NATURAL-HISTORY OF CENTRAL TOPOGRAPHIC ISLANDS FOLLOWING EXCIMER-LASER PHOTOREFRACTIVE KERATECTOMY

Purpose: To assess the incidence and natural history of central cornea l topographic islands following excimer laser photorefractive keratect omy (PRK) and photoastigmatic refractive keratectomy (PARK). Setting: A dedicated corneal diseases and refractive surgery unit within a Nati onal Health Service Trust ophthalmology unit in the United Kingdom. Me thods: Corneal topographic analysis was performed in a prospective stu dy of 100 eyes of 75 consecutive patients who had PRK. All PRK/PARK ex cimer laser photorefractive procedures were performed by two surgeons observing a standardized protocol using a VISX 20/20 excimer laser. Me an preoperative myopic error was 5.54 diopters (D) +/- 3.44 (SD). Corn eal topographic analysis was performed on all eyes preoperatively, 1 w eek postoperatively, and monthly thereafter for a minimum of 6 months or until central islands, if present, resolved. All patients had a min imum 12 months follow-up. Results: Postoperatively, 29 eyes (29%) demo nstrated central corneal topographic islands of greater than 3.00 D to pographic power by computerized videokeratography (CVK). All central i slands were identified in the first 4 weeks postoperatively. In all ca ses the differential dioptric power, created by the central islands wi thin the ablation zone, decreased rapidly; within 6 months, 26 (90%) c entral islands had fully resolved without further treatment, and the r emaining 3 (10%) resolved within 1 year of photorefractive surgery. Th e occurrence of central islands was related to higher preoperative myo pic spherical equivalent (P = .01), greater attempted laser correction (P = .01), and greater projected depth of ablation (P = .01) (Student 's two-tailed t-test). Conclusions: Central corneal topographic island s occurred in a significantly higher proportion of eyes having excimer laser photorefractive surgery than previously believed. The islands w ere associated with decreased unaided vision, reduced best spectacle-c orrected acuity, and other troublesome visual symptoms; however, the c entral islands, along with their associated visual effects, usually re solved without surgical intervention within 6 months postoperatively.