Hypertensive vascular changes in retinas of spontaneously hypertensive rats demonstrated by corrosion casts

Purpose. To elucidate changes in the capillary network in the deep retina of spontaneously hypertensive rats (SHR). Methods. We used 6-, 9- and 15-month-old SHR and 7- to 15-month-old normal Wistar Kyoto rats (WKy) as controls. Their systolic blood pressure was measured without anesthesia, and the ocular fundus was observed under ether anesthesia. Rats were then anesthetized and perfused through the common carotid arteries and jugular veins. Freshly prepared Mercox was injected. Ocular tissues were digested with 20% KOH. The casts were observed with a Hitachi S-2360N SEM. Results. In general, after 6-7 months of hypertension SHR showed tortuosity of retinal vessels which continued to increase, general narrowing of the arteries, localized constriction of the veins, arterio-venous crossing defects, and marked capillary changes such as caliber irregularity, narrowing, bead-like capillaries, loop formation and localized obliteration. Later, after the blood pressure had been sustained at a high level for a long time, marked capillary constriction which first affected the superficial capillary network led to a scattered capillary network and finally to capillary drop-out. Conclusion. These morphological changes in capillary networks were probably due to the structural damage of the endothelial cells, possibly facilitated by compression of the precapillary arterioles. The severity of these changes was usually proportional to the degree and duration of hypertension. These findings demonstrate the retinal capillary changes related to hypertension.