Exogenous NMN protects against retinal degeneration in mice lacking Nampt and may have efficacy against diverse retinal degenerative diseases. (A–C) Nampt−rod/−rod mice receiving daily intraperitoneal injections of 150 mg/kg NMN beginning at P5 had improved retinal function on ERG (n=12 vehicle/5 NMN; 2-way mixed ANOVA with Bonferroni post-hoc test) compared to vehicle-treated mice, consistent with relative preservation of the outer nuclear layer on histology (D; see arrows). (E–G) Nampt−cone/−cone mice receiving daily intraperitoneal injections of 150 mg/kg NMN beginning at P5 also had improved retinal function on ERG (n=9 vehicle/5 NMN; 2-way mixed ANOVA with Bonferroni post-hoc test). Retinal NAD+ deficiency is a feature of multiple mouse models of retinal dysfunction, including light-induced degeneration (H; n=10–12/group; 2-tailed, unpaired t-test), streptozotocin-induced diabetic retinopathy (I; n=5/group; 2-tailed, unpaired t-test), and age-associated retinal dysfunction (J; n=5/group; 2-tailed, unpaired t-test). Graphs depict mean + S.E.M. (H–J) or mean ± S.E.M. (A–C, E–G) (* p < .05; ** p < .01; *** p < .001; # p < .0001).