lombardo et al. used

atomic force microscopy to determine IOL optic surface adhesiveness and found that hydrophobic acrylic IOLs showed the highest adhesive properties, followed by hydrophilic acrylic IOL, PMMA IOLs and finally silicone IOLs. (Lombardo, Carbone et al. 2009) In addition, Oshika et al. examined the adhesive forces between IOLs and bovine collagen sheets and demonstrated that acrylic IOLs formed the strongest adhesions to the capsular bag, followed by PMMA IOLs and silicone IOLs. (Oshika, Nagata et al. 1998) An animal study in which rabbits underwent phacoemulsification with IOL implantation confirmed the latter results. (Oshika, Nagata et al. 1998) Three weeks after IOL implantation, acrylic IOLs showed the strongest adhesions with the capsular bag, followed by PMMA and silicone IOLs.

Linnola et al. hypothesize that IOL materials show differences in IOL adhesion due to a different affinity to proteins in the capsular bag. (Linnola, Sund et al. 2003) Extracellular matrix proteins, such as fibronectins, vitronection and collagen type IV, may be involved in IOL adhesion to the capsular bag. According to Linnola et al., these proteins are present in plasma but also available in the aqueous humor after cataract surgery due to break down of the blood-aqueous barrier. (Linnola, Sund et al. 2003) In an in vitro study in which different IOLs were incubated for 1 week with extracellular matrix proteins, each IOL material was found to have a different affinity to these proteins. (Linnola, Sund et al. 2003) Fibronectin bound significantly better to hydrophobic acrylic IOLs, whereas collagen type IV bound significantly better to hydrophilic acrylic IOLs and vitronectin to silicone IOLs. A histological study using human pseudophakic autopsy eyes also showed that fibronectin was the primary protein between acrylic IOLs and the capsular bag. (Linnola, Werner et al. 2000) In addition, acrylic IOLs explanted from human autopsy eyes contained significantly more fibronectin and vitronectin compared to silicone or PMMA eyes. (Linnola, Werner et al. 2000) These results indicate that different IOL materials use different proteins to bind to the capsular bag and that acrylic IOLs generally form the strongest adhesions with the capsular bag.

#### **2.2 IOL design**

The IOL design is of interest in avoiding postoperative IOL rotation and achieving good postoperative outcomes. The overall IOL diameter has been shown to be a major factor in the prevention of IOL rotation. (Chang 2003) Chang et al. compared two different sizes of the same toric IOL: the STAAR AA4203TF model with a diameter of 10.8 mm and the STAAR AA4203 TL model with a diameter of 11.2 mm. The longer STAAR model was found to have a much better rotational stability compared to the shorter STAAR model. Currently available toric IOLs however have a total IOL diameter ranging from 11.0 mm to 13.0 mm (Table 1), which has been shown to be effective in avoiding IOL rotation. (Ahmed, Rocha et al. 2010; Alio, Agdeppa et al. 2010; Holland, Lane et al. 2010; Entabi, Harman et al. 2011)

Regarding the IOL haptics design, two different IOL designs are available: plate haptic IOLs, such as the Acri.Comfort and STAAR toric IOLs, and loop haptic IOLs, such as Acrysof and Rayner T-flex toric IOLs (Figure 1). Buckhurst et al. hypothesize that loop haptic IOLs have a better early rotational stability compared to plate haptic IOLs due to the longer haptics and consequently more contact between haptics and capsular bag. (Buckhurst, Wolffsohn et al. 2010) Plate haptics, however, are thought to be less susceptible to the compression of the capsular bag, which may prevent late IOL rotation. (Patel, Ormonde et al. 1999) Patel et al. compared the early (2 weeks) and late (2 weeks to 6 months) rotation of plate and loop haptic silicone IOLs in a randomised study. (Patel, Ormonde et al. 1999) Even though early postoperative rotation were comparable, late postoperative rotation was significantly higher in loop haptic IOLs compared to plate haptic IOLs: 6.8 degrees versus 0.6 degrees, respectively. However, Prinz et al. recently compared plate-haptic and loop-haptic acrylic

Fig. 1. Currently available loop haptic (**A**) and plate haptic (**B**) toric intraocular lenses (IOLs).

IOLs and did not find a significant difference in early and late rotation. (Prinz, Neumayer et al. 2011) Since both the plate and loop haptic IOLs in this study were made of acrylic material, it is possible that adhesion of the acrylic IOL to the capsular bag prevented postoperative rotation. This indicates that for acrylic IOLs, plate and loop haptics demonstrate equally good rotational stability.

## **3. Patient selection**

270 Astigmatism – Optics, Physiology and Management

which has been shown to be effective in avoiding IOL rotation. (Ahmed, Rocha et al. 2010;

Regarding the IOL haptics design, two different IOL designs are available: plate haptic IOLs, such as the Acri.Comfort and STAAR toric IOLs, and loop haptic IOLs, such as Acrysof and Rayner T-flex toric IOLs (Figure 1). Buckhurst et al. hypothesize that loop haptic IOLs have a better early rotational stability compared to plate haptic IOLs due to the longer haptics and consequently more contact between haptics and capsular bag. (Buckhurst, Wolffsohn et al. 2010) Plate haptics, however, are thought to be less susceptible to the compression of the capsular bag, which may prevent late IOL rotation. (Patel, Ormonde et al. 1999) Patel et al. compared the early (2 weeks) and late (2 weeks to 6 months) rotation of plate and loop haptic silicone IOLs in a randomised study. (Patel, Ormonde et al. 1999) Even though early postoperative rotation were comparable, late postoperative rotation was significantly higher in loop haptic IOLs compared to plate haptic IOLs: 6.8 degrees versus 0.6 degrees, respectively. However, Prinz et al. recently compared plate-haptic and loop-haptic acrylic

Fig. 1. Currently available loop haptic (**A**) and plate haptic (**B**) toric intraocular lenses

(IOLs).

Alio, Agdeppa et al. 2010; Holland, Lane et al. 2010; Entabi, Harman et al. 2011)

## **3.1 Monofocal toric IOLs**

## **3.1.1 Minimal astigmatism**

Achieving success with toric IOLs depends on the selection of suitable patients. Depending on the toric IOL model, the minimal available toric IOL power at the IOL plane is 1.0 D for the Acri.Comfort or Rayner toric IOLs and 1.5 D for the AcrySof toric IOLs (Table 1). At the corneal plane, this corresponds to a minimal corneal power of approximately 0.75 to 1.00 D, respectively. Taking into consideration the amount of astigmatism induced by the surgery, patients must have a corneal astigmatism of at least 1.00 to 1.25 D in order to be candidates for a toric IOL.

## **3.1.2 Corneal astigmatism**

Patients with regular bow-tie astigmatism are most suitable for toric IOL implantation. Corneal topography is therefore important for detecting irregular astigmatism and keratoconus. Two systems are available to perform corneal topography: placido-disk videokeratoscopy and Scheimpflug imaging. Even though measurements of corneal curvature obtained with both systems show moderate to good correlations, important differences exist between these two systems that may be relevant in toric IOL candidates. (Savini, Barboni et al. 2009; Symes, Say et al. 2010) A Placido-disk videokeratoscope reconstructs a curvature description of the anterior surface of the cornea based on the reflections of light-emitting Placido rings. (Jongsma, De Brabander et al. 1999) However, this does not reflect the corneal shape since it does not include information about the posterior corneal surface and the corneal thickness. (Belin and Khachikian 2009) Some corneal ectatic disorders, such as keratoconus, present with changes on the posterior corneal surface before any changes may be seen on the anterior corneal surface. (Tomidokoro, Oshika et al. 2000; Belin and Khachikian 2009) Furthermore, Placido-disk videokeratoscopy only gathers data from the central 8 to 9 mm of the cornea, which limits the detection of peripheral pathologies, such as pellucid marginal degeneration. (Walker, Khachikian et al. 2008)

Elevation-based topography uses a rotating Scheimpflug camera to capture cross sectional images of the anterior segment, which are then merged into a 3-dimensional reconstruction of the cornea, anterior chamber, iris and lens. This allows to evaluate the entire corneal surface (limbus to limbus) and allows for evaluation of the posterior corneal surface. Before conducting corneal topography or ocular biometry, ensure that the patient has refrained from contact lens wear for an appropriate time. Soft contact lenses should be discontinued for at least 1 week and hard contact lenses for approximately 2 weeks.

#### **3.1.3 Other considerations**

Other pre-existent ocular pathologies may be a contraindication for toric IOL implantation. Patients with Fuchs' endothelial dystrophy or a different corneal dystrophy might need a keratoplasty in the future and are therefore not good candidates for toric IOL implantation. Patients with potential bag instability like patients with pseudoexfoliation syndrome or trauma induced zonulolysis are also bad candidates.

## **3.2 Multifocal toric IOLs**

Patient selection is crucial for achieving success with multifocal toric IOLs. The first step is to determine if the patient is a suitable candidate for a multifocal IOL. The ideal patient is motivated about achieving spectacle independency for both distance and near vision, understands the limitations of multifocal IOLs and has realistic expectations. (Assil, Christian et al. 2008)

The second step is to determine possible ocular co-morbidities. Multifocal IOLs split the available light between distance and near focus. Therefore, ocular co-morbidities that affect the visual acuity or the quality of vision are a relative or absolute contraindication for multifocal toric IOLs. These include amblyopia, corneal pathology (such as keratoconus, corneal scar or Fuchs' endothelial dystrophy), maculopathy (such as macular degeneration or diabetic retinopathy), glaucoma and uveitis. (Assil, Christian et al. 2008; Kohnen, Kook et al. 2008) An extensive preoperative ophthalmic examination is therefore required, including corneal topography, endothelial cell count, ophthalmoscopy and preferably optical coherence tomography.

## **4. IOL calculation**

#### **4.1 Keratometry**

Accurate keratometry measurements must be obtained to ensure successful astigmatism correction with toric IOLs. Clinical studies on toric IOLs describe various methods of keratometry: IOLMaster automated keratometry, manual keratometry, autokeratorefractometry, corneal topography, or a combination of these techniques. (Bauer, de Vries et al. 2008; Chang 2008; Dardzhikova, Shah et al. 2009; Ahmed, Rocha et al. 2010; Gayton and Seabolt 2010; Holland, Lane et al. 2010) Keratometry measurements obtained by automated keratometry, manual keratometry and corneal topography have been shown to have a high repeatability and are generally well comparable between devices. (Santodomingo-Rubido, Mallen et al. 2002; Findl, Kriechbaum et al. 2003; Elbaz, Barkana et al. 2007; Shirayama, Wang et al. 2009) However, differences between devices have been reported, indicating that keratometry values should not be used interchangeably. (Santodomingo-Rubido, Mallen et al. 2002; Elbaz, Barkana et al. 2007; Shirayama, Wang et al. 2009)

## **4.2 Surgically induced astigmatism**

Another important aspect to consider in toric IOL calculation is the amount of astigmatism induced by the surgery itself. The expected amount of surgically induced astigmatism (SIA) has to be incorporated into the toric IOL power in order to select the most appropriate toric IOL model. (Hill 2008) However, the exact amount of SIA is difficult to predict and depends on several factors. The location of the incision is an important factor to consider, since corneal incisions lead to flattening of the incised meridian. An incision at the steep meridian of the cornea will flatten this meridian and will result in steepening of the orthogonal meridian due to the coupling (flattening/steepening) effect, which will reduce overall corneal astigmatism. (Borasio, Mehta et al. 2006) Consequently, an incision located at the flat meridian will increase overall corneal astigmatism. Furthermore, temporal incisions have

Patients with potential bag instability like patients with pseudoexfoliation syndrome or

Patient selection is crucial for achieving success with multifocal toric IOLs. The first step is to determine if the patient is a suitable candidate for a multifocal IOL. The ideal patient is motivated about achieving spectacle independency for both distance and near vision, understands the limitations of multifocal IOLs and has realistic expectations. (Assil,

The second step is to determine possible ocular co-morbidities. Multifocal IOLs split the available light between distance and near focus. Therefore, ocular co-morbidities that affect the visual acuity or the quality of vision are a relative or absolute contraindication for multifocal toric IOLs. These include amblyopia, corneal pathology (such as keratoconus, corneal scar or Fuchs' endothelial dystrophy), maculopathy (such as macular degeneration or diabetic retinopathy), glaucoma and uveitis. (Assil, Christian et al. 2008; Kohnen, Kook et al. 2008) An extensive preoperative ophthalmic examination is therefore required, including corneal topography, endothelial cell count, ophthalmoscopy and preferably optical

Accurate keratometry measurements must be obtained to ensure successful astigmatism correction with toric IOLs. Clinical studies on toric IOLs describe various methods of keratometry: IOLMaster automated keratometry, manual keratometry, autokeratorefractometry, corneal topography, or a combination of these techniques. (Bauer, de Vries et al. 2008; Chang 2008; Dardzhikova, Shah et al. 2009; Ahmed, Rocha et al. 2010; Gayton and Seabolt 2010; Holland, Lane et al. 2010) Keratometry measurements obtained by automated keratometry, manual keratometry and corneal topography have been shown to have a high repeatability and are generally well comparable between devices. (Santodomingo-Rubido, Mallen et al. 2002; Findl, Kriechbaum et al. 2003; Elbaz, Barkana et al. 2007; Shirayama, Wang et al. 2009) However, differences between devices have been reported, indicating that keratometry values should not be used interchangeably. (Santodomingo-Rubido, Mallen et al. 2002; Elbaz, Barkana et al. 2007;

Another important aspect to consider in toric IOL calculation is the amount of astigmatism induced by the surgery itself. The expected amount of surgically induced astigmatism (SIA) has to be incorporated into the toric IOL power in order to select the most appropriate toric IOL model. (Hill 2008) However, the exact amount of SIA is difficult to predict and depends on several factors. The location of the incision is an important factor to consider, since corneal incisions lead to flattening of the incised meridian. An incision at the steep meridian of the cornea will flatten this meridian and will result in steepening of the orthogonal meridian due to the coupling (flattening/steepening) effect, which will reduce overall corneal astigmatism. (Borasio, Mehta et al. 2006) Consequently, an incision located at the flat meridian will increase overall corneal astigmatism. Furthermore, temporal incisions have

trauma induced zonulolysis are also bad candidates.

**3.2 Multifocal toric IOLs** 

Christian et al. 2008)

coherence tomography.

**4. IOL calculation 4.1 Keratometry** 

Shirayama, Wang et al. 2009)

**4.2 Surgically induced astigmatism** 

been shown to induce less SIA compared to superior incisions. (Tejedor and Murube 2005) This is possibly due to a higher incidence of against-the rule astigmatism in the elderly cataract population or due to a more peripheral location of the temporal incision on the cornea. (Fledelius and Stubgaard 1986; Kohnen, Dick et al. 1995) The size of the incision has also been shown to influence the amount of SIA: smaller incisions generally produce less SIA. (Kohnen, Dick et al. 1995) Other factors that are of influence are the amount of preoperative corneal astigmatism, suture use and patients' age. (Storr-Paulsen, Madsen et al. 1999) Developments in phacoemulsification techniques have led to an improved management of SIA. The shift to smaller incisions has reduced the need for suturing, thus decreasing SIA. In addition, the recent development of microincisional cataract surgery, surgery performed throught incisions smaller than 2.0 mm, aims to further reduce the SIA.

