Purpose: To measure contrast sensitivity in C57BL/6, the most commonly used mouse in behavioral neuroscience, and to study the effect of sex, age, and miotic drugs on the contrast sensitivity function. In addition, the authors tested a mutant in which plasticity in the cerebellum is impaired by expressing a protein kinase C inhibitor. This inhibitor is also expressed in the retina, possibly affecting vision.
Methods: The gain of the optokinetic reflex (OKR) decreases as stimuli become more difficult to see. Recording OKR gains evoked by moving sine gratings shows whether the stimulus was distinguished from a homogeneous background and how well the stimulus was distinguished.
Results: Female mice have lower OKR gains than male mice (both groups: n = 10, P = 0.001). A similar difference was observed between 4-month-old (n = 10) and 9-month-old (n = 5) C57Bl/6 mice (P = 0.001). These differences could not be detected with earlier dichotomic tests. C57BL/6 mice are able to see contrasts as low as 1%, well below the previously reported 5% threshold. Pilocarpine had no significant effect on contrast sensitivity (both groups: n = 10, P = 0.89). Vision in L7-PKCi mutants was unaffected (both groups: n = 10, P = 0.82).
Conclusions: OKR gains decrease as stimuli become more difficult to see, making the OKR a powerful tool to quantify contrast sensitivity. In C57BL/6 these response magnitudes vary greatly between sexes and between mice that differ only a few months in age. Therefore, it is important to match groups according to age and sex in experiments that require unimpaired vision. Otherwise, impaired vision can be misinterpreted as a learning or motor problem.