Laser-Assisted Subepithelial Keratectomy (LASEK) 

Updated: Mar 28, 2017
Author: Brad Feldman, MD; Chief Editor: Michael Taravella, MD 

Overview

Background

Laser-assisted subepithelial keratectomy (LASEK) is a laser surgical procedure for the correction of refractive error. LASEK is specifically used to correct astigmatism, hyperopia (farsightedness), and myopia (nearsightedness). It is a "hybrid" technique between laser assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK). The LASEK technique attempts to decrease the occurrence of flap-related complications associated with LASIK and, as in PRK, is specifically helpful in patients with corneas that are otherwise too thin for LASIK. By retaining a flap of corneal epithelium, LASEK may decrease the risk of infection and incidence of corneal haze, while reducing recovery time and postoperative discomfort when compared with PRK.

History of the Procedure

Concepts of corneal refractive surgery, such as keratectomy, keratotomy, and thermokeratoplasty, were first described in 1898 by Lans who published a set of experiments that focused on treating astigmatism in rabbits.

Refractive surgery, as it is known today, was not realized until 1966 when Pureskin first appreciated its potential with the demonstration that refractive changes could be made by removing central tissue underneath a corneal flap. Barraquer later showed that the corneal disc could be resected and frozen so that it could be reshaped using a cryolathe. However, his technique used complex equipment and had high intraoperative and postoperative complication rates, and the freezing resulted in damage to the disc itself.

In the late 1980s, Ruiz and Barraquer performed the first published keratomileusis in situ. They followed principles formulated by Krumeich using a microkeratome to remove a portion of the cornea followed by a second plano cut, the thickness and diameter of which established refractive change. The first disc was then repositioned and sutured back onto the cornea. These initial attempts were complex and unpredictable, often leading to keratoconus and other irregular astigmatisms.

Burratto and Pallikaris then combined the microkeratome technique with the use of the excimer laser to ablate tissue and to induce refractive change. Buratto performed excimer laser ablation on the posterior surface of the resected corneal disc before replacing and resuturing it back to its original position. Pallikaris then used the excimer laser ablation on the corneal stromal bed under a hinged flap in rabbit corneas. Pallikaris attempted this technique on blind human eyes in 1989 and on sighted human eyes in 1991, thereby creating a refractive surgical technique similar to the procedures currently in practice.

In 1993, Slade developed an automated microkeratome to refine the creation of the flap. Slade was one of the first surgeons to perform LASIK in the United States.

Since its introduction, LASIK has been associated with various complications, specifically when performed on eyes with decreased corneal thickness, irregular astigmatism, dryness, preexisting ocular surface disease, or glaucoma, to the point where several of these entities have become relative contraindications to performing LASIK. For these reasons, LASEK was developed to reduce the chance of complications that occur secondary to LASIK while inducing less discomfort than PRK.

Italian ophthalmologist Camellin is credited with developing the original LASEK procedure when he described the Camellin technique in ophthalmic literature in 1999. This technique involved the use of alcohol to separate the corneal epithelium from the stroma to create an epithelial sheet that could be repositioned over the ablated stroma. Since then, this method has evolved into multiple techniques, including Butterfly LASEK developed by Vinciguerra and Camesasca in 2002, cruciform LASEK described by Amolis in 2002, and gel-assisted LASEK created by McDonald in 2004.[1] Each of these techniques is described in Intraoperative details.

Problem

Ocular refraction is defined as the ability of the eye to bend light rays to focus them on the retina. The cornea, the lens, and the axial length of the eye are the main contributors to the eye's refraction capability. The total refractive power of an emmetropic (or normal length) eye is approximately 58 diopters (D), of which 43 D come from the cornea and the remaining 15 D from the lens, aqueous, and vitreous. Astigmatism, myopia (nearsightedness), and hyperopia (farsightedness) are common forms of refractive error that cause irregularities of the bending of light rays, thereby leading to blurred or distorted vision.

Myopia (nearsightedness) is a condition in which the eye is too long or the refractive power is too great, causing objects to focus at a point before the retina rather than upon the retina itself (see the image below).

Illustration of myopia. Illustration of myopia.

This inability to focus appropriately leads to an inability to see distant objects clearly. This problem tends to first appear in school-aged children and may progress through adolescence but usually stabilizes in early adulthood.

