Testing of concentric visual field constriction by means of scotopic visually evoked potentials.

Using scotopic visually evoked potentials (VEP), an objective test of concentric absolute field defects is presented. At 0.8 log units above the mean VEP threshold, the full field, the central area of 50 degrees diameter, and the complementary peripheral field were flash stimulated. In 13 normal subjects the peripheral VEP response was larger in amplitude and shorter in latency compared to the central response. In four cases of concentric field restriction due to hysteria and malingering, the same results were found. In three cases of retinitis pigmentosa and advanced glaucoma, the peripheral VEP sensitivity was worse than the central one or no response could be found. The amount of stray light was estimated as the difference of the thresholds for central and peripheral stimulation (1.6 to 1.8 log units) in a patient with a residual central field of 20 degrees.