Behavioral evaluation of visual function of rats using a visual discrimination apparatus

A visual discrimination apparatus was developed to evaluate the visual sensitivity of normal pigmented rats (n = 13) and S334ter-line-3 retinal degenerate (RD) rats (n = 15). The apparatus is a modified Y maze consisting of two chambers leading to the rats' home cage. Rats were trained to find a one-way exit door leading into their home cage, based on distinguishing between two different visual alternatives (either a dark background or black and white stripes at varying luminance levels) which were randomly displayed on the back of each chamber. Within 2 weeks of training, all rats were able to distinguish between these two visual patterns. The discrimination threshold of normal pigmented rats was a luminance level of −5.37 ± 0.05 log cd/m2; whereas the threshold level of 100-day-old RD rats was −1.14 ± 0.09 log cd/m2 with considerable variability in performance. When tested at a later age (about 150 days), the threshold level of RD rats was significantly increased (−0.82 ± 0.09 log cd/m2, p < 0.03, paired t-test). This apparatus could be useful to train rats at a very early age to distinguish between two different visual stimuli and may be effective for visual functional evaluations following therapeutic interventions.