Electrophysiological Differences Between Early and Late Onset Amblyopia.

Pattern onset visual evoked potentials (VEPs) have been recorded from 11 young adult strabismic amblyopes with a clear history of onset before 18 months of age and 10 of later onset. Results have been compared with results from 15 normal control subjects. 30’ checks were used at a series of contrast levels. The early and late onset amblyopes showed a similar range of reduced acuities in their amblyopic eyes. Latencies of the CII VEP component were significantly shorter than normal from both amblyopic and fellow eyes of early onset amblyopes (ANOVA: both P<0.02), with no difference between the eyes. In the late onset group the latency from the amblyopic eye was significantly longer than normal (P<0.0001) and longer than the latency from the fellow eye (P<0.002). There are important differences between early and late onset amblyopia in man, which are likely to be significant clinically because the conditions required for recovery in animal experiments are different following early and late onset deprivation.