**5.1 Marking techniques**

Preoperative reference and axis marking techniques could be broadly categorized as manual methods, image-guided systems, and intraoperative aberrometrybased methods.

The three-step manual technique is at present most commonly used [47], which is fairly accurate [48]. The first step is preoperative marking of the reference axis, which is commonly placed in the horizontal 3'o and 9'o clock positions. The second step is intraoperative alignment of the reference mark. The marking may be performed with a skin marking pen or needle. The patient should be sitting erect in a straight-ahead gaze while marking the reference axis. A change in patient position from sitting to supine may induce significant cyclotorsion; studies reported up to 28° of cyclotorsion in 68% of cases [49]. The manual marking methods have been limited by smudging of the dye, irregular, and broad marks.

Image-guided systems and intraoperative aberrometry have advantages compared with manual marking. The image-guided system based on the concept of landmarks to place the axis marks [50], which could be iris crypts, nevi, brush fields, etc. The systems capture a preoperative reference image and calculated the location of these marks and their distance in degrees from the target IOL axis. Then the system generated a final plan which provides simple angular directions from each reference mark to the planned axis of IOL placement.

There are a few image-guided systems at present such as CALLISTO Eye and Z Align (Carl Zeiss Meditec, Jena, Germany), VERION (Alcon, Fort Worth, Texas), TrueGuide (TrueVision 3D Surgical System, Santa Barbara, Calif), Osher Toric Alignment System (OTAS, Haag-Streit, Koeniz, Switzerland), and iTrace System (Tracey Technologies, Houston, Tx). Besides alignment, image-guided systems also contribute to planning the incisions, capsulorhexis size, and optimal IOL centration.

### **5.2 Intraoperative toric IOL alignment**

Intraoperative IOL positioning is the key procedure to sustain rotation stability. During IOL alignment, the IOL should be left about 3–5° anticlockwise of the final desired lens position, followed by complete OVD removal and hydration of the wounds. Most open-loop IOLs can be rotated only clockwise, and a complete rerotation will be needed if the IOL rotates further clockwise of the target axis.

The image-guided systems and intraoperative aberrometry could be definitely more useful than manual alignment. As mentioned above, the image-guided systems capture a preoperative reference image and an intraoperative image and then match the two images with respect to each other using landmarks. During the operation, a graphic overlay is then superimposed on the surgical field along the target axis, which provides a guide for toric IOL alignment. The image-guided systems and intraoperative aberrometry have improved the precision of toric IOL alignment, with <5° of deviation from the intended axis in the majority of cases.

(Rayner 600S IOL) was reported to have excellent rotational stability: average

[62]. In a study by Oshika et al., 6431 eyes are implanted with toric IOLs, and realignment was performed in 0.653% of cases [63]. An early repositioning performed after 1 week of primary cataract surgery had optical outcomes.

surgery, an IOL exchange, piggyback IOLs procedures may be considered.

undergoing multifocal IOLs may not tolerate residual astigmatism of <1 D, and multifocal IOLs without toric design perform best with less than 0.75 D of

(FineVision POD F) [73] also showed great performance.

interfere with the postoperative outcomes.

**7. Multifocal toric IOLs**

*Toric Intraocular Lenses*

*DOI: http://dx.doi.org/10.5772/intechopen.90153*

cylinder [67].

**8. Special cases**

and expanding.

**41**

In cases with more than 10° of rotation, realignment of the toric IOL is needed

IOL tilt could also induce astigmatism: tilting toric IOLs aligned at 180° would decrease with-the-rule astigmatism, bringing in undercorrection, while aligned at 90° increased against-the-rule astigmatism, bringing in overcorrection [64].

Meanwhile, LASIK, customized surface ablation, or femtosecond laser-assisted intrastromal keratotomies could also be used to correct residual astigmatism [65]. Some toric rotation check, such as https://www.astigmatismfix.com/, could help determine the amount of IOL rotation, and the expected residual refraction. When the large residual cylinder not amenable to correction by rotation alone or refractive

Toric designs are even more required in multifocal IOLs [66] because patients

In previous studies [68–72], toric multifocal IOLs achieved good visual performance, with UDVA better than 20/40 in more than 97% of patients, uncorrected near visual acuity better than 20/40 in 100% of patients, spectacle independence in more than 80% of patients, and residual refractive astigmatism lower than 0.50 D in 38–79% of patients. Toric trifocal IOLs such as a trifocal spherical hydrophilic IOL

