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Heather Prior, Rachel Tuininga, Kerri Letwin, Amber Tuininga; Adult zebrafish with cataracts show reduced OKR and altered color perception. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2962.
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The zebrafish has become a versatile and tractable model organism in the study of ocular genetics. Although much work has focused on larval stages of development, adult fish also provide a useful experimental system, and can be particularly valuable in the investigation of age-associated ocular conditions such as cataracts. We are in the process of developing an in vivo adult zebrafish cataract model and show two techniques that can quantify differences in visual acuity between normal and cataractous fish.
Cataracts were induced in adult zebrafish by intraocular injection of 3.0% hydrogen peroxide. Visual acuity in these cataractous fish as well as normal fish was then evaluated using the optokinetic response (OKR) and another behaviorally-based assay for color vision. For OKR analysis, fish were immobilized on a sponge base in a beaker under anesthetic. After being revived, they were placed within a rotating drum of white/black stripes under a dissecting microscope and camera and the eye movements were recorded. To assess visual perception of color, fish were placed into test chambers of either rectangular or V-shape. After acclimation to the test environment, colored sheets were placed at opposite ends of the test chambers and the position of the fish with respect to each colored stimulus was recorded.
The OKR of individual fish was recorded before and after cataract induction. Average eye movements were significantly reduced in all cataractous fish. At a rotation speed of 13.6 rpm, eye movements averaged 1.8 per second pre-cataract and 1.0 per second post-cataract. For analysis of behavior in response to colored stimuli, yellow and green were used because they elicited the greatest discriminatory response in healthy fish. Before cataracts, fish exhibited a marked proximity preference for the green stimulus over yellow in both test chambers (3.11 times as often). After cataracts, fish did not show a significant color preference, and exhibited an altered swimming behavior that suggested reduced ability to distinguish the colored stimuli.
These studies indicate that adult zebrafish can be used for quantifiable measurements of visual changes in cataractous fish using behaviorally based techniques such as OKR and color discrimination. These techniques could be used for further investigation of cataracts in adult fish, and also applied to other zebrafish models of ocular disease.
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