IRD1 and IRD2 Mice, Naturally Occurring Models of Hereditary Retinal Dysfunction, Show Late-Onset and Progressive Retinal Degeneration

Purpose: To elucidate whether Institute for Cancer Research (ICR) derived retinal dysfunction (IRD) 1 and IRD2 mice, spontaneous mouse models of rod-cone and rod dysfunction, respectively, develop age-related retinal degeneration. Materials and Methods: Morphological and morphometric examinations were performed in the retinas of both mutants from 1 to 18 months of age. The rate of apoptotic cell death was determined by TUNEL techniques. Electroretinography was performed on the IRD2 mice at various ages. Age-matched ICR mice were used as controls. Results: IRD1 and IRD2 mice showed a decrease in the thickness of the outer nuclear layer and a higher frequency of TUNEL-positive photoreceptor cells at 6 months of age compared with controls, and showed almost complete absence of the outer nuclear layer at 18 months of age. Light deprivation had no effect on the severity of the retinal degeneration. There were no differences in the number of cone nuclei among ICR, IRD1, and IRD2 mice at 12 months of age and the cones of the IRD2 mice were still functional at this age. Conclusions: IRD1 and IRD2 mice showed late-onset and progressive retinal degeneration.