Histologic evaluation of ophthalmoscopically subvisible retinal laser exposures.

Four exposures of rhesus monkey macula to helium-neon (He-Ne) laser irradiation of 6.4 mw. at 100 msec, produced no ophthalmoscopically visible lesions; however, microscopic lesions were detected. Of the four exposures, one produced a small burn, another had no detectable effect, and the two remaining exposures produced identical lesions consisting only of vesicular cytoplasmic swelling and depigmentation of tioo contiguous retinal pigment epithelial cells. The variation in effect of the irradiation is attributed to inhomogeneity of pigment granule distribution in the pigment epithelium. The exposures in this experiment were approximately 40 per cent below the median effective dose for minimal ophthalmoscopically visible change.