Threshold damage doses for helium-neon (He-Ne) laser radiation were determined in 20 Rhesus monkey eyes at seven selected sites, ranging from 50° nasal to 30° temporal to the macula. The mean damage threshold at the macula was found to be lowest of all examined sites, while the area between the optic disc and the macula was highest. Planimetry measurements of the retinal structures on an excised eye showed the comparative thickness of the nerve fiber layer to be most consistent with the relative sensitivity at the various sites. This layer was found to be thickest at the areas least sensitive to laser irradiation, suggesting that the optic nerve fibers act as an attenuating medium. The high sensitivity of the macula is attributed chiefly to the high density of pigment granules in the macular pigment epithelial cells.
Lappin PW, Coogan PS. Relative Sensitivity of Various Areas of the Retina to Laser Radiation. Arch Ophthalmol. 1970;84(3):350-354. doi:10.1001/archopht.1970.00990040352015