Flap management during LASIK after radial keratotomy.

To the Editor: Radial keratotomy (RK) can be effective in reducing low to moderate amounts of myopia. Occasionally, a patient will “under-respond” to the RK procedure and be left with significant residual myopia. The refractive surgeon may then be presented with a situation where the patient desires more myopic reduction, but the surgeon does not want to perform another RK (for fear of inducing permanent, bothersome glare). The excimer laser can be helpful in treating residual myopia in undercorrected RK patients. A decision whether to perform photorefractive keratectomy (PRK) or laser in situ keratomileusis (LASIK) needs to be made. Photorefractive keratectomy, after significant RK undercorrection, has been shown to cause a higher incidence of visually significant haze.1-3 LASIK has shown promise in these patients because of the elimination of the healing variable as a result of “hiding” the laser treatment under a flap. There have been scattered reports of incision separation when making a flap in a cornea after a previous RK. I have experienced this—my patient was 3 years after RK and had thin, apparently well healed incisions. After noting that there was potential for incision separation if I continued to lift the flap, I stopped lifting. I then placed a 27-gauge cannula on a glass syringe filled with balanced salt solution (BSS) under the flap, near the hinge, and hydrodissected the flap off the stromal bed. Once the flap was floating on a “pillow” of BSS, it was quite easy to flip it over with minimal stress on the RK incisions. I have used this flap hydrodissection technique when performing LASIK on 20 eyes with previous RKs, and have not had any flaps show evidence of incision separation. It is of note that after lifting the flap out of the way, I immediately dry off the stromal bed to minimize the chance of changing the hydration characteristics of the cornea just prior to the excimer ablation.