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H. Langrova, H. Jaegle, A. Messias, E. Zrenner, A. Kurtenbach; Visual Acuity Estimates From Visual Evoked Potentials: A Comparison of Two Methods. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3314. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
The use of the Visual Evoked Cortical Potential (VEP) as an objective method for measuring visual acuity has gained increasing popularity over the last 30 years. A number of methods have been proposed, which differ in stimulus timing, contrast and spatial parameters as well as electrode placement. The aim of this study was to compare two methods with respect to comparability and repeatability.
Subjective measurements of visual acuities were ascertained using the Freiburg Acuity Test (FrACT) and the ETDRS chart. Objective measurements were made using transient sweep VEPs, based on the method of Hajek & Zrenner (1988), and steady-state VEPs, adapted from Wolf & Bach (2006). Each VEP was recorded twice and with 2 different electrode placements (10-20, Laplace). Ten healthy subjects, 4 male, 6 female, aged between 26 and 67 years were included. Visual acuities were measured by all 4 methods with best optical correction and using Bangerter occlusion foils, which