Many studies have measured the amount of SIA following cataract surgery with incision sizes ranging from less than 2 mm up to 3.4 mm. However, it is difficult to compare these studies, because they use variable incision locations and sizes and variable follow-up durations. STAAR and MicroSil toric IOLs require a 2.8 and 3.4 mm incision for IOL implantation, respectively (Table 1). Incision sizes of 2.8 to 3.2 mm have been shown to induce a SIA of 0.4 to 0.8 D for temporal incisions, 0.6 D for superior incisions and 0.9 to 1.2 D for on-axis incisions. (Alio, Rodriguez-Prats et al. 2005; Borasio, Mehta et al. 2006; Moon, Mohamed et al. 2007; Morcillo-Laiz, Zato et al. 2009; Wang, Zhang et al. 2009) Acrysof toric IOLs require a 2.2 mm incision for IOL implantation. These incisions have been shown to induce a SIA of 0.2 to 0.3 D for temporal incisions and 0.4 D for superior incisions. (Lee, Kwon et al. 2009; Wang, Zhang et al. 2009; Visser, Ruiz-Mesa et al. 2011) Finally, Acri.Lisa and Rayner toric IOLs may be implanted through sub 2.0 mm incisions. Microincision cataract surgery has been shown to result in a SIA of approximately 0.3 D for temporal incisions, 0.5 D for superior incisions and 0.4 D for on-axis incisions. (Alio, Rodriguez-Prats et al. 2005; Kaufmann, Krishnan et al. 2009; Lee, Kwon et al. 2009; Morcillo-Laiz, Zato et al. 2009) In practice, the most accurate method to determine the SIA is for every surgeon to personalize the amount of SIA induced by cataract surgery in his/her patient population. This may be done by analysing preoperative and postoperative corneal astigmatism changes using a standard vector analysis. (Alpins 2001; Holladay, Moran et al. 2001)

#### **5. IOL implantation**

#### **5.1 Marking techniques**

Crucial to the efficacy of toric IOLs is exact alignment of the toric IOL at the calculated alignment axis. Accurate marking of the alignment axis should be performed with the patient in an upright position in order to prevent cyclotorision in the supine position. Cyclotorsion of the eye from the upright to supine position is approximately 2 to 4 degrees on average, but can be up to 15 degrees in individual patients. (Arba-Mosquera, Merayo-Lloves et al. 2008; Chang 2008; Febbraro, Koch et al. 2010) Cyclotorsion is a well known aspect in refractive surgery and compensated for during laser refractive surgery. (Febbraro, Koch et al. 2010)

Most clinical studies on toric IOLs describe using a 3-step marking procedure for toric IOL implantation. The first step consists of preoperative limbal marking of the horizontal axis of the eye with the patient sitting upright to correct for cyclotorsion. This may be done with the patient seated at the slitlamp and with a coaxial thin slit turned to 0-180 degrees. (Mendicute, Irigoyen et al. 2008; Alio, Agdeppa et al. 2010; Koshy, Nishi et al. 2010) The limbus is than marked at the horizontal position with either a sterile ink pen or a needle. Another technique to mark the horizontal axis is by using a bubble-marker, such as a Nuijts/Lane Toric Reference Marker (ASICO) (Figure 2) or a Bakewell BubbleLevel (Mastel Precision, Rapid City, US), or by using a gravity marker with a calibrated horizontal position, such as the LRI Gravity Marker (Rumex, Sint Petersburg, Florida, US). (Bauer, de Vries et al. 2008; Ahmed, Rocha et al. 2010; Gayton and Seabolt 2010) Intraoperatively, the preoperative horizontal marks are used to position an angular graduation instrument. The actual alignment axis is marked using a toric axis marker.

Fig. 2. Preoperative marking of the horizontal axis of the eye using the Nuijts/Lane Toric Reference Marker with bubble-level (ASICO). This is done with the patient sitting upright to correct for cyclotorsion.

One study has evaluated the accuracy of a 3-step marking procedure for toric IOL implantation. (Visser, Berendschot et al. 2011) The mean errors in horizontal axis marking, alignment axis marking and toric IOL alignment were 2.4 ± 0.8 (maximum 8.7) degrees, 3.3 ± 2.0 (maximum 7.7) degrees and 2.6 ± 2.6 (maximum 10.5) degrees, respectively. Together, these 3 errors led to a mean total error in toric IOL alignment of 4.9 ± 2.1 degrees. However, for the individual patient, this may be as high as 10 degrees. This indicates that great accuracy in toric IOL alignment is necessary in all patients in order to achieve the most optimal astigmatism correction with toric IOLs.

Currently, new techniques have become available to ensure accurate intraoperative alignment of toric IOLs. Osher has described an iris-fingerprinting technique, in which preoperative detailed images of the eye are obtained. (Osher 2010) The desired alignment axis is drawn in this image. A printout of this image is than used during surgery to align the toric IOL based on iris characteristics. A second technique to accurately align toric IOLs is by intraoperative wavefront aberrometry (ORange, WaveTec Vision Systems). This device is connected to the operating microscope and enables intraoperative measurement of residual refraction. (Packer 2010) It allows to accurately position toric IOLs, based on actual residual refractive cylinder results. A third device, the SG3000 (Sensomotoric Instruments, Teltow, Germany) uses real-time eye-tracking, based on iris and blood vessel characteristics. (Visser, Berendschot et al. 2011) Preoperatively, a detailed image of the eye is captured, in which blood vessel and iris characteristics are visible. Simultaneously, keratometry is performed and the location of the steep and flat corneal meridians are shown in this image. Intraoperatively, the preoperative image is matched with the live surgery-image from the operating microscope, based on blood vessel and iris characteristics. Using a microscope embedded display, the overlay showing the desired alignment axis is visible in the operating microscope, allowing exact alignment of the toric IOL. In addition, this eyetracking technology may also be used for other aspects in lens implantation surgery, including planning of the incisions and capsulorrhexis and optimal centration of multifocal IOLs.

## **5.2 Surgery**

274 Astigmatism – Optics, Physiology and Management

limbus is than marked at the horizontal position with either a sterile ink pen or a needle. Another technique to mark the horizontal axis is by using a bubble-marker, such as a Nuijts/Lane Toric Reference Marker (ASICO) (Figure 2) or a Bakewell BubbleLevel (Mastel Precision, Rapid City, US), or by using a gravity marker with a calibrated horizontal position, such as the LRI Gravity Marker (Rumex, Sint Petersburg, Florida, US). (Bauer, de Vries et al. 2008; Ahmed, Rocha et al. 2010; Gayton and Seabolt 2010) Intraoperatively, the preoperative horizontal marks are used to position an angular graduation instrument. The

Fig. 2. Preoperative marking of the horizontal axis of the eye using the Nuijts/Lane Toric Reference Marker with bubble-level (ASICO). This is done with the patient sitting upright to

One study has evaluated the accuracy of a 3-step marking procedure for toric IOL implantation. (Visser, Berendschot et al. 2011) The mean errors in horizontal axis marking, alignment axis marking and toric IOL alignment were 2.4 ± 0.8 (maximum 8.7) degrees, 3.3 ± 2.0 (maximum 7.7) degrees and 2.6 ± 2.6 (maximum 10.5) degrees, respectively. Together, these 3 errors led to a mean total error in toric IOL alignment of 4.9 ± 2.1 degrees. However, for the individual patient, this may be as high as 10 degrees. This indicates that great accuracy in toric IOL alignment is necessary in all patients in order to achieve the most

Currently, new techniques have become available to ensure accurate intraoperative alignment of toric IOLs. Osher has described an iris-fingerprinting technique, in which preoperative detailed images of the eye are obtained. (Osher 2010) The desired alignment axis is drawn in this image. A printout of this image is than used during surgery to align the toric IOL based on iris characteristics. A second technique to accurately align toric IOLs is by

actual alignment axis is marked using a toric axis marker.

correct for cyclotorsion.

optimal astigmatism correction with toric IOLs.

A standard phacoemulsification technique may be performed with a 1.5 to 3.4 mm limbal incision, depending on the toric IOL model to be implanted (Table 1). A well centered capsulorrhexis with 360 degree overlap of the IOL optics should be achieved. The optic diameter is 6.0 mm for Acrysof, Acri.lisa, MicroSil and STAAR toric IOLs and 5.75 or 6.25 mm for Rayner toric IOLs. The ideal capsulorrhexis diameter is therefore 5.0 to 5.5 mm.

After the phacoemulsification is completed and the ophthalmic viscosurgical device is injected, the foldable toric IOL is inserted through the limbal incision. The marks on the toric IOL indicate the flat meridian or plus cylinder axis of the toric IOL and should be aligned with the marked alignment axis. First, gross alignment is achieved by rotating the IOL clockwise while it is unfolding, until approximately 20 to 30 degrees short of the desired position. After the ophthalmic viscosurgical device is removed, the IOL is rotated to its final position by exact alignment of the reference marks on the toric IOL with the limbal axis marks.

In the event of a complication during surgery that might compromise the stability of the toric IOL, such as zonular damage, vitreous loss, capsulorrhexis tear, or capsular rupture, conversion to a standard non-toric IOL may be required.

#### **5.3 Postoperative axis measurement**

Postoperatively, the orientation axis of the toric IOL must be verified to confirm optimal alignment and ensure no postoperative IOL rotation has occurred. Postoperative assessment of toric IOL alignment can be achieved by several methods. The most commonly used method in the clinic is assessment using a sliltlamp with rotating slit. Since the IOL marks are located at the periphery of the IOL optic, full mydriasis of the pupil is required. An objective method to determine postoperative toric IOL alignment is by wavefront aberrometry (Figure 3). (Carey, Leccisotti et al. 2010) Combined wavefront aberrometers and corneal topographers, such as the Keratron Onda (Optikon, Rome, Italy), iTrace (Tracey Technologies, Houston, TX, USA) and OPD-scan (Nidek, Gamagori, Japan), discriminate between aberrations caused by the cornea and by the internal ocular system. (Carey, Leccisotti et al. 2010; Visser, Berendschot et al. 2010) This method therefore directly determines the orientating of the toric IOL. Pupil dilation is not required.

Fig. 3. Combined wavefront aberrometery and corneal topography allows to objectively determine the postoperative orientation of the toric intraocular lens axis. In this example, Corneal wavefront aberrometry (**A**) and Ocular wavefront aberrometry (**B**) were performed using the Keratron Onda (Optikon, Rome). The Internal aberrations (**C**) are calculated by subtracting the Corneal aberrations from the Ocular aberrations. In this example, corneal astigmatism was -2.09 diopters (D) at 156 degrees and ocular astigmatism was -0.26 D at 103 degrees. The internal astigmatism was -2.18 D at 70 degrees, which indicates that the toric intraocular lens axis is located at 70 degrees.

Realignment of a rotated toric IOL should ideally be performed as soon as possible and preferably before 2 weeks postoperatively because of the formation of adhesions between the capsular bag and IOL optics. (Linnola, Sund et al. 2003; Chang 2009)

#### **6. Clinical outcomes**

276 Astigmatism – Optics, Physiology and Management

Fig. 3. Combined wavefront aberrometery and corneal topography allows to objectively determine the postoperative orientation of the toric intraocular lens axis. In this example, Corneal wavefront aberrometry (**A**) and Ocular wavefront aberrometry (**B**) were performed using the Keratron Onda (Optikon, Rome). The Internal aberrations (**C**) are calculated by subtracting the Corneal aberrations from the Ocular aberrations. In this example, corneal astigmatism was -2.09 diopters (D) at 156 degrees and ocular astigmatism was -0.26 D at 103 degrees. The internal astigmatism was -2.18 D at 70 degrees, which indicates that the toric

intraocular lens axis is located at 70 degrees.

#### **6.1 Monofocal toric IOLs**

Table 2 provides an overview of the main outcomes of clinical studies on toric IOLs. In order to compare the visual outcomes, LogMAR values have been converted into Snellen values.

#### **6.1.1 Visual outcomes**

One randomized clinical trial has been conducted on toric IOLs. Holland et al. included 517 patients: 256 patients received unilateral implantation of an Acrysof toric IOL (T3, T4 or T5) and 261 patients received unilateral implantion with a spherical control IOL. (Holland, Lane et al. 2010) One year postoperatively, significantly more patients in the toric group achieved an UDVA of 20/40 or better compared to the control group: 92% versus 81% of patients, respectively. Furthermore, an UDVA of 20/20 or better was achieved in significantly more patients with a toric IOL compared to a control IOL ( 41% versus 19% of patients). As expected, the CDVA results in both groups were comparable: 93% of toric and 90% of control patients achieved a CDVA of 20/25 or better. Ahmed at al. have conducted a large non-randomized cohort study to evaluate bilateral AcrySof toric IOL (T3, T4 or T5) implantation in 117 patients (234 eyes). At 6 months postoperatively, 99% of patients had a bilateral UDVA of 20/40 or better and 63% of 20/20 or better. The mean binocular UDVA was 0.05 ± 0.11 LogMAR, equivalent to 0.89 ± 0.23 Snellen. In addition, the binocular CDVA was 0.03 ± 0.14 LogMAR, equivalent to 0.93 ± 0.30 Snellen. Many smaller non-randomized studies on Acrysof toric IOLs have been performed. (Bauer, de Vries et al. 2008; Chang 2008; Mendicute, Irigoyen et al. 2008; Zuberbuhler, Signer et al. 2008; Dardzhikova, Shah et al. 2009; Lane, Ernest et al. 2009; Ruiz-Mesa, Carrasco-Sanchez et al. 2009; Statham, Apel et al. 2009; Gayton and Seabolt 2010; Kim, Chung et al. 2010; Koshy, Nishi et al. 2010; Tsinopoulos, Tsaousis et al. 2010; Visser, Ruiz-Mesa et al. 2011) The majority of these studies examined the T3 to T5 toric IOLs, with low to moderately high cylinder powers. Most studies show a mean postoperative UDVA ranging from 0.63 to 0.90 Snellen. (Bauer, de Vries et al. 2008; Mendicute, Irigoyen et al. 2008; Ruiz-Mesa, Carrasco-Sanchez et al. 2009; Statham, Apel et al. 2009; Gayton and Seabolt 2010; Koshy, Nishi et al. 2010) An UDVA of 20/40 or better was reported in 81 to 95% of eyes. (Bauer, de Vries et al. 2008; Mendicute, Irigoyen et al. 2008; Dardzhikova, Shah et al. 2009; Gayton and Seabolt 2010) In addition, 26 to 36% of eyes achieved an UDVA of 20/20 or better. (Bauer, de Vries et al. 2008; Dardzhikova, Shah et al. 2009; Ruiz-Mesa, Carrasco-Sanchez et al. 2009; Gayton and Seabolt 2010) The reported BDVA ranges from 0.79 to 1.01. (Bauer, de Vries et al. 2008; Mendicute, Irigoyen et al. 2008; Zuberbuhler, Signer et al. 2008; Ruiz-Mesa, Carrasco-Sanchez et al. 2009; Gayton and Seabolt 2010; Kim, Chung et al. 2010) One study has examined the high cylinder toric IOLs (T6 to T9) and showed a mean UDVA of 0.61 ± 0.26 and an UDVA of 20/40 or better in 83% of eyes. (Visser, Ruiz-Mesa et al. 2011) In order to determine how effective toric IOLs are in achieving the maximal visual outcome, we have calculated the visual potential index (VPI), which is defined as the ratio of postoperative UDVA to postoperative CDVA. (Visser, Ruiz-Mesa et al. 2011) For the Acrysof toric IOL, the VPI in the majority of studies ranged between 73 and 96%. This indicates that the uncorrected visual outcome with this IOL is 73 to 96% of the maximal visual outcome.

Rayner T-flex toric IOL implantation has been evaluated in two relatively small studies. (Stewart and McAlister 2010; Entabi, Harman et al. 2011) Entabi et al. evaluated Rayner toric IOL implantation in 33 eyes with a mean corneal astigmatism of 2.94 ± 0.89 D. (Entabi, Harman et al. 2011) Four months postoperatively, the mean UDVA was 0.28 ± 0.23 LogMAR, equivalent to 0.52 ± 0.28 Snellen. Stewart et al. evaluated T-flex toric IOL implantation in 14 eyes. (Stewart and McAlister 2010) Over 90% of eyes achieved an UDVA of 20/40 or better and the mean UDVA was 0.16 ± 0.16 LogMAR, equivalent to 0.69 ± 0.25 Snellen. The VPI in both studies was 80 and 91%. (Stewart and McAlister 2010; Entabi, Harman et al. 2011)

One study has examined visual outcomes following Acri.Comfort toric implantation in 21 eyes of 12 patients with moderate to high astigmatism. (Alio, Agdeppa et al. 2010) The mean preoperative corneal astigmatism was 3.73 ± 1.79 D.

At 3 months postoperatively, the mean UDVA was 0.65 ± 0.22 and 76% of eyes achieved an UDVA of 20/40 or better. The mean postoperative CDVA was 0.85 ± 0.15 and the VPI was 76%.

