Lesion Duration and Curvature Change in the Cornea Following Exposure to a Carbon Dioxide Laser

摘要

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 1/e radius of r = sigma = 2.65 mm at the corneal plane. The 1/e radiant exposure required for a 50% probability (ED50) of producing a minimum visible lesion within 30 minutes postexposure was 4.71 J/sq cm. The 1/e 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 1/e 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)