A sensory mechanism for amblyopia: electrophysiological studies.

Steady-state visual evoked potentials were elicited by the appearance/disappearance of sinusoidal gratings of varying spatial frequency for both eyes of amblyopic subjects at temporal frequences from 2--32 Hz. The amblyopic eyes showed reduced responses relative to those of the nonamblyopic eyes across a wide range of spatial frequencies, the difference between the 2 eyes being most marked for high spatial frequencies and low temporal frequencies. Both the nonamblyopic and the amblyopic eyes showed a linear relation between the evoked potential amplitude and the logarithm of the stimulus contrast; however, the slope of the line was flatter for the amblyopic eyes. Possible neural mechanisms for the amblyopic eyes' reduced responses to spatial contrast are considered.