The optokinetic response in zebrafish and its applications.

The optokinetic response (OKR) is a stereotyped eye movement in response to movement in he surround. The OKR serves to stabilize the visual image on the retina, and allows for high resolution vision. Due to its high selection value, all vertebrates display this basic behavior. Here, we review the properties of the OKR with a focus on the zebrafish, including methodological aspects of measuring eye movements in small larvae. The genetic amenabilities of the zebrafish model permit the use of this reflexive behavior in genetic screens. Such approaches have led to the isolation of mutant strains with specific defects in the visual pathway. In addition to the use of the OKR as a screening assay, mutations with characteristic abnormalities in the execution of this behavior will enable the analysis of sensory-motor control in great detail. A case in point is the belladonna mutation, where an axonal misrouting effect at the optic chiasm leads to a reversed OKR with a number of interesting properties.