The second line of evidence that retinal degeneration caused by prom1-null mutations is time- or age-dependent and involves the RPE is that visual impairment and retinal degeneration in prom1-null frogs was preceded by ever an increasing size and number of deposits of cellular debris in the subretinal space, which then extended further into the outer segment layer and eventually through the ELM into the inner retina (Figs 1–4). This evidence concerns the gene PROM1 and retinal degeneration.