In photoreceptors, the photo-isomerization of 11-cis-retinal chromophore into alltrans-retinal is the first step of the photo-transduction cascade. To regain light sensitivity after light exposure, photoreceptors need to recycle their chromophore. This is done through the retinoid visual cycle, which involves a series of enzymatic reactions taking place in photoreceptors as well as in the cells of the retinal-pigmented epithelium (RPE) (reviewed by JC Saari (Saari, 2000)). Rpe65, a gene specifically expressed in RPE, has recently been identified as the isomerohydrolase (Jin et al., 2005; Moiseyev et al., 2005), one of the key enzymes of the retinoid visual cycle. As a consequence, when Rpe65 is mutated, the retinoid visual cycle is disrupted, and the sensitivity to light of the photoreceptors is drastically reduced.