Laser retinal thermal damage threshold: impact of small-scale ocular motion

The impact of the small-scale ocular motion that occurs during steady gaze on the retinal thermal damage threshold for long-duration laser exposures is investigated. Exposure durations from 100 msec to 50 sec are considered. Experimentally recorded eye movement data are input into a numerical simulation to calculate the increase in temperature experienced by the retina during an exposure to a continuous wave laser. Calculations are for a small retinal beam spot. An Arrhenius damage integral is used to estimate the thermal damage threshold. The impact of the ocular movements is expressed as a relief factor chi, defined as the ratio of the theoretical damage threshold in the presence of ocular motion to the threshold calculated assuming no eye motion. The relief factor is found to be 1.05 for a 100-msec exposure, increasing to 1.3 for a 50-sec exposure. The relief factor is described well by the equation chi=1.12tau(0.037) for exposure durations tau in the range 100 msec to 50 sec.