Effect of constant light on the morphology of the retina in domestic chick (Gallus g. domesticus): A scanning electron microscope study

Abstract

Light induces variable levels of damage to the retina and often, death of the photoreceptor cells. It is reported that chick retina, having abundant melanin in the retinal pigment epithelium, undergoes no or minimal damage from exposure to light. However, the morphology of cone and rod photoreceptor cells after continuous exposure of light has not been studied in detail. The present study investigated the detailed changes of photoreceptor cells, by scanning electron microscopy (SEM). Domestic chicks (Gallus g. domesticus) from post-hatch day (PH) 1 to 7 were initially reared at 700 lux at 12 h light (L):12 h dark (D). From PH 7 to 18, they were exposed to 12L:12D (control) and 24L:0D (constant light) cycles at 700 lux. At PH18, chicks were sacrificed, their eyes enucleated and preserved in Karnovsky’s fixative. The retina was then separated from the adherent choroid, mounted on photoreceptor side up and processed for SEM. There was significant damage to rod and cone outer segments from both dorsal and ventral part of the retina and a decrease in the abundance of cells of the inner nuclear layer in constant light, compared to that found in 12L:12D cycles. It is likely that constant light affects the retinal cells in the vertical pathway, which could alter the phototransduction process.