Clinical analysis of steep central islands after excimer laser photorefractive keratectomy

R. R. Krueger, N. F. Saedy and P. J. McDonnell
Doheny Eye Institute, University of Southern California School of Medicine, Los Angeles, USA.

PURPOSE: To examine topographic irregularities known as steep central islands that may occur after excimer laser refractive surgery and affect visual acuity. METHODS: We reviewed the computed corneal topographic maps of 35 eyes that had undergone excimer laser photorefractive keratectomy with an excimer laser for compound myopic astigmatism or anisometropic myopia. Steep central islands were defined as areas of steepening of at least 3 diopters and 1.5 mm in diameter. A classification system was developed based on the presence of steep central islands during the postoperative period as follows: class 0, absent; class 1, present at 1 week; class 2, present at 1 month; class 3, present at 3 months. RESULTS: Steep central islands were seen in 25 eyes (71%) at 1 week, 18 eyes (51%) at 1 month, seven eyes (20%) at 3 months, and four eyes (11%) at 6 months. After surgery without nitrogen gas blowing, 16 of 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-corrected visual acuity of 2 Snellen lines or more was seen in eight of 18 eyes with class 2 or 3 steep central islands at 1 month and three of 18 eyes 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 months. In all eyes with only class 2 steep central islands, loss of at least 1 Snellen line of best spectacle-corrected visual acuity at 1 month was associated with visual restoration at 3 months when the island was no longer present. CONCLUSION: Loss of best spectacle-correlated visual acuity is associated with steep central island formation, and may prolong visual rehabilitation after excimer laser photorefractive keratectomy.