Vascular changes in retinas of spontaneously hypertensive rats demonstrated by corrosion casts

The changes in the capillary network of the retina in spontaneously hypertensive rats (SHR) were demonstrated by scanning and transmission electron microscopy. Corrosion casts with scanning electron microscopy provided a three-dimensional view of the microvasculature of the rat retina and could detect the conspicuous features of the retinal vasculature in SHR. In general, when hypertension lasted for 6-7 months in SHR, tortuosity of the retinal vessels was noted, and later the SHR retina showed increased tortuosity and generalized narrowing of the vessels, localized constriction of the veins, arteriovenous crossing defects, and marked capillary changes, such as caliber irregularity, narrowing, bead-like capillaries, loop formation and localized obliteration. At a later stage, when the blood pressure had been sustained for a long time, there was marked capillary constriction which first affected the superficial capillary network, then scattered capillary network constriction and finally capillary dropout. Transmission electron microscopy revealed narrow capillary lumina and thin endothelium with scarce cytoplasmic components and damaged pericytes. These morphological changes in the capillary network were probably due to structural damage to the endothelial cells, facilitated possibly by compression of the precapillary arterioles. The severity of these changes was usually proportional to the degree and duration of hypertension. These findings indicate that the retinal capillary changes are probably related to hypertension.