**4. Corneal refractive surgery**

Corneal refractive procedures used to correct myopia include excimer laser refractive surgery and corneal addition procedures.

Excimer laser refractive surgery for myopia works by removing corneal stroma to lessen the refractive power of the cornea and to bring the image of a viewed object into focus onto the retina rather than in front of it. Corneal addition procedures work by inserting ring segments, a donor lenticule or hydrogel lens inside the cornea, or using compression sutures to steepen the cornea.

#### **4.1. Corneal ablation by excimer laser**

This procedure includes lamellar procedures, such as LASIK, and procedures involving surface ablation:


This is divided into two main procedure groups: surface treatments and flap treatments.

In surface treatments, the skin on the surface of the cornea is removed by physical scraping or peeling and the laser is applied to the surface of the stroma. The laser corrects myopia in modifying the shape of the corneal stroma. In PRK, the surface skin is left to heal naturally with the aid of a contact lens; in laser epithelial keratomileusis (LASEK) or epipolis (Greak for surface) LASIK, known as EpiLASIK, the removed dead skin is replaced and acts like a bandage, while new skin regenerates below it [106].

Flap treatment, called laser-assisted in situ keratomileusis (LASIK), employs a blade or a femtosecond laser to cut a thin flap on the surface of the cornea. The flap is peeled back, and the excimer laser is applied within the body of the cornea stroma. At the end of the proce‐ dure, the flap is replaced. A variant of LASIK in sub-Bowman's keratomileusis (SBK), also referred to as "thin-flap LASIK", which differs from LASIK only in that the thickness of the flap is less [106].

#### **4.2. Laser-asssisted stromal in situ keratomileusis (LASIK)**

refractive power of the eye is reduced, by augmenting the anterior radius of curvature of the cornea (flattening the curvature of the anterior corneal surface) or by insertion of an appro‐ priate synthetic intraocular lens (IOL). Several surgical techniques are available for the

Several effective options for laser refractive surgery are available to patients, which provide the opportunity to meet more of the needs of an individual patient. These techniques are divided into two groups: those involving surgery on the cornea (corneal refractive surgery) and those involving surgery on the lens (lenticular refractive surgery). Procedures that involve altering the cornea are collectively referred to as keratorefractive surgery, refractive kerato‐

Corneal refractive procedures used to correct myopia include excimer laser refractive surgery

Excimer laser refractive surgery for myopia works by removing corneal stroma to lessen the refractive power of the cornea and to bring the image of a viewed object into focus onto the retina rather than in front of it. Corneal addition procedures work by inserting ring segments, a donor lenticule or hydrogel lens inside the cornea, or using compression sutures to steepen

This procedure includes lamellar procedures, such as LASIK, and procedures involving

This is divided into two main procedure groups: surface treatments and flap treatments.

In surface treatments, the skin on the surface of the cornea is removed by physical scraping or peeling and the laser is applied to the surface of the stroma. The laser corrects myopia in modifying the shape of the corneal stroma. In PRK, the surface skin is left to heal naturally with the aid of a contact lens; in laser epithelial keratomileusis (LASEK) or epipolis (Greak for surface) LASIK, known as EpiLASIK, the removed dead skin is replaced and acts like a

Flap treatment, called laser-assisted in situ keratomileusis (LASIK), employs a blade or a femtosecond laser to cut a thin flap on the surface of the cornea. The flap is peeled back, and

treatment of myopia (www.medpagetoday.com).

plasty, or refractive corneal surgery [28].

**4. Corneal refractive surgery**

and corneal addition procedures.

**4.1. Corneal ablation by excimer laser**

**•** Photorefractive keratectomy (PRK)

**•** Laser-assisted stromal in situ keratomileusis (LASIK)

**•** Laser-assisted subepithelial keratomileusis (LASEK)

bandage, while new skin regenerates below it [106].

**•** Epithelial laser-assisted in situ keratomileusis (Epi-LASIK)

the cornea.

