Experimental argon laser photocoagulation. II. Effects on the optic disc
D. J. Apple, G. J. Wyhinny, M. F. Goldberg and E. H. Polley
Eight monkeys and five humans were subjected to photocoagulation with
single argon laser burns of varying intensity on the optic nerve head.
Energies greater than 400 milliwatts, 0.2 second and 100 mu spot size
consistently caused neural parenchymal damage, even in the absence of
heat-generating pigment epithelium. Papillary burns in monkeys and humans
created with powers less than 400 mW showed only small, focal
submicroscopic areas of degeneration, and were therefore considered
relatively safe except for the occasional involvement of critical foveal
fibers in which scotomas of disproportionately greater severity than one
would expect from the size of the lesion could result. The threshold for
toxicity following peripapillary photocoagulation is lower, because the
burned pigment epithelium can radiate heat into the adjacent optic nerve
fibers. Normal capillaries within the optic nerve were seldom destroyed or
occluded, even after high energy densities. In normal vessels, we have
found it impossible to create a highly selective lesion without
concurrently causing neural damage about the vessel.
