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LASEK Complications

Jae Bum Lee, MD, PhD

Massachusetts Eye and Ear Infirmary, Schepens Eye Research Institute,

Harvard Medical School

Boston, MA

Laser epithelial keratomileusis (LASEK), is a modified photorefractive keratectomy (PRK) technique that is based on the detachment of an epithelial flap after the application of an alcohol solution. The flap is repositioned after laser ablation (1). In LASEK, there may be a slight learning curve as in PRK or laser in situ keratomileusis (LASIK). In our experience, most of the complications occurred in the initial 30 cases. Alcohol leakage during the surgery was the most common complication in the beginning. With experience, making the epithelial flap was relatively not so difficult after several cases. LASEK does not have the serious complications associated with LASIK because a stromal flap is not created.

Figures 1 through 5 illustrate the stages involved in LASEK.

The laser epithelial keratomileusis procedure was performed as follows. A preincision of the corneal epithelium was performed with a special microtrephine with 8.00-mm diameter, 70-µm-deep calibrated blade (Janach, J 2900S) (Fig. 1). The trephine was designed to leave a hinge of approximately 80 degrees at the 12 o’clock position. An alcohol solution cone (Janach, J 2905) with an 8.5-mm diameter was placed on the eye. Twenty percent alcohol solution, made with distilled water, was placed for 25 to 30 seconds (Fig. 2). A dry Weck cel sponge was used to remove the alcohol from the cone. The cornea and conjunctiva were washed thoroughly with a balanced salt solution. Epithelial debridement was performed with an epithelial microhoe (Janach, J 2915A) (Fig. 3). The epithelial flap was gently detached, gathered, and folded at the 12 o’clock position (Fig. 4). At this point, the treatment proceeded similar to traditional PRK.

After laser ablation, the stromal surface was irrigated with balanced salt solution and the epithelial flap was repositioned using a spatula (Janach, J 2920A) (Fig. 5). After repositioning the epithelial flap, we left the epithelial flap to adhere to the underlying stromal bed for 1 minute. At the end of the surgery, a therapeutic contact lens (diameter 14.2 mm, base curve (BC) 8.7 mm) was applied to the eye. After complete reepithelialization, ofloxacine 0.3% and fluorometholon 0.1% were administered four times daily for the first postoperative month, three times daily for the second month, twice daily for the third month, and then once per day for the fourth month. We also checked uncorrected visual acuity, corrected visual acuity, and refractive errors after surgery. Subepithelial haze was graded from zero to four and postoperative pain was graded from zero to three. All patients were asked about their surgical preference.

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Figure 5 The epithelial flap is repositioned over the ablated stroma.

SHORT-TERM COMPLICATIONS

LASEK Procedure-Related Complications

Alcohol Leakage During the Surgery

Alcohol leakage during the surgery usually occurred in the initial cases. The rate of alcohol leakage decreased approximately 1% to 2% after the first several cases. When the alcohol solution cone is applied on the cornea, too much tension on the cone and high magnification of the operating microscope should be avoided to minimize the incidence of alcohol leakage. Before applying the alcohol solution cone, a brief explanation to anticipate pressure on the eye and blurred vision makes the patients more cooperative. When an alcohol leak occurs, it should immediately be absorbed with a dry cellulose sponge and the cornea and conjunctiva irrigated thoroughly with balanced salt solution. These patients reported postoperative pain, but no eye complications, such as conjunctival and corneal erosion or limbal cell deficiency, developed later.

Incomplete Epithelial Detachment

Incomplete epithelial detachment, such as tear in the flap, buttonhole, or fragmented flap, usually occurred in the initial cases (Fig. 6). The rate of incomplete epithelial detachment decreased to less than 5% after a brief learning curve.

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To avoid creating an incomplete epithelial flap, precise and sufficient epithelial trephinization on the cornea is required. When the initial trephinized edge is cut and lifted, the detachment can proceed in a similar fashion as a continuous curvilinear capsulorrhexis in cataract surgery. Too much tension during this step may result in a tear or buttonhole in the flaps. Alcohol exposure may be prolonged in contact lens wearers whose epithelium tends to be more adherent. If the epithelial detachment is difficult, an additional 10-second

Figure 6 Fragmented epithelial flaps are placed on the stromal bed after surgery.

exposure to alcohol is usually helpful to facilitate flap creation. If flap detachment is unsuccessful, one can easily convert to PRK.

