Abstract
Purpose: :
Zebrafish are a good model to study visual physiology due to the similarity of their retina to other vertebrates, their short life cycle, and the availability of genetically altered mutants. By using the optokinetic response (OKR), one can study the visual acuity of adult fish objectively. Bugeye zebrafish have a mutation in the lrp2 gene and enlarged eyes, which are known risk factors for myopia and glaucoma. This study utilizes OKR to demonstrate significantly impaired vision for mutant adult zebrafish with a phenotype of enlarged eyes.
Methods: :
The absolute spatial acuity of zebrafish was determined by observing OKR at a low frequency grating and then increasing the frequency until the OKR was no longer observed. To obtain visual acuity in cycles per degree (cpd), trigonometric analysis was utilized: cpd= 1/ [2arctan (h/(2a))]. Where a is the distance from the center of the lens to the grating, and h is the length of one cycle of the smallest grating at which OKR was observed. The absolute spatial acuity of bugeye fish was then compared to that of wildtype (AB) fish of the same age.
Results: :
The bugeye fish displayed a significant deficit in absolute spatial acuity when compared to AB fish. The visual acuity of bugeye fish was notably more variable than AB, which might be because mutation in the lrp2 gene has variable penetrance. Also, there did not appear to be a relationship between eye size and visual acuity. This might suggest that retinal defect, rather than eye size, is the cause of visual deficiency in bugeye fish.
Conclusions: :
OKR is widely used to analyze the visual performance of larval zebrafish. The use of OKR to detect visual deficit in adult bugeye fish indicates that OKR is also a reliable method for observing visual deficit of adult zebrafish. Thus, visual acuity of zebrafish can be studied over time, which would be useful in studies of disease progression and treatment success.
Keywords: visual acuity • myopia • intraocular pressure