Visual function was measured with optomotor response (OMR) testing at 5, 9, 13, 17, and 21 weeks of age, as previously described37 (link)39 using the OptoMotry system (Cerebral Mechanics, USA).40 (link) Briefly, a mouse was placed on a central pedestal in an enclosed chamber of monitors, which display rotating vertical sine wave gratings of varying spatial frequency (with contrast set at 100%) or varying grating contrast (with spatial frequency set at 0.103 cycles/degree). A trained observer marked when the characteristic head tracking movement occurred (or did not occur) through a programmed staircase method to calculate the visual threshold. Measurements from the left and right eye were averaged for a combined visual threshold score. Contrast threshold results were converted to Michelson contrast values.41 (link)