The therapeutic potential of AAV-mediated gene delivery to the retina has best been illustrated by the positive results from three phase I clinical trials for Leber's Congenital Amaurosis (LCA), a rare autosomal recessive blinding disease caused by loss of function mutations in the visual cycle enzyme retinol isomerase (RPE65) required to synthesize 11-cis retinal [1]–[3]. Here, RPE65 is linked to Leber congenital amaurosis.