PNA staining (a, b) revealed that cone photoreceptors were abundant in the central and peripheral regions of the untreated, P14 Rpe65−/−::Rho−/− mouse retina, a pattern similar to that seen in the P14, wild type mouse retina (see Fig 1a, b). Cones degenerate in the Rpe65−/−::Rho−/−retina by 5 weeks of age (c), remaining only in the dorsal and temporal retina. D: dorsal; V: ventral; T: temporal; N: nasal. DKO: Rpe65−/−::Rho−/− double knockout mouse. Scale bars (a, c) = 500 μM. Scale bar (b) = 100 μM.