Application of zebrafish oculomotor behavior to model human disorders.

To ensure high acuity vision, eye movements have to be controlled with astonishing precision by the oculomotor system. Many human diseases can lead to abnormal eye movements, typically of the involuntary oscillatory eye movements type called nystagmus. Such nystagmus can be congenital (infantile) or acquired later in life. Although the resulting eye movements are well characterized, there is only little information about the underlying etiology. This is in part owing to the lack of appropriate animal models. In this review article, we describe how the zebrafish with its quick maturing visual system can be used to model oculomotor pathologies. We compare the characteristics and assessment of human and zebrafish eye movements. We describe the oculomotor properties of the zebrafish mutant belladonna, which has non-crossing optical fibers, and is a particularly informative model for human oculomotor deficits. This mutant displays a reverse optokinetic response, spontaneous oscillations that closely mimic human congenital nystagmus and abnormal motor behavior linked to circular vection.