Ex vivo and computer model study on retinal thermal laser-induced damage in the visible wavelength range

Excised bovine eyes are used as models for threshold determination of 532-nm laser-induced thermal damage of the retina in the pulse duration regime of 100 micros to 2 s for varying laser spot size diameters. The thresholds as determined by fluorescence viability staining compare well with the prediction of an extended Thompson-Gerstman computer model. Both models compare well with published Rhesus monkey threshold data. A previously unknown variation of the spot size dependence is seen for different pulse durations, which allows for a more complete understanding of the retinal thermal damage. Current International Commission on Nonionized Radiation Protection (ICNIRP), American National Standards Institute (ANS), and International Electromechanical Commission (IEC) laser and incoherent optical radiation exposure limits can be increased for extended sources for pulsed exposures. We conclude that the damage mechanism at threshold detected at 24 and 1 h for the nonhuman primate model is retinal pigment epithelium (RPE) cell damage and not thermal coagulation of the sensory retina. This work validates the bovine ex vivo and computer models for prediction of thresholds of thermally induced damage in the time domain of 10 micros to 2 s, which provides the basis for safety analysis of more complicated retinal exposure scenarios such as repetitive pulses, nonconstant retinal irradiance profiles, and scanned exposure.