In hyperopia (farsightedness), the eye is too short or the refractive error is too weak because the cornea is too flat (see the image below).

Illustration of hyperopia. Illustration of hyperopia.

This irregularity causes an inability of the eye to bring near objects into clear focus because light entering the eye focuses behind the retina rather than directly on it. Because younger individuals may accommodate (or adjust) to focus near objects, the blurred vision associated with hyperopia is often not appreciated until later years as the eye loses this ability to accommodate.

In astigmatism, the refractive power of the eye is not the same in all meridians (see the image below).

Illustration of an astigmatic cornea. Illustration of an astigmatic cornea.

For example, the eye may exhibit more myopia horizontally than vertically. It is usually secondary to an irregular curvature of the cornea that prevents light from properly focusing on the retina.

Epidemiology

Frequency

Astigmatism, myopia, and hyperopia are relatively common in the general population. Myopia and hyperopia have an estimated prevalence of 33% and 25%, respectively. The prevalence of astigmatism varies with the definition used as clinically significant astigmatism. As many as 75% of the population has at least minor, clinically insignificant astigmatism present in either one eye or both eyes. Specifically, in the general population, 44% have greater than 0.50 D, 10% have greater than 1 D, and 8% have greater than 1.50 D.

A refractive surgery survey conducted in 2004 regarding 2003 practices identified LASIK as the most common refractive surgical procedure, with wavefront-guided ablation as an increasingly popular entity, increasing from 13% to 60% during 2002-2003 alone. Of the more than 1000 ophthalmologists who participated in this retrospective study, 71% were found to perform PRK, and 41% were found to perform LASEK. Of those ophthalmologists who performed LASEK, more than one half only performed this procedure when LASIK was not an option.

Another survey focused on the refractive surgery practices of the United States Army Warfighter Refractive Eye Surgery Program (WRESP) during 2000-2003. Of the more than 16,000 patients over these 4 years, nearly three quarters of cases involved surface ablative procedures, namely PRK or LASEK. PRK was performed on 64.7% of eyes, LASEK was performed on 8.7% of eyes, and LASIK procedures were performed on the remaining 26.6% of eyes.

Indications

The major indications for refractive surgery include astigmatism, myopia, and hyperopia, specifically in patients who are intolerant of or who desire to be free from glasses or contact lenses. Typically, up to 10 D of myopia and 4 D of hyperopia are the limits of corneal refractive surgery, but the US Food and Drug Administration (FDA) has approved treatment of as much as 14 D of myopia, 6 D of hyperopia, and 6 D of cylinder.

Since the popularization of laser-assisted in situ keratomileusis (LASIK), surface ablative procedures, such as photorefractive keratectomy (PRK) and laser-assisted subepithelial keratectomy (LASEK), have usually been confined to individuals in whom LASIK is not recommended. However, due to the potential structural and other advantages of surface procedures, there are now many ophthalmologists who suggest surface procedures over LASIK, or who will endorse both equally. The characteristics that may prompt an ophthalmologist to recommend surface ablation over LASIK include the following:

  • Thin corneal pachymetry

  • Steep or flat corneas

  • Wide scotopic pupil (controversial)

  • LASIK complications in fellow eye

  • Predisposition to trauma

  • Irregular astigmatism

  • Glaucoma suspects

  • Recurrent erosion syndrome

  • Dry eye syndrome

  • Epithelial basement membrane disease

  • Corneal scars

  • Persistent epithelial infiltrates (typically related to soft contact lens wear or prior viral conjunctivitis)

Highly irregular astigmatism, specifically keratoconus, as well as severe dry eye syndrome can serve as contraindications to LASEK as well as to LASIK.

Relevant Anatomy

The cornea accounts for two thirds of the refractive power that acts to focus light rays on the back of the eye. Of this, approximately 80% of the refractive power is created by the air-tear interface. Average cornea diameter is approximately 11 mm vertically and 12 mm horizontally.

The cornea consists of 5 layers. From superficial to deep, these layers are the corneal epithelium, Bowman’s layer, the stroma, the Descemet membrane, and the endothelium.

