Purpose:
Congenital nystagmus (CN) is a disorder characterized by involuntary conjugate, horizontal oscillations of both eyes, present at birth or shortly after. CN is associated with substantial visual impairments that often lead to reduced occupational and social functioning. The study of CN has been largely confined to humans and few other higher vertebrates, making it very difficult to track down the origin and the underlying neuronal processing of CN. Recently, we discovered that achiasmatic zebrafish belladonna (bel) mutants display spontaneous oscillations (SOs) of the eyes that closely resemble CN in humans. Being relatively simple, inexpensive, and highly accessible, the zebrafish bel mutant is a very promising animal model for CN. In order to further value the use of zebrafish as a CN disease model, we conducted an in-depth analysis of the SO waveforms in zebrafish bel mutants and related them to CN waveforms obtained in humans.
Methods:
Zebrafish bel mutants spontaneously display oscillations of the eyes in presence of a still black and white sine-wave grating. Eye movements were recorded with a CCD camera via real-time image processing and subjected to extensive offline analysis. In addition to statistical analysis, we inspected the different types of waveforms and categorized them according to the established CN waveform classification.
Results:
The waveform characteristics of the SOs in zebrafish bel mutants possess variability comparable to those in human CN. We found instances of all waveform classes pertaining to human CN. Despite their qualitative similarity, SO and human CN waveforms differ in quantitative aspects.
Conclusions:
Our detailed analysis revealed that the SOs in zebrafish bel mutants are---albeit quantitatively different---essentially identical to human CN with respect to their waveform. Thus, zebrafish bel mutants are a reasonable model for human CN and, as such, may help advance our understanding of human CN and potentially lead to new treatment algorithms.
Keywords: nystagmus • ocular motor control • eye movements