Photoreceptor degeneration in the eyes of an amphisbaenian in response to constant light or constant darkness

Abstract

Eye morphology and behavioral responses were studied in Bipes biporus (Cope) exposed to normal photoperiods, constant light, and constant darkness. Control animals had retinas with a reduced number of outer segments relative to the typical vertebrate retina. In addition, many of these outer segments were poorly formed, suggesting a capability for light detection but not for image formation. Constant light led to detached retinas and eventual degeneration of outer segments. Earliest signs of detachment appeared in younger animals, but no subsequent age differences were found. Constant dark-induced changes were similar to light-induced changes except that dark-induced changes were not so severe, did not depend on age, and included loss of pigment from cells in the pigmented epithelium. Retinal damage in constant dark animals suggests that free-living Bipes biporus are occasionally exposed to light. Dark-seeking behavior of normal animals diminishes after exposure to constant light.