Differences in the neural basis of human amblyopia: the distribution of the anomaly across the visual field

Spatio-temporal contrast sensitivities to horizontally-oriented Gaussian-weighted patches of sinusoidal grating stimuli were determined across the nasal and temporal visual fields of strabismic and non-strabismic, anisometropic amblyopes. The visual field distribution of the amblyopic anomaly differs in strabismic and non-strabismic, anisometropic eyes. In strabismus the peripheral region of one or both hemifields is spared; in non-strabismic, anisometropic cases the loss is evenly distributed across the binocular visual field but is not present in the monocular temporal field. These findings suggest that the non-strabismic forms of amblyopia in humans result from binocular competitive imbalance in early life. The strabismic results pose two problems for the present competitive model of amblyopia: in strabismus, amblyopia is mainly limited to central vision and shows an asymmetric distribution.