The bugeye mutant zebrafish exhibits visual deficits that arise with the onset of an enlarged eye phenotype.

PURPOSE

The bugeye mutant has an enlarged eye phenotype, presumably because of elevated intraocular pressure. Since elevated intraocular pressure is a significant risk factor for glaucoma, the bugeye zebrafish mutant may be a model organism for the disease.

METHODS

The optomotor response (OMR) was used to assess visual responsiveness in both larval and adult zebrafish. Electroretinograms (ERGs) were recorded to measure outer retinal function, and histologic analyses were performed on WT and mutant eyes.

RESULTS

At 5 days old, bugeye mutants have an OMR, ERGs, and retinal morphology indistinguishable from those of wild-type (WT) animals. By 2 months of age, bugeye mutants begin to develop an enlarged eye phenotype. At 3 months, some mutants show deficits in the OMR assay, including lower contrast sensitivity. The data suggest that there is a correlation between the size of the enlarged eye and the degree of OMR deficit. Histologic analysis of the bugeye mutant retina revealed decreases in retinal ganglion cell densities by 3 months. By 5 months, the mutant's ERG b-wave had smaller amplitudes and longer latencies at brighter light intensities than those of the WT fish.

CONCLUSION

After phenotypic onset at 3 months, the bugeye mutants begin to develop visual deficits. At 3 months, bugeye mutants exhibit a decrease in retinal cell densities and by 5 months, they show diminished outer retinal function. In summary, the bugeye mutant provides a means of studying glaucoma-associated phenotypes in the zebrafish.