Ciliary neurotrophic factor (CNTF) protects retinal cone and rod photoreceptors by suppressing excessive formation of the visual pigments.

The retinal pigment epithelium (RPE)-dependent visual cycle provides 11--retinal to opsins in the photoreceptor outer segments to generate functional visual pigments that initiate phototransduction in response to light stimuli. Both RPE65 isomerase of the visual cycle and the rhodopsin visual pigment have recently been identified as critical players in mediating light-induced retinal degeneration. These findings suggest that the expression and function of RPE65 and rhodopsin need to be coordinately controlled to sustain normal vision and to protect the retina from photodamage.