Figure 5. Cone function slowly declines with age in the Cngb1–/– dog.
(A) Photopic single-flash ERG tracings in response to the following stimuli in the light-adapted eye present on a background of 30 cd/m2: –0.4, 0.0, 0.4, 0.9, 1.4, and 1.9 log cds/m2 (top to bottom tracings), and at the bottom, a photopic 33-Hz flicker response at 0.4 log cds/m2. (B and C) Change in the mean (± SD) photopic a-wave (B) and b-wave (C) amplitudes in response to the 0.4 log cds/m2 stimulus with age. The mean photopic a-wave amplitude for Cngb1–/– dogs was significantly lower at 42 and 66 months of age (P < 0.05, Student’s t test). The mean photopic b-wave was significantly reduced at 66 months of age (P < 0.01, Student’s t test). n = 2 Cngb1–/– dogs at each time point; n = 3 controls at 14 and 36 months; and n = 2 controls at 72 months. (D and E) Results of vision testing showing the percentage of dogs that made the correct exit choice (D) and the time taken to exit (E). At all ages tested, the affected dogs had reduced visual function at the lowest light level. Bright light vision was maintained in all age groups tested. Control dogs: n = 6; Cngb1–/– dogs: n = 3 for 4-month-old and 12- to 24-month-old dogs and n = 4 for 36- to 48-month-old dogs.