Analysis of anterior and posterior corneal curvature changes using Orbscan technology in radial keratotomy eyes exposed to hypoxia.

PURPOSE: To study the changes in anterior and posterior corneal curvatures in radial keratotomy (RK) and normal eyes exposed to hypoxia using Orbscan (Bausch & Lomb) technology. SETTING: Department of Ophthalmology, Madigan Army Medical Center, Tacoma, Washington, USA. METHODS: At sea level, 11 RK subjects and 10 control subjects were exposed to ocular surface hypoxia in 1 eye by filtering humidified, compressed 100% nitrogen (0% oxygen) through an airtight goggle system for 2 hours. The contralateral eye was exposed to humidified, compressed air (21% oxygen) simultaneously through the airtight goggle system. Orbscan analysis was performed in each subject before and immediately after gas exposure. This analysis included measurement of the anterior axial and posterior axial corneal curvatures as well as corneal pachymetry. RESULTS: In the RK eyes exposed to 100% nitrogen gas, there was a statistically significant flattening in the anterior axial corneal curvature (P = .0012) and in the posterior axial corneal curvature (P = .0067). Radial keratotomy and control eyes exposed to air and control eyes exposed to 100% nitrogen gas demonstrated no statistically significant change in the anterior axial or posterior axial corneal curvature. CONCLUSIONS: Corneal hypoxia induced a statistically significant flattening in the anterior axial and posterior axial corneal curvatures in eyes that had had RK. There was no significant change in these curvatures in RK eyes exposed to air and in control eyes exposed to air or 100% nitrogen gas.

Refractive surgery safety at altitude.

Over the years, many climbers and other visitors to high altitude have been attracted to refractive surgery in hopes of lessening their dependence on glasses. Although there has been a gradual refinement of these procedures over time, they continue to have the potential for visual changes with altitude exposure. The goal of this review is to provide guidance to clinicians as to how to better advise their patients on the pros and cons of these procedures.