Small teleost fish are increasingly used for studying the genetic basis of vision. In particular, zebrafish (Danio rerio) and medaka (Oryzias latipes) are commonly used vertebrate model organisms in developmental research, including research on the development of visual function. A multitude of behavior-based visual tests are established for larvae that have been successfully used to identify and characterize visual defects in genetically manipulated strains of these species. Testing the visual system of adult fish has proven to be more difficult for a number of reasons, including complications in restraining fish, or shoaling and dominance behavior interfering with visual behavior in population screening assays. In this paper, we present a simple and cost-effective method to quantitatively measure the optokinetic response (OKR) of individual adult zebrafish and medaka, which can be used to characterize visual capabilities of adult fish. This method can be applied to any fish species of similar size.