Characterizing visual performance in mice: An objective and automated system based on the optokinetic reflex.

Abstract

Testing optokinetic head or eye movements is an established method to determine visual performance of laboratory animals, including chickens, guinea pigs, mice, or fish. It is based on the optokinetic reflex which causes the animals to track a drifting stripe pattern with eye and head movements. We have developed an improved version of the optomotor test with better control over the stimulus parameters, as well as a high degree of automation. The stripe pattern is presented on computer monitors surrounding the animal. By tracking the head position of freely moving animals in real time, the visual angle under which the stripes of the pattern appeared was kept constant even for changing head positions. Furthermore, an algorithm was developed for automated evaluation of the tracking performance of the animal. Comparing the automatically determined behavioral score with manual assessment of the animals' tracking behavior confirmed the reliability of our methodology. As an example, we reproduced the known contrast sensitivity function of wild type mice. Furthermore, the progressive decline in visual performance of a mouse model of retinal degeneration, rd10, was demonstrated.

A system to measure the Optokinetic and Optomotor response in mice

“…Thus the tested spatial frequencies vary during the experiment. Digital presentation techniques (with projectors [16, 9] or monitors [1, 17, 18, 7]) significantly speed up experiments by allowing the presentation of a large array of stimuli in quick succession. By simulating a virtual cylinder a constant grating can be presented in the field of view of the animal.…”

“…By simulating a virtual cylinder a constant grating can be presented in the field of view of the animal. The actual physical distance to the stimulus has to be readjusted dynamically based on the location of the animal, either manually, by the observer [1], or automatically through software control [18, 7]. …”

“…During OMR measurements, stimuli consisting of striped patterns with distinct luminosities, contrasts, spatial or temporal frequencies can be presented in a sequential [12, 7] or step-wise manner [1, 19, 18]. The ability of mice to detect and react to these stimuli by head/body movements is judged for each individual condition by a human observer [1, 19] resulting in determination of threshold criteria [4, 1].…”

“…Body movements in mice were previously quantified using video-tracking by determining the speed of movement of the center of mass and the angular body velocity derived through a linear regression of the whole body [12]. A different approach used an automated approximation of the head movement (based on the snout location and the center of mass) to determine whether or not an animal saw a stimulus [18]. Based on this binary “yes” or “no” decision the spatial tuning of the visual system was derived by determining a contrast sensitivity curve.…”

“…The authors used a velocity threshold of ≤ 50 °/s to discard methodological artifacts. A different study [18] used commercial tracking software (Viewer3, Biobserve GmbH, Germany) and approximated the head location based on the snout location and the center of mass. The authors used a velocity threshold of ≤ 2.5 ×stimulus velocity to discard irregular movements.…”