216 Advances in Eye Surgery

surface ablation:

LASIK has become the single most common elective operation with over 35 million procedures performed worldwide by 2010 [1, 97]. Brilliant ideas with bioengineering accomplishments have led to correct about 90% of refractive errors in about a 10-min process with a less discomfort, a recovery time of a few hours and dramatic visual results overnight. www.lon‐ donvisionclinic.com)

The concept that refractive error could be corrected by sculpting corneal stromal tissue to change corneal curvature was the brainchild of Jose Ignacio Barraquer Moner in 1948 [24, 26, 27]. Barraquer developed a procedure he coined "keratomileusis" [25], which involved resecting a disc of anterior corneal tissue that was then frozen in liquid nitrogen, placed on a modified watchmaker's lathe, and milled to change corneal curvature. The word "keratomi‐ leusis," which is derived from the Greek roots *keras* (hornlike = cornea) and *smileusis* (carving), literally means "sculpting" of the "cornea" [97].

LASIK, the most common procedure for corneal refractive surgery to correct myopia [33, 114], combines lamellar corneal surgery with the accuracy of the excimer laser.

After immobilization of the eye by the positioning of a succion ring, a partial-thickness lamellar corneal flap is cut using a microkeratome (with an oscillating blade to shave 100–200 µm corneal flap, ranging in size from 9 to 10.5 mm); the excimer laser ablation is then performed after the flap to expose the corneal stroma; the laser is then focused and centered over the pupil with the patient looking at affixation light and a preprogrammed excimer ablation of the stroma is performed. The flap is after reflected onto the treated corneal stromal bed [19].

One of the critical steps in this procedure is creation of the corneal flap. Traditionally, the flap was created using mechanical microkeratomes, but during the last few years there has been the emergence of the new ultrashort-pulse lasers (picosecond and femtosecond) [66, 77, 114, 125]. There have been a number of technological advancements to overcome the difficulties associated with intraoperative flap and microkeratome-related complications [33]. The femtosecond laser is one such technology. Current clinical applications of femtosecond lasers have been developed to create flaps for LASIK [59, 96]. The femtosecond laser is a focusable infrared (1053 nm) laser; it employs ultrafast pulses in the 100-fs (100×10−15-s) duration range and makes closely spaced spots which are focused at a preset depth to photodisrupt tissue within the corneal stroma without inflammation and collateral tissue damage. Each laser pulse generates a small amount of microplasma, which results in microscopic gas bubbles in the interface and creates the flap. During treatment, the cornea is flattened with a suction appla‐ nating lens to immobilize the eye and to allow treatment of a geometrically simpler planar cornea [77]. Adjacent pulses are scanned across the cornea in a controlled pattern without causing significant inflammation or damage to the surrounding tissue, which possibly results in safer and more predictable flaps [125, 66].

The femtosecond laser was developed as a replacement of the microkeratome; it permits surgeons to customize and create a partial-thickness lamellar corneal flap and customize its diameter within the corneal stroma, providing more accuracy in flap thickness than with previous methods.

#### *4.2.1. Advantages of the femtosecond laser vs mechanical microkeratomes*


In LASIK, a larger flap is desired (up to 9 or 10 mm in diameter), in high myopes and in patients with large pupils to compensate for any decentration.

With the femtosecond laser, a smaller flap is possible if centered over the optical zone.

**•** the femtosecond laser has been reported to minimize aberrations and to be less dependent on corneal curvature;

#### *4.2.2. Disadvantages*


In recent studies, outcomes of a femtosecond laser for LASIK (IntraLase, IntraLase Corp., Irvine, CA) [29, 40, 62, 118;] demonstrated more predictable flap thickness, an insignificant increase in higher-order aberrations (HOAs) after flap creation, better uncorrected visual acuity (UCVA), and decreased epithelial injury relative to mechanical microkeratomes. The refractive outcomes after uncomplicated LASIK are relatively stable several years after surgery. The flap perimeter and interface undergo slow wound healing, which allows for early and stable refractive corrections [33, 101]. Although standard laser treatment eliminates conventional refractive errors, it can induce new HOAs that adversely affect the postoperative quality of vision, especially with respect to deterioration of the contrast functions [32, 81, 128]. A clinical refraction, composed of sphere, cylinder, and axis, describes what we now call lower-order aberrations. There exist other types of optical aberrations in the visual pathway of the eye, such as coma and spherical aberration, collectively called higher order. Change in the corneal shape after LASIK toward an oblate pattern is believed to be responsible for inducing spherical aberrations and HOAs after refractive surgery [15, 30].

