Comparison of pattern-onset, -reversal and -offset VEPs in treated amblyopia

There are differences in the properties of visual evoked potentials (VEPs) to various forms of pattern stimulation and it is not clear how these differences reflect macular and parmacular function in amblyopic and normal eyes. We assessed pattern-onset, -reversal and -offset VEPs from amblyopic eyes and compared them with the responses from the fellow eyes, and from controls, to gauge the relative effectiveness of these stimulus modes.

The three modes of pattern stimulation were presented sequentially in a single recording run to enable direct comparisons to be made for identical recording conditions. Half-field stimulation was used, as this elicits components over the ipsilateral and contralateral occipital scalp relative to the stimulated half-field, which reflect stimulation of macular and paramacular areas of the visual field. Eighteen amblyopes treated by occlusion and 20 control children were studied.

Multivariate analysis of variance showed significant differences between ambylopic and fellow eyes in amblyopes: pattern-onset components were significantly attenuated and ipsilateral reversal components were significantly prolonged in amblyopic eyes. When fellow eyes of amblyopes were compared with the eyes of controls, the reversal P100 and offset P110 and N165 components showed significant differences.

Ipsilateral reversal components and onset CII and contralateral P105 were the most affected in amblyopic eyes. The subnormal findings for the fellow eyes of amblyopes suggest that occlusion may have a long-standing physiological effect on the patched eye, not normally clinically apparent.