Epithelial Healing

The duration to complete epithelialization in LASEK seems similar to PRK. The epithelium usually healed in 3 to 5 days. Two to 3% of eyes healed 6 days after surgery. Epithelialization can be delayed in cases of incomplete epithelial detachment, contact lens intolerance, and severe infiltrate. In these situations, additional eye drops such as 1% hyaluronic acid may improve the epithelial healing.

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might be the cause (3). Half of the eyes with contact lens intolerance, mostly in their 40s, had filamentary keratitis after the application of the pressure patch and with the cessation of eye drops including lubricant solution (Fig. 7). These observations suggest that performing LASEK in those older than 40 should be reconsidered. A flat base-curve therapeutic contact lens (BC 8.7-mm) and frequent lubrication with preservative-free artificial tears is recommended to minimize contact lens intolerance.

Infiltrates

Infiltrates seen after LASEK are usually mild and are frequently associated with postoperative pain and tearing (Fig. 8). These sterile infiltrates may be multiple with no associated ocular discharge and are typical when alcoholic exposure time exceeds 40 seconds. Infiltrates are less after LASEK compared to PRK, presumably because the epithelial flap covers the ablated stroma and prevents the migration of inflammatory cells from the tear fluid. The use of nonsteroidal anti-inflammatory eye drops in the first several postoperative days further lessens the accumulation of white blood cells in the cornea.

Infections

Corneal infection after LASEK is rare. In our experience, there was no severe infectious keratitis. The risk of infection is reduced because the epithelial flap acts as an effective protective barrier against microorganisms. If corneal infection occurs, it could be easily recognized before complete epithelialization. An enlarging white infiltrate indicative of infection should be treated with antibiotics immediately. In cases wherein there is no purulent discharge but there are multiple infiltrates, topical steroids could be cautiously added to counteract a possible immune reaction secondary to the nonsteroidal antiinflammatory drug.

Dry Eye

Of the patients who want to undergo refractive surgery, a large number cannot tolerate contact lenses because of either preexisting dry eye or secondary dry eye syndrome caused by long-term contact lens usage. Commonly, these patients continue to report dry eye after surgery. Despite an improvement of visual acuity and a grossly normal ocular surface after successful correction of the refractive error, symptoms such as ocular fatigue, discomfort, and irritation persist. Additionally, the signs of dry eye syndrome such as conjunctival injection and superficial punctate keratopathy were often observed (Fig. 9). A recent study (4,5) reported a decrease in tear flow and tear film stability after PRK. The decreased amount of tear secretion after PRK was attributed to sensory deprivation caused by corneal sensory nerve damage (6,7). Corneal sensitivity after PRK has been noted to be initially reduced, but it returns to almost normal levels within 3

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Figure 8 Corneal infiltrate in the periphery of the cornea is observed.

months postoperatively (8–10). Therefore, dry eye symptoms are expected to improve approximately 3 to 6 months after surgery. There are several other possible causes of dry eye syndrome after LASEK. First, because of long-term use of multiple medications, including steroids, after surgery, these eye drops may have a toxic effect on the ocular surface. Second, the change of tear flow dynamics brought about by a flattened corneal surface result in an alteration of the surface tension and tear film layer stability. Third, most patients do not wear glasses after surgery, but if worn they could protect the eye from wind and prevent tear evaporation. Fourth, usage of the contact bandage lens might aggravate the dry eye symptom after LASEK.

Dry eye symptoms might be worsened if patients have a Schirmer test of less than 5 mm before surgery or are older than 40. Careful observation and prompt treatment for dry eye are required after LASEK, particularly in the early postoperative period. Frequent lubrication with preservative-free artificial tears and ointment during nighttime is helpful. Humidification at home or office may also be beneficial. If the symptoms are severe, punctal plugs are recommended.

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Figure 9 Superficial punctate keratopathy from dry eye often observed after LASEK.

Laser-Related Complications

Undercorrection

Residual myopia is caused by insufficient initial treatment more commonly observed with high degrees of myopia. If there is an undercorrection and the patient is not satisfied with the level of vision, additional treatment may be performed. It is usually best to wait until the refraction is stable. In our experience, when LASEK enhancement after primary LASEK was performed, there was no difficulty in making the epithelial flap using the same technique as in a primary LASEK procedure.

