Retinal vascular changes in rats with inherited hypercholesterolemia--corrosion cast demonstration

To demonstrate specific hypercholesterolemic changes in the retinal vascular architecture.

Corrosion casts of 12- to 18-month-old rats with inherited hypercholesterolemia (RICO) and of control Wistar Kyoto (WKy) rats were examined with a scanning electron microscope (SEM). The diameters of the retinal arteries, veins and capillaries were measured in photographs with a caliber micrometer. The capillary branches were counted in the micrographs with the use of Adobe Photoshop. The retinal capillaries were examined by transmission electron microscopy (TEM).

SEM examination of the vascular casts of 15-month-old RICO rats showed slight tortuosity of large vessels at the posterior pole of the retina. The precapillary arterioles branching from the major artery were longer and straighter than normal. Retinal capillary changes such as caliber irregularity and narrowing in the capillary network were more severe in 18-month-old RICO rats. The most prominent finding was marked straightening of the capillaries in the inner and outer layers of the capillary network, which looked like fine strings. Intercapillary spaces became wider, and finally capillaries looked scattered. The diameter of the retinal capillaries lumen in RICO rats was significantly narrower than that in WKy rats (p < 0.0001). The capillary branches were fewer in 18-month-old RICO rats than that in 18-month-old WKy rats (p < 0.0001). Neither local stenosis or obstruction in the arterioles and venules nor any arteriovenous crossing defect was seen in young and old RICO rats. Transmission electron microscopy of 16-month-old RICO rat retinas revealed that the capillaries in the inner and outer plexiform layers contained scarce cytoplasmic components, vacuoles in endothelial cells and basement membranes of irregular thickness. Capillary pericytes were swollen and irregular in shape, contained vacuolated mitochondria and scarce cytoplasmic components.

These findings indicate that the retinal capillary changes are probably related to hypercholesterolemia.