The eyes of 100-day-old Beagles were exposed to 35 MeV protons at surface doses of 70, 125, 240, and 480 rad. Dose-dependent responses in the adnexa were observed 5 days after irradiation and in the crystalline lens, with a slitlamp biomicroscope, beginning at 30 days and appearing most marked 50-130 days post exposure. A grading system was established to quantitate the degree of lens involvement. An apparent "threshold" dose for vision-impairing lens opacifications occurring within 6 months of exposure was found to be between 70-125 rad surface dose. Large vacuoles and plaques, aberrant lens fiber cells, and subcapsular epithelial hyperplasia and metaplasia were the most profound histologic changes, occurring in the crystalline lenses of eyes receiving surface doses of 240 and 480 rad. Similar but less severe lens pathology was seen at a surface dose of 125 rad. Eyes receiving 480 rad also had corneal keratinization and vascularization, iridic atrophy, depigmentation, and entropion uveae. Detailed clinical and histopathologic observations are reported.

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