STEEP CENTRAL ISLANDS AFTER MYOPIC PHOTOREFRACTIVE KERATECTOMY

Purpose: To investigate the formation of steep central islands and the ir reduction under modified experimental conditions. Setting: Universi ty Eye Hospital Munster and Schwind Co., Kleinostheim, Germany. Method s: Corneas of enucleated intact bovine eyes were treated with the Schw ind Keratom. Ail experimental conditions were repeated six times in si x different corneas. Eight experimental groups were looked at. Fluence was 180 to 200 mJ/cm(2). Ablation mode (phototherapeutic keratectomy [PTK] and standard myopic photorefractive keratectomy [PRK]), internal repetition rate (3 to 30 Hz), and ablation diameter (5 to 8 mm) and d epth (4 to 15 diopters [D] in PRK) were varied. Modifications to reduc e or avoid steep central islands included blowing nitrogen gas and aer osol over the cornea, cleaning the cornea of fluid, and using an anti- central-island software program. Results: In PTK, an increase in the i nternal repetition rate resulted in a decrease in the height of the st eep central island. In standard PRK, increasing refractive correction to -8.0 D and increasing the ablation diameter resulted in an increase in sleep central island power. The anti-central-island program, blowi ng aerosol, and cleaning the cornea reduced the formation ai steep cen tral islands and blowing nitrogen gas eliminated them. Conclusion: Ste ep central islands are created by a wide-field ablation process and ar e probably caused by many factors, Both software and hardware modifica tions be used to reduce their formation.