The corneal epithelium consists of 5-7 layers of stratified squamous epithelium. Defects in this layer may cause severe pain secondary to the rich sensory innervation. Fortunately, damage to the epithelium is quickly repaired in healthy eyes. The Bowman layer, on the other hand, is not replaced after injury, and this tough layer of collagen fibers may become opacified and replaced by scar tissue after trauma. The stroma makes up about 500 µm (90%) of the average 550-µm central corneal thickness. Its 200-250 lamellae (flattened bundles of collagen) give the cornea its clarity, strength, and shape. The lamellae are produced by scattered stromal fibroblasts or keratocytes. Keratocytes are also responsible for wound healing if the cornea becomes damaged.

The Descemet membrane serves as the acellular basement membrane of the corneal endothelium. Like the Bowman layer, it is not replaced after injury and may result in scar formation. The deepest layer of the cornea is a monolayer of endothelial cells whose primary function is the maintenance of corneal fluid balance, thereby maintaining clarity across the cornea. Unlike the epithelium, these cells rarely undergo mitosis and instead decrease in number with age. See the images below for illustration of the layers of the cornea and corneal topography.

Illustration depicting the layers of the human cor Illustration depicting the layers of the human cornea.
Histologic slide of the human cornea identifying i Histologic slide of the human cornea identifying its layers: (1) corneal stratified squamous epithelium with underlying Bowman layer, (2) stroma with keratocytes dispersed throughout, (3) Descemet membrane, and (4) single layer of endothelium. Image courtesy of Mission for Vision. Retrieved from http://www.missionforvisionusa.org/anatomy/2005/10/cornea.html.
Example of placido based corneal topography. This Example of placido based corneal topography. This image depicts a large quantity of “with-the-rule” corneal astigmatism. The warmer colors represent steeper areas and the cooler colors represent flatter areas of the cornea. This illustration demonstrates symmetric steepness along the vertical meridian and relative flattening along the horizontal meridian.

Contraindications

Contraindications common to laser assisted in situ keratomileusis (LASIK), laser assisted subepithelial keratectomy (LASEK), and photorefractive keratectomy (PRK) include the following:

  • Unstable refractive error

  • Refractive error outside the range of correction (The range varies according to the surgeon's experience, the laser used, and the laser strategy; however, it is typically approximately 9-14 D of myopia, 4-6 D of hyperopia, and 2-6 D of astigmatism.)

  • Keratoconus or forme fruste keratoconus

  • Pellucid marginal degeneration

  • Significant dry eye syndrome

  • Active inflammation of external eye

  • Autoimmune disease

  • History of or active herpes simplex keratitis, because of the concern of eliciting reactivation of the virus

  • Active collagen vascular disease

  • Uncontrolled diabetes

  • Uncontrolled glaucoma

  • Pregnancy or breastfeeding

  • Use of medications that may adversely affect corneal wound healing, such as Accutane (isotretinoin), Cordarone (amiodarone hydrochloride), and Imitrex (sumatriptan)

  • Presence of a pacemaker

Contraindications unique to LASEK and PRK include the following:

  • Concern regarding postoperative pain

  • Requirement of rapid visual recovery

Unlike LASIK, patients with thin, flat, or steep corneas may still be candidates for LASEK and PRK.

 

Workup

Other Tests

See Preoperative details.

 

Treatment

Preoperative Details

Preoperative testing and workup for laser-assisted subepithelial keratectomy (LASEK) include the following:

  • Uncorrected visual acuity (UCVA)

  • Best spectacle-corrected visual acuity (BSCVA)

  • Manifest and cycloplegic refraction

  • Tonometry

  • Slit lamp examination

  • Dilated fundus examination

  • Ultrasound corneal pachymetry

Corneal topography

This test, completed by approximately 93% of surgeons performing refractive procedures, is used to assess the shape and the curvature of the corneal surface.

Several types of topography are noted (see the image below).

Example of placido based corneal topography. This Example of placido based corneal topography. This image depicts a large quantity of “with-the-rule” corneal astigmatism. The warmer colors represent steeper areas and the cooler colors represent flatter areas of the cornea. This illustration demonstrates symmetric steepness along the vertical meridian and relative flattening along the horizontal meridian.

In placido-based topography, a series of light rings is projected onto the eye, outlining the cornea. By measuring the distance between these rings at various points, the unit creates a color-coded map that illustrates the contour of the corneal surface. Irregularities in this contour may be secondary to keratoconus or history of contact lens use.

