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C. M. Knapp, R. J. McLean, F. A. Proudlock, I. Gottlob; A Comparison of OKN Asymmetry in Normal and Amblyopic Subjects. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4879.
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It is well documented that there is a horizontal OKN asymmetry in amblyopic subjects with a preference to nasalward moving stimuli. No horizontal asymmetry exists in the normal adult visual system. Vertical OKN asymmetry is less well understood, however from our previous work, there is no evidence of a vertical asymmetry. We investigated vertical and horizontal OKN asymmetry in normal and amblyopic subjects.
The right eye of 17 healthy volunteers and the amblyopic eye of 16 strabismic subjects were investigated for OKN gain asymmetry whilst viewing a square wave grating movingat 10, 20 and 40°/s covering 70° horizontally and 50° vertically. An asymmetry index score was calculated from horizontal and vertical OKN gains. The asymmetry indices for normal and amblyopic subjects were compared.
A horizontal OKN asymmetry with nasalward preference was evident in a subset of the amblyopic group whilst no asymmetry was seen with normal subjects. No vertical OKN asymmetry was seen in either the amblyopic or normal subject groups. We found no correlation between the horizontal asymmetry and vertical asymmetry in amblyopes (r = 0.14, 0.28 and 0.01 for 10°/s, 20°/s and 40°/s, respectively). The correlation between horizontal asymmetry and vertical asymmetry was stronger in controls at faster velocities (r = -0.01, 0.63 and 0.45 for 10°/s, 20°/s and 40°/s, respectively). The spread of the asymmetries was greater for the vertical than for the horizontal axis and the spread of asymmetries increased with increasing target
We found no correlation between horizontal and vertical asymmetries for amblyopes suggesting that abnormal visual cortical development which leads to preference for nasalward stimuli does not lead to an equivalent vertical bias. In contrast there was a correlation between horizontal and vertical asymmetry in controls at faster velocites.
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