The VEP Vernier response and its sensitivity to moderate amblyopia in children.

Abstract

Abstract: : Purpose:Vernier and Snellen acuity are well correlated in amblyopia and losses on vernier acuity are often larger than grating acuity. This motivates attempts to develop vernier acuity tests for pre–verbal children. One method uses the swept parameter VEP to estimate the acuity threshold by extrapolating the response function to zero signal amplitude. Here we examined the entire response function over large supra–threshold ranges for both vernier and grating sweeps. Methods:Sweep VEP response functions for 4 stimuli were averaged across 39 amblyopic children (mean age 55 mo) and 19 normal children (mean 64 mo). Grating stimuli were swept between 32 and 2 c/deg using 7.51 Hz pattern–reversal, 3.76 Hz and 15 Hz on–off modulation. The vernier alignment/misalignment grating was swept from 0.5 to 8 arcmin and was presented at 3.76 Hz. Results:Mean amblyopic optotype acuity was 0.55 logMAR and mean interocular acuity difference was 0.39 logMAR. Group response functions for all grating acuity measures did not differ between amblyopic and fellow eyes or between normal and amblyopic eyes. In contrast, vernier response functions became progressively different between fellow and amblyopic eyes as the size of the offset increased. Conclusions:Compared with an analysis based on thresholds alone, it is likely that multivariate analysis of the vernier VEP response incorporating both the slope and the extrapolated threshold of the function will more accurately differentiate the normal from abnormal state, as well as possess more sensitivity and specificity for amblyopia.

Keywords: amblyopia • visual acuity • visual cortex