Corneal tomography

This test, using either scanning slit-beam or Scheimpflug technology, gives information about corneal thickness and posterior corneal curvature, in addition to the anterior corneal curvature information that is presented on standard corneal topographic maps. There is some evidence that this information may help in screening for keratoconus or forme fruste keratoconus.[2]

Corneal optical coherence tomography

Although not commonly performed, literature suggests that epithelial thickness profiles can help in the diagnosis of keratoconus.[3] Anterior segment optic coherence tomography (OCT) is an instrument that can produce such maps.

Infrared pupillometry

This test, performed by approximately 44% of surgeons, allows for an accurate and reproducible measurement of pupil size. The correlation between pupil size and postrefractive symptoms of glare, halos, or night vision problems is now controversial.[4]

Wavefront analysis

The majority of ophthalmologists who perform refractive surgery use this preoperative measurement, often as part of their planning for wavefront-optimized or wavefront-guided surgical treatments.

This analysis attempts to depict optical aberration of the corneal surface in an effort to find irregular astigmatism and refractive error. The technology analyzes the interaction of light within the optical system in the eye. By specifically focusing on oscillations of light waves within the optical path to depict the exiting locus of light points as they relate to the pupillary plane, the technology may detect corneal and lenticular imperfection.

The analysis results in a 2-dimensional wavefront map, wherein a green color indicates minimal wavefront distortion, a blue color indicates myopia, and a red color indicates hyperopia.

Schirmer test

This screening test, performed by approximately 35% surgeons preoperatively, may help quantify the severity of dry eye, which is an important factor when considering any refractive surgery.

Intraoperative Details

Several LASEK techniques are noted, and some of these techniques are described below. Each technique focuses on creating an epithelial flap under which an excimer laser is used to sculpt the corneal tissue. Camellin developed the first of these techniques, and it serves as the most widely used form of LASEK. Common to all procedures, topical anesthetic is applied prior to surgery, typically a combination of 0.05% proparacaine and 4% tetracaine. The eye is then prepped and draped in a sterile fashion with a lid speculum placed to maximize exposure.

Standard Camellin technique

The first step in this procedure involves creating a sharp, partial-thickness incision using a trephine blade to circumscribe the flap area. This blade is a finer tool than the microkeratome used in laser assisted in situ keratomileusis (LASIK) so that it enables the surgeon to cut through the outer corneal epithelium without penetrating deeper corneal layers, specifically the Bowman layer, which promotes scar tissue formation. Using the trephine, the surgeon applies constant downward pressure upon the cornea to create a 270-degree incision with a hinge.

Next, the surgeon typically uses a holding well to cover the eye with a solution of ethanol in sterile water, balanced salt solution (BSS), or physiologic solution for approximately 20-30 seconds to loosen the epithelial edges. Although the concentration of ethanol varies between surgeons, the current standard practice uses approximately 18-25% ethanol solution. This concentration has been shown to allow sharp wound edges and a clean, smooth Bowman layer. Greater concentrations of ethanol, as well as other chemical agents, such as 0.5% proparacaine, iodine, cocaine, and alkali-n-heptanol, have been associated with inflammatory response with a damaging effect on stromal keratocytes. Also, although mechanical epithelial debridement has also been shown to be effective, this technique often causes defects on the Bowman layer, which can result in corneal haze and irregularity.

Once the surface of the eye has been immersed in the alcohol appropriately, a sponge is used to dry the area and BSS is used to rinse the area. Usually, the area is also irrigated with an antihistamine in an effort to minimize the amount of histamine induced by the alcohol. An epithelial microhoe starts the flap, followed by use of the short end of an epithelial detaching spatula to detach the epithelium from the Bowman layer. Although the initial exposure to alcohol should not exceed 35 seconds, alcohol may be reapplied at this time for as long as an additional 15 seconds if the epithelial flap does not loosen easily secondary to adhesions or other epithelial irregularities.

Once loosened, the flap is folded at the 12-o'clock position to maintain hydration of the epithelium. The longer side of the spatula is then passed over the stromal surface to remove any debris. The flap typically consists of epithelium with its basement membrane attachment intact, which provides support to the epithelium throughout surgical manipulation. The point of detachment after alcohol submersion appears to be within the epithelial basement membrane or between the basement membrane and the Bowman layer.