Aspheric ablation profiles are designed to minimize further inducing spherical aberration by precompensating for its induction or by aiming to maintain the original Q value of the cornea. Wavefront-optimized LASIK compensates specifically for the induced spherical aberration by increasing the pulse energy in the periphery, with good reported visual outcomes [16, 33, 46, 94], and minimization of induced HOA. However, aspheric ablation profiles are not designed to decrease preoperative HOAs. Wavefront-guided ablation profiles are designed to customize the ablation pattern centered on the individual aberration profile of each eye to eliminate the preexisting HOAs and avoid inducing more aberrations. Limitation of such customized treatments in terms of induced changes in corneal asphericity and spherical aberration has been previously reported [30, 33]. There are contradicting reports comparing the results of visual outcome and HOAs between wavefront-guided and aspheric (wavefront-optimized) profiles [33, 43, 65, 69, 75, 82, 88, 100, 112].

#### **4.3. Photorefractive keractectomy (PRK)**

causing significant inflammation or damage to the surrounding tissue, which possibly results

The femtosecond laser was developed as a replacement of the microkeratome; it permits surgeons to customize and create a partial-thickness lamellar corneal flap and customize its diameter within the corneal stroma, providing more accuracy in flap thickness than with

**•** Unlike mechanical microkeratomes, which can have variable flap thickness, the femtosec‐ ond laser minimizes irregular flap thickness and epithelial injury as it etches a lamellar flap

**•** Potential biomechanical and histopathological advantages with femtosecond laser flap

In LASIK, a larger flap is desired (up to 9 or 10 mm in diameter), in high myopes and in patients

**•** the femtosecond laser has been reported to minimize aberrations and to be less dependent

**•** risk of diffuse lamellar keratitis which is reduced with intensive perioperative topical

In recent studies, outcomes of a femtosecond laser for LASIK (IntraLase, IntraLase Corp., Irvine, CA) [29, 40, 62, 118;] demonstrated more predictable flap thickness, an insignificant increase in higher-order aberrations (HOAs) after flap creation, better uncorrected visual acuity (UCVA), and decreased epithelial injury relative to mechanical microkeratomes. The refractive outcomes after uncomplicated LASIK are relatively stable several years after surgery. The flap perimeter and interface undergo slow wound healing, which allows for early and stable refractive corrections [33, 101]. Although standard laser treatment eliminates conventional refractive errors, it can induce new HOAs that adversely affect the postoperative quality of vision, especially with respect to deterioration of the contrast functions [32, 81, 128]. A clinical refraction, composed of sphere, cylinder, and axis, describes what we now call lower-order aberrations. There exist other types of optical aberrations in the visual pathway of the eye, such as coma and spherical aberration, collectively called higher order. Change in the corneal shape after LASIK toward an oblate pattern is believed to be responsible for

inducing spherical aberrations and HOAs after refractive surgery [15, 30].

With the femtosecond laser, a smaller flap is possible if centered over the optical zone.

in safer and more predictable flaps [125, 66].

*4.2.1. Advantages of the femtosecond laser vs mechanical microkeratomes*

with large pupils to compensate for any decentration.

previous methods.

218 Advances in Eye Surgery

creation.

at a desired corneal depth.

on corneal curvature;

corticosteroids [19, 33].

*4.2.2. Disadvantages*

**•** increased cost,

**•** surgical time,

PRK is a procedure in which the cornea is reshaped using an excimer laser. PRK evolves epithelial removal and photoablation of Bowman's layer and anterior corneal tissue. In contrast to LASIK, there is no need for flap creation with a microkeratome. PRK can be used in thinner corneas, where creation of a flap may leave less tissue than desired (usually 250 µm of cornea tissue) remaining to the posterior stroma.

PRK was the most commonly performed surgical procedure until the introduction of laser in situ keratomileusis (LASIK) in the mid-1990s. PRK is safe and effective, but the risk of corneal haze, especially in high myopia, is significant. Postoperative pain and slow visual rehabilita‐ tion limit the use of PRK (www.jaypeedigital.com).

PRK was first introduced in 1987 [73], and the techniques have continually been modified since then.