But on the other hand, the selection of multifocal toric IOLs should be more restricted than monofocal toric IOLs, especially for the following candidates: (1) patients who had unrealistic expectations of visual quality when having related ocular comorbidities; (2) patients who may not tolerate dysphoric symptoms such

multifocal IOLs, such as abnormal κ or α angle, etc. Thus, a comprehensive ocular examination should be undertaken to rule out any ocular comorbidities that may

Normally, cases with irregular astigmatism, corneal ectatic disorders, postrefractive surgery, post-keratoplasty, and high myopia are not ideal candidates for toric IOL implantation, partly because they are unlikely to achieve complete refractive correction with toric IOLs. However, the amount of astigmatism may be partly reduced, decreasing spectacle dependence. And such cases may be considered for surgery after adequate counseling. As a consequence, the applications of toric IOLs are expanding to include special cases such as pellucid marginal degeneration [74, 75], mild keratoconus with cataract [76], astigmatism after keratoplasty [77–80], and high astigmatism [81]; even toric trifocal IOLs were used in high astigmatism cases [82]. In general, the indications of toric IOL are still controversial

as glare and halos; and (3) patients who had specific contraindications for

1.83° 1.44° at 6 months and no lens rotated more than 5° [61].

Compared with manual marking, Elhofi et al. had observed more precise alignment with VERION image-guided system [51], which offers comprehensive astigmatism management, the incision location optimization, toric IOL power calculation, as well as decreasing SIA.

However, Solomon et al. claimed that, compared with the surgeon's standard of care, the use of the VERION combined with intraoperative aberrometry (Optiwave Refractive Analysis system with VerifEye) did not significantly optimize the outcomes [52]. The accuracy of CALLISTO Eye is also very effective [53], and it also assists in planning the position of limbal relaxing incisions.

### **6. Complications**

Postoperative toric IOL misalignment is the major complication after toric IOL implantation. Toric IOL misalignment could harm visual quality. In a recent experimental study, 5° IOL axis rotation from the intended position determined a decay in the image quality of 7.03%, 10° of IOL rotation caused 11.09% decay, and 30° rotation caused 45.85% decay [54].

Toric IOL misalignment may be attributed to three factors: (1) inaccurate preoperative prediction of the axis of IOL alignment; (2) inaccurate intraoperative alignment; and (3) postoperative IOL rotation. IOL rotation may be observed as early as 1 hour after surgery, and a majority of rotations occur within the initial 10 days [18]. Early IOL rotation likely results from incomplete OVD removal, whereas late postoperative rotation is influenced by the IOL architecture, design, and axial length. In a recently published case report, the toric IOL was rotated more than 115° shortly after a neodymium: YAG (Nd:YAG) laser posterior capsulotomy [55].

Rotational stability of the IOL varies with design and material and strength of IOL capsular bag adhesions. Maximum rotational stability has been observed with hydrophobic acrylic lenses, followed by Hydrophobic acrylic, hydrophilic acrylic, PMMA and silicone. Loop haptic IOLs are better than plate-haptic IOLs on postoperative rotation stability when using silicone IOL, but they are similar when using acrylic IOL. A study of AT TORBI 709 M, which had one-piece hydrophilic acrylic with hydrophobic surface and a supporting four-haptic design, had rotation of more than 5° in 10% cases in 6 months [56]. Another study of AT TORBI 709 M reported 13% eyes had rotation of more than 10° [57], while another study reported 100% rotation of more than 10° [58]. Scialdone et al. found similar results in rotation stability between AT TORBI 709 M and AcrySof toric IOLs [59]. A long-term of 2-year study of AcrySof toric IOLs (hydrophobic acrylic IOL with Flexible loop haptic) reported postoperative rotation of more than 10° in 1.68% eyes, more than 5° in 23.3% eyes [18]. A recent cohort study [60] of 1273 eyes showed that AcrySof toric IOL was less likely to rotate, with 91.9% of eyes rotated 5° in AcrySof toric IOL eyes compared with 81.8% in TECNIS Toric IOL eyes (P < 0.0001); rotation 10° (97.8% Acrysof vs. 93.2% TECNIS, P = 0.0002) and 15° (98.6% Acrysof vs. 96.4% TECNIS, P = 0.02). Furthermore, a hydrophilic IOL with C-flex design

The image-guided systems and intraoperative aberrometry could be definitely more useful than manual alignment. As mentioned above, the image-guided systems capture a preoperative reference image and an intraoperative image and then match the two images with respect to each other using landmarks. During the operation, a graphic overlay is then superimposed on the surgical field along the target axis, which provides a guide for toric IOL alignment. The image-guided systems and intraoperative aberrometry have improved the precision of toric IOL alignment, with <5° of deviation from the intended axis in the majority of cases. Compared with manual marking, Elhofi et al. had observed more precise alignment with VERION image-guided system [51], which offers comprehensive astig-

However, Solomon et al. claimed that, compared with the surgeon's standard of care, the use of the VERION combined with intraoperative aberrometry (Optiwave Refractive Analysis system with VerifEye) did not significantly optimize the outcomes [52]. The accuracy of CALLISTO Eye is also very effective [53], and it also

Postoperative toric IOL misalignment is the major complication after toric IOL implantation. Toric IOL misalignment could harm visual quality. In a recent experimental study, 5° IOL axis rotation from the intended position determined a decay in the image quality of 7.03%, 10° of IOL rotation caused 11.09% decay, and 30°

Toric IOL misalignment may be attributed to three factors: (1) inaccurate preoperative prediction of the axis of IOL alignment; (2) inaccurate intraoperative alignment; and (3) postoperative IOL rotation. IOL rotation may be observed as early as 1 hour after surgery, and a majority of rotations occur within the initial 10 days [18]. Early IOL rotation likely results from incomplete OVD removal, whereas late postoperative rotation is influenced by the IOL architecture, design, and axial length. In a recently published case report, the toric IOL was rotated more than 115° shortly after

Rotational stability of the IOL varies with design and material and strength of IOL capsular bag adhesions. Maximum rotational stability has been observed with hydrophobic acrylic lenses, followed by Hydrophobic acrylic, hydrophilic acrylic, PMMA and silicone. Loop haptic IOLs are better than plate-haptic IOLs on postoperative rotation stability when using silicone IOL, but they are similar when using acrylic IOL. A study of AT TORBI 709 M, which had one-piece hydrophilic acrylic with hydrophobic surface and a supporting four-haptic design, had rotation of more than 5° in 10% cases in 6 months [56]. Another study of AT TORBI 709 M reported 13% eyes had rotation of more than 10° [57], while another study reported 100% rotation of more than 10° [58]. Scialdone et al. found similar results in rotation stability between AT TORBI 709 M and AcrySof toric IOLs [59]. A long-term of 2-year study of AcrySof toric IOLs (hydrophobic acrylic IOL with Flexible loop haptic) reported postoperative rotation of more than 10° in 1.68% eyes, more than 5° in 23.3% eyes [18]. A recent cohort study [60] of 1273 eyes showed that AcrySof toric IOL was less likely to rotate, with 91.9% of eyes rotated 5° in AcrySof toric IOL eyes compared with 81.8% in TECNIS Toric IOL eyes (P < 0.0001); rotation 10° (97.8% Acrysof vs. 93.2% TECNIS, P = 0.0002) and 15° (98.6% Acrysof vs. 96.4% TECNIS, P = 0.02). Furthermore, a hydrophilic IOL with C-flex design

matism management, the incision location optimization, toric IOL power

assists in planning the position of limbal relaxing incisions.

a neodymium: YAG (Nd:YAG) laser posterior capsulotomy [55].

calculation, as well as decreasing SIA.

rotation caused 45.85% decay [54].

**6. Complications**

*Intraocular Lens*

**40**

(Rayner 600S IOL) was reported to have excellent rotational stability: average 1.83° 1.44° at 6 months and no lens rotated more than 5° [61].

In cases with more than 10° of rotation, realignment of the toric IOL is needed [62]. In a study by Oshika et al., 6431 eyes are implanted with toric IOLs, and realignment was performed in 0.653% of cases [63]. An early repositioning performed after 1 week of primary cataract surgery had optical outcomes.

IOL tilt could also induce astigmatism: tilting toric IOLs aligned at 180° would decrease with-the-rule astigmatism, bringing in undercorrection, while aligned at 90° increased against-the-rule astigmatism, bringing in overcorrection [64].

Meanwhile, LASIK, customized surface ablation, or femtosecond laser-assisted intrastromal keratotomies could also be used to correct residual astigmatism [65]. Some toric rotation check, such as https://www.astigmatismfix.com/, could help determine the amount of IOL rotation, and the expected residual refraction. When the large residual cylinder not amenable to correction by rotation alone or refractive surgery, an IOL exchange, piggyback IOLs procedures may be considered.
