Long-term observations of proton-irradiated monkey eyes.

Fifteen owl monkeys (30 eyes) that received proton irradiation of discrete areas of the retina and choroid have been observed for 3 1/2 years or more after irradiation. The dose delivered to the retina varied from a single dose of 1,600 to 4,750 proton rads and from 10,250 to 18,250 rads delivered in five fractions over a period of one month. Fundus examination, fluorescein angiography, and light and electron microscopy revealed chorioretinal changes at the area of irradiation. The part of the retina adjacent to the chorioretinal scar showed preservation of normal retinal vascular architecture on trypsin digest studies of the retina and on electron microscopic examination, even 1 mm from the edge of the scar. The results of this study suggest that proton beam irradiation may markedly reduce delayed ocular complications, especially radiation retinopathy, which is common to other forms of radiotherapy in the treatment of intraocular tumors.