Several studies have evaluated the visual outcomes following silicone toric IOL implantation. Microsil toric IOL implantation has been shown to result in an UDVA of 20/40 or better in 68 to 85% of eyes. (De Silva, Ramkissoon et al. 2006; Dick, Krummenauer et al. 2006) In addition, the mean postoperative UDVA and BDVA were 0.63 ± 0.22 and 0.76 ± 0.19, respectively. (De Silva, Ramkissoon et al. 2006) Studies using STAAR toric IOLs have shown an UDVA of 20/40 or better in 66 to 84% of eyes and a mean UDVA ranging from 0.54 to 0.62. (Ruhswurm, Scholz et al. 2000; Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002; Chang 2003) The VPI was 83% for MicroSil toric IOLs and 66 to 68% for STAAR toric IOLs. (Ruhswurm, Scholz et al. 2000; Leyland, Zinicola et al. 2001; De Silva, Ramkissoon et al. 2006)

#### **6.1.2 Refractive outcomes**

The randomized controlled trial on Acrysof toric IOLs has shown a significantly better refractive cylinder outcome in patients implanted with a toric IOL compared to patients with a monofocal IOL: 88% of eyes with a toric IOL achieved an residual refractive cylinder of 1.00 D or less, compared to 48% of eyes in the control group. Fifty-three percent of patients with a toric IOL achieved a residual refractive cylinder of 0.5 D or less. In addition, the mean residual refractive cylinder in the toric group was significantly lower compared to the control group (-0.59 D versus -1.22 D, respectively). Other studies on Acrysof toric IOLs show a residual refractive cylinder of 1.00 D or less in about 80 to 100% of eyes and a mean residual refractive cylinder ranging from -0.28 to -0.75 D. (Ahmed, Rocha et al. 2010; Kim, Chung et al. 2010; Visser, Ruiz-Mesa et al. 2011)

After Rayner toric IOL implantation, the mean residual refractive cylinder has been shown to range from -0.89 to -0.95 D. (Stewart and McAlister 2010; Entabi, Harman et al. 2011) Acri.Comfort toric IOL implantation resulted in a mean residual refractive cylinder of –0.45 ± 0.63. (Alio, Agdeppa et al. 2010) Furthermore, based on a vector analysis of the refractive outcomes, the Acri.Comfort IOL has been shown to correct 91% of pre-existing astigmatism. (Alio, Agdeppa et al. 2010) (Ruhswurm, Scholz et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002)


N = number of eyes; FU = follow-up; SD = standard deviation; D = dioptres; ° = degrees; % = percentage; UDVA = uncorrected distance visual acuity; BDVA = best-corrected distance visual acuity; VPI = visual potential index; RCT = randomised controlled trial; PCS = prospective cohort study; RS = retrospective study; \* = converted from LogMAR to Snellen; ^= obtained by wavefront abberometry

Table 2. Literature on monofocal toric IOLs

278 Astigmatism – Optics, Physiology and Management

studies ranged between 73 and 96%. This indicates that the uncorrected visual outcome with

Rayner T-flex toric IOL implantation has been evaluated in two relatively small studies. (Stewart and McAlister 2010; Entabi, Harman et al. 2011) Entabi et al. evaluated Rayner toric IOL implantation in 33 eyes with a mean corneal astigmatism of 2.94 ± 0.89 D. (Entabi, Harman et al. 2011) Four months postoperatively, the mean UDVA was 0.28 ± 0.23 LogMAR, equivalent to 0.52 ± 0.28 Snellen. Stewart et al. evaluated T-flex toric IOL implantation in 14 eyes. (Stewart and McAlister 2010) Over 90% of eyes achieved an UDVA of 20/40 or better and the mean UDVA was 0.16 ± 0.16 LogMAR, equivalent to 0.69 ± 0.25 Snellen. The VPI in both studies was 80 and 91%. (Stewart and McAlister 2010; Entabi,

One study has examined visual outcomes following Acri.Comfort toric implantation in 21 eyes of 12 patients with moderate to high astigmatism. (Alio, Agdeppa et al. 2010) The mean

At 3 months postoperatively, the mean UDVA was 0.65 ± 0.22 and 76% of eyes achieved an UDVA of 20/40 or better. The mean postoperative CDVA was 0.85 ± 0.15 and the VPI was

Several studies have evaluated the visual outcomes following silicone toric IOL implantation. Microsil toric IOL implantation has been shown to result in an UDVA of 20/40 or better in 68 to 85% of eyes. (De Silva, Ramkissoon et al. 2006; Dick, Krummenauer et al. 2006) In addition, the mean postoperative UDVA and BDVA were 0.63 ± 0.22 and 0.76 ± 0.19, respectively. (De Silva, Ramkissoon et al. 2006) Studies using STAAR toric IOLs have shown an UDVA of 20/40 or better in 66 to 84% of eyes and a mean UDVA ranging from 0.54 to 0.62. (Ruhswurm, Scholz et al. 2000; Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002; Chang 2003) The VPI was 83% for MicroSil toric IOLs and 66 to 68% for STAAR toric IOLs. (Ruhswurm, Scholz et al. 2000; Leyland, Zinicola et al. 2001; De

The randomized controlled trial on Acrysof toric IOLs has shown a significantly better refractive cylinder outcome in patients implanted with a toric IOL compared to patients with a monofocal IOL: 88% of eyes with a toric IOL achieved an residual refractive cylinder of 1.00 D or less, compared to 48% of eyes in the control group. Fifty-three percent of patients with a toric IOL achieved a residual refractive cylinder of 0.5 D or less. In addition, the mean residual refractive cylinder in the toric group was significantly lower compared to the control group (-0.59 D versus -1.22 D, respectively). Other studies on Acrysof toric IOLs show a residual refractive cylinder of 1.00 D or less in about 80 to 100% of eyes and a mean residual refractive cylinder ranging from -0.28 to -0.75 D. (Ahmed, Rocha et al. 2010; Kim,

After Rayner toric IOL implantation, the mean residual refractive cylinder has been shown to range from -0.89 to -0.95 D. (Stewart and McAlister 2010; Entabi, Harman et al. 2011) Acri.Comfort toric IOL implantation resulted in a mean residual refractive cylinder of –0.45 ± 0.63. (Alio, Agdeppa et al. 2010) Furthermore, based on a vector analysis of the refractive outcomes, the Acri.Comfort IOL has been shown to correct 91% of pre-existing astigmatism. (Alio, Agdeppa et al. 2010) (Ruhswurm, Scholz et al. 2000; Leyland, Zinicola et al. 2001; Till,

this IOL is 73 to 96% of the maximal visual outcome.

preoperative corneal astigmatism was 3.73 ± 1.79 D.

Harman et al. 2011)

Silva, Ramkissoon et al. 2006)

**6.1.2 Refractive outcomes** 

Yoder et al. 2002)

Chung et al. 2010; Visser, Ruiz-Mesa et al. 2011)

76%.

Regarding the silicone toric IOL, the postoperative residual astigmatism ranged from -0.84 to -1.23 D. (Ruhswurm, Scholz et al. 2000; Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Chang 2003; De Silva, Ramkissoon et al. 2006; Dick, Krummenauer et al. 2006) About 70% of eyes implanted with a STAAR toric IOLs achieved a residual refractive cylinder of 1.0 D or less and approximately 50% achieved a residual refractive cylinder of 0.5 D or less. (Ruhswurm, Scholz et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002)

## **6.1.3 Spectacle independence**

Spectacle independence following toric IOL implantation has been reported in approximately 60% of patients implanted with a toric IOL, compared to 36% of patients implanted with a control IOL. (Holland, Lane et al. 2010) However, patients in this study only received unilateral toric IOL implantation. Lane et al. offered patients from the aforementioned study fellow-eye implantation with the same IOL (Acrysof toric IOL or Acrysof non-toric IOL), allowing bilateral examination of spectacle independence. (Lane, Ernest et al. 2009) Almost all patients (97%) with a toric IOL reported not using spectacles for distance vision, compared to half of the patients in the control group. Finally, Ahmed et al. examined spectacle use in bilaterally implanted patients and found that 69% of patients never used spectacles for distance vision. (Ahmed, Rocha et al. 2010)

## **6.1.4 Rotational stability**

Crucial to the efficacy of all toric IOLs is the position of the IOL with regards to the intended alignment axis, since every degree of misalignment leads to residual astigmatism. Misalignment of the IOL may be caused by two factors: inaccurate placement of the IOL and rotation of the IOL. Currently, a misalignment of more than 10 degrees is generally regarded as the indication for surgical repositioning.

Rotational stability used to be an issue in toric pseudophakic IOLs made of silicone material. For example, STAAR toric IOLs were found to have a high incidence of eyes with more than 10 degrees of IOL misalignment: 14 to 45% for the shorter TF model 10 to 14% for the longer TL model. (Ruhswurm, Scholz et al. 2000; Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002; Chang 2003) Consequently, this resulted in a high rate of surgical repositioning. (Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Chang 2003) MicroSil toric IOLs were more rotationally stable and showed a misalignment of more than 10 degrees in 2 to 10% of eyes. (De Silva, Ramkissoon et al. 2006; Dick, Krummenauer et al. 2006)

As shown in Table 2, acrylic toric IOLs are generally more rotationally stable than silicone IOLs. For the Acrysof toric IOLs, the mean postoperative misalignment is less than 4 degrees and a misalignment of more than 10 degrees is rare. (Bauer, de Vries et al. 2008; Chang 2008; Ahmed, Rocha et al. 2010; Holland, Lane et al. 2010)

In most clinical studies, the postoperative orientation of the toric IOL axis was measured via the slitlamp. Since this measuring reticule on the slitlamp uses 5 degree steps, it is not a very accurate method to determine postoperative IOL rotation. A few studies have used digital photography to examine the postoperative IOL rotation, which is more accurate. Weinand et al. obtained digital images immediately after Acrysof IOL implantation and again at 6 months postoperatively. (Weinand, Jung et al. 2007) Rotation of the eye was compensated for by matching images based on specific blood vessel characteristics. The mean postoperative IOL rotation of Acrysof IOLs was 0.9 degree, with a maximum of 1.8 degrees.

Regarding the silicone toric IOL, the postoperative residual astigmatism ranged from -0.84 to -1.23 D. (Ruhswurm, Scholz et al. 2000; Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Chang 2003; De Silva, Ramkissoon et al. 2006; Dick, Krummenauer et al. 2006) About 70% of eyes implanted with a STAAR toric IOLs achieved a residual refractive cylinder of 1.0 D or less and approximately 50% achieved a residual refractive cylinder of 0.5 D or less.

Spectacle independence following toric IOL implantation has been reported in approximately 60% of patients implanted with a toric IOL, compared to 36% of patients implanted with a control IOL. (Holland, Lane et al. 2010) However, patients in this study only received unilateral toric IOL implantation. Lane et al. offered patients from the aforementioned study fellow-eye implantation with the same IOL (Acrysof toric IOL or Acrysof non-toric IOL), allowing bilateral examination of spectacle independence. (Lane, Ernest et al. 2009) Almost all patients (97%) with a toric IOL reported not using spectacles for distance vision, compared to half of the patients in the control group. Finally, Ahmed et al. examined spectacle use in bilaterally implanted patients and found that 69% of patients

Crucial to the efficacy of all toric IOLs is the position of the IOL with regards to the intended alignment axis, since every degree of misalignment leads to residual astigmatism. Misalignment of the IOL may be caused by two factors: inaccurate placement of the IOL and rotation of the IOL. Currently, a misalignment of more than 10 degrees is generally regarded

Rotational stability used to be an issue in toric pseudophakic IOLs made of silicone material. For example, STAAR toric IOLs were found to have a high incidence of eyes with more than 10 degrees of IOL misalignment: 14 to 45% for the shorter TF model 10 to 14% for the longer TL model. (Ruhswurm, Scholz et al. 2000; Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002; Chang 2003) Consequently, this resulted in a high rate of surgical repositioning. (Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Chang 2003) MicroSil toric IOLs were more rotationally stable and showed a misalignment of more than 10 degrees in 2 to 10% of eyes. (De Silva, Ramkissoon et al. 2006; Dick, Krummenauer et al.

As shown in Table 2, acrylic toric IOLs are generally more rotationally stable than silicone IOLs. For the Acrysof toric IOLs, the mean postoperative misalignment is less than 4 degrees and a misalignment of more than 10 degrees is rare. (Bauer, de Vries et al. 2008; Chang 2008;

In most clinical studies, the postoperative orientation of the toric IOL axis was measured via the slitlamp. Since this measuring reticule on the slitlamp uses 5 degree steps, it is not a very accurate method to determine postoperative IOL rotation. A few studies have used digital photography to examine the postoperative IOL rotation, which is more accurate. Weinand et al. obtained digital images immediately after Acrysof IOL implantation and again at 6 months postoperatively. (Weinand, Jung et al. 2007) Rotation of the eye was compensated for by matching images based on specific blood vessel characteristics. The mean postoperative IOL rotation of Acrysof IOLs was 0.9 degree, with a maximum of 1.8 degrees.

(Ruhswurm, Scholz et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002)

never used spectacles for distance vision. (Ahmed, Rocha et al. 2010)

**6.1.3 Spectacle independence** 

**6.1.4 Rotational stability** 

2006)

as the indication for surgical repositioning.

Ahmed, Rocha et al. 2010; Holland, Lane et al. 2010)

Using a similar digital imaging technique, a different study showed that Acrysof toric IOLs rotate 2.66 ± 1.99 degrees on average in the first 6 months postoperatively. (Koshy, Nishi et al. 2010) Finally, Kwartz et al. compared the rotational stability of Acrysof IOLs and Akreos IOLs and showed that both IOLs rotate 2 to 3 degrees within a 2-year period. (Kwartz and Edwards 2010) However, both latter studies did not compensate for cyclotorsion of the eye between measurements both with the patient in an upright position, which has been shown to be approximately 2 degrees. (Viestenz, Seitz et al. 2005; Wolffsohn and Buckhurst 2010) This indicates that the postoperative rotation of Acrysof IOLs is most likely less than 1 degree. The exact postoperative rotation of other acrylic IOLs, such as the Rayner toric or Acri.Comfort toric IOLs, has not been examined yet.

Finally, ocular trauma may cause rotation of a toric IOL. (Chang 2009) In human cadaver eyes implanted with a toric IOL, trauma without leakage from the old incision site resulted in IOL rotation of approximately 6 degrees. Trauma with leakage from the incision site was associated with IOL rotation of approximately 40 degrees. (Pereira, Milverton et al. 2009) However, these human cadaver eyes received post-mortem phacoemulsification with toric IOL implantation, indicating that the IOL had not fused with the capsular bag. This would have resulted in an increased IOL rotation and is possibly not an optimal model to examine toric IOL rotation following ocular trauma.

## **6.1.5 Economic evaluation**

Two studies have performed an economic evaluation of toric IOL implantation versus monofocal IOL implantation during cataract surgery. (Laurendeau, Lafuma et al. 2009; Pineda, Denevich et al. 2010) Laurendeau et al. estimated the lifetime costs of cataract surgery with bilateral toric or monofocal IOLs in patients with pre-existing corneal astigmatism in four European countries (France, Italy, Germany and Spain). In this study, 70% of patients with bilateral monofocal IOLs needed spectacles for distance vision, compared to 26% of patients with bilateral toric IOLs. The resulting reduction in costs in patients with toric IOLs depended on the national spectacle costs and ranged from €308 for Spain to €692 for France. However, this study did not evaluate the possible non-financial benefits of toric IOL implantation, such as the patients' visual functioning and health-related quality of life.

Pineda et al. assessed the economic value of an improved uncorrected visual acuity in patients with pre-existing corneal astigmatism and cataract treated with toric or monofocal IOLs in the US. (Pineda, Denevich et al. 2010) Patient with toric IOLs saved \$34 in total costs with toric IOLs versus monofocal IOLs. These savings increased to \$393 among patients who achieved an UDVA of 20/25 or better. The costs per QALY (quality-adjusted life years; a measure of disease burden combining quality and quantity of life) for toric IOLs was \$349 compared with monofocal IOLs. This indicates that toric IOLs are highly cost-effective. (WHO 2011) In addition, toric IOLs were more cost-effective than monofocal IOLs combined with an intraoperative refractive correction such as limbal relaxing incisions.