Overcorrection

Patients with overcorrection may experience blurred vision when viewing objects up close. LASEK has been observed to cause slight hypercorrection compared to PRK. A possible explanation is the hyperosomolar property of the 20% dilute alcohol solution absorbs some water content of the cornea during alcoholic application, resulting in relative dryness of the stroma and more ablation during the procedure. A nomogram adjustment of 5% to 10% reduction compared to the PRK computed treatment is recommended.

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LONG-TERM COMPLICATIONS

Wound Healing-Related Complications

Corneal Haze

Corneal haze corresponds to a corneal healing response after excimer laser treatment induced by activation and migration of keratocytes and newly synthesized collagen (11). Factors that may be related to increased haze include depth of ablation, presence of an epithelial flap, and, to a lesser extent, laser beam homogeneity and epithelial removal

Figure 10 Corneal haze, +3 grade, seen in a case of high myopia after LASEK.

method during treatment. One of the reported advantages of LASEK is it produces less corneal haze than PRK. For low to moderate myopia, using a four-point scale, the mean corneal haze score at 1 month after PRK was 0.86±0.45 compared to 0.46±0.24 after LASEK. This was found to be statistically significant (1). Twenty-three percent of LASEK-treated eyes showed a corneal haze of not less than +1 grade at 1 month. By 6 months, only 2% had a +1 grade corneal haze.

Although the detailed underlying cellular events remain unclear, the epithelial flap is observed to expand and lengthen enough to cover the cut epithelial border and seal the bare stroma, thereby preventing or decreasing the release of cytokines and growth factors

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from the stroma and damaged epithelium. The decrease in the initial inflammatory damage to the stroma is believed to reduce anterior stromal keratocyte apoptosis and subsequent replenishment with activated keratocytes, leading to less synthesis of collagens (12). However, despite the presence of an intact epithelial flap, moderate to severe haze was still occasionally observed in high diopters of myopic treatment (Fig. 10). LASEK is therefore recommended in low to moderate myopia only.

Corticosteroid-Induced Elevated Intraocular Pressure

Raised intraocular pressure (IOP) related to topical steroid use occurs more frequently with high-potency steroids such as FML Forte 0.25% and dexamethasone phosphate 0.1%. In LASEK, in which the corneal haze is expected to be minimal, mild potency steroids may be sufficient to reduce haze formation. But it is still necessary to monitor the IOP after LASEK while the patient continues to use topical steroids.

Laser-Related Complications

Glare/Halos

The incidence of glare and halo after LASEK seems to be similar to PRK. Halos occur when the pupil size in dim light exceeds the effective optical zone size or when there is decentered ablation. A halo may be a pronounced form of spherical aberration. Persistent halos are rare and, when present, their effect tends to diminish with time.

Decentration

Decentration can occur if the laser beam is not precisely aligned with the surgeon’s eyepiece before the procedure or if there is poor patient fixation. Maloney proposed that a decentration less than 0.50 mm would not cause subjective symptoms such as glare and halo (13). Machat suggested that decentration more than 1.0 mm would create significant monocular diplopia, asymmetric night glare, reduced image quality, and blurred visual acuity (14). Decentration may be less after LASEK than PRK. Although a histological evaluation was not performed, a smoother and more regular surface can be seen through the operating microscope after epithelial debridement with 20% ethanol in LASEK than mechanical debridement in PRK (15). Patients can therefore fixate better through the more regular surface during the laser ablation, decreasing the incidence of decentration. Although a number of approaches have been used to treat the effects of decentration, at present none has been proven to be completely satisfactory. When treating decentration, however, it is recommended to treat the residual myopia and to decenter the ablation in the opposite quadrant. The advent of eye-tracking and wavefront technology may further minimize the incidence or provide the solution to decentration problems.

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SUMMARY

In summary, complications of LASEK are less than that of LASIK and comparable to PRK. It reduces the incidence of significant postoperative pain and corneal haze observed in PRK and avoids the various flap and interface-related problems associated with LASIK. Caution is needed in the use of alcohol and contact lenses. Patient selection criteria, including age, amount of refractive error, and dry eye status, should be considered. Further investigations in LASEK are needed with regard to experience flap viability, corneal haze response, and development of a standard nomogram.

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