Photochemical and thermal retinal damage thresholds from an extended (413 nm) krypton laser source

The power levels required to induce funduscopic minimal visible lesions (MVLs) from a violet (413 nm) extended-source (subtending 1.0 degree of visual field on the retina, ∼ 250 μm spot size) krypton laser exposure were investigated in the rhesus monkey. Exposure durations were 20 sec, to yield a photochemical damage mechanism and 0.1 sec, which as a result of greater radiant exposure levels, likely would lead to retinal damage through a thermal mechanism. The ED50 threshold and 95% fudicial limits evaluated at 48 Hrs post-exposure for the 20 sec post exposure duration were 6.54 mW (8.41 mW – 4.92 mW). For the 0.1 sec laser exposures, the ED50 was 88.6 mW (105.0 mW-78.3 mW), evaluated at 24 Hrs post-exposure. These findings are shown to be consistent with a photochemical damage mechanism for the longer exposure duration (20 sec) and a thermal mechanism for the shorter (0.1 sec) exposure.