#### **6.2 Multifocal toric IOLs**

Four different toric multifocal IOL models are currently available (Table 3): the diffractiverefractive Restor IQ toric (Alcon) with an add power of 3.0 D, the diffractive Acri.Lisa toric (Carl Zeiss Meditec) with a +3.75 D add, the refractive M-flex T (Rayner) with an add power of either +3.00 or +4.00 D, and the Lentis Mplus toric (Oculentis) with a +3.0 D


\* = Highest cylinder powers are custom made;

Table 3. Currently available Multifocal Toric IOLs

\* = Highest cylinder powers are custom made;

Table 3. Currently available Multifocal Toric IOLs

sector-shaped nearvision segment. So far, two studies have been published on multifocal toric IOLs. The first study is a case series describing refractive lens exchange with Acri.Lisa toric implantation in 10 eyes of 6 patients. (Liekfeld, Torun et al. 2009) Postoperatively, the UDVA was 20/40 or better in all eyes and the mean reduction in refractive cylinder was 95%. Near and intermediate visual acuities were not evaluated. The second study is a prospective cohort study, in which 45 eyes with cataract and corneal astigmatism were implanted with an Acri.Lisa toric IOL (Figure 4). (Visser, Nuijts et al. 2011) Three months postoperatively, a residual refractive cylinder of -1.00 D or less was achieved in almost 90% of eyes. The UDVA was 0.04 ± 0.15 LogMAR (equivalent to 0.91 ± 0.31 Snellen) and 98% of eyes achieved an UDVA of 20/40 or better. The monocular UNVA and UIVA (at 60 cm distance) were 0.20 ± 0.16 LogMAR (equivalent to 0.63 ± 0.23 Snellen) and 0.40 ± 0.16 LogMAR (equivalent to 0.40 ± 0.15 Snellen), respectively. For intermediate distances, multifocal IOLs with an +3.0 D add power have been shown to lead to better uncorrected visual outcomes, compared to a multifocal IOL with a +3.75 D or +4.0 add power. (de Vries, Webers et al.; Alfonso, Fernandez-Vega et al. 2010) However, so far no studies have been published on the Restor IQ toric, M-flex T, or Lentis Mplus toric IOLs.

Fig. 4. Slitlamp image of the Acri.LISA toric multifocal intraocular lens.

## **6.3 Toric IOLs in irregular astigmatism**

Even though toric IOLs are most suitable for the correction of regular bow-tie astigmatism, these IOLs have also been shown to be effective in patients with irregular astigmatism. In patients with a corneal ectasia disorder, such as keratoconus or pellucid marginal degeneration (PMD), cataract surgery or refractive lens exchange with an acrylic or silicone toric IOL implantation has been described. (Sauder and Jonas 2003; Navas and Suarez 2009; Luck 2010; Visser, Gast et al. 2011) Two case reports have described Acrysof toric IOL implantation, with cylinder powers up to 6.0 D, in patients with keratoconus. (Navas and Suarez 2009; Visser, Gast et al. 2011) Postoperatively, there was a marked improvement in UDVA and a 70 to 80% reduction in refractive astigmatism, indicating that the toric IOLs were effective. Sauder et al. report a keratoconus patient who underwent cataract surgery with a Microsil toric IOL (cylinder power 12.0 D) implantation. (Sauder and Jonas 2003) Postoperatively, the BDVA increased from 0.4 to 0.8 with a residual refractive cylinder of - 2.5 D. Luck et al. describe 1 case of a customized Acri.Comfort toric IOL implantation, with a cylinder power of 16.0 D, in a patient with PMD. (Luck 2010) Postoperatively, the residual refractive cylinder was 1.25 and the UDVA and BDVA were 20/30 and 20/20, respectively. Cataract surgery with toric IOL implantation has also been described in patients with high post-keratoplasty astigmatism. (Tehrani, Stoffelns et al. 2003; Kersey, O'Donnell et al. 2007; Statham, Apel et al. 2010; Stewart and McAlister 2010) A case series by Kersey et al. describes 7 post-keratoplasty patients who underwent cataract surgery with Microsil toric IOL (mean IOL cylinder of 10.12 D) implantation. (Kersey, O'Donnell et al. 2007) One month postoperatively, the mean UDVA and BDVA were 20/50 and 20/30, respectively, with a mean residual refractive cylinder of 2.75 D. In addition, Stewart et al. compared visual and refractive outcomes following cataract surgery with Rayner toric IOL implantation in non-keratoplasty patients (n = 14) and in post-keratoplasty patients (n=8). (Stewart and McAlister 2010) One month postoperatively, the postoperative residual refractive cylinder in post-keratoplasty patients was significantly higher compared to non-keratoplasty patients (2.88 ± 2.22 D versus 0.89 ± 0.48 D). As a result, the mean UDVA in post-keratoplasty patients was 0.50 ± 0.48 LogMAR (equivalent to 0.32 Snellen), which was significantly lower than in non-keratoplasty patients (0.16 ± 0.16 LogMAR/ 0.69 Snellen). The BDVA between both groups was comparable: 0.18 ± 0.17 LogMAR (equivalent to 0.66 Snellen) in post-keratoplasty patients and 0.12 ± 0.15 LogMAR (equivalent to 0.76 Snellen) in non-keratoplasty patients.

These case reports and case series indicate that toric IOLs may be used to correct irregular astigmatism. It should be emphasized however that toric IOL implantation is a suitable option in keratoconus patients only if the risk of progression is minimal. Therefore, before implantation of the toric IOL, the patients' risk of progression should be evaluated. In addition, toric IOLs are probably most suitable for patients with mild to moderate amounts of irregular astigmatism, who can be satisfactory corrected using spectacles. It is possibly a less suitable option in patients whom rigid gas permeable contact lenses have been prescribed primarily to correct high levels of irregular astigmatism. (Goggin, Alpins et al. 2000)

## **7. Complications**

#### **7.1 Misalignment**

The most important complication of toric IOLs is misalignment of the IOL with regards to the intended alignment axis. In these cases surgical re-alignment may be performed to realign the toric IOL. The overall cumulative incidence of surgical repositioning of STAAR toric IOLs in the literature is 6.6%. (Ruhswurm, Scholz et al. 2000; Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002; Chang 2003) The indication for surgical repositioning in studies using STAAR toric IOLs was a rotation of more than 20 to 30

toric IOL implantation has been described. (Sauder and Jonas 2003; Navas and Suarez 2009; Luck 2010; Visser, Gast et al. 2011) Two case reports have described Acrysof toric IOL implantation, with cylinder powers up to 6.0 D, in patients with keratoconus. (Navas and Suarez 2009; Visser, Gast et al. 2011) Postoperatively, there was a marked improvement in UDVA and a 70 to 80% reduction in refractive astigmatism, indicating that the toric IOLs were effective. Sauder et al. report a keratoconus patient who underwent cataract surgery with a Microsil toric IOL (cylinder power 12.0 D) implantation. (Sauder and Jonas 2003) Postoperatively, the BDVA increased from 0.4 to 0.8 with a residual refractive cylinder of - 2.5 D. Luck et al. describe 1 case of a customized Acri.Comfort toric IOL implantation, with a cylinder power of 16.0 D, in a patient with PMD. (Luck 2010) Postoperatively, the residual refractive cylinder was 1.25 and the UDVA and BDVA were 20/30 and 20/20, respectively. Cataract surgery with toric IOL implantation has also been described in patients with high post-keratoplasty astigmatism. (Tehrani, Stoffelns et al. 2003; Kersey, O'Donnell et al. 2007; Statham, Apel et al. 2010; Stewart and McAlister 2010) A case series by Kersey et al. describes 7 post-keratoplasty patients who underwent cataract surgery with Microsil toric IOL (mean IOL cylinder of 10.12 D) implantation. (Kersey, O'Donnell et al. 2007) One month postoperatively, the mean UDVA and BDVA were 20/50 and 20/30, respectively, with a mean residual refractive cylinder of 2.75 D. In addition, Stewart et al. compared visual and refractive outcomes following cataract surgery with Rayner toric IOL implantation in non-keratoplasty patients (n = 14) and in post-keratoplasty patients (n=8). (Stewart and McAlister 2010) One month postoperatively, the postoperative residual refractive cylinder in post-keratoplasty patients was significantly higher compared to non-keratoplasty patients (2.88 ± 2.22 D versus 0.89 ± 0.48 D). As a result, the mean UDVA in post-keratoplasty patients was 0.50 ± 0.48 LogMAR (equivalent to 0.32 Snellen), which was significantly lower than in non-keratoplasty patients (0.16 ± 0.16 LogMAR/ 0.69 Snellen). The BDVA between both groups was comparable: 0.18 ± 0.17 LogMAR (equivalent to 0.66 Snellen) in post-keratoplasty patients and 0.12 ± 0.15 LogMAR

These case reports and case series indicate that toric IOLs may be used to correct irregular astigmatism. It should be emphasized however that toric IOL implantation is a suitable option in keratoconus patients only if the risk of progression is minimal. Therefore, before implantation of the toric IOL, the patients' risk of progression should be evaluated. In addition, toric IOLs are probably most suitable for patients with mild to moderate amounts of irregular astigmatism, who can be satisfactory corrected using spectacles. It is possibly a less suitable option in patients whom rigid gas permeable contact lenses have been prescribed primarily to correct high levels of irregular astigmatism. (Goggin, Alpins et al.

The most important complication of toric IOLs is misalignment of the IOL with regards to the intended alignment axis. In these cases surgical re-alignment may be performed to realign the toric IOL. The overall cumulative incidence of surgical repositioning of STAAR toric IOLs in the literature is 6.6%. (Ruhswurm, Scholz et al. 2000; Sun, Vicary et al. 2000; Leyland, Zinicola et al. 2001; Till, Yoder et al. 2002; Chang 2003) The indication for surgical repositioning in studies using STAAR toric IOLs was a rotation of more than 20 to 30

(equivalent to 0.76 Snellen) in non-keratoplasty patients.

2000)

**7. Complications 7.1 Misalignment** 

degrees, whereas a misalignment of more than 10 degrees is currently considered the indication for re-alignment. Consequently, the reported incidence for surgical repositioning of STAAR toric IOLs is an underestimation. Regarding the MicroSil toric IOL, the overall cumulative incidence of surgical repositioning in the literature is 6.7%. (De Silva, Ramkissoon et al. 2006; Dick, Krummenauer et al. 2006) For acrylic toric IOLs the overall cumulative incidence of surgical repositioning was much lower: 0.3% for Acrysof toric IOLs, 2.1% for Rayner toric IOLs and 0% for Acri.lisa toric IOLs. (Alio, Agdeppa et al. 2010; Stewart and McAlister 2010; Entabi, Harman et al. 2011) However, only a few studies have been performed on Rayner and Acri.Lisa toric IOLs.

#### **7.2 Posterior capsule opacification**

Posterior capsule opacification (PCO) has been reported in several studies using Acrysof toric IOLs, but the exact incidence of PCO is unclear. (Ahmed, Rocha et al. 2010; Gayton and Seabolt 2010; Koshy, Nishi et al. 2010; Visser, Ruiz-Mesa et al. 2011) In the majority of these studies, PCO did not compromise the visual outcome and a neodymium:YAG posterior capsulotomy was not required. Too few studies have been performed with Rayner toric or Acri.Comfort toric IOLs to evaluate the incidence of PCO. Regarding the MicroSil toric IOLs, Dick et al. reported PCO in 7% of eyes and a neodymium:YAG capsulotomy in 6% of eyes within a follow-up of 3 months. (Dick, Krummenauer et al. 2006) The reported incidence of neodymium:YAG capsulotomy in patients with STAAR toric IOLs ranged from 3.8% after a follow-up of 7 months to 36.5% after a follow-up of several years. (Sun, Vicary et al. 2000; Jampaulo, Olson et al. 2008)

Both IOL material and IOL design can influence the development of PCO. Two metaanalyses and one Cochrane systematic review have been published concerning the PCO and neodymium:YAG capsulotomy rates of different IOL biomaterials and optic edge designs. (Cheng, Wei et al. 2007; Li, Chen et al. 2008; Findl, Buehl et al. 2010) Silicone IOLs were associated with lower PCO rates than acrylic IOLs, but this difference did not reach statistical significance in the Cochrance systematic review. (Cheng, Wei et al. 2007; Li, Chen et al. 2008; Findl, Buehl et al. 2010) The neodymium:YAG capsulotomy rate for acrylic and silicone IOLs was comparable. (Cheng, Wei et al. 2007; Li, Chen et al. 2008; Findl, Buehl et al. 2010) In addition, sharp-edged acrylic and sharp-edged silicone IOLs were significantly more effective than round-edged IOLs in the prevention of PCO and neodymium:YAG capsulotomy. (Cheng, Wei et al. 2007; Findl, Buehl et al. 2010) Currently available toric IOLs all have a sharp-edged design (Acrysof toric, Rayner toric, Acri.Comfort toric and MicroSil toric), or an almost sharp-edged design (STAAR toric). However, as mentioned by Nanavaty et al., considerable variation in sharp-edge design exists due to differences in sharpness of the edge. (Nanavaty, Spalton et al. 2008) If a neodymium:YAG capsulotomy has to be performed in patients with a toric IOL, the mean IOL rotation was only 1.4 degrees with a maximum of 5 degrees, indicating that IOL rotation is not an issue. (Jampaulo, Olson et al. 2008)

#### **7.3 Other**

Other complications reported in the literature are rare and are those generally associated with cataract surgery: corneal oedema, macular oedema, elevated intraocular pressure, a retinal hole or retinal detachment. (Ahmed, Rocha et al. 2010; Holland, Lane et al. 2010; Visser, Ruiz-Mesa et al. 2011)

## **8. Conclusion**

In the last decade, many advancements have been made in toric IOL design and surgical techniques, which have led to an increased success of toric IOLs. Currently used acrylic toric IOLs demonstrate good rotational stability and a low incidence of surgical repositioning. Clinical studies on toric IOLs demonstrate excellent uncorrected distance visual outcomes and a low residual refractive cylinder. Consequently, most patients with bilateral toric IOLs achieve spectacle independence for distance vision. Toric IOL implantation has been shown to be a highly cost-effective procedure. Regarding the new multifocal toric IOLs, initial clinical results are promising with excellent uncorrected distance visual outcomes and acceptable near and intermediate visual outcomes. However, more clinical studies are required to evaluate the visual outcomes and spectacle dependency following multifocal toric IOL implantation. Toric IOL implantation has also been shown to be an effective treatment option in patients with irregular corneal astigmatism. However, care should be taken to evaluate whether a patient is a suitable candidate for this treatment option. Future developments in toric IOL implantation include the clinical use of new techniques for more accurate intraoperative alignment of toric IOLs.

## **9. Acknowledgement**

The authors would like to thank Mari Elshout for his assistance in the layout of the artwork.

### **10. References**


In the last decade, many advancements have been made in toric IOL design and surgical techniques, which have led to an increased success of toric IOLs. Currently used acrylic toric IOLs demonstrate good rotational stability and a low incidence of surgical repositioning. Clinical studies on toric IOLs demonstrate excellent uncorrected distance visual outcomes and a low residual refractive cylinder. Consequently, most patients with bilateral toric IOLs achieve spectacle independence for distance vision. Toric IOL implantation has been shown to be a highly cost-effective procedure. Regarding the new multifocal toric IOLs, initial clinical results are promising with excellent uncorrected distance visual outcomes and acceptable near and intermediate visual outcomes. However, more clinical studies are required to evaluate the visual outcomes and spectacle dependency following multifocal toric IOL implantation. Toric IOL implantation has also been shown to be an effective treatment option in patients with irregular corneal astigmatism. However, care should be taken to evaluate whether a patient is a suitable candidate for this treatment option. Future developments in toric IOL implantation include the clinical use of new techniques for more

The authors would like to thank Mari Elshout for his assistance in the layout of the artwork.

