Flash visual evoked potential (VEP) in amblyopia and optic nerve disease

Amblyopia and optic atrophy are two very different causes of unilateral long-standing visual impairment. Yet, in some patients the differential diagnosis is not always manifest and standard clinical tests may fail to provide accurate information. We tested the efficacy of a nonstandard clinical test [flash visual evoked potentials (VEP's)] and quantitative multivariate statistical techniques as aids in the assessment of this differential. Thirty-three patients were separated into four groups (normal, anisometropic amblyopia, strabismic amblyopia, and unilateral optic atrophy). Non-patterned flash VEP's were obtained using several different temporal frequency rates. Patients with optic atrophy had significantly reduced VEP's in the affected eye at all temporal frequencies. Strabismic amblyopes, but not anisometropic amblyopes, often showed supranormal responses in the affected eye at the higher temporal frequencies. Finally, by using discriminant analysis (DA) we were able to classify correctly almost 70% of the patients, well above chance level of 25%. This DA provided very good sensitivity and specificity. We have shown that the use of flash VEP's and of multivariate statistical techniques may provide an effective way to diagnose amblyopia differentially from optic atrophy.