The most frequently performed procedures for low-to-moderate myopia utilize the excimer laser, which was first approved for this purpose by the FDA in 1995. A surface ablation technique, PRK was the first procedure performed.

Surgical procedure: An optical zone of 6 mm with a transition zone up to 8 mm is used. The central 6–9 mm of epithelium is removed by one of the several methods: mechanical scraping with a spatula or blade with or without topical alcohol, scraping with an automated brush, using the laser to reduce the thickness and then scrape the residual or to remove epithelium to Bowman's layer, or removing the epithelium with a keratome. The exposed surface is then ablated with laser followed by the placement of a bandage contact lens. A multipass technique is also used for PRK: The total amount of correction is separated into multiple smaller treatments of equal values of sphere and cylinder [91].

The total of these small treatments is equal to the actual-targeted correction. The laser is stopped during 15 s between each pass. All passes are performed during the same surgical procedure. The passes are set so that the operating time at each pass is less than 20 s [91, 92]. Postoperatively, a soft contact lens is inserted on the eye. Corticosteroid drops (fluorometho‐ lone (FML)) and nonsteroidal anti-inflammatory drugs (ketorolac tromethamine (Acular)) are given every 4 h for the first day and then thrice daily for the next 48 h. Antibiotic drops (ofloxacin 0.3%) are given every 4 h. For myopia more than −6 D, corticosteroids are given twice daily for the first postoperative month, four times daily for the second month, thrice daily for the third month, twice daily for the fourth month, and once daily for the fifth month. Corticosteroids are tapered after the first month follow-up exam. For myopia less than −6 D, corticosteroids are given only during the first week after surgery. Oral analgesics are also prescribed for pain during the first 72 h after surgery [91].

PRK is extremely useful in patients with thin corneas and in patients prone to flap dislocation such as military personnel or contact sports athletes.

Surface ablation techniques compared with LASIK have

#### **4.4. Advantage**

More residual posterior corneal stromal tissue is preserved

No stromal flap-related complications.

#### *4.4.1. Disadvantages*

More discomfort

Slower recovery of vision (due to the longer re-epithelialization time and potential develop‐ ment of subepithelial haze) [19, 107].

#### *4.4.2. Complications*

The corneal wound healing response after PRK is usually more complex than after LASIK for the same amount of correction [76].


#### **4.5. Laser-assisted subepithelial keratomileusis**

#### LASEK is indicated in


given every 4 h for the first day and then thrice daily for the next 48 h. Antibiotic drops (ofloxacin 0.3%) are given every 4 h. For myopia more than −6 D, corticosteroids are given twice daily for the first postoperative month, four times daily for the second month, thrice daily for the third month, twice daily for the fourth month, and once daily for the fifth month. Corticosteroids are tapered after the first month follow-up exam. For myopia less than −6 D, corticosteroids are given only during the first week after surgery. Oral analgesics are also

PRK is extremely useful in patients with thin corneas and in patients prone to flap dislocation

Slower recovery of vision (due to the longer re-epithelialization time and potential develop‐

The corneal wound healing response after PRK is usually more complex than after LASIK for

prescribed for pain during the first 72 h after surgery [91].

such as military personnel or contact sports athletes.

No stromal flap-related complications.

ment of subepithelial haze) [19, 107].

the same amount of correction [76].

**•** Overcorrection and undercorrection

**4.5. Laser-assisted subepithelial keratomileusis**

**•** thin corneas without any signs of keratoconus,

**•** deep set eyes and small palpebral fissure,

**•** low-to-moderate myopia with or without astigmatism

**•** extreme keratometric values (as in steep or flat corneas),

**•** Haze or corneal scar formation

**4.4. Advantage**

220 Advances in Eye Surgery

*4.4.1. Disadvantages*

More discomfort

*4.4.2. Complications*

**•** Regression

**•** Dry eyes

**•** Infectious keratitis

LASEK is indicated in

Surface ablation techniques compared with LASIK have

More residual posterior corneal stromal tissue is preserved


LASEK is also indicated in patients and for patients who are prone to trauma, such as military personnel and athletes [116]. Although there is a newer method of creating the epithelial flap mechanically by an epikeratome, without the use of alcohol, LASEK is still considered by many surgeons, for a personal preference or because of the affordability of the mechanical epikera‐ tome.