Ahmed, II, G. Rocha, et al. (2010). "Visual function and patient experience after bilateral implantation of toric intraocular lenses." *J Cataract Refract Surg* 36(4): 609-16. Alfonso, J. F., L. Fernandez-Vega, et al. (2010). "Intermediate visual function with different multifocal intraocular lens models." *J Cataract Refract Surg* 36(5): 733-739. Alio, J., J. L. Rodriguez-Prats, et al. (2005). "Outcomes of microincision cataract surgery versus coaxial phacoemulsification." *Ophthalmology* 112(11): 1997-2003. Alio, J. L., M. C. Agdeppa, et al. (2010). "Microincision cataract surgery with toric intraocular

Alpins, N. (2001). "Astigmatism analysis by the Alpins method." *J Cataract Refract Surg* 27(1):

Arba-Mosquera, S., J. Merayo-Lloves, et al. (2008). "Clinical effects of pure cyclotorsional errors during refractive surgery." *Invest Ophthalmol Vis Sci* 49(11): 4828-36. Assil, K. K., W. K. Christian, et al. (2008). Patient Selection and Education. Mastering

Bauer, N. J., N. E. de Vries, et al. (2008). "Astigmatism management in cataract surgery with the AcrySof toric intraocular lens." *J Cataract Refract Surg* 34(9): 1483-8. Bayramlar, H. H., M. C. Daglioglu, et al. (2003). "Limbal relaxing incisions for primary

lens implantation for correcting moderate and high astigmatism: pilot study." *J* 

Refractive IOLs: The Art and Science. D. F. Chang. Thorofare, USA, SLACK

mixed astigmatism and mixed astigmatism after cataract surgery." *J Cataract Refract* 

**8. Conclusion** 

accurate intraoperative alignment of toric IOLs.

*Cataract Refract Surg* 36(1): 44-52.

Incorporated: 331-431.

*Surg* 29(4): 723-8.

**9. Acknowledgement** 

**10. References** 

31-49.


Ferrer-Blasco, T., R. Montes-Mico, et al. (2009). "Prevalence of corneal astigmatism before

Findl, O., W. Buehl, et al. (2010). "Interventions for preventing posterior capsule

Findl, O., K. Kriechbaum, et al. (2003). "Influence of operator experience on the performance

Fledelius, H. C. and M. Stubgaard (1986). "Changes in refraction and corneal curvature

Gayton, J. L. and R. A. Seabolt (2010). "Clinical Outcomes of Complex and Uncomplicated

Goggin, M., N. Alpins, et al. (2000). "Management of irregular astigmatism." *Curr Opin* 

Hill, W. (2008). "Expected effects of surgically induced astigmatism on AcrySof toric

Hoffmann, P. C. and W. W. Hutz (2010). "Analysis of biometry and prevalence data for corneal astigmatism in 23,239 eyes." *J Cataract Refract Surg* 36(9): 1479-85. Holladay, J. T., J. R. Moran, et al. (2001). "Analysis of aggregate surgically induced refractive

Holland, E., S. Lane, et al. (2010). "The AcrySof Toric Intraocular Lens in Subjects with

Jampaulo, M., M. D. Olson, et al. (2008). "Long-term Staar toric intraocular lens rotational

Jongsma, F. H. M., J. De Brabander, et al. (1999). "Review and Classification of Corneal

Kato, N., I. Toda, et al. (2008). "Five-year outcome of LASIK for myopia." *Ophthalmology*

Kaufmann, C., A. Krishnan, et al. (2009). "Astigmatic neutrality in biaxial microincision

Kersey, J. P., A. O'Donnell, et al. (2007). "Cataract surgery with toric intraocular lenses can

Kim, M. H., T. Y. Chung, et al. (2010). "Long-term efficacy and rotational stability of AcrySof

Kohnen, T., B. Dick, et al. (1995). "Comparison of the induced astigmatism after temporal

Kohnen, T., D. Kook, et al. (2008). "[Use of multifocal intraocular lenses and criteria for

optimize uncorrected postoperative visual acuity in patients with marked corneal

toric intraocular lens implantation in cataract surgery." *Korean J Ophthalmol* 24(4):

clear corneal tunnel incisions of different sizes." *J Cataract Refract Surg* 21(4): 417-

intraocular lens results." *J Cataract Refract Surg* 34(3): 364-7.

Group, 1-Year Study." *Ophthalmology* 117(11): 2104-11.

cataract surgery." *J Cataract Refract Surg* 35(9): 1555-62.

patient selection]." *Ophthalmologe* 105(6): 527-32.

stability." *Am J Ophthalmol* 146(4): 550-553.

Topographers." *Lasers Med Sci* 14: 2-19.

astigmatism." *Cornea* 26(2): 133-5.

of ultrasound biometry compared to optical biometry before cataract surgery." *J* 

during growth and adult life. A cross-sectional study." *Acta Ophthalmol (Copenh)*

Cataractous Eyes After Lens Replacement with the AcrySof Toric IOL." *J Refract* 

change, prediction error, and intraocular astigmatism." *J Cataract Refract Surg* 27(1):

Cataracts and Corneal Astigmatism A Randomized, Subject-Masked, Parallel-

cataract surgery." *J Cataract Refract Surg* 35(1): 70-5.

*Cataract Refract Surg* 29(10): 1950-5.

64(5): 487-91.

*Surg* 14: 1-7.

61-79.

115(5): 839-844 e2.

207-12.

24.

*Ophthalmol* 11(4): 260-6.

opacification." *Cochrane Database Syst Rev*(2): CD003738.


Osher, R. H. (2010). "Iris fingerprinting: new method for improving accuracy in toric lens

Oshika, T., T. Nagata, et al. (1998). "Adhesion of lens capsule to intraocular lenses of

Packer, M. (2010). "Effect of intraoperative aberrometry on the rate of postoperative enhancement: retrospective study." *J Cataract Refract Surg* 36(5): 747-55. Patel, C. K., S. Ormonde, et al. (1999). "Postoperative intraocular lens rotation: a randomized

Pereira, F. A., E. J. Milverton, et al. (2009). "Miyake-Apple study of the rotational stability of

Pineda, R., S. Denevich, et al. (2010). "Economic evaluation of toric intraocular lens: a shortand long-term decision analytic model." *Arch Ophthalmol* 128(7): 834-40. Prinz, A., T. Neumayer, et al. (2011). "Rotational stability and posterior capsule opacification

Ruhswurm, I., U. Scholz, et al. (2000). "Astigmatism correction with a foldable toric intraocular lens in cataract patients." *J Cataract Refract Surg* 26(7): 1022-7. Ruiz-Mesa, R., D. Carrasco-Sanchez, et al. (2009). "Refractive lens exchange with foldable

Santodomingo-Rubido, J., E. A. Mallen, et al. (2002). "A new non-contact optical device for

Sauder, G. and J. B. Jonas (2003). "Treatment of keratoconus by toric foldable intraocular

Savini, G., P. Barboni, et al. (2009). "Agreement between Pentacam and videokeratography

Shimizu, K., A. Misawa, et al. (1994). "Toric intraocular lenses: correcting astigmatism while

Shirayama, M., L. Wang, et al. (2009). "Comparison of corneal powers obtained from 4

Statham, M., A. Apel, et al. (2009). "Comparison of the AcrySof SA60 spherical intraocular

amounts of corneal astigmatism." *Clin Experiment Ophthalmol* 37(8): 775-9. Statham, M., A. Apel, et al. (2010). "Correction of astigmatism after penetrating keratoplasty using the Acri.Comfort toric intraocular lens." *Clin Exp Optom* 93(1): 42-4. Stewart, C. M. and J. C. McAlister (2010). "Comparison of grafted and non-grafted patients

Storr-Paulsen, A., H. Madsen, et al. (1999). "Possible factors modifying the surgically induced astigmatism in cataract surgery." *Acta Ophthalmol Scand* 77(5): 548-51. Sun, X. Y., D. Vicary, et al. (2000). "Toric intraocular lenses for correcting astigmatism in 130

lens and the AcrySof Toric SN60T3 intraocular lens outcomes in patients with low

with corneal astigmatism undergoing cataract extraction with a toric intraocular

toric intraocular lens." *Am J Ophthalmol* 147(6): 990-6, 996 e1.

in corneal power assessment." *J Refract Surg* 25(6): 534-8.

controlling axis shift." *J Cataract Refract Surg* 20(5): 523-6.

different devices." *Am J Ophthalmol* 148(4): 528-535 e1.

lens implant." *Clin Experiment Ophthalmol* 38(8): 747-757.

eyes." *Ophthalmology* 107(9): 1776-81; discussion 1781-2.

ocular biometry." *Br J Ophthalmol* 86(4): 458-62.

lenses." *Eur J Ophthalmol* 13(6): 577-9.

polymethylmethacrylate, silicone, and acrylic foldable materials: an experimental

comparison of plate and loop haptic implants." *Ophthalmology* 106(11): 2190-5;

the Acrysof Toric intraocular lens after experimental eye trauma." *Eye (Lond)* 24(2):

of a plate-haptic and an open-loop-haptic intraocular lens." *J Cataract Refract Surg*

orientation." *J Cataract Refract Surg* 36(2): 351-2.

study." *Br J Ophthalmol* 82(5): 549-53.

discussion 2196.

376-8.

37(2): 251-7.


http://www.who.int/choice/en/ (Accessd 18-03-2011).


## **Surgical Correction of Astigmatism During Cataract Surgery**

Arzu Taskiran Comez1 and Yelda Ozkurt2

*1Canakkale Onsekiz Mart University, School of Medicine, Department of Ophthalmology, Canakkale 2Fatih Sultan Mehmet Training and Research Hospital, Eye Clinic, Istanbul Turkey* 

## **1. Introduction**

292 Astigmatism – Optics, Physiology and Management

Wolffsohn, J. S. and P. J. Buckhurst (2010). "Objective analysis of toric intraocular lens

Zuberbuhler, B., T. Signer, et al. (2008). "Rotational stability of the AcrySof SA60TT toric

rotation and centration." *J Cataract Refract Surg* 36(5): 778-82.

intraocular lenses: a cohort study." *BMC Ophthalmol* 8: 8.

Naturally occurring (idiopathic) astigmatism is frequent, with up to 95% of eyes having detectable astigmatism. It is estimated that approximately 70% of the general cataract population has at least 1.00 D of astigmatism, and approximately 33% of patients undergoing cataract surgery are eligible for treatment of preexisting astigmatism.1,2

Today, cataract surgery is regarded as a refractive surgery, aiming pseudophakic emmetropia, which makes eliminating corneal astigmatism critical.3-8

Ferrer-Blasco et al studied prevalance of corneal astigmatism before cataract surgery and found that; in 13.2% of eyes no corneal astigmatism was present; in 64.4%, corneal astigmatism was between 0.25 and 1.25 diopters (D) and in 22.2%, it was 1.50 D or higher.9

This finding implies that, when planning a surgery, both the spherical and the astigmatic components should be taken into account to achieve post-operative outcomes as close to emmetropia as possible.

Due to new developments in phacoemulsification devices, changes in operation techniques and the use of small incisions in cataract surgery which reduce the operation-induced astigmatism or make an inconsiderable change in the existing corneal astigmatism, the general aim of cataract surgery has gone from simple cataract extraction to ensuring the best visual acuity and quality without spectacle dependence. With the wide-spread use of phakic, aphakic, bifocal, multifocal and accommodative intraocular lenses (IOLs); all surgeons aim to eliminate any small ametropia, especially astigmatism, existing before or after cataract surgery.

There are several techniques for dealing with the pre-existing astigmatism intraoperatively as well as postoperative approaches for dealing with residual or induced astigmatism. However; the most important and critical step in treating the astigmatism is to find out the exact source, magnitude and axis of the astigmatism and making the decision about which technique is appropriate for that patient. The cylindrical component is evaluated by automated and/or manifest refraction, placido ring reflections, keratometry and/or corneal topography and wavefront aberrometry primarily, but other factors need to be taken into account, such as age of the patient and the corneal characteristics of both eyes.

*Refractive astigmatism*; also called total astigmatism; as determined by retinoscopy or by subjective refraction, is made up of both corneal and internal astigmatism. *Corneal astigmatism* occurs due to unequal curvature along the two principal meridians of the anterior cornea and *internal astigmatism* is due to factors such as the toricity of the posterior surface of the cornea, unequal curvatures of the front and back surfaces of the crystalline lens, or tilting of the crystalline lens with respect to the optic axis of the cornea. The combination of the corneal and the internal astigmatism gives the eye's *total(refractive) astigmatism*. Corneal astigmatism is often classified according to the axis of astigmatism as being either with-the rule (WTR), oblique or against-the-rule (ATR).

It is well accepted that there is some relationship between the eye's corneal and internal astigmatism. In 1890, Javal proposed a rule that predicted the *refractive (total) astigmatism* of the eye based on the corneal astigmatism.10

Javal's rule states: A*<sup>t</sup>* =*k* + *p*(A*c)* where A*<sup>t</sup>* is the *refractive (total) astigmatism* and A*<sup>c</sup>* is the corneal astigmatism. The terms *k* and *p* are constants approximated by 0.5 and 1.25, respectively. This rule relies on the fact that residual astigmatism is thought to be constant and ATR in most people (that is, -0.50 D ATR). Keller and colleagues investigated the relationship between corneal and total astigmatism by measuring corneal astigmatism with a computer-assisted videokeratoscope and the results from this study supported Javal's rule.11 To quantify the discrepancy between corneal and refractive astigmatism measurements, the corneal astigmatism value measured by topography or keratometry is substracted from the refractive cylinder measured by wavefront or manifest refraction and the vectorial difference is known as the ocular residual astigmatism (ORA), which is expressed in diopters.12,13

Keratometry, topography, and refraction, all provide useful information regarding the astigmatic status of patients. If the astigmatism measured by these tools is not in agreement either in magnitude, axis, or both, then the surgeon needs to evaluate all the datas again in order to optimise the visual outcome. Corneal topography provides a qualitative and quantitative image map based on evaluation of the corneal curvature14. Most topographers evaluate 8,000 to 10,000 specific points over the entire cornea and center the acquisition on the corneal apex. Topographers that incorporate scanning slit photography also measure the power and the astigmatism of the posterior corneal surface, which may improve correlation with the refractive astigmatism.15 In contrast to topography measurements, manual keratometry has only four data points within 3 mm to 4 mm of the central anterior surface of the cornea. An other device, automated keratometer, although not sensitive for accuracy of axis with low magnitudes of astigmatism, may be useful in screening astigmatism. Corneal topography and keratometry are considered "objective" measures of corneal refractive power. Although cataract surgery relies primarily on keratometry or topography and subjective refraction data; corneal or limbal incisional precedures to correct pre- or postoperative astigmatism have to involve keratometry, topography, refraction or a combination of corneal and refractive parameters using vector planning due to the fact that treatment of refractive astigmatism without regard to corneal astigmatism may result in a significant amount of remaining corneal astigmatism or even an increase in corneal astigmatism.

The history of surgical treatment for astigmatism dates back to the late 1800s. Various authors tried various techniques including limbal and corneal incision in the steep meridian, anterior transverse incisions, and nonperforating corneal incisions.16-25 The use of keratotomy to correct refractive error, facilitated in the mid-nineteenth century when

*Refractive astigmatism*; also called total astigmatism; as determined by retinoscopy or by subjective refraction, is made up of both corneal and internal astigmatism. *Corneal astigmatism* occurs due to unequal curvature along the two principal meridians of the anterior cornea and *internal astigmatism* is due to factors such as the toricity of the posterior surface of the cornea, unequal curvatures of the front and back surfaces of the crystalline lens, or tilting of the crystalline lens with respect to the optic axis of the cornea. The combination of the corneal and the internal astigmatism gives the eye's *total(refractive) astigmatism*. Corneal astigmatism is often classified according to the axis of astigmatism as

It is well accepted that there is some relationship between the eye's corneal and internal astigmatism. In 1890, Javal proposed a rule that predicted the *refractive (total) astigmatism* of

Javal's rule states: A*<sup>t</sup>* =*k* + *p*(A*c)* where A*<sup>t</sup>* is the *refractive (total) astigmatism* and A*<sup>c</sup>* is the corneal astigmatism. The terms *k* and *p* are constants approximated by 0.5 and 1.25, respectively. This rule relies on the fact that residual astigmatism is thought to be constant and ATR in most people (that is, -0.50 D ATR). Keller and colleagues investigated the relationship between corneal and total astigmatism by measuring corneal astigmatism with a computer-assisted videokeratoscope and the results from this study supported Javal's rule.11 To quantify the discrepancy between corneal and refractive astigmatism measurements, the corneal astigmatism value measured by topography or keratometry is substracted from the refractive cylinder measured by wavefront or manifest refraction and the vectorial difference is known as the ocular residual astigmatism (ORA), which is

Keratometry, topography, and refraction, all provide useful information regarding the astigmatic status of patients. If the astigmatism measured by these tools is not in agreement either in magnitude, axis, or both, then the surgeon needs to evaluate all the datas again in order to optimise the visual outcome. Corneal topography provides a qualitative and quantitative image map based on evaluation of the corneal curvature14. Most topographers evaluate 8,000 to 10,000 specific points over the entire cornea and center the acquisition on the corneal apex. Topographers that incorporate scanning slit photography also measure the power and the astigmatism of the posterior corneal surface, which may improve correlation with the refractive astigmatism.15 In contrast to topography measurements, manual keratometry has only four data points within 3 mm to 4 mm of the central anterior surface of the cornea. An other device, automated keratometer, although not sensitive for accuracy of axis with low magnitudes of astigmatism, may be useful in screening astigmatism. Corneal topography and keratometry are considered "objective" measures of corneal refractive power. Although cataract surgery relies primarily on keratometry or topography and subjective refraction data; corneal or limbal incisional precedures to correct pre- or postoperative astigmatism have to involve keratometry, topography, refraction or a combination of corneal and refractive parameters using vector planning due to the fact that treatment of refractive astigmatism without regard to corneal astigmatism may result in a significant amount of remaining corneal astigmatism or even an increase in corneal

The history of surgical treatment for astigmatism dates back to the late 1800s. Various authors tried various techniques including limbal and corneal incision in the steep meridian, anterior transverse incisions, and nonperforating corneal incisions.16-25 The use of keratotomy to correct refractive error, facilitated in the mid-nineteenth century when

being either with-the rule (WTR), oblique or against-the-rule (ATR).

the eye based on the corneal astigmatism.10

expressed in diopters.12,13

astigmatism.

