New data on the variation of laser induced retinal-damage threshold with retinal image size

In earlier studies, we examined the dependence of the laser induced retinal damage threshold on retinal image size for extended-source ocular exposures. We reported the spot-size dependence of the retinal threshold (based on ophthalmic observations at 24 h postexposure) for two pulsewidth regimes: nanosecond-duration (Q-switched) pulses from a doubled Nd:yttrium–aluminum–garnet laser and microsecond-duration pulses from a flashlamp-pumped dye laser at 590 nm. In either case, the retinal threshold was shown to vary with the area (i.e., diameter squared) for image diameters >5 mrad. More recently, we have collected additional data for the intermediate spot-size range (1.5–10 mrad) and have compared both the absolute values and the spot-size trend of retinal thresholds determined via ophthalmoscopic observation at 1 h postexposure to the analogous threshold data collected with observations at 24 h postexposure. These additional data and analyses reinforce our earlier conclusions regarding the threshold vs. spot-size trend and are compared to and reconciled with results from previously published extended-source ocular damage studies. The experimental spot-size trends are also contrasted to the existing laser safety standard treatments of maximum permissible exposure levels for extended-source ocular exposures.