Computer modeling of laser damage to the eye

The effects of laser damage in the eye have been studied with an electrophysiological measure, the Visual Evoked Potentials (VEP). The VEP is generated by placing surface electrodes at the back of a subject's head, and having the subject watch a pattern of alternating light and dark bars. The spatial frequency of the bar pattern, measured in cycles per degree, increases as the bars become finer. The bar pattern changes in time, as the light bars become dark, and visa versa. The rate of this change is the temporal frequency, measured in Hertz. The VEP amplitudes referred to in this paper are a sum of the first three even harmonics of the temporal frequency (since the pattern change two times for every temporal cycle). As spatial frequency increases, a point will be reached where the subject will no longer be able to resolve the bars, and the VEP amplitude will become indistinguishable from noise. This spatial frequency is a measure of visual acuity. A computer model has been developed to simulate vision loss from lesions on the retina. It has been checked against experimental data from Rhesus monkeys with burns made under laboratory conditions. Vision was checked before and after the burns with VEP at a temporal frequency of six Hertz. This model divides the visual field into concentric rings centered about the visual axis. Each ring contributes to the VEP by an amount that depends on its eccentricity, or radius in degrees, as well as the spatial frequency.(ABSTRACT TRUNCATED AT 250 WORDS)