Snellen suggested that a corneal incision placed perpendicular to the step corneal meridian might induce flattening along that meridian.16 In 1885, Schiötz placed a 3.5 mm limbal penetrating incision in the steep meridian to reduce iatrogenic astigmatism of 17 D occurred after cataract surgery.17 Faber performed perforating anterior transverse incisions to reduce idiopathic astigmatism18. Lucciola reported the first cases of non-penetrating corneal incisions in 1886, where he also attempted to reduce astigmatism by flattening the steep corneal meridian in ten patients19. In 1894, Bates described 6 patients who developed flattening of the cornea in the meridian after a surgical or traumatic scar was intersected20. Later, Lans first appreciated that the flattening that occurs in a corneal meridian after placing a transverse incision was associated with steepening in the opposite meridian.21 He also demonstrated that the deeper and the longer incisions had more effect.21 In 1940s, Sato began an extensive investigation of radial and astigmatic keratotomy.22-25

However, early and late investigations of the techniques for astigmatic keratotomy are attributed to the works of Thornton, Buzard, Price, Nordan, Grene, Lindstrom, Troutman and Nichamin.26-36

Nordan proposed a relatively simple method of straight transverse keratotomy, with target corrections in the range on 1-4 diopters.29 Lindstrom developed a technique, as well as a nomogram, including an age factor.30

Thornton proposed a technique that included up to 3 pairs of arcuate incisions in varying optical zone sizes and with consideration of age and timing after surgery, respectively.26 Consequently, Troutman, who fancied wedge resection for reduction of postcorneal transplant astigmatism, also discussed the benefits of corneal relaxing incisions to decrease residual astigmatism.31 Corneal transplant surgery and radial keratotomy surgery both stimulated the development of astigmatic keratotomy. Thornton's technique involved making paired arcuate incisions placed at the 7.0 mm and 8.0 mm optical zones, following a curve on the cornea, while Chayez et al recommended optical zone sizes as small as 5.0 mm. 26,37

Nichamin developed an extensive nomogram for AK at the time of cataract surgery; titled *"Intralimbal relaxing incision nomogram for modern phaco surgery,*" which has age adjustments for correction of against-the-rule astigmatism and with-the-rule astigmatism. It utilizes an empiric blade-depth setting of 600 μm. 32-36

A detailed look in those various techniques for correcting pre-existing corneal astigmatism at the time of cataract surgery are discussed below.

## **2. Correction with incisions**

#### **2.1 Creating a clear corneal phacoemulsification incision on the steep axis of astigmatism**

Improved spherical and astigmatic outcomes are now well-recognized benefits of modern small incision cataract surgery. Although standard 2.8-3.2-mm phacoemulsification provides satisfactory results in terms of safety, efficiency, and refractive outcomes, studies have shown that microincision cataract surgery (MICS) -defined as cataract surgery performed through an incision of less than 2 mm-, is a minimally invasive procedure with increased safety and less surgically induced astigmatism.38-45 Also a recent study has shown that biaxial microincisional cataract surgery with enlargement of one incision to 2.8 mm is not astigmatically neutral, demonstrating a statistically significantly larger Surgically induced astigmatism SIA than that attributable to measurement error.46 During cataract surgery it is possible to reduce the pre-existing astigmatism by modifying the length, shape, type and the localization of the incision.37-39,47-54 The simplest way to do this, is to create a clear corneal incision at the steep corneal axis, whether superiorly, temporally, or obliquely, to profit the flattening effect of the incision which can help to reduce the astigmatism along that axis. This approach is usually sufficient for most eyes.3-5,15,49,54 However, a small incision can correct only astigmatism up to 1 D and sometimes this technique may not be easy due to localization of the steep meridian such as the difficulty while creating superonasal or inferonasal incision at the left eye. For this technique, identifying and marking the axis of the astigmatism preoperatively is critically important to ensure the exact placement of the surgical incision to flatten the cornea. Mild to moderate corneal astigmatism can be corrected or reduced by modifying the length of the corneal incision, as well as its depth and distance from the corneal center. 15,54

A study by Giasanti et al, indicated that a clear corneal incision of 2.75 mm for cataract surgery induced little change of astigmatism in eyes with low preoperative corneal cylinder, regardless of the incision site.55 However, a retrospective study describes larger changes induced by superior rather than temporal 2.8-mm incision, which had been considered nearly astigmatism neutral.56 A similar result was obtained by Borasio et al, when comparing the 3.2 mm clear corneal temporal incisions(CCTI) with clear corneal on-axis incision(CCOI) results in terms of surgically induced astigmatism, that CCTI induced less SIA than CCOI.57

However, recent evidence revealed that incisions between 1.6 to 2.3 mm had better outcomes in terms of induced astigmatism, focal wound related flattening of the peripheral cornea and corneal surface irregularity than small-incision cataract surgery. 41,58,59

Surgically induced astigmatism (SIA) is the condition in which a patients' preoperative and postoperative values differ. The methods used to determine the SIA are; Jaffe and Cleymans vector analysis method and Fourier polar and rectangular vector analysis methods as described by Thibos et al.60,61 However, if the pre and postoperative axes are identical and the sign convention is preserved, a simple substraction may also be used. Several studies have shown that temporal incisions result in with-the-rule (WTR) astigmatism, whereas superior incisions result in against-the-rule (ATR) astigmatism. 41,62-65

Altan-Yaycioglu et al compared superotemporal incisions in the right eye versus superonasal incisions in the left eye and have shown that superotemporal incisions yielded less against-the-rule astigmatism and surgically induced astigmatism values compared to superonasal incision group (p < 0.001).51

Various experts reported surgically induced astigmatism values with small incisions between 0.6-1D induced with 3.5 and 4mm incisions.66-68 Kohnen et al. reported a statistically significant difference in surgically induced corneal astigmatism after temporal and nasal unsutured limbal tunnel incisions.69 Ozkurt et al. investigated the astigmatism outcomes of temporal versus nasal clear corneal 3.5-mm incisions and found that temporal incisions yielded less total and surgically induced astigmatism.70

It is not clearly identified why temporal incisions create lesser astigmatic affect compared with the superior, but it may probably be due to the fact that the temporal limbus is farther from the visual axis than the superior limbus. In addition, the pressure the eyelid exerts on the superior incision may be another factor increasing or creating astigmatism on that localization.

In summary, temporal incisions should be used for negligible astigmatism, and nasal and superior incisions should be used when the steep axis is located at approximately 180° and 90°, respectively.

#### **2.2 Opposite side clear corneal incision (OCCI)**

296 Astigmatism – Optics, Physiology and Management

possible to reduce the pre-existing astigmatism by modifying the length, shape, type and the localization of the incision.37-39,47-54 The simplest way to do this, is to create a clear corneal incision at the steep corneal axis, whether superiorly, temporally, or obliquely, to profit the flattening effect of the incision which can help to reduce the astigmatism along that axis. This approach is usually sufficient for most eyes.3-5,15,49,54 However, a small incision can correct only astigmatism up to 1 D and sometimes this technique may not be easy due to localization of the steep meridian such as the difficulty while creating superonasal or inferonasal incision at the left eye. For this technique, identifying and marking the axis of the astigmatism preoperatively is critically important to ensure the exact placement of the surgical incision to flatten the cornea. Mild to moderate corneal astigmatism can be corrected or reduced by modifying the length of the corneal incision, as

A study by Giasanti et al, indicated that a clear corneal incision of 2.75 mm for cataract surgery induced little change of astigmatism in eyes with low preoperative corneal cylinder, regardless of the incision site.55 However, a retrospective study describes larger changes induced by superior rather than temporal 2.8-mm incision, which had been considered nearly astigmatism neutral.56 A similar result was obtained by Borasio et al, when comparing the 3.2 mm clear corneal temporal incisions(CCTI) with clear corneal on-axis incision(CCOI) results in terms of

However, recent evidence revealed that incisions between 1.6 to 2.3 mm had better outcomes in terms of induced astigmatism, focal wound related flattening of the peripheral

Surgically induced astigmatism (SIA) is the condition in which a patients' preoperative and postoperative values differ. The methods used to determine the SIA are; Jaffe and Cleymans vector analysis method and Fourier polar and rectangular vector analysis methods as described by Thibos et al.60,61 However, if the pre and postoperative axes are identical and the sign convention is preserved, a simple substraction may also be used. Several studies have shown that temporal incisions result in with-the-rule (WTR) astigmatism, whereas

Altan-Yaycioglu et al compared superotemporal incisions in the right eye versus superonasal incisions in the left eye and have shown that superotemporal incisions yielded less against-the-rule astigmatism and surgically induced astigmatism values compared to

Various experts reported surgically induced astigmatism values with small incisions between 0.6-1D induced with 3.5 and 4mm incisions.66-68 Kohnen et al. reported a statistically significant difference in surgically induced corneal astigmatism after temporal and nasal unsutured limbal tunnel incisions.69 Ozkurt et al. investigated the astigmatism outcomes of temporal versus nasal clear corneal 3.5-mm incisions and found that temporal

It is not clearly identified why temporal incisions create lesser astigmatic affect compared with the superior, but it may probably be due to the fact that the temporal limbus is farther from the visual axis than the superior limbus. In addition, the pressure the eyelid exerts on the superior incision may be another factor increasing or creating astigmatism on that

In summary, temporal incisions should be used for negligible astigmatism, and nasal and superior incisions should be used when the steep axis is located at approximately 180° and

cornea and corneal surface irregularity than small-incision cataract surgery. 41,58,59

well as its depth and distance from the corneal center. 15,54

surgically induced astigmatism, that CCTI induced less SIA than CCOI.57

superior incisions result in against-the-rule (ATR) astigmatism. 41,62-65

incisions yielded less total and surgically induced astigmatism.70

superonasal incision group (p < 0.001).51

localization.

90°, respectively.

In this technique, the corneal incisions are made on opposite sites 180 degrees apart, on the steepest meridian of cornea. It is based on the assumption that a healing tissue forms between those incisions, and this tissue-adding effect results with flattening of the cornea. The incisions were facilitated by creating two biplanar 3.2mm incisions 180 degrees from each other along the steep meridian of the cornea, 1.5-2mm inside the edge of the limbal vessels. They require no additional expertise, instrumentation, time, or cost.

Lever and Dahan were the first to apply a pair of OCCI on the steep axis to correct preexisting astigmatism during cataract surgery.71 They modified the standard approach of clear corneal incision, adding an identical incision on the opposite side (180 degrees away). In their series of 33 eyes, mean keratometric astigmatism changed from 2.80 D preoperatively to 0.75 D postoperatively.71 Other studies found similar reductions. 72,73

This method is effective for correction of mild to moderate corneal astigmatism, but in eyes with higher degrees of astigmatism it is recommended to use an alternative method or a combination of two or more methods.74 Disadvantages of this method include the increased risk of endophthalmitis due to the penetrating nature of the incisions as compared to non-penetrating methods. For control of leakage in this method nylon sutures may be used for wound closure.71

In conclusion, paired OCCIs on the steep axis are useful for correcting mild to moderate preexisting astigmatism during cataract surgery. Employing this technique during routine phacoemulsification using a 3.2 mm incision does not require additional instruments and therefore can be performed without altering the surgical setting.

#### **2.3 The limbal relaxing incision (LRI) technique**

This technique consists of performing two small curvilinear incisions at the limbus which produce a flattening of meridian along which they are performed due to the tissue addition effect along with steepening of the orthogonal meridian.(*fitting together effect*).

Performing LRIs is a preferred technique to reduce pre-existing astigmatism at the time of cataract surgery in eyes with low to moderate, and even high, astigmatism. They also appear to have potential advantages over corneal relaxing incisions or arcuate keratotomy by being a quick, easy to perform technique with low technology and low cost, causing less distortion and irregularity on corneal topographies and less variability in refraction as they are placed at the limbus. They can provide earlier stability in postoperative vision and have been found to produce less glare and patient discomfort with lower risks of corneal perforation and overcorrection of astigmatism.1,74-76 Kaufmann et al compared LRI and on-axis incisions(OAI) and found that, the flattening effect was 0.41 D in the OAI group and 1.21 D in the LRI group (p = 0.002). 77 The amount of astigmatism reduction achieved at the intended meridian was significantly more favorable with the LRI technique, which remained consistent throughout the follow-up period.77

The disadvantages are that LRIs are surgeon dependent resulting in some degree of variability and unpredictability and have less flattening effect due to their localization far from the optical center of the cornea. This means, they must be large to have any substantial effect on corneal curvature. However limbal incisions over 120 degrees of arc, especially when placed nasally or temporally, may denervate the cornea at that location, creating dry eye and healing problems. Furthermore, they are contraindicated in ectatic corneal disorders since the results are unpredictable and they may further destabilize the cornea.

Corneal pachymetry can be helpful but most surgeons empirically treat at 500-600 microns with a preset diamond or disposable metal blade.

With LRI technique the decrease in the mean astigmatism is reported to be between 25-52% by various authors.74,77-80.

Nichamin et al. recommended that the proper incision depth for LRIs is approximately 90% of the thinnest corneal depth around the limbus.1 The cutting depth of an empiric blade is commonly set to 600 µm.1 However Dong et al adjusted the cutting depth according to the preoperative corneal thickness considering that patients have variable corneal thicknesses, and showed that a cutting depth of less than 90% also achieved an acceptable correction effect on astigmatism.81

Asymmetrical incisions (e.g. single LRI) have a higher coupling ratio than symmetrical incisions (e.g. paired LRIs). Dong et al also stated that, performing the single LRI with CCI appears to produce similar effects to performing the paired LRI with CCI.81

Nichamin has developed two nomograms, which specify the use of LRIs according to the type of astigmatism and the patient's age. The standard Nichamin nomogram does not use pachymetry or adjustable blade-depth settings, but rather an empirical blade depth of 600 micrometers.32,33

For higher orders of astigmatism, a combination of CRI's and LRI's may be used. The length, depth, and placement of these incisions, as well as the age of the patient, will all affect the outcome of these incisions.

#### **2.4 Single or paired peripheral corneal relaxing incisions (CRIs)**

Corneal relaxing incisions(CRIs) run parallel to the limbus which can be single or paired, straight or arcuate, may treat slightly greater amounts of astigmatism (about 1-3D) as LRIs. They straddle the meridian of the steepest corneal curvature. These can be placed either at the time of surgery or post-operatively. They may be necessary when implanting multifocal intraocular lenses in eyes with more than 1 diopter of astigmatism.

