Effect of Q-switched laser flashes on visual detection

Abstract

Luminance thresholds for visual detection can be increased for some time following exposure to bright, eye-safe flashes of light. Since the energy threshold for retinal damage decreases dramatically for shorter pulses, it is unclear whether laser flashes as short as 20 ns can produce effects on visual performance before safe exposure energies are exceeded. Using five trained rhesus monkeys as subjects, we psychophysically measured the duration of vision loss for sine-wave luminance gratings (10-cd/square meter mean luminance) after foveal exposure to a 20-ns laser pulse (Q-switched doubled neodymium:glass, 530-nm wavelength). The laser beam was presented in Maxwellian view and expanded to subtend a visual angle of 12.5°. For laser exposures ranging up to the retinal maximum permissible exposure (388 μJ), we found no loss in the detectability of high contrast (98 %) gratings of 1, 4, and 12 cycles/deg. However, low (10%) contrast gratings were rendered undetectable for various amounts of time depending on the grating spatial frequency. Recovery times were least for 4-cycles/deg gratings and greatest for 1 and 12-cycles/deg gratings.