Purpose: C57/Bl6, Cpfl1(-/-) (cone photoreceptors function loss 1; pure rod function), Gnat1a(-/-) (rod α-transducin; pure cone function), and Rpe65(-/-);Rho(-/-) double-knockout mice were studied to distinguish the respective contributions of the different photoreceptor (PR) systems that enable light perception and mediate a visual reflex in adult Rpe65(-/-) mice, with a simple behavioral procedure.
Methods: Visual function was estimated using a rotating automated optomotor drum covered with vertical black-and-white stripes at spatial frequencies of 0.025 to 0.5 cycles per degree (cyc/deg) in both photopic and scotopic conditions. Mouse strains with different luminances were tested to evaluate the contribution and the light-intensity threshold of each PR system.
Results: Stripe rotation elicited head movements in the wild-type (WT) animals in photopic and scotopic conditions, depending on the spatial frequency, whereas the Cpfl1(-/-) mice show a reduced activity in the photopic condition and the Gnat1a(-/-) mice an almost absent response in the scotopic condition. A robust visual response was obtained with Rpe65(-/-) knockout mice at 0.075 and 0.1 cyc/deg in the photopic condition. The residual rod function in the Rpe65(-/-) animals was demonstrated by testing Rpe65(-/-);Rho(-/-) mice that present no response in photopic conditions.
Conclusions: The optomotor test is a simple method of estimating the visual function and evaluating the respective contributions of rod and cone systems. This test was used to demonstrate that in Rpe65(-/-) mice, devoid of functional cones and of detectable 11-cis-retinal protein, the rods mimic cone function in part, by mediating vision in photopic conditions.