Scanning electron microscopy of the retina in an animal model of hereditary blindness.

Scanning electron microscopy was performed on retinas from normal and a mutant strain of chickens suffering from congenital blindness with retinal degeneration. Both surface and cryofractured transverse views of the retina were examined. Photoreceptors were generally seen to degenerate along a central to peripheral gradient: the more damaged receptors located centrally while areas of normal appearing photoreceptors were located toward the ora serrata. Pathological changes included deformed and missing outer segments and short, swollen inner segments. Reactive changes in overlying pigment epithelium (PE) were also noted over areas displaying advanced photoreceptor degeneration. PE changes included both hypertrophy and dystrophy of cells, detached cells, and formation of clusters or nodules along Bruch's membrane or in the sub-retinal space among photoreceptor inner segments. Among the 6 types of photoreceptors in the chicken retina (1 type of rod and 5 types of cones), more intact double cones were identified in areas undergoing retinal degeneration than other types. Double cones may be more resistant to the factor(s) involved in cellular death.