Structure of the vitreoretinal border region in spontaneously hypertensive rats (SHR rats).

The morphology of the vitreoretinal border region, also termed the inner limiting membrane, was studied in spontaneously hypertensive rats (SHR rats), in Wistar Kyoto rats (WKY rats), and in Buffalo rats (BUF rats). The region was examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) in order to visualize a possible increase in thickness with raised arterial pressure. The median thickness of the lamina densa in TEM in the three groups varied from 34 to 68 nm. In hypertensive SHR rats the lamina densa showed thickening up to the 10th month and was unchanged thereafter. The same pattern was shown in WKY rats, although the thickness increased also after the tenth month in these controls. In BUF rats, however, the lamina densa decreased in thickness with age. The median thickness of the whole vitreoretinal border region varied between: SHR rats: 42 and 84 nm (SEM) and 51 and 127 nm (TEM); WKY rats: 84 nm (SEM) and 51 and 68 nm (TEM); BUF rats: 42 nm (SEM) and 34 and 68 nm (TEM). SHR rats showed in SEM an increase in thickness with age. In TEM, however, only one very old hypertensive rat had a thickened vitreoretinal border region. In WKY rats both SEM and TEM showed an increase in thickness with age, whereas BUF rats showed a decrease. Fundus photographs disclosed narrow, straight and irregular retinal arterioles in hypertensive SHR rats. Light microscopy of older SHR rats demonstrated retinal degeneration from the outer photoreceptor layer to the inner nuclear layer. This was also found in some of the older WKY rats.