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Pathology

Photoreceptor cells are differentiated postmitotic retinal neurons that normally function throughout the life of an individual. Some visual cell dropout occurs naturally as a result of aging, but rod and cone survival into the seventh decade and beyond is normally more than sufficient to preserve vision. A higher rate of visual cell loss is seen in many genetic conditions, but the rate of loss is still relatively slow compared to most experimental animal models of retinal degeneration. At the same time the morphological endpoints of both genetic and experimental retinal degenerations are so similar that they invite comparisons and inferences into etiology and prevention based primarily on studies with animals. In the case of photic injury in animal models, one sees loss of rod photoreceptors, with a relative sparing of cones.[18,19]Rod cell loss is graded, most pronounced in the central superior hemisphere, and often particularly severe in the region 1–2 mm superior to the optic …