VEP Vernier and Grating Acuity Deficits and Treatment Effects in Children With Untreated Amblyopia: A Longitudinal Prospective Study

Abstract

Abstract: : Purpose: Vernier and Snellen acuity measures are well correlated in amblyopia whereas grating acuity underestimates amblyopia. Here we compared the relative sensitivity of VEP vernier and grating acuity measures to the amblyopic deficit in a group of previously untreated children. Our method uses the swept parameter VEP to estimate the acuity threshold by extrapolating the response function to zero signal amplitude. We also studied suprathreshold function by examining the entire VEP response function for vernier displacement and spatial frequency sweeps.<br Methods: Normal children (n=16) and previously untreated anisometropic amblyopes (n=12) were studied longitudinally during clinical treatment. Vernier displacement and spatial frequency sweep response functions were averaged across subjects at key treatment milestones in amblyopes. Normals underwent the same assessment (every 4 months) for 12 months. Grating stimuli were swept between 32 and 2 c/deg using 7.51 Hz pattern–reversal, and 15 Hz on–off modulation. The vernier alignment/misalignment grating was swept from 0.5 to 8 arcmin at 3.76 Hz. Results: Entry and exit mean amblyopic optotype acuity was 0.64 and 0.32 LogMAR respectively. Entry and exit mean interocular acuity difference was 0.57 and 0.31 LogMAR respectively. Mean followup post occlusion was 121 days. Grating acuity response functions initially showed clear interocular differences which reduced to an insignificant level and remained so after treatment. Vernier offset response functions showed a marked interocular difference even for larger offsets. Differences remained at the end of treatment over a range of small, near threshold offsets. Conclusions: Vernier offset response functions reflect residual optotype acuity losses better than spatial frequency response functions. 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 provide more sensitivity and specificity for amblyopia.

Keywords: amblyopia • visual development: infancy and childhood • electrophysiology: clinical