PRPH2 and retinal disorder: Early RPE involvement in some cases of PRPH2-retinopathy and the p.M216K mutation in RHO remain unexplained as both genes are expressed in the photoreceptors.15,16 One early symptom common to these disorders is reduced vision in the dark; it is plausible to speculate that the impaired night vision is caused by an abnormal visual cycle in the affected RPE while the cone function is spared due to the Müller cell-mediated visual cycle.17