The norpA photoreceptor has been used as a model system for studying progressive retinal dystrophies in humans because the loss of its function leads to rapid light-dependent retinal degeneration as a result of excessive endocytosis of stable rhodopsin-arrestin complexes and accumulation of internalized rhodopsin in late endosomes [11], [12], [14]. This evidence concerns the gene RHO and inherited retinal dystrophy.