After fixing the head of the mouse in the rig and calibrating the eye movements, lock the camera arm at the central position. Run the visual stimulation and eye tracking software. For photopic OKR measurement, ensure the drum grating oscillates horizontally with a sinusoidal trajectory.
For scotopic OKR, to achieve scotopic visual stimulation, cover the screen of each monitor with a customized filter made of five layers of 1.2 neutral density film, and turn the room light off. Apply one drop of pilocarpine solution to the right eye, and wait 15 minutes to shrink the pupil to a proper size for eye tracking under the scotopic condition. Ensure the drop stays on the eye and is not wiped away by the mouse.
Afterward, rinse the right eye with saline to thoroughly wash away the pilocarpine solution. Finally, pull down the curtain to completely seal the enclosure, which prevents stray light from interfering with the scotopic vision. Run the visual stimulation and the eye tracking software.
For scotopic OKR measurement, ensure the drum grating drifts at a constant velocity from left to right, the temporonasal direction about the left eye. The OKR gain varied with the values of spatial frequency, oscillation frequency, and the direction of movement grating. The spatial frequency tuning curve of the OKR behavior peaked at an intermediate spatial frequency of 0.16 cycles per degree.
The oscillation frequency tuning curve monotonically declined as the oscillation frequency of the drum grating increased. The horizontal OKR could also be induced by gratings moving in different directions, but the strongest horizontal OKR behavior was elicited by the temporonasal motion. Following 45 minutes of continuous OKR stimulation, the amplitude of the OKR behavior was significantly potentiated.
