Abstract
Purpose: :
The optomotor response is a reflexive head movement in response to a rotating grating that has been used extensively with mice in order to quantify visual acuity and contrast sensitivity thresholds in numerous disease models. Our goal was to develop an improved device for studying the mouse optomotor response, while at the same time keeping the cost of the device significantly lower than that of commercially available packages.
Methods: :
We constructed the apparatus on a mobile cart consisting of two levels. The lower level contains a standard video projector emitting horizontally through a motorized filter wheel and wide angle lens onto a first-surface mirror oriented at 45 degrees. The mirror projects the image upward through a glass plate that comprises the support for the device’s second level. On the second level sits a 14-inch diameter cylinder with a small mouse platform in the center. Suspended above the platform is a video camera using infrared illumination to observe movements of the mouse’s head. A custom MATLAB graphical user interface controls stimulus presentation (using the open source Psychtoolbox) according to a staircase protocol based on user input.
Results: :
Our design allows presentation of a continuous grating over the entire cylindrical screen, in contrast to the commercial package whose ‘virtual cylinder’ contains 4 discontinuities where LCD screens meet. Another advantage of our system is the motorized filter wheel allowing the user to shift from scotopic to photopic stimulus levels from within the MATLAB environment, eliminating the need to manually place a filter between mouse and stimulus. The filter wheel design also permits use of interference filters, thereby allowing presentation of narrow band monochromatic gratings. Preliminary testing of wild-type mice indicates that this device can be used to rapidly and reproducibly determine visual acuity and contrast sensitivity thresholds. Characterization of the optomotor response in BBS4 knockout, transducin knockout, and DBA/2J mice is currently underway.
Conclusions: :
We successfully developed a hardware and software package for quantifying visual acuity and contrast sensitivity thresholds in the mouse using the optomotor response. Our apparatus represents both functional improvements and a very significant cost savings relative to a widely used commercial package.
Keywords: vision and action • visual acuity • pattern vision