Early investigations of the corneal incision techniques for astigmatism reduction included surgeons Thornton, Buzard, Price, Grene, Nordan, and Lindstrom in the early 1980s.26-30

Osher and Maloney described straight transverse keratotomy incisions in combination with cataract surgery while some others made variations on incision length, depth, number and their localization on the optical zone.76,82-86 In 1994, Kershner, coined the term *'keratolenticuloplasty'* meaning simultaneously reshaping the cornea through relaxing incisions and implanting an IOL to correct refractive error.87-92

Corneal relaxing incisions couple which refers to changes in corneal curvature occuring in the incised meridian and in the unincised orthogonal meridian 90 degrees away. Along the meridian of the incision and central to the incision, cornea flattens, while the meridian 90 degrees away steepens. The combination of flattening of the steeper axis with steepening of the flatter axis yields the total amount of astigmatism correction. This is called *coupling or flattening/steeping ratio*.30 If the amount of flattening in the steep meridian is equal to the amount of steeping in the flat meridian, then the *coupling ratio* is accepted to be 1, and no change in the spherical equivalent value occurs.30,83 Lindström found that coupling ratio was 1:1 when a straight 3-mm keratotomy or a 45 to 90 degree arcuate keratotomy incision facilitated at 5 to 7 mm-diameter optical zones; showing that the coupling ratio depends on the length, location and the depth of the incision. 30

Thornton described that, all transverse or arcuate corneal incisions will flatten the cornea in the meridian in which they are placed and treat astigmatism by acting as if tissue had been

Corneal pachymetry can be helpful but most surgeons empirically treat at 500-600 microns

With LRI technique the decrease in the mean astigmatism is reported to be between 25-52%

Nichamin et al. recommended that the proper incision depth for LRIs is approximately 90% of the thinnest corneal depth around the limbus.1 The cutting depth of an empiric blade is commonly set to 600 µm.1 However Dong et al adjusted the cutting depth according to the preoperative corneal thickness considering that patients have variable corneal thicknesses, and showed that a cutting depth of less than 90% also achieved an acceptable correction

Asymmetrical incisions (e.g. single LRI) have a higher coupling ratio than symmetrical incisions (e.g. paired LRIs). Dong et al also stated that, performing the single LRI with CCI

Nichamin has developed two nomograms, which specify the use of LRIs according to the type of astigmatism and the patient's age. The standard Nichamin nomogram does not use pachymetry or adjustable blade-depth settings, but rather an empirical blade depth of 600

For higher orders of astigmatism, a combination of CRI's and LRI's may be used. The length, depth, and placement of these incisions, as well as the age of the patient, will all affect the

Corneal relaxing incisions(CRIs) run parallel to the limbus which can be single or paired, straight or arcuate, may treat slightly greater amounts of astigmatism (about 1-3D) as LRIs. They straddle the meridian of the steepest corneal curvature. These can be placed either at the time of surgery or post-operatively. They may be necessary when implanting multifocal

Early investigations of the corneal incision techniques for astigmatism reduction included surgeons Thornton, Buzard, Price, Grene, Nordan, and Lindstrom in the early 1980s.26-30 Osher and Maloney described straight transverse keratotomy incisions in combination with cataract surgery while some others made variations on incision length, depth, number and their localization on the optical zone.76,82-86 In 1994, Kershner, coined the term *'keratolenticuloplasty'* meaning simultaneously reshaping the cornea through relaxing

Corneal relaxing incisions couple which refers to changes in corneal curvature occuring in the incised meridian and in the unincised orthogonal meridian 90 degrees away. Along the meridian of the incision and central to the incision, cornea flattens, while the meridian 90 degrees away steepens. The combination of flattening of the steeper axis with steepening of the flatter axis yields the total amount of astigmatism correction. This is called *coupling or flattening/steeping ratio*.30 If the amount of flattening in the steep meridian is equal to the amount of steeping in the flat meridian, then the *coupling ratio* is accepted to be 1, and no change in the spherical equivalent value occurs.30,83 Lindström found that coupling ratio was 1:1 when a straight 3-mm keratotomy or a 45 to 90 degree arcuate keratotomy incision facilitated at 5 to 7 mm-diameter optical zones; showing that the coupling ratio depends on

Thornton described that, all transverse or arcuate corneal incisions will flatten the cornea in the meridian in which they are placed and treat astigmatism by acting as if tissue had been

appears to produce similar effects to performing the paired LRI with CCI.81

**2.4 Single or paired peripheral corneal relaxing incisions (CRIs)** 

intraocular lenses in eyes with more than 1 diopter of astigmatism.

incisions and implanting an IOL to correct refractive error.87-92

the length, location and the depth of the incision. 30

with a preset diamond or disposable metal blade.

by various authors.74,77-80.

effect on astigmatism.81

micrometers.32,33

outcome of these incisions.

added to the keratotomy site.83 However, he also stated that a true 1:1 coupling ratio can only occur when the corneal incisions act as tissue added but at the same time the corneal circumference is not changed; which is achieved only with short, concentric and arcuate incisions.83

Although the corneal relaxing incision technique is a quick and easy procedure - despite worldwide accepted nomograms - the results of this technique are still less predictable, especially with higher levels of astigmatism, and can change the axis of the astigmatism or induce irregular astigmatism.

The maximal effect of incisions occurred when they are placed around the 5 to 7mmdiameter optical zone. Clinical use of paired arcuate incisions should be avoided in optical zones of 5 mm or less. Optical zones of 6, 7,8, and 9 mm offer technically easier surgery and less risk of glare to the patient by staying far from the visual axis.

The biggest effect is obtained by the first pair of incisions and the second pair may add only 20-30% flattening effect. Effect can not be increased by adding more pairs than 2 pairs of incisions. There is some debate about the acceptable maximum length of these incisions but the approach accepted by most surgeons is that incisions should not be made greater than three clock hours long.14

If we summarize the basic concepts for corneal incisions;


## **3. Corrections with intraocular lenses**

## **3.1 Toric IOL (T-IOL) implantation**

T-IOLs are popular for advantage of being precise, predictable, and reliable correction of moderate to high astigmatism, requiring no new skills for the surgeon. They offer the possibility of correcting not only spherical equivalent refraction, but also the astigmatism during phacoemulsification cataract surgery.

The toric IOL was first devised by Shimizu et al. in 1992.93 At the same year Grabow and Shepherd implanted the first foldable silicone toric plate haptic IOL. 94,95

Implanting a toric IOL is a single-step, reliable, small-incision approach with a result that is independent of the postoperative tissue healing response. They have distinct advantages compared with treatments involving corneal or limbal tissue incisions.3,27,30,72,78,87,95- 102 Toric IOL implantation is accepted as procedure that correct higher degrees of cylinder than can corneal procedures.93,103,104 However a recent study by Poll et al, demonstrates that toric IOL implantation and peripheral corneal relaxing incisions yielded similar results regarding surgical correction of astigmatism at the time of phacoemulsification cataract surgery achieving comparable results with mild-to-moderate astigmatism.105

Their effective correction of astigmatism relies on performing accurate keratometry, choosing appropriate lens as in any cataract surgery, and perfect insertion technique with no postoperative rotation. The success of a toric IOL can be judged not only by its ability to reduce refractive astigmatism, but also by its ability to maintain a stable position in the capsular bag in the longer term. The most frequent cause of T-IOL rotation following an uncomplicated cataract surgery is because of capsular bag shrinkage due to fibrosis. 106

By taking serial fundus photographs, Viestenz et al documented that rotation (or torsion) of an eye by 3 degrees was present in 36% of patients which may lead to overestimation or underestimation of the presumed spontaneous rotation of an implanted toric IOL.107 Their results show that 11.5 degrees of toric IOL rotation would lead to residual astigmatism that is 40% of the initial astigmatic power and 3 degrees, 10% of the initial power.107 Rotation of the lens by 15 degrees reduces the astigmatic correction by about 50%. With 30 degrees of rotation, all the toric power is nearly lost.108 Kershner has demonstrated that this problem may occur in only fewer than 6% of cases.96

The first study evaluating the rotational stability of a toric IOL(STAAR 4203T; STAAR Surgical Company,USA) showed this plate-haptic design to undergo rotations of more than 30 degrees in fewer than 5% of cases.106 Results from the phase1 FDA trial, showed that, in 95% of cases, the toric IOL was within 30 degrees of the intended axis, with a mean achieved reduction in refractive cylinder of 1.25D. 109

De Silva et al. showed in a series of 21 MicroSil 6116TU toric IOLs with Z-haptics (HumanOptics, Germany) that the mean rotation of this lens was 5.2 degrees and the maximum rotation was 15 degrees.110

Chang demonstrated in a series of 50 STAAR TL toric IOLs (STAAR Surgical Company,USA) a maximum rotation of 20 degrees and 72% of the IOLs were within 5 degrees of the intended axis.111 A smaller diameter version of this STAAR IOL (STAAR TF toric IOL) demonstrated rotation of up to 80 degrees and required subsequent repositioning in 50% of cases.111 Other currently used toric IOLs include the T-flex 573T and T-flex 623T (Rayner, United Kingdom), and the Acri.LISA Toric 466TD and AT TORBITM 709M (Acri.Tec, Germany).

Holland et al compared the AcrySof Toric intraocular lens (IOL) and an AcrySof spherical IOL to investigate the rotational stability of the AcrySof Toric IOL (Alcon Laboratories, Inc., Fort Worth, TX) in subjects with cataracts and preexisting corneal astigmatism and found out that Acrisof toric IOL showed favorable efficacy, rotational stability and distance vision spectacle freedom with a mean rotation of <4 degrees (range, 0-20 degrees).112

As with all plate-haptic IOLs, the T-IOLs should only be implanted with an intact capsule and a complete, continuous curvilinear capsulorhexis. The careful removal of viscoelastic from between the posterior capsule and the lens is important to prevent the early rotation of the IOL. Although some eyes may require an Nd:YAG capsulotomy for posterior capsular opacification, there have been no reports of subsequent off-axis deviation of the IOL. Jampaulo et al evaluated 115 eyes in which Staar toric IOL models AA4203TF and AA4203TL (Staar Surgical Co, Monrovia, California, USA) were implanted and found out that the mean difference in axis alignment was 1.36 degrees and no case had axis change more than 5 degrees after Nd:YAG capsulotomies.113

than can corneal procedures.93,103,104 However a recent study by Poll et al, demonstrates that toric IOL implantation and peripheral corneal relaxing incisions yielded similar results regarding surgical correction of astigmatism at the time of phacoemulsification cataract

Their effective correction of astigmatism relies on performing accurate keratometry, choosing appropriate lens as in any cataract surgery, and perfect insertion technique with no postoperative rotation. The success of a toric IOL can be judged not only by its ability to reduce refractive astigmatism, but also by its ability to maintain a stable position in the capsular bag in the longer term. The most frequent cause of T-IOL rotation following an uncomplicated cataract surgery is because of capsular bag shrinkage due to fibrosis. 106 By taking serial fundus photographs, Viestenz et al documented that rotation (or torsion) of an eye by 3 degrees was present in 36% of patients which may lead to overestimation or underestimation of the presumed spontaneous rotation of an implanted toric IOL.107 Their results show that 11.5 degrees of toric IOL rotation would lead to residual astigmatism that is 40% of the initial astigmatic power and 3 degrees, 10% of the initial power.107 Rotation of the lens by 15 degrees reduces the astigmatic correction by about 50%. With 30 degrees of rotation, all the toric power is nearly lost.108 Kershner has demonstrated that this problem

The first study evaluating the rotational stability of a toric IOL(STAAR 4203T; STAAR Surgical Company,USA) showed this plate-haptic design to undergo rotations of more than 30 degrees in fewer than 5% of cases.106 Results from the phase1 FDA trial, showed that, in 95% of cases, the toric IOL was within 30 degrees of the intended axis, with a mean achieved

De Silva et al. showed in a series of 21 MicroSil 6116TU toric IOLs with Z-haptics (HumanOptics, Germany) that the mean rotation of this lens was 5.2 degrees and the

Chang demonstrated in a series of 50 STAAR TL toric IOLs (STAAR Surgical Company,USA) a maximum rotation of 20 degrees and 72% of the IOLs were within 5 degrees of the intended axis.111 A smaller diameter version of this STAAR IOL (STAAR TF toric IOL) demonstrated rotation of up to 80 degrees and required subsequent repositioning in 50% of cases.111 Other currently used toric IOLs include the T-flex 573T and T-flex 623T (Rayner, United Kingdom),

Holland et al compared the AcrySof Toric intraocular lens (IOL) and an AcrySof spherical IOL to investigate the rotational stability of the AcrySof Toric IOL (Alcon Laboratories, Inc., Fort Worth, TX) in subjects with cataracts and preexisting corneal astigmatism and found out that Acrisof toric IOL showed favorable efficacy, rotational stability and distance vision

As with all plate-haptic IOLs, the T-IOLs should only be implanted with an intact capsule and a complete, continuous curvilinear capsulorhexis. The careful removal of viscoelastic from between the posterior capsule and the lens is important to prevent the early rotation of the IOL. Although some eyes may require an Nd:YAG capsulotomy for posterior capsular opacification, there have been no reports of subsequent off-axis deviation of the IOL. Jampaulo et al evaluated 115 eyes in which Staar toric IOL models AA4203TF and AA4203TL (Staar Surgical Co, Monrovia, California, USA) were implanted and found out that the mean difference in axis alignment was 1.36 degrees and no case had axis change

and the Acri.LISA Toric 466TD and AT TORBITM 709M (Acri.Tec, Germany).

spectacle freedom with a mean rotation of <4 degrees (range, 0-20 degrees).112

more than 5 degrees after Nd:YAG capsulotomies.113

surgery achieving comparable results with mild-to-moderate astigmatism.105

may occur in only fewer than 6% of cases.96

reduction in refractive cylinder of 1.25D. 109

maximum rotation was 15 degrees.110

Some studies showed that T-IOL implantation is more effective than limbal relaxing incisions(LRIs) and that it is reliable in reducing postoperative refractive astigmatism, consistent in producing a uncorrected visual acuity(UCVA) of 20/40 or better, has a low incidence of early positional problems with long-term stability.96,114-118 Other clinical studies have used the T-IOLs to correct excessive astigmatism by combining the lens with LRIs or using multiple T- IOLs in a piggyback fashion.74,119,120

Methods of marking the cornea during surgery and insertion techniques have been published, aiming to minimize any further error.121,122 Cyclotorsion may occur when the patient is supine, so it is essential to mark the patient's eye in an upright position prior to surgery.

## **3.2 Piggy-back toric-IOLS (piggy-back T-IOLs)**

Piggybacking system for IOLs is a combination of two IOLs implanted together to treat residual refractive error. These IOLs can be implanted during cataract surgery or clear lens extraction and IOL insertion (primary piggyback implantation) or as a secondary procedure following the initial IOL implantation (secondary piggyback implantation). Although the availability of the toric intraocular lens (IOL) provided the opportunity to correct some astigmatism; the limited power of lenses available, resulted in significant undercorrection in patients with high astigmatism.120

Piggyback T-IOLs are a combination of two toric IOLs implanted in the same fashion as spherical IOLs to provide satisfying vision for the high astigmatic patient. The only difference between piggyback implantation with spherical silicone IOLs and toric silicone IOLs, relate to the axis of implantation.120

As rotation is the main complication for one toric IOL, it is obvious that implantation of two IOLs together may exaggerate these problems; including rotation of both IOLs in opposite directions. Although rotation is rare, to avoid counter-rotation problems, Gills sutured 2 toric lenses together and implanted them through a 6.0 mm scleral incision in a patient with high astigmatism.119

The other concerns about piggybacking IOLS are; pupillary capture of the optic, interlenticular opacification(ILO), pigment dispersion, iridocyclitis, glaucoma and hyphema.123-129

Pigment dispersion and pigmentary glaucoma have been reported with placement of IOLs with sharp anterior optic edges in the ciliary sulcus.126,127 IOLs with rounded anterior optic edges are required for piggybacking.124 An unusual and rare complication of piggyback IOL insertion is posterior capsular rupture (PCR).129

Proper preoperative planning along with IOL type and patient selection are the most critical steps for performing this technique successfully. Orienting the toric lens by using preoperative keratometry or corneal topography to determine the steep axis of cylinder may not produce accurate results due to possibility of the cylinder changes induced by the cataract incision.117

Multiple peer-reviewed publications have demonstrated the effectiveness of both primary and secondary placement of piggyback spherical and toric IOLs as well as their possible complications.119,120,123-132

With the proper evaluation of the patient and excluding cases with pigment dispersion, elevated intraocular pressures, loose zonules from trauma or pseudoexfoliation, posterior synechia, and low endotelial cell values; implanting piggyback T-IOLs can achieve acceptable results and may represent a good choice for correcting high astigmatism or residual cylindrical ametropia in eyes that falls outside the range for accurate correction with other surgical procedures, or with a history of previous corneal or limbal keratotomies and/or T-IOL implantation and in eyes that are not good candidates for LASIK or PRK due to ocular surface disease or suspicious corneal topography.