Ablation with the 193-nm excimer laser is then carried out. The laser is focused and centered onto the pupil, enabling ablation of the tissue at the level of the Bowman layer. This is in contrast to LASIK, in which the ablative energy is transmitted to the midstromal region. During this treatment, the patient must maintain fixation. Modern lasers are typically equipped with a tracking mechanism that allows the laser to follow most small eye movements and to increase the accuracy of the ablations. Within this technique, Camellin proposed a 10% reduction in the attempted correction when treating myopia up to 10 D and a 20% reduction when treating 10-20 D relative to photorefractive keratectomy (PRK) in an effort to prevent overcorrection.

Once laser ablation is complete, another spatula is used to return the epithelial flap to its original position. Intact hemidesmosomal structures in the basal epithelium allow adhesion of the epithelial cells to ablated stroma after repositioning of the flap, a feature necessary to promote proper healing that may be disrupted by ethanol toxicity. Lastly, a soft bandage contact lens is applied, usually for 3 days. See the images below for intraoperative details.

This image depicts the epithelial flap of a porcin This image depicts the epithelial flap of a porcine eye as it is folded along its hinge to reveal the surface for laser ablation. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
This image, taken intraoperatively on a rabbit eye This image, taken intraoperatively on a rabbit eye, depicts the creation of the epithelial flap using the microkeratome. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
Image of corneal haze following refractive surgery Image of corneal haze following refractive surgery, as viewed through a slit lamp. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.

Azar flap technique

The Azar flap technique is similar to the standard Camellin technique, as described above, with the soaking of the corneal surface in ethanol, except this technique uses either one arm of a jeweler's forceps or one arm of a modified Vannas scissors to delineate the wound edge rather than a trephine blade. This difference allows customized variations for different corneal types.

The epithelial flap is pushed aside using a dry, nonfragmenting cellulose sponge, after which the excimer laser ablates the tissue appropriately. In this procedure, an anterior chamber cannula is used to hydrate the stroma and to float the epithelial flap back to its original position, after which the area is allowed to dry for 2-5 minutes.

Vinciguerra Butterfly technique

This technique maintains the limbal connection of the epithelial stem cells and the limbal vascular connections in an effort to increase epithelial viability, thereby improving visual recovery time and reducing discomfort.

Using a special spatula, a thin paracentral epithelial incision is made from the 8-o'clock position to the 11-o'clock position. Then, 20% alcohol in BSS is placed on the cornea for 5-30 seconds, allowing the epithelium to be separated from the Bowman layer. The spatula is used to further separate the epithelium from its underlying layer, from the center to the periphery in both directions, thereby creating 2 flaps from the original single paracentral line. The surgeon then retracts the sheets of epithelium toward the limbus. While holding these sheets in place using the retractor, the surgeon uses the excimer laser to ablate the tissue. The surface is smoothed with a hyaluronic acid masking solution, and the stretched epithelium is repositioned with overlapping margins.

McDonald gel-assisted technique

This alcohol-free technique uses viscous hydroxypropyl cellulose 0.3% (GenTeal Gel, Novartis Ophthalmics) to allow the separation of the epithelial flap and to prevent dehydration. After applying this gel below the epithelium with a cannula, with fine holes along the side, the cells are stripped using microkeratome suction. Within this procedure, 5% sodium chloride may be used to stiffen the epithelial cells before their manipulation, as the gel does not offer this property.

Once the gel is in position, the cells may be manipulated as the surgeon uses Vannas scissors to cut down the middle of the cornea. Within the gel cushion, the epithelium is pushed to the periphery without compromising cellular viability. After the flap has been created and folded, the gel is removed from the Bowman layer using a wet Weck-cel sponge, after which ablation may be performed. Once laser ablation is complete, the gel is again applied so that the epithelial sheet may be repositioned and a bandage contact lens may be placed.

Amolis cruciform technique

The Amolis cruciform technique is very similar to the standard Camellin technique, except a rotating microbrush is used to cut a cross into the epithelium to allow creation of the flap. Like the Butterfly technique, this method is aimed to protect the epithelial limbal stem cells and vascular connections in an effort to increase epithelial viability.

Epipolis laser in situ keratomileusis or epikeratome laser-assisted keratomileusis

Epipolis laser in situ keratomileusis or epikeratome laser-assisted keratomileusis (epi-LASIK) was developed by Pallikaris as a revision of the traditional LASEK procedure. Within this technique, the use of alcohol to float the flap is replaced with an epikeratome tool, which mechanically cuts and lifts the flap of epithelium. As discussed above, alcohol may cause potentially toxic responses in the cornea. This technique attempts to use the principles of LASEK without the use of alcohol, thereby promoting faster healing and less pain for patients. Additionally, the epikeratome leads to a precise, reproducible separation within the epithelium, thereby further eliminating many of the flap complications associated with LASIK.

