THE COMBINED EFFECT OF DIABETES AND IONIZING-RADIATION ON THE RETINALVASCULATURE OF THE RAT

The clinical impression that pre-existing diabetes exacerbates radiati on injury to the retinal vasculature was studied in STZ diabetic rats. Half of 2 groups of streptozotocin (STZ)-induced diabetic rats and 1 group of normal animals had their right eyes irradiated with 1000 cGy of 90 KVP x-rays. The prevalence of acellular capillaries in trypsin d igests of the retinal vasculature was quantified for each of the 6 gro ups of animals at 6.5 months post-irradiation. The prevalence of acell ular capillaries in both non-irradiated diabetic groups was significan tly higher than in controls while the irradiated animals in each of th e three main categories showed a statistically significant increase co mpared to their non-irradiated equivalents. However, the net increase in acellular capillaries following irradiation was much greater in rat s with an 8 month term of pre-existing diabetes (180%) than in those w hich had only been diabetic for 3 months (36%). The results of this st udy suggest a synergistic relationship between pre-existing diabetes a nd ionising radiation in the development of retinal vasculopathy, and that the potentiation of the vascular damage is dependent on the durat ion of diabetes prior to radiation exposure.