LASEK involves the creation of an epithelial flap that is put back in position after the laser treatment. Detachment of the epithelial flap is created with placement of a diluted solution of alcohol (typical 15–20%) in a well. Alcohol weakens the adhesions of the basal epithelial cells to the anterior stroma.

#### *4.5.1. Surgical procedure[20, 18, 116]*

In brief, after topical anesthesia and lid speculum application, positioning marks are used to mark the corneal surface, and then a semi-sharp circular well is used to administer 18% alcohol for 25–35 s on the corneal epithelial surface [18, 20, 116]. Using vannas scissors and jeweler's forceps, the margins of the delineated area are freed, leaving two to three clock-hours of intact margins for the hinge. Using a Merocel sponge, the loosened epithelium is then peeled back. After standard laser ablation, the epithelial sheet is gently repositioned with the aid of intermittent irrigation. The epithelium is carefully realigned using the preplaced positioning marks and allowed to dry for 3–5 min. Antibiotics and steroids eye drops are given and a bandage contact lens is placed to reduce the mechanical friction by the eyelid and to reduce postoperative pain [8, 91].

#### **4.6. Epithelial laser-assisted in situ keratomileusis (Epi-LASIK)**

Epi-LASIK is an innovative new procedure designed to create a thin flap in the epithelium with an epikeratome. Epi-LASIK is also an excellent alternative for patients with thin and steep of flat cornea [84]. The layer is preserved and replaced following the reshaping of the cornea using the excimer laser. Unlike LASER, which uses alcohol to separate the epithelium and the process can kill epithelial cells, Epi-LASEK permits the cells to live and continue to survive following replacement [60]. Preliminary clinical results suggest that Epi-LASEK is a safe and efficient method for the correction of low myopia [14, 83].

#### *4.6.1. Complications*

Postoperative dry eye syndrome Postoperative haze

#### **4.7. Corneal addition procedures**

These procedures include the following:


The procedure is used to correct greater degrees of myopia. Complications include irregular astigmatism, delayed visual recovery, and prolonged epithelial defects.


#### **4.8. Corneal relaxation procedures**

Radial keratotomy (peripheral deep stromal radial incisions) has been abandoned (www.med‐ pagetoday.com).

RK for myopia involves deep, radial corneal stroma incisions, which weaken the paracentral and peripheral cornea and flatten the central cornea. Patients with low-to-moderate myopia (up to 5 D) achieve the best results with RK in terms of the highest levels of UCVA. Stability of refraction after RK is lower than with many other refractive surgical procedures. The procedure was abandoned because of the long-term complication of bullous keratopathy secondary to endothelial cell loss.

Arcuate keratotomy (paired peripheral stromal incisions parallel to the limbus); the most often used to treat astigmatism after corneal graft surgery.

**•** Limbal relaxing incisions (deep limbal incisions of varying arc) are used during cataract surgery to reduce preexisting corneal astigmatism. These incisions are a valuable tool for correcting mild astigmatism. There are several nomograms for determining the number and length of peripheral corneal relaxing incisions (PCRIs). For example, www.lricalcula‐ tor.com features Nichamin and Donnenfeld nomograms; *Cataract and Refractive Surgery* (Kohnen and Koch, 2006) features Koch's nomogram. A PCRI is performed by creating a deep (usually about 600 µm) incision or pair of incisions in the peripheral cornea anteri‐ or to the corneal limbus and vascular arcade. The length and placement of the inci‐ sion(s) depend upon the axis and amount of cylinder. PCRIs work well if the SE is close to plano (due to the coupling effect), and the astigmatism is less than 2.00 D. If necessa‐ ry, it is possible to add or lengthen a PCRI at a later date. Patients with more significant astigmatism (>2.00 D) typically have greater success with LASIK or PRK than with PCRIs (Focal Point, 2014).

#### *4.8.1. Corneal thermocoagulation*

**4.7. Corneal addition procedures**

222 Advances in Eye Surgery

These procedures include the following:

that was previously frozen and reshaped

**4.8. Corneal relaxation procedures**

secondary to endothelial cell loss.

used to treat astigmatism after corneal graft surgery.

pagetoday.com).

