Structural and physiological responses to prolonged constant lighting in the cone-rich retina of Arvicanthis ansorgei.

Cone photoreceptor death is a leading cause of blindness in industrialised countries. Despite this, there are few mammalian models available to study cone pathophysiology. The diurnal rodent Arvicanthis possesses a high cone percentage and ease of maintenance. We recently described the effect of ambient light conditions on cyclic disc shedding, and observed that 24 h of constant illumination ("LL") completely disrupted the normal rhythmic process and increased cone shedding fourfold. The current study was undertaken to see whether protracted constant illumination (7 days LL) would further perturb cone (and rod) turnover, and possibly lead to photoreceptor degeneration. Whereas control (cyclic lighting) retinas exhibited a typical early morning burst in phagosomes, LL retinas exhibited only low uniform numbers of rod and cone phagosomes across 24 h, with no peak of shedding at any time. Morphometric and immunohistochemical analyses of Arvicanthis retinas after 7 days LL (300 lux) showed no structural changes compared to control retinas.