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S. I. Chen, A. Chandna, M. W. Pettet, A. M. Norcia; Experience-Dependent Plasticity of Form and Motion Mechanisms in Human Amblyopia. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4703.
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Deprivation of patterned visual input during early visual development leads to both anatomical and functional losses in the deprived eye. Disagreement exists (human literature) as to whether the non-deprived eye shows super-normal behavior. Here we use spectral analysis of Visual Evoked Potential (VEP) responses to isolate relative position and motion/transient responses in previously untreated children who experienced deprivation of high-spatial frequency input in one eye due to chronic optical defocus (anisometropia).
Normal children (n=16) and previously untreated amblyopes (n=12) under eight years old were studied longitudinally during clinical treatment. VEP responses to a 3.76Hz Vernier displacement stimulus were subjected to spectral analysis. Positional responses (first harmonic) and motion/transient responses (second harmonic) were the main outcome measures compared before and after occlusion therapy.
Position-specific responses are super-normal in the non-deprived eye and markedly subnormal in the deprived eye prior to treatment. Motion/transient responses, on the other hand show no difference from normal in the non-deprived eye and milder losses in the deprived eye. After occlusion of the initially deprived eye, the position signal decreased in the initially non-deprived eye and increased in the initially deprived eye. No measurable effect of occlusion occurred for the motion/transient response.
These results suggest that position and motion/transient signals arise from separate mechanisms with very different sensitivity to optical deprivation and conversely, to reversal of the deprivation effect by occlusion therapy.
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