Figure 16. Strain differences in perimeter length. Three genotypes, one wild type (WT), C57Bl/6J, and two models of retinal degeneration were compared, IRBP^−/− and rd8, at two ages, postnatal days 30 and 720. The sample sizes were four to five animals for each genotype at P30 and three animals per genotype at P720. IRBP^−/− had a longer perimeter length at P30 and P720 compared to WT. There was no change between P30 and P720 for either IRBP^−/− or WT. However, while rd8 did not differ in the average perimeter length of each cell at P30, it was greater at P720 compared to WT.