**•** Intracorneal ring segments (e.g., INTACS); the most commonly used to treat keratoconus. **•** Epikeratophakia (removal of epithelium and placement of a donor lenticule of Bowman's layer and anterior stroma). Epikeratophakia (also known as epikeratoplasty and onlay lamellar keratoplasty) was introduced by Werblin et al. It involves removal of the epithelium from the central cornea and preparation of a peripheral annular keratotomy. No microker‐ atome is used. A lyophilized donor lenticule (consisting of Bowman's layer and anterior

The procedure is used to correct greater degrees of myopia. Complications include irregular

**•** Keratophakia (intrastromal implantation (insertion) of a donor lenticule of corneal stroma

**•** Compression sutures (to modify refractive error by steepening the cornea and reducing astigmatism). Corneal addition procedures, except intracorneal ring segments, are not

Radial keratotomy (peripheral deep stromal radial incisions) has been abandoned (www.med‐

RK for myopia involves deep, radial corneal stroma incisions, which weaken the paracentral and peripheral cornea and flatten the central cornea. Patients with low-to-moderate myopia (up to 5 D) achieve the best results with RK in terms of the highest levels of UCVA. Stability of refraction after RK is lower than with many other refractive surgical procedures. The procedure was abandoned because of the long-term complication of bullous keratopathy

Arcuate keratotomy (paired peripheral stromal incisions parallel to the limbus); the most often

**•** Limbal relaxing incisions (deep limbal incisions of varying arc) are used during cataract surgery to reduce preexisting corneal astigmatism. These incisions are a valuable tool for correcting mild astigmatism. There are several nomograms for determining the number and length of peripheral corneal relaxing incisions (PCRIs). For example, www.lricalcula‐ tor.com features Nichamin and Donnenfeld nomograms; *Cataract and Refractive Surgery* (Kohnen and Koch, 2006) features Koch's nomogram. A PCRI is performed by creating a deep (usually about 600 µm) incision or pair of incisions in the peripheral cornea anteri‐ or to the corneal limbus and vascular arcade. The length and placement of the inci‐ sion(s) depend upon the axis and amount of cylinder. PCRIs work well if the SE is close

stromal) is reconstituted and sewn into the annular keratomy site.

astigmatism, delayed visual recovery, and prolonged epithelial defects.

currently in widespread use (www.medpagetoday.com).

**•** Intracorneal lens (implantation of hydrogel lens within the corneal stroma).

Thermokeratoplasty (heating the peripheral cornea to shrink collagen and steepen the central corneal curvature) can be used to treat hyperopia or presbyopia.

#### **4.9. Criteria for corneal refractive surgery [8, 53]:**

Inclusion criteria (10 [53]:


Informed consent must be obtained from all patients after they receive a detailed description of surgical procedure and a thorough review of its known risks.

To be a candidate for either type of refractive procedure, the patient must have adequate central cornea thickness, regular topography, adequate pupil size, healthy and adequate tear film, and no absolute or relative contraindications to the procedure. LASIK is generally avoided in patients with previous corneal surgery, including PCRIs, in favor of surface ablation. With either procedure, the ablation can be a standard conventional, a wavefront-guided or a wavefront-optimized treatment. Conventional ablation treats lower-order or spherocylindri‐ cal aberrations. Wavefront-guided treatment reduces preexisting HOAs and reduces induction of new aberrations by creating a customized ablation profile. Wavefront-optimized ablation provides a customized treatment profile based on the patient's refraction and only treats the HOAs that would be induced by the alteration of this refraction.

Exclusion criteria [8, 53]:


#### **4.10. Preoperative evaluation**

The preoperative evaluation, a comprehensive medical eye evaluation includes history, examination, diagnosis, and initiation of management (www.rutzeneye.com).

The history should incorporate the elements of the comprehensive medical eye evaluation in order to consider the patient's visual needs and any ocular pathology. In general, a thorough **history may include the following items**:


**The comprehensive eye examination evaluates an evaluation of the physiologic function and the anatomic status of the eye, visual system, and its related structures. This includes the following elements (www.corneasociety.ca)**:


**•** Greater than 2.5 D of difference in sphere and cylinder between eyes

**•** Active ocular or systemic disease likely to affect corneal wound healing

examination, diagnosis, and initiation of management (www.rutzeneye.com).

