CCND1 and retinitis pigmentosa 1: The relevance of cone rings extends beyond the S334ter RP model with well documented studies highlighting the appearance of dark patches or ‘‘holes of photoreceptors” in both animal models such as the cyclin D1 (cd1) mutant and P23H-line1 rat [37, 38], plus human retinal dystrophy, inherited retinal degeneration, and photo-pigment genetic perturbations in M-opsin cones [39–42].