PDE6B and retinal degeneration: Rd1 mouse is an animal model of rapid retinal photoreceptor degeneration; the phenotype is mainly caused by mutations in the β subunit of rod cGMP-phosphodiesterase (PDE6β), which results in cGMP accumulation in the retina (Wang et al., 2017), eventually causing early onset severe retinal degeneration (Bowes et al., 1990).