Lesion Duration and Curvature Change in the Cornea Following Exposure to a Carbon Dioxide Laser.
Final rept. Jul 76-Jun 78,
SCHOOL OF AEROSPACE MEDICINE BROOKS AFB TX
Pagination or Media Count:
The corneas of Dutch belted rabbits were exposed for 0.5 sec to the radiation from a carbon dioxide laser lambda 10.6 microns emitting a Gaussian beam with a 1e radius of r sigma 2.65 mm at the corneal plane. The 1e radiant exposure required for a 50 probability ED50 of producing a minimum visible lesion within 30 minutes postexposure was 4.71 Jsq cm. The 1e radiant exposure is the incident beam energy delivered in 0.5 sec divided by the area of a circle of radius r 2.65 mm, the beam radius at the 1e point. Corneas with lesions resulting from suprathreshold exposures were examined at specified intervals for 1 year postexposure and the ED50 determined as a function of lesion duration. Two methods for assessing permanent corneal damage clinically are discussed and compared. Pre- and postexposure corneal curvature measurements made during a year of observations show that the curvature of the irradiated corneas decreased by a factor of 2 to 3 over those in a nonirradiated control group. Randomly recurring postexposure edema in many irradiated corneas caused curvature increases which tended to mask the decrease expected from corneal collagen shrinkage. Mechanisms which could affect the results of this and other studies are presented. Parallels between induced corneal curvature changes and resulting changes in refractive error and visual performance are presented and evaluated. Author