Epi-LASEK technique

The theoretical advantage of Epi-LASIK over LASEK is the avoidance of alcohol and its potentially negative effects on flap viability. However, without the use of alcohol, the epithelium in the peripheral flap remains adherent, and flap separation may be difficult. Camellin developed Epi-LASEK, a technique that combines alcohol application with epikeratome use for flap creation.[5]

Sub-Bowman keratomileusis (SBK)

Also known as “thin-flap” LASIK, this technique aims to combine the benefits of surface ablation and LASIK. Instead of creating a epithelial flap, in SBK, a thin anterior flap (90-110 μ m) of epithelium, the Bowman layer, and the stroma is created with a femtosecond laser, which is a tool that provides a level of precision in flap creation previously unattainable with the microkeratome. This technique theoretically maintains both the postoperative comfort and flap viability advantages of LASIK while minimizing the depth of ablation and loss of corneal structural integrity seen in LASIK. Possible disadvantages of SBK compared with LASEK and surface ablative procedures include increased ablation depths and decreased corneal sensitivity. The risk of flap complications may be increased compared with standard LASIK.

Postoperative Details

In all of the procedures discussed above, a soft bandage contact lens is placed on the cornea at the closing of surgery and remains on the eye for several days to allow complete re-epithelialization. Healing of the corneal surface defect normally takes 3-10 days. This healing time is dependent on numerous factors, including the size of the area treated, the baseline health of the cornea, the patient's immune response, the concentration and the duration of medications applied intraoperatively, and the presence of coexisting medical problems, specifically diabetes. Approximately 78% of patients show complete closure of the defect by day 3 and 98.8% by day 7. If the contact lens is removed before closure is complete, the flap may peel away with the lens. If re-epithelialization remains incomplete at 3 days, the original lens may be replaced by a new lens for 3 additional days.

Topical steroids and antibiotics should be used until the defect is healed to limit inflammation and prevent infection. Steroids are typically continued for 3 weeks or longer, up to several months.

Typically, approximately 50% of patients experience mild-to-moderate postoperative pain, lasting 1-2 days postoperatively. This percentage may be lower compared with PRK but is definitely higher as compared with LASIK.

Functional vision recovery follows a pattern similar to re-epithelialization, also taking 3-10 days. This period is similar to PRK but exceeds the less than 24-hour recovery associated with LASIK.

In addition, the most commonly encountered adverse effect is light sensitivity with halo effect. This occurrence is similar to that seen in LASIK and PRK.

Complications

Although laser assisted subepithelial keratectomy (LASEK) avoids many of the flap-associated complications of laser assisted in situ keratomileusis (LASIK), including free caps, incomplete pass of the microkeratome, flap wrinkles, epithelial ingrowth, flap melt, interface debris, corneal ectasia, and diffuse lamellar keratitis, LASEK has its own disadvantages.

Complications associated with LASEK include the following:

  • Conversion of procedure into photorefractive keratectomy (PRK) - 10%

    • The 50-µm thin epithelial flap may not be strong enough to be repositioned and may instead need to be removed, thus converting the procedure into PRK.

    • Although most patients who undergo LASEK are within the parameters of PRK and are not likely to suffer adverse effects of this complication, those patients who are high myopes may have a greater likelihood of corneal haze associated with PRK.

  • Pain (greater than LASIK in 80% of patients)

  • Epithelial defects

  • Corneal scarring/haze (< 1-2%)

    • Although LASEK may carry a decreased rate of corneal haze relative to PRK, it may still develop secondary to an inflammatory response to the surgical manipulation of the corneal surface.

    • The inflammation leads to the formation of an opacified cellular layer that appears as a white haze and restricts light from transmitting to the back of the eye, thus causing a defect in vision (see the image below).

      Image of corneal haze following refractive surgery Image of corneal haze following refractive surgery, as viewed through a slit lamp. Image courtesy of Ronald R. Krueger, MD, Cole Eye Institute, The Cleveland Clinic Foundation.
    • The risk of scar formation increases with increasing ablation depth, and scars are common when treating more than 8 D of myopia.

