Since its introduction by Camellin in 1999,1 LASEK has gained widespread acceptance and has become, together with LASIK and PRK, one of the keratorefractive procedures most frequently performed today. LASEK's success can be attributed to the fact that, because it does not create a permanent stromal interface, the procedure minimally affects corneal stability and reduces the possibility of future complications. Compared with PRK, a proper LASEK procedure can provide patients with more comfort and better vision in the immediate postoperative period. When an enhancement is necessary, LASEK can be easily and safely repeated without the use of alcohol.LASEK VERSUS LASIK
Unlike LASIK, LASEK does not use a microkeratome, and it therefore avoids potentially serious flap-induced complications. The possibility of treating higher degrees of refractive errors as well as thinner, steeper, and flatter corneas is among the advantages of LASEK when compared with LASIK. Conversely, LASEK cannot currently compete with LASIK in terms of quick visual recovery and comfort, although this difference is decreasing due to advances in the management of LASEK patients postoperatively. The presence of an epithelial flap in LASEK is crucial to the prevention of haze in most patients. However, haze prevention may depend on the number and vitality of the cells that survive the effects of alcohol exposure, among other contributing factors (eg, the amount of ablated tissue, type of laser, local temperature increase). The recent trend toward mitomycin C use in keratorefractive surgery has been an important advance in the prevention of haze, which sometimes occurs after the treatment of high-magnitude refractive errors. Concerns exist, however, about the long-term consequences of using such a potent drug.2LASEK VERSUS PRK
Despite its current popularity, LASEK is not without controversy. Some surgeons who prefer PRK hold that the lost vitality of the alcohol-treated epithelium slows re-epithelialization and prolongs discomfort. I disagree with this view. The LASEK protocol varies widely among surgeons. Some leave the alcohol on the cornea for as long as 50, 60, or (as I have seen sometimes) 120 seconds. As Gabler et al3 demonstrated, after 30 seconds of 20% alcohol exposure, only 20% of cells are dead, but, after 60 seconds, all cells are killed. If an epithelial flap of living cells covers the stroma, it is logical to conclude that the postoperative evolution, in the short and long term, may differ from that of the opposite situation. Although a controversial idea, I think that, in a substantial number of patients, a living epithelial flap placed over the ablated surface may effectively stop the cascade of events associated with PRK (eg, pain, an exaggerated wound-healing response, haze, and regression). On the other hand, a sheet consisting only of alcohol-intoxicated cells can accomplish a protective function, at best. Some of my colleagues and I believe that the term LASEK, strictu sensu, should be restricted for cases where the epithelial flap is lifted using an exposure time to 20% ethanol of up to 30 seconds. Ideally, a perfect LASEK procedure would permit the creation of an epithelial flap without any disturbance of cells. Our nonalcohol technique can accomplish this goal, primarily in myopic LASEK retreatment cases.LIMITATIONS AND VARIATIONS
A real drawback of conventional LASEK is its reliance on alcohol to create an epithelial flap. Depending on the concentration and time of exposure, ethanol can be harmful to the epithelial cells. Because the adhesiveness of the epithelium varies between patients, it is crucial to perform LASEK correctly in terms of using an alcohol exposure time that is appropriate for each patient. In this regard, our Epi-Test can be of great help.
Attempts to perform LASEK without alcohol4 have not had great success. The butterfly technique, developed by Paolo Vinciguerra, MD,5 allows a reduction of the alcohol exposure time and minimally disturbs the connections between the treated area and the limbal cells, and it theoretically facilitates the re-epithelialization process. This technique is not commonly known outside Italy, however.
Recently, the FDA approved the Epilift system (Visijet, Inc.; Irvine, CA) and the Centurion SES Epikeratome (Norwood Eyecare, Duluth, GA), both for the EpiLASIK procedure in which a mechanical separator is used instead of alcohol to detach the epithelium from Bowman's layer. If these systems work as proclaimed, they will be major breakthroughs in advancing nonlamellar keratorefractive surgery.6EPI-TEST
During LASEK, a useful maneuver called the Epi-Test7 requires the surgeon, after the alcohol has been washed from the surface of the epithelium, to firmly massage over top of the epithelium with the tip of a dry sponge, while avoiding tearing the epithelium. Afterward, one of three things will occur. The epithelium may fold easily, indicating that the alcohol-exposure time is adequate (in some cases, excessive) and that the rest of the procedure will proceed with ease. Alternatively the epithelium may fold minimally, or only in certain areas, meaning that the alcohol time is borderline. In such a case, repeating the massage will help the detachment and usually be sufficient to warrant a good flap. Finally, the epithelium may not fold at all, indicating that the application of alcohol should be repeated. The usefulness of the Epi-Test is twofold. It indicates whether the action of alcohol was sufficient, and the massage contributes to the separation of the epithelial sheet from the underlying stroma. In my hands, the Epi-Test has been a useful tool, and I strongly recommend it to all those surgeons, experienced or not, performing conventional LASEK.LASEK RETREATMENTS
As with other refractive techniques, an enhancement is periodically necessary with LASEK. One of the great differences between LASEK and PRK is the behavior of the epithelium during the enhancement. The adherence of the epithelium to the previously ablated area of stroma is generally strong in PRK. When an enhancement is needed, in the majority of PRK cases, the surgeon will have to work hard to remove all the cells in the central cornea. Conversely, when repeating myopic LASEK on an eye, I was greatly surprised to see how easily the epithelium detached after brief exposure to the alcohol solution. This discrepancy was even more dramatic when I performed the Epi-Test. The difference I observed led to my idea of eliminating the use of alcohol in myopic LASEK retreatments.
