CLINICAL ANALYSIS OF STEEP CENTRAL ISLANDS AFTER EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY

Purpose: To examine topographic irregularities known as steep central islands that may occur after excimer laser refractive surgery and affe ct visual acuity. Methods: We reviewed the computed corneal topographi c maps of 35 eyes that had undergone excimer laser photorefractive ker atectomy with an excimer laser for compound myopic astigmatism or anis ometropic myopia. Steep central islands were defined as areas of steep ening of at least 3 diopters and 1.5 mm in diameter. A classification system was developed based on the presence of steep central islands du ring the postoperative period as follows: class 0, absent; class 1,pre sent at 1 week; class 2, present at 1 month; class 3, present at 3 mon ths.Results: Steep central islands were seen in 25 eyes (71%) at 1 wee k, 18 eyes (51%) at 1 month, seven eyes (20%) at 3 months, and four ey es (11%) at 6 months. After surgery without nitrogen gas blowing, 16 o f 25 patients had class 2 or 3 steep central islands compared with two of 10 eyes when gas blowing was used. Loss of best spectacle-correcte d visual acuity of 2 Snellen lines or more was seen in eight of 18 eye s with class 2 or 3 steep central islands at 1 month and three of 18 e yes at 3 months. A similar loss occurred in one of 17 eyes with class 0 or 1 steep central islands at 1 month and none of 17 eyes at 3 month s. In all eyes with only class 2 steep central islands, loss of at lea st 1 Snellen line of best spectacle-corrected visual acuity at 1 month was associated with visual restoration at 3 months when the island wa s no longer present. Conclusion: Loss of best spectacle-corrected visu al acuity is associated with steep central island formation, and may p rolong visual rehabilitation after excimer laser photorefractive kerat ectomy.