Posterior and anterior permeability defects? Morphologic observations on streptozotocin-treated rats

Structural abnormalities of the blood-ocular barrier were examined in streptozotocin (STZ)-treated hyperglycemic rats, after 9 days, 6 months, and 10 months' duration of "diabetes," and in normoglycemic control animals using the horseradish peroxidase tracer technique combined with light and electron microscopy. The most frequent abnormalities consisted of small areas of diffuse dense staining by the tracer of (1) the retinal pigment epithelium and (2) the nonpigmented ciliary epithelium. Pigment epithelium abnormalities occurred occasionally in both groups of animals with approximately equal frequency and extent. Ciliary body abnormalities occurred also in both groups, but were frequent; statistically, the probability of these changes was not significantly different between the two groups. At the ora serrata, tracer escape was present through the retinal pigment epithelium into subretinal space and retina. Retinal vascular leakage occurred rarely and may be related to tracer toxicity rather than hyperglycemia. Thus, using the HRP method, we cannot confirm the claim that sustained STZ-induced hyperglycemia causes breakdown of the blood-retinal barrier in the rat.