Damage threshold from large retinal spot size repetitive-pulse laser exposures.

The retinal damage thresholds for large spot size, multiple-pulse exposures to a Q-switched, frequency doubled Nd: YAG laser (532 nm wavelength, 7 ns pulses) have been measured for 100 mu m and 500 mu m retinal irradiance diameters. The ED50, expressed as energy per pulse, varies only weakly with the number of pulses, n, for these extended spot sizes. The previously reported threshold for a multiple-pulse exposure for a 900 mu m retinal spot size also shows the same weak dependence on the number of pulses. The multiple-pulse ED50 for an extended spot-size exposure does not follow the n(-1/4) dependence exhibited by small spot size exposures produced by a collimated beam. Curves derived by using probability-summation models provide a better fit to the data.