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S. Bonfield, J. Tejedor, N. T. Bech-Hansen, J. E. McRory, W. K. Stell; Spatiotemporal Contrast Sensitivity Characteristics of Optokinetic Responses in Chicks and in Normal and Cacna1f-Mutant Mice. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2988.
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© ARVO (1962-2015); The Authors (2016-present)
Testing of visual function is a powerful tool for assessing the effects of acquired or inherited changes in retinal circuitry. Optokinetic responses (OKR), including nystagmus or head movements to compensate for displacement of wide-field visual pattern stimuli, are reflexive measures that require no training and therefore are widely applicable to animal as well as human testing. Here we report the first comprehensive characterization of spatial and temporal frequency tuning of photopic OKRs at threshold contrast, in normal young chickens and in adult mice having mutations in the calcium channel alpha1-subunit gene Cacna1f.
A computer-graphics optokinetic system (OptoMotry; Cerebral Mechanics, Lethbridge, AB, Canada) provided a virtual cylinder of horizontally rotating vertical B/W sine-wave gratings. Animals were light-adapted and tested in subjective daytime, mean luminance 55 cd/m2. The operator systematically varied contrast from 0-98%, rotation speed 0.75-50 deg/sec, and spatial frequency 0.019-2.0 cy/deg, and subjectively determined contrast sensitivity threshold (minimum % contrast to elicit OKR). Subjects were male HyLine White Leghorn chicks, 6-12 days old (n=3-13), and adult mice (wild type: C57BL/6; and Cacna1f mutants: G305X males, G305X heterozygous females, nob2 males; all n=1-2).
Spatiotemporal tuning was similar in chicks and mice. Minimum contrast thresholds lay along a diagonal straight line representing V=12-15deg/sec; thresholds were slightly higher, and optimal spatial frequencies (Sf) and temporal frequencies (Tf) were 4-5x lower, in mice than in chicks.
The OKR of chicks and mice was responsive to a wide range of spatial and temporal frequencies. Optimal OKR contrast sensitivity was a linear function of Sf and Tf in all animals tested, suggesting that the OKR is tuned to stimulus velocity. OKR evidence suggests that nob2 males see normally, heterozygous G305X females have some vision, but G305X males are blind.
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