Figure 7. Maximum spatial acuity of the optokinetic reflex (OKR) responses. Although both Pde6b⁺ mouse lines responded to spatial frequencies characteristic of wild-type mice with no significant difference between the two mouse lines, only young 4-week-old C3H/HeOu mice reliably responded with a tracking reflex and only to relatively low spatial frequencies (0.062±0.02 cyc/deg). The number of C3H/HeOu mice with an OKR response decreased steadily with age and approached zero at 24 weeks. The FVB/N mice did not have a detectable OKR at any age. The fit is exponential with an R-square value of 0.92.