## **4. Conclusion**

There are numerous techniques for dealing with astigmatism both during and after cataract surgery. Good uncorrected postoperative distance visual acuity can be obtained for a high percentage of cataract patients with preexisting corneal astigmatism. Corneal astigmatism can be treated effectively at the time of cataract surgery with either toric IOLs, corneal or limbal relaxing incisions or combination of all. There are advantages and disadvantages to each method. The appropriate patient-based plan of either one or a combination of these different surgical techniques, can provide a greater ability to correct cylindrical errors intraoperatively, achieving improved visual acuity and visual quality independent of spectacles. It should be kept in mind that postoperative keratorefractive surgery may also be available to enhance the condition of patients who achieve less-than-optimal astigmatic results.

## **5. References**


acceptable results and may represent a good choice for correcting high astigmatism or residual cylindrical ametropia in eyes that falls outside the range for accurate correction with other surgical procedures, or with a history of previous corneal or limbal keratotomies and/or T-IOL implantation and in eyes that are not good candidates for LASIK or PRK due

There are numerous techniques for dealing with astigmatism both during and after cataract surgery. Good uncorrected postoperative distance visual acuity can be obtained for a high percentage of cataract patients with preexisting corneal astigmatism. Corneal astigmatism can be treated effectively at the time of cataract surgery with either toric IOLs, corneal or limbal relaxing incisions or combination of all. There are advantages and disadvantages to each method. The appropriate patient-based plan of either one or a combination of these different surgical techniques, can provide a greater ability to correct cylindrical errors intraoperatively, achieving improved visual acuity and visual quality independent of spectacles. It should be kept in mind that postoperative keratorefractive surgery may also be available to enhance the condition of patients who achieve less-than-optimal astigmatic

[1] Nichamin LD. Astigmatism control. Ophthalmol Clin North Am 2006;19(4):485-493. [2] Xu L, Zheng DY. Investigation of corneal astigmatism in phacoemulsification surgery candidates with cataract. Zhonghua Yan Ke Za Zhi 2010;46(12):1090-4. [3] Kohnen T, Koch DD. Methods to control astigmatism in cataract surgery. Curr Opin

[4] Gills JP. Treating astigmatism at the time of surgery. Curr Opin Ophthalmol 2002;

[5] Nordan LT, Lusby FW. Refractive aspects of cataract surgery. Curr Opin Ophthalmol

[6] Nielsen PJ. Prospective evaluation of surgically induced astigmatism and astigmatic

[7] Fine IH, Hoffman RS. Refractive aspects of cataract surgery. Curr Opin Ophthalmol

[8] Buckhurst PJ, Wolffsohn JS, Davies LN, Naroo SA. Surgical correction of astigmatism

[9] Ferrer-Blasco T, Montés-Micó R, Peixoto-de-Matos SC, González-Méijome JM, Cerviño

[12] Alpins NA. New method of targeting vectors to treat astigmatism. J Cataract Refract

[13] Alpins NA. Astigmatism analysis by the Alpins method. J Cataract Refract Surg 2001;

[10] Grosvenor T. Etiology of astigmatism. Am J Optom Physiol Opt 1978; 55: 214–218. [11] Keller PR, Collins MJ, Carney LG, DavisBA, Van Saarloos PP. The relation between

during cataract surgery. Clin Exp Optom 2010;93(6): 409-18.

corneal and total astigmatism. Optom Vis Sci 1996; 73: 86–91.

keratotomy effects of various self-sealing small incisions. J Cataract Refract Surg

A. Prevalence of corneal astigmatism before cataract surgery. J Cataract Refract

to ocular surface disease or suspicious corneal topography.

Ophthalmol 1996; 7(1):75–80.

**4. Conclusion** 

results.

**5. References** 

13(1):2–6.

1995;6(1):36–40.

1995; 21:43–48.

1996;7:21-25.

Surg 2009;35(1):70-5.

Surg 1997;23:65-75.

27:31-49.


[37] Chayez S, Chayet A, Celikkol L, Parker J, Celikkol G, Feldman ST. Analysis of

[38] Lyle WA, Jin G. Prospective evaluation of early visual and refractive effects with small clear corneal incision for cataract surgery. J Cataract Refract Surg 1996; 22:1456-1460. [39] Masket S, Tennen DG. Astigmatic stabilization of 3.0 mm. temporal clear corneal

[40] Alio JL, Rodriguez-Prats JL, Galal A, et al.Outcomes of microincision cataract surgery versus coaxial phacoemulsification. Ophthalmology 2005;112(11):1997-2003. [41] Kaufmann C, Krishnan A, Landers J, Esterman A, Thiel MA, Goggin M. Astigmatic

[42] Long DA, Monica LM. A prospective evaluation of corneal curvature changes with 3.0-

[43] Masket S, Wang L, Belani S. Induced astigmatism with 2.2- and 3.0-mm coaxial

[44] Hayashi K, Yoshida M, Hayashi H. Postoperative corneal shape changes:microincision

[45] Wilczynski M, Supady E, Piotr L, Synder A, Palenga-Pydyn D, Omulecki W.

[46] Kaufmann C, Thiel MA, Esterman A, Dougherty PJ, Goggin M. Astigmatic change in

[48] Merriam JC, Zheng L, Urbanowicz J, Zaider M, Lindstrom B. The effect of incisions for cataract on corneal curvature. Ophthalmology 2003;110(9):1807-1813. [49] Tejedor J, Murube J. Choosing the location of corneal incision based on pre-existing astigmatism in phacoemulsification. Am J Ophthalmol 2005;139(5):767-776. [50] Rauz S, Reynolds A, Henderson HW, Joshi N. Variation in astigmatism following the

[51] Altan-Yaycoglu R, Evyapan PA, Akova YA. Astigmatism induced by oblique clear corneal incision: right vs. left eyes. Can J Ophthalmol 2007;42(4):557-61. [52] Ermis S, Ubeyt U, Ozturk F. Surgically induced astigmatism after superotemporal and

[53] Altan-Yaycioglu R, Akova YA, Akca S, Gür S, Oktem C. Effect on astigmatism of the

[54] Gonçalves FP, Rodrigues AC. Phacoemulsification using clear cornea incision in

[55] Giasanti F, Rapizzi E, Virgili G, et al. Clear corneal incision of 2.75 mm for cataract

steepest meridian. Arq Bras Oftalmol 2007;70(2):225-8.

cylinder. Eur J Ophthalmol 2006;16:385–393.

cataract incisions. J Cataract Refract Surg 1996; 22: 1451-1455.

phacoemulsification incisions. J Refract Surg 2009;25(1):21-24.

microincision. J Cataract Refract Surg 2009;35(9):1563-1569.

1996;121:65–76.

2009;1555-62.

2009;35(2):233-239.

1990;16(1):83-87.

11(5):656-660.

2004;30(6):1316-1319.

Surg 2007;23(5):515-8.

astigmatic keratotomy with a 5.0-mm optical clear zone. Am J Ophthalmol

neutrality in biaxial microincision cataract surgery. J Cataract Refract Surg

to 3.5-mm corneal tunnel phacoemulsification. Ophthalmology 1996;103(2):226-232.

versus small-incision coaxial cataract surgery. J Cataract Refract Surg

Comparison of surgically induced astigmatism after coaxial phacoemulsification through 1.8 mm microincision and bimanual phacoemulsification through 1.7 mm

biaxial microincisional cataract surgery with enlargement of one incision: a prospective controlled study. Clin Experiment Ophthalmol 2009;37(3):254-61. [47] Armeniades CD, Boriek A, Knolle GE,Jr. Effect of incision length, localization and shape

on local corneoscleral deformation during cataract surgery. J Cataract Refract Surg

single-step,self-sealing clear corneal section for phacoemulsification. Eye 1997;

superonasal clear corneal incisions in phacoemulsification. J Cataract Refract Surg

location of clear corneal incision in phacoemulsification of the cataract. J Refract

surgery induces little change of astigmatism in eyes with low preoperative corneal


[74] Gills JP, Van Der Karr M, Cherchio M. Combined toric intraocular lens implantation

[75] Budak K, Friedman NJ, Koch DD. Limbal relaxing incisions with cataract surgery. J

[76] Müller-Jensen K, Fischer P, Siepe U. Limbal relaxing incisions to correct astigmatism in

[77] Kaufmann C, Peter J, Ooi K, Phipps S, Cooper P, Goggin M. Limbal relaxing incisions

[78] Gills JP, Gayton JL. Reducing pre-existing astigmatism. In: Gills JP, Fenzl R, Martin RG, editors. Cataract surgery: the state of the art. Thorofare (NJ): Slack; 1998. pp. 53–66. [79] Bayramlar HH, Dağlioğlu MC, Borazan M. Limbal relaxing incisions for primary

[80] Carvalho MJ, Suzuki SH, Freitas LL*,* Branco BC, Schor P, Lima *AL.* Limbal relaxing

[81] Dong HK, Won RW, Jin HL, Mee KK. The Short Term Effects of a single limbal relaxing incision combined with clear corneal incision. Korean J Ophthalmol 2010; 24(2): 78–82. [82] Gills JP, Rowsey JJ. Managing coupling in secondary astigmatic keratotomy. Int

[83] Thornton SP. Theory behind corneal relaxing incisions/Thornton nomogram. En: Gills

[84] Osher RH. Paired transverse relaxing keratotomy: a combined technique for reducing

[85] Maloney WF, Alpins NA, Kershner RM, Epstein, RJ, Fichman, RA, Wallace, BW.

[86] Shepherd JR. Induced astigmatism in small incision cataract surgery. J Cataract Refract

[87] Kershner RM. Keratolenticuloplasty. In: Gills JP, Sanders DR, eds. Surgical Treatment of

[88] Kershner RM. Keratolenticuloplasty: arcuate keratotomy for cataract surgery and

[89] Kershner RM,ed. Refractive Keratotomy for Cataract Surgery and the Correction of

[90] Kershner RM. Clear corneal cataract surgery and the correction of myopia, hyperopia,

[91] Kershner RM. Clear corneal arcuate incision addresses astigmatism. Ocular Surgery

[92] Kershner RM. Correction of astigmatism in clear cornea cataract surgery. In: Gills J, ed.

[93] Shimizu K, Misawa A, Suzuki Y. Toric intraocular lenses: correcting astigmatism while

controlling axis shift. J Cataract Refract Surg 1994;20:523–526.

A Complete Surgical Guide for Correcting Astigmatism. Thorofare, NJ: Slack,

clear corneal cataract surgery. J Refract Surg 1999;15:586–589.

surgery. J Cataract Refract Surg 2005;31:2261–2265.

astigmatism. J Cataract Refract Surg 1989;15:32-37.

Astigmatism. Thorofare, NJ: Slack, Inc.; 1994: 143-155.

astigmatism. J Cataract Refract Surg 1995;21:274-277

and astigmatism. Ophthalmology 1997;104:381-389.

Astigmatism. Thorofare, NJ: Slack, Inc.; 1994.

Surg 2002;28:1585-1588.

Surg 2003;29:723–728.

Ophthalmol Clin 2003;43:29–41.

2007;23:499–504.

1992: 123-43.

1995;13(5):35-37.

Surg 1989;15:85–8.

News 1996;14:21:46-48.

Inc.;2002:49-64.

Cataract Refract Surg 1998;24:503–508.

and relaxing incisions to reduce high pre-existing astigmatism. J Cataract Refract

versus on-axis incisions to reduce corneal astigmatism at the time of cataract

mixed astigmatism and mixed astigmatism after cataract surgery. J Cataract Refract

incisions to correct corneal astigmatism during phacoemulsification*.* J Refract Surg

JP, Martin RG, Sanders DR. Sutureless Cataract Surgery. Thorofare, NJ. SLACK Inc;

Managing astigmatism during cataract surgery. Ocular Surgery News


[115] Rushwurm I, Scholz U, Zehetmayer M, et al. Astigmatism correction with a foldable

[116] Leyland M, Zinicola E, Bloom P, Lee N. Prospective evaluation of a plate haptic toric

[117] Nguyen TM, Miller KM. Digital overlay technique for documenting toric intraocular

[118] Till JS, Yoder PR, Wilcox TK, et al. Toric intraocular lens implantation: 100 consecutive

[119] Gills JP. Sutured piggyback toric intraocular lenses to correct high astigmatism. J

[120] Gills JP, Van Der Karr MA. Correcting high astigmatism with piggy back toric intraocular lens implantation. J Cataract Refract Surg 2002;28:547-549. [121] Ma JJK, Tseng SS. Simple method for accurate alignment in toric phakic and aphakic intraocular lens implantation. J Cataract Refract Surg 2008;34(10):1631–1636. [122] Graether JM. Simplified system of marking the cornea for a toric intraocular lens. J

[123] Shugar JK, Schwartz T. Interpseudophakos Elschnig pearls associated with late

[124] Gayton JL, Apple DJ, Peng Q et al. Interlenticular opacification: clinicopathological

[125] Werner L, Mamalis N, Stevens S, Hunter B, Chew JJ, Vargas LG. Interlenticular

[126] Chang WH, Werner L, Fry LL, Johnson JT, Kamae K, Mamalis N. Pigmentary

[127] Iwase T, Tanaka N. Elevated intraocular pressure in secondary piggyback intraocular

[128] Chang DF, Masket S, Miller KM, et al. ASCRS Cataract Clinical Committee.

[129] Packer M. The perils of piggybacking. Cataract & Refractive Surgery Today 2009; 9

[130] Akaishi L, Tzelikis PF, Gondim J, Vaz R. Primary piggyback implantation using the

[131] Akaishi L, Tzelikis PF. Primary piggyback implantation using the ReStor intraocular

[132] Jin H, Limberger IJ, Borkenstein AF, Ehmer A, Guo H, Auffarth GU. Pseudophakic eye

lens implantation. J Cataract Refract Surg 2005;31(9):1821-1823.

rupture. J Cataract Refract Surg 2009;35(8):1445- 1458.

lens: case series. J Cataract Refract Surg 2007;33(5):791-795.

hyperopic shift: a complication of piggyback posterior chamber intraocular lens

correlation of a complication of posterior chamber piggyback intraocular lenses. J

opacification: dual-optic versus piggyback intraocular lenses. J Cataract Refract

dispersion syndrome with a secondary piggyback 3-piece hydrophobic acrylic lens. Case report with clinicopathological correlation. J Cataract Refract Surg

Complications of sulcus placement of single-piece acrylic intraocular lenses: recommendations for backup IOL implantation following posterior capsule

Tecnis ZM900 multifocal intraocular lens: case series. J Cataract Refract Surg

with obliquely crossed piggyback toric intraocular lenses. J Cataract Refract Surg

lens axis orientation. J Cataract Refract Surg 2000;26:1496-1504.

intraocular lens. Eye 2001;15(2):202-205.

Cataract Refract Surg 2003;29:402-404.

cases. J Cataract Refract Surg 2002;28:295-301.

Cataract Refract Surg 2009;35(9):1498–1500.

Cataract Refract Surg 2000;26:330–336.

Surg 2006;32(4):655-661.

2007;33(6):1106-1109.

2007;33(12):2067-2071.

2010;36(3):497- 502.

(7):29–33.

implantation. J Cataract Refract Surg 1999;25:863–867.

toric intraocular lens in cataract patients. J Cataract Refract Surg 2000;26:1022-1027.

## *Edited by Michael Goggin*

This book explores the development, optics and physiology of astigmatism and places this knowledge in the context of modern management of this aspect of refractive error. It is written by, and aimed at, the astigmatism practitioner to assist in understanding astigmatism and its amelioration by optical and surgical techniques. It also addresses the integration of astigmatism management into the surgical approach to cataract and corneal disease including corneal transplantation.

Photo by robertprzybysz / iStock

Astigmatism - Optics, Physiology and Management

Astigmatism

Optics, Physiology and Management

*Edited by Michael Goggin*