Steep central islands after myopic photorefractive keratectomy

Purpose: To investigate the formation of steep central islands and their reduction under modified experimental conditions. Setting: University Eye Hospital Munster and Schwind Co., Kleinostheim, Germany. Methods: Corneas of enucleated intact bovine eyes were treated with the Schwind Keratom. Ail experimental conditions were repeated six times in six 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 depth (4 to 15 diopters [D] in PRK) were varied. Modifications to reduce or avoid steep central islands included blowing nitrogen gas and aerosol over the cornea, cleaning the cornea of fluid, and using an anti-central-island software program. Results: In PTK, an increase in the internal repetition rate resulted in a decrease in the height of the steep 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, blowing aerosol, and cleaning the cornea reduced the formation ai steep central islands and blowing nitrogen gas eliminated them. Conclusion: Steep central islands are created by a wide-field ablation process and are probably caused by many factors, Both software and hardware modifications be used to reduce their formation.