Electroretinographic study of the C57BL/6-mi(vit)/mi(vit) mouse model of retinal degeneration

Purpose. The C57BL/6-mi(vit)/mi(vit) mouse model of retinal degeneration is characterized by slow progressive loss of photoreceptor cells, concomitant loss of rhodopsin, and uneven pigmentation of the retinal pigment epithelium. The purpose of this study was to determine how these alterations affected the electroretinogram (ERG). Methods. Scotopic ERGs were measured in two litters of mi(vit)/mi(vit) mice beginning at 4 weeks and continued in the same animals at 2-week intervals through 18 weeks. Results. The mean of the maximum b-wave amplitude (V(max)) at 4 weeks was 234 ± 14 μV in mi(vit)/mi(vit) mice, which did not differ significantly from controls (266 ± 26 μV). With increasing age, all components of the ERG decreased and by 12 weeks, the mean of the V(max) had decreased to 170 μV. At 18 weeks, the mean V(max) was 75 μV, and the b- to a-wave ratio was still > 1.0. Comparison of these physiologic data to previously reported morphologic and biochemical data showed a high correlation between the b-wave amplitude and the number of photoreceptor cell nuclei (r = 0.9772) as well as the b-wave amplitude and rhodopsin levels (r = 0.9019). Conclusions. The loss of all components of the ERG and the lack of a negative-type ERG suggested that the primary cells altered in the mi(vit)/mi(vit) mouse were the photoreceptors. The high correlations between the ERG amplitude and the number of photoreceptor nuclei indicate that the V(max) of the ERG is a good measure of the degree of photoreceptor loss.