Metformin treatment did not affect photoreceptor function (Supplementary Material, Fig. S4G) or survival (Supplementary Material, Fig. S4H and I), confirming that the adverse effects of metformin in the P23H-1 rat model and P23H KI mouse model are specific to rhodopsin and not a general feature associated with retinal degeneration. Here, RHO is linked to retinal degeneration.