Monocular Visual Acuity Measurement in Adult bugeye Zebrafish Using Optokinetic Response

Abstract

Purpose: Zebrafish are a valuable model organism for studying the human visual system due to their similar eye physiology and function to human eyes. Several studies have demonstrated that studying the optokinetic response (OKR) is a reliable method for measuring binocular visual acuity of adult zebrafish. Bugeye zebrafish have a recessive mutation in the low density lipoprotein receptor-related protein 2 and a phenotype of enlarged eyes. The bugeye mutants display varying degrees of asymmetry in eye size. This study demonstrates that OKR can be utilized to obtain visual acuities that differ between the right and left eye for bugeye zebrafish which have asymmetrical eyes.

Methods: The OKR was recorded for fish immobilized and submerged in a stationary tank with a grating stimulus rotating in the background. 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. Then a black screen was placed in the tank to block visual stimulus to one eye and the process was repeated. Binocular and monocular visual acuities were recorded in cycles per degree (cpd). Finally, the eye volume of the zebrafish was obtained by measuring the coronal, sagittal, and transverse radii of the eye from images and using the following equation: V=4/3π(r_c r_s r_t).

Results: The bugeye zebrafish with asymmetrical eye size displayed visual acuities that were often different between the left and the right eye. Furthermore, it was observed that binocular visual acuity was better than the acuity of either eye alone. This facilitation is also a characteristic of human visual acuity. A correlation between eye volume and visual acuity was not observed.

Conclusions: Visual acuity is often an important component of ocular disease development and therapy. Zebrafish mainly have a monocular visual field, thus occluding half of the visual field during OKR measurements is sufficient for obtaining monocular visual acuities. The use of monocular visual acuity measurements in zebrafish will allow researchers the ability to monitor visual function in both eyes independently. This approach allows for treating/manipulating one eye and utilizing the other eye as control, which may result in more meaningful data.

Keywords: 754 visual acuity