  • Keratitis (0.5-1%)

    • The risk of keratitis is theoretically less than that of PRK, as the retained epithelial flap should act as a protective barrier. Postoperative infection is more likely when epithelial coverage is incomplete or when the surgical duration is longer than average.

    • Additionally, contact lenses may serve as a source of infection, as they are known to often be contaminated with microorganisms. Likely, because contact lenses are not used postoperatively in LASIK, LASIK has a lower incidence of keratitis (about 0.2%).

    • The occurrence of causative organisms of LASEK-associated keratitis is as follows:

      • Gram-positive bacteria (55.6%)

      • Atypical mycobacteria (19.4%)

      • Gram-negative bacteria (13.9%)

      • Fungal (< 1%)

      • Viral (< 1%)

  • Dry eye syndrome associated with recurrent erosions

    • This complication is secondary to decreased corneal sensation due to corneal denervation. It may last from a few weeks to 1 year, although, on average, it lasts 1-4 weeks.

    • Although this complication occur in LASEK and LASIK, it is more likely to be associated with a longer duration in LASIK.

  • Overcorrection (1%, incidence similar to LASIK and PRK)

  • Undercorrection (10-15%, incidence similar to LASIK and PRK)

  • Macular cyst formation (< 0.1%)

  • Irregular astigmatism (< 1%): This complication is secondary to decentration of the laser optical zone or uneven healing, leading typically to a wavy corneal surface.

  • Regression

Outcome and Prognosis

The United States Army WRESP Survey (2000-2003) concluded that photorefractive keratectomy (PRK), laser assisted in situ keratomileusis (LASIK), and laser assisted subepithelial keratectomy (LASEK) achieved comparable postoperative outcomes.[6] LASEK, specifically, has been found to be an effective procedure, with 76% efficacy in attaining 20/20 uncorrected visual acuity (UCVA) and 99% efficacy in attaining 20/40 UCVA. In a study of 421 eyes, an efficacy index comparing preoperative best spectacle-corrected visual acuity (BSCVA) to postoperative UCVA found improvement in 94.7% of patients after LASEK.

LASEK is also relatively predictable, with 83% achievement within 0.5 D of the target refraction and 98.4% within 1 D at the 6-month follow-up visit in 152 patients. At 4 years out, approximately 7% of patients need secondary surgical correction, predominantly because of the initial undercorrection in those with a high preoperative refractive error. The image below shows a more detailed table comparing the refractive techniques.

Relative differences of laser assisted in situ ker Relative differences of laser assisted in situ keratomileusis (LASIK), laser assisted subepithelial keratectomy (LASEK), and photorefractive keratectomy (PRK). Adapted from Taneri S, et al: Evolution, techniques, clinical outcomes, and pathophysiology of LASEK: review of the literature. Surv Ophthalmol 2004 Nov-Dec; 49(6): 576-602.

Although controversy surrounds the relative benefit of LASEK compared with PRK or EpiLASIK, a meta-analysis revealed no significant difference between LASEK outcomes and PRK outcomes over time.[7] Both procedures are equally acceptable and likely have similar outcomes to EpiLASIK.

Future and Controversies

Many refractive surgeons view laser assisted subepithelial keratectomy (LASEK) as the answer for patients who desire laser correction but who are not ideal candidates for laser assisted in situ keratomileusis (LASIK), most commonly secondary to corneal thinning or irregularities. However, these patients must be educated that many of the risk factors associated with LASIK apply to LASEK as well.

Although LASEK avoids many of the flap-associated complications of LASIK, such as free caps, incomplete pass of the microkeratome, flap wrinkles, epithelial ingrowth, and flap melt, it continues to have its own disadvantages, specifically postoperative discomfort and prolonged visual recovery as the patient awaits complete epithelial closure. Additionally, although probably lower than in photorefractive keratectomy (PRK), the risk of corneal haze continues.

Furthermore, like LASIK and PRK, LASEK is a relatively new procedure, developed within the past decade. Although the use of the excimer laser is FDA approved for LASIK, it is accepted as only an off-label use for LASEK. No studies have been conducted on the long-term effects of these procedures on the cornea, so their final effects, stability, and prognosis may only be theorized.

Of the choices, no one procedure has been established as ideal for all patients. Therefore, each surgeon must determine which refractive technique is appropriate on an individual basis.