**4.10. Preoperative evaluation**

address

224 Advances in Eye Surgery

**•** Chief complaint

**•** Review of systems

indicated)

features)

**•** Ocular dominance

**history may include the following items**:

**•** History of present ocular disease

other treatments and medications)

**the following elements (www.corneasociety.ca)**:

at distance and when appropriate at near

**•** Manifest and cyclogic refractions

**•** Ocular alignment and motility

**•** Previous ocular surgery, corneal diseases, glaucoma, or history of ocular trauma

The preoperative evaluation, a comprehensive medical eye evaluation includes history,

The history should incorporate the elements of the comprehensive medical eye evaluation in order to consider the patient's visual needs and any ocular pathology. In general, a thorough

**•** Demographic data including name, date of birth, gender, ethnicity, race, occupation,

**•** Present status of visual function (e.g., patient's self-assessment of visual status, visual needs,

**•** Ocular history (e.g., prior eye diseases, injuries, surgery, including refractive surgery, or

**The comprehensive eye examination evaluates an evaluation of the physiologic function and the anatomic status of the eye, visual system, and its related structures. This includes**

**•** Visual acuity UCVA, with current correction (the power of the present correction recorded)

**•** Measurement of best spectacle-corrected visual acuity (BSCVA) (with refraction when

**•** External examination (e.g., lids, lashes, and lacrimal apparatus; orbit; and pertinent facial

any recent or current ocular symptoms, and use of eyeglasses or contact lenses)

**•** Social history such as occupation, smoking history, alcohol use, family and living

**•** Systemic history, allergies and adverse reactions to medications,

**•** Family and social histories: pertinent familial ocular and systemic disease


Anterior segment structures examination includes a close inspection and biomicroscopic evaluation before and after dilation. Posterior segment structures evaluation (examination) requires (needs) a dilated pupil. The peripheral retina examination needs the use of the indirect fundus ophthalmoscopy or slit lamp fundus biomicroscopy. The examination of the macula and optic nerve needs the use of the slit lamp biomicroscope, with diagnostic lenses and OCT.

#### (www.rutzeneye.com)

The evaluation of myopia requires an assessment of both the refractive status of the eye, the patient's current mode of correction, symptoms, and visual needs. Refraction is often per‐ formed in conjunction with a comprehensive medical eye (American Academy of Ophthal‐ mology Preferred. Practice Patterns Committee. Preferred Practice Patterns Guidelines. Comprehensive Adult Medical Eye Evaluation, 2005). Evaluations of myopia include visual acuity, refraction, and refinement. The depth of the corneal lesion can be measured using an optical pachymeter [31]. The combination of manifest refraction, slit-lamp examination, and keratometry is generally sufficient for detecting the most anterior abnormalities.

#### **4.11. Postoperative care**

Postoperatively, antibiotics such as tobramycin (Tobrex; Alcon Laboratories, Inc, Fort Worth, Texas, USA), diclofenac 0.1% drops (Basel, Switzerland), and corticosteroids such as dexame‐ thasone 0.1% or prednisolone acetate 1% eyedrops


**3.** The drops of FML are tapered gradually three times a day for two weeks and switched to two times a day for two weeks [8]. Lubrication is prescribed as required [91]. After a LASIK, a shield is placed on the eye and taped to the forehead. Patients are instructed to wear their eye shield at night during the week, and not to rub the eyes or swim underwater in order to prevent flap displacement or infectious keratitis.

#### **4.12. Postoperative evaluation [8]**

After surgical procedure, the postevaluation includes:


Residual stromal bed (RSB) is estimated by two methods: (1) preoperative pachymetry minus predicted flap thickness (according to Pérez-Santonja and associates [86, 87]) minus calculated ablation depth and (2) postoperative pachymetry (using the latest available pachymetry data) minus predicted flap thickness.If enhancement procedures were performed, the RSB is estimated using the sum of the calculated ablation depths for all procedures including the safety and efficacy indexes: Safety = (BCVA postoperative/BCVA preoperative); Efficacy = (UCVA postoperative/BCVA preoperative).

