• canine;
  • dystrophy;
  • retina;
  • RPE65;
  • testing;
  • vision


Objective  The increasing importance of canine retinal dystrophy models means accurate vision testing is needed. This study was performed to evaluate a four-choice vision testing technique for any difference in outcome measures with repeated evaluations of the same dogs.

Animals studied  Four 11-month-old RPE65-deficient dogs.

Procedures  Vision was evaluated using a previously described four-choice vision testing device. Four evaluations were performed at 2-week intervals. Vision was assessed at six different white light intensities (bright through dim), and each eye was evaluated separately. The ability to select the one of the four exit tunnels that was open at the far end was assessed (‘choice of exit’) and recorded as correct or incorrect first tunnel choice. ‘Time to exit’ the device was also recorded. Both outcomes were analyzed for significance using anova. We hypothesized that performance would improve with repeated testing (more correct choices and more rapid time to exit).

Results  ‘Choice of exit’ did not vary significantly between each evaluation (P = 0.12), in contrast ‘time to exit’ increased significantly (P = 0.012), and showed greater variability in dim light conditions.

Conclusions  We found no evidence to support the hypothesis that either measure of outcome worsened with repeated testing; in fact, the ‘time to exit’ outcome worsened rather than improved. The ‘choice of exit’ gave consistent results between trials. These outcome data indicate the importance of including a choice-based assessment of vision in addition to measurement of device transit time.