The performance properties of the amblyopic visual system

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1977

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A series of psychophysical and electrophysiological studies were performed in order to define some of the performance properties of the visual system of humans with naturally occurring amblyopia of varying etiology. In subjects with strabismic and/or anisometropic amblyopia, photopic luminosity curves are essentially the same for the amblyopic and non-amblyopic eyes; however, increment threshold spectral sensitivity functions are lower across the entire visible spectrum and do not show the dip in the yellow region of the curve characteristic of the non-amblyopic eye. Application of the subtractive interaction model of Sperling and Harwerth (1971) suggests that the anomaly may be accounted for on the basis of abnormal lateral interactions in the amblyopic eye. Psychophysical studies of contrast sensitivity showed markedly abnormal threshold contrast sensitivity across a wide range of spatial frequencies, and at high spatial frequencies the duration versus contrast reciprocity function of the amblyopic eye has a lower slope and a longer integration time than that of the non-amblyopic eye. These deficits evident at the psychophysical threshold are also evident in the suprathreshold visual evoked response as a lower signal to noise ratio, and phase shift of the amblyopic eye relative to the non-amblyopic eye. Both the amblyopic and non-amblyopic eyes showed a linear relationship between the log of the stimulus contrast and the VER amplitude; however, the slope of the line for the amblyopic eye was flatter. Contrast sensitivity functions for two subjects with amblyopia ex-anopsia were also markedly abnormal, and the results of these subjects differed from those of the strabismic and anisometropic amblyopes in terms of their responses to flicker. The results of these various studies have been considered in the light of recent electrophysiological studies of animals reared with induced strabismus, anisometropia or lid closure.

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