When scientific evidence is insufficient, we must rely on common sense. While performing LASEK, I prefer a sheet of living cells instead of dead cells or nothing (as in PRK). On the other hand, it is difficult to uphold the statement that living cells do not change the healing dynamics. Because ophthalmologists have limited knowledge about corneal wound-healing response, fully confirming the benefit of having or not having living cells present is impossible.NONALCOHOL LASEK RETREATMENTS
The technique that follows is mainly applicable to myopic LASEK retreatments; its efficacy in hyperopic retreatments cannot be guaranteed. The key to a successful myopic procedure lies in the correct realization of the Epi-Test without alcohol. If the test is negative (no folding of the epithelium is observed), diluted alcohol must be used.Technique
I prepare an eye as per a LASEK procedure, and cut the epithelium with a trephine (rotated approximately 5° to both sides), and exert sufficient pressure to ensure a neat groove. Next, I dry the treatment surface area, while enhancing the visibility as much as possible. With the tip of a dry sponge, I perform an Epi-Test as previously described while covering the area limited by the groove. The folding of the epithelium must be clearly visible (Figure 1). With the help of a microhoe (Figure 2) or a bent needle, I confirm the cutting of the epithelium at the groove, beginning at the 6-o'clock position, and complete its separation until the hinge is reached. Normally, the flap will detach easily after this point (Figure 3), and, with the help of a spatula, I gather the flap at the 12-o'clock position. I keep the flap moist. After performing the laser ablation, I carefully reposition the epithelial flap and protect it with a contact lens.Postoperative Course
Before this article was written, I performed 15 nonalcohol LASEK retreatments, with a follow-up of 1 to 4 months. The nonalcohol-treated flaps were thinner and smaller than the ones made with ethanol, a difference is probably related to the absence of epithelial edema in the thinner flaps. Additionally, there was no postoperative inflammation, and the eyes appeared as though they had not undergone surgery.
The postoperative course was fantastic. In all cases (including two bilateral retreatments), discomfort was absent or minimal, notably less than that observed in some conventional LASEK patients. Also, all re-treated patients had good functional vision during the first week postoperatively, similar to what has been reported following EpiLASIK. These results were reported to me by Thomas V. Claringbold III, MD, in November 2004. Contact lenses were removed between postoperative days 3 and 4 (this was routine, but I am sure it can be done earlier), and patients experienced a quick return of BCVA.
Leaving the epithelium over the ablated area is the foundation of the LASEK procedure. The epithelial flap protects the crude surface left after the ablation and reduces discomfort and haze, which are the two main reasons for PRK's losing popularity approximately 4 or 5 years ago.8-10
For three hyperopic eyes scheduled for nonalcohol LASEK retreatment, only one procedure could be successfully completed. The other two cases may have lost candidacy because of the larger size of the flap, the effect of the different ablation pattern on the postoperative epithelial adhesiveness, and/or the fact that hyperopic LASEK is generally more difficult.
I would advise the surgeon to perform an Epi-Test in all myopic eyes requiring a LASEK enhancement, including those with previous PRK, before using alcohol.Final Point
In most of my LASEK-over-PRK retreatments, I had difficulty detaching the epithelium over the previously ablated area. Dr. Camellin warned about this common problem and suggested performing LASEK as well, although the resulting flap frequently will have a hole in its center.1CONCLUSION
Nonalcohol LASEK retreatments are not only possible but also desirable. The avoidance of a toxic substance such as ethanol, the ease of the procedure, and the good postoperative course are strong reasons to anticipate that, when an enhancement is needed, nonalcohol LASEK will be the procedure of choice. In the near future, it will be interesting to compare EpiLASIK enhancements with my nonalcohol LASEK retreatment technique. Information from a comparison will probably provide refractive surgeons with important knowledge about the corneal wound-healing response.
More than 5 years after its introduction, LASEK is recognized internationally as a valid procedure. Several respected surgeons have even adopted LASEK as their preferred technique.
Jorge Muravchik, MD, is in private practice at Clínica de Ojos in Colón, Argentina. He states that he does not hold a financial interest in any of the products or companies mentioned herein. Dr. Muravchik may be reached at +54 2473 42 1207; firstname.lastname@example.org. Cimberle M. LASEK may offer the advantages of both LASIK and PRK. Ocular Surgery News International Edition. 1999;10;3:28.
2. Chang SW. Early corneal edema following topical application of mitomycin-C. J Cataract Refract Surg. 2004;30:1742-1750.
3. Gabler B, Winkler von Mohrenfels C, Dreiss AK, et al. Vitality of epithelial cells after alcohol exposure during laser-assisted subepithelial keratectomy flap preparation. J Cataract Refract Surg. 2002;28:1841-1846.
4. McDonald M. Refractive surgery: the next generation. Paper presented at: The 105th Annual Meeting of the AAO, November 2001, New Orleans, LA.
5. Vinciguerra P. LASEK butterfly technique. Video presented at: The XIX Congress of the ESCRS; September 2001; Amsterdam, Holland.
6. Pallikaris IG, Naoumidi II, Kalyvianaki MI, Katsanevaki VJ. Epi-LASIK: comparative histological evaluation of mechanical and alcohol-assisted epithelial separation. J Cataract Refract Surg. 2003;29:1496-1501.
7. Samalonies LB. LASEK techniques. Eyeworld. 2002;7;9:31.
8. McDonald M, Forstot SL, Hardten DR, et al. Is PRK dead? Eyeworld. 1999;4;4:55-58.
9. Lee JB, Seong GJ, Lee JH, et al. Comparison of laser epithelial keratomileusis and photorefractive keratectomy for low to moderate myopia. J Cataract Refract Surg. 2001;27:565-570.
10. Autrata R, Rehurek J. Laser-assisted subepithelial keratectomy for myopia: two-year follow-up. J Cataract Refract Surg. 2003;29:661-668.