(A, B) Scotopic and photopic ERG were recorded to evaluate the before and after effects of light damage (LD) on Nmnat1E257K/− mutant mice compared to control age-matched littermates (n ≥ 5 per genotype). (C, D) H&E staining and retinal morphometry show marked photoreceptor degeneration in 10 weeks-old mutant mice after light exposure at 8 weeks of age compared to controls. RPE= retinal pigment epithelium, ONL= outer nuclear layer, INL= inner nuclear layer, OPL= outer plexiform layer, IPL= inner plexiform layer, GCL= ganglion cell layer, OS= outer segment, IS= inner segment.