#### **4.13. Results and outcome measures[53, 116]**

Primary outcome measures include uncorrected visual accuity, refractive stability, predicta‐ bility, loss of the best spectacle-corrected visual acuity, aberrometry, contrast sensitivity, and adverse event profile. Evaluation is based on measurement of [53, 116]:

**Efficacy** measured by the mean postoperative UCVA and the efficacy index, which is the ratio of mean postoperative UCVA to mean preoperative BSCVA.

**Predictability** measured by the mean postoperative SE within ±0.50 D, and within ±1.00 D of the intended correction; and the percentages of eyes within ±0.50 D and ±1.00 D of emmetropia (target refraction); a lesser likelihood of undercorrection and on the other hand, the more overcorrection seen postoperatively.

**Safety** measured by lost of two or more lines of BSCVA and the mean postoperative BSCVA; and the safety index, which is the ratio of mean postoperative BSCVA to mean preoperative BSCVA. The percentage of eyes that lost 1 or more lines of BSCVA at a period of time (six and 12 months) posttreatment [116].

**Retreatment and complications** percentage of treated eyes retreated for residual myopia and overcorrection.

### **4.14. LASIK complications [8]**

**3.** The drops of FML are tapered gradually three times a day for two weeks and switched to two times a day for two weeks [8]. Lubrication is prescribed as required [91]. After a LASIK, a shield is placed on the eye and taped to the forehead. Patients are instructed to wear their eye shield at night during the week, and not to rub the eyes or swim underwater

in order to prevent flap displacement or infectious keratitis.

**•** Visual acuity is measured using a standard Snellen acuity chart at 6 m.

adverse event profile. Evaluation is based on measurement of [53, 116]:

of mean postoperative UCVA to mean preoperative BSCVA.

Residual stromal bed (RSB) is estimated by two methods: (1) preoperative pachymetry minus predicted flap thickness (according to Pérez-Santonja and associates [86, 87]) minus calculated ablation depth and (2) postoperative pachymetry (using the latest available pachymetry data) minus predicted flap thickness.If enhancement procedures were performed, the RSB is estimated using the sum of the calculated ablation depths for all procedures including the safety and efficacy indexes: Safety = (BCVA postoperative/BCVA preoperative); Efficacy =

Primary outcome measures include uncorrected visual accuity, refractive stability, predicta‐ bility, loss of the best spectacle-corrected visual acuity, aberrometry, contrast sensitivity, and

**Efficacy** measured by the mean postoperative UCVA and the efficacy index, which is the ratio

**Predictability** measured by the mean postoperative SE within ±0.50 D, and within ±1.00 D of the intended correction; and the percentages of eyes within ±0.50 D and ±1.00 D of emmetropia (target refraction); a lesser likelihood of undercorrection and on the other hand, the more

**Safety** measured by lost of two or more lines of BSCVA and the mean postoperative BSCVA; and the safety index, which is the ratio of mean postoperative BSCVA to mean preoperative

After surgical procedure, the postevaluation includes:

**4.12. Postoperative evaluation [8]**

**•** Cycloplegic refraction

**•** Slit-lamp biomicroscopy

**•** Applanation tonometry **•** Corneal topography

**•** Dilated funduscopy

**•** UCVA **•** BSCVA

226 Advances in Eye Surgery

**•** Measurement of manifest refraction

(UCVA postoperative/BCVA preoperative).

**4.13. Results and outcome measures[53, 116]**

overcorrection seen postoperatively.

Keratome and flap complications (miscreated flaps, flap striae, interface inflammation, traumatic flap tears with initial flap lift, loss of suction, and epithelial defects, etc.)

Intraoperative complications such as ectasia, flap striae, flap dislocation ;Laser complications such as misinformation/improper ablation, decentered or improperly registered ablation, reduced quality of vision ; complications of healing/infection/inflammation such as recurrent corneal erosions, Infectious keratitis, epithelial ingrowth, diffuse lamellar keratitis (DLK), post-LASIK dry eye syndrome ; other complications of LASIK such as intraocular pressure meas‐ urement after LASIK optic neuropathy and glaucoma (www.operationauge.com).
