THE COMBINED EFFECTS OF DIABETES AND IONIZING-RADIATION ON THE RAT RETINA - AN ULTRASTRUCTURAL-STUDY

The combined effect of STZ-diabetes and ionising radiation on the rat retina was investigated. Wistar rats, which had been diabetic for 6 mo nths, were irradiated with a single dose of x-rays (1500 cGy) and the ultrastructural effects evaluated at 4-10 mths post-irradiation. At 4 months post-irradiation, the outer nuclear layer of the retina was gre atly reduced in thickness and the photoreceptor outer segments were di sorganised and reduced in length. In addition, the nerve fibre layer c ontained many cytoid bodies and there were many redundant basement mem brane tubes throughout the inner retina. By 6 months post-irradiation, the photoreceptor cells were virtually absent, bringing the external limiting membrane into close apposition to the RPE. Throughout large a reas of the outer retina, RPE cells were hypertrophic and some had pro liferated into the inner retina. In many regions, proliferating retina l capillaries were observed within the RPE layer, and at 8 months post -irradiation, some vessels extended into the inner retina accompanied by RPE cells. At 10 months post-irradiation, the RPE was atrophic and degenerative with retinal glial cells coming into contact with Bruch's membrane, In some areas, the glia which had breached Bruch's membrane had invaded the underlying choriod. Where glial cells contacted the c horiocapillaries, the vessels assumed the appearance of retinal vessel s with plump endothelia and no fenestrations. This study has described a progressive inner retinal ischemia, with cytoid bodies, capillary n on-perfusion and general atrophy of the inner retina intensifying mark edly with increasing post-irradiation time. The results suggest that i rradiated STZ-diabetic rats may provide a useful model of outer retina l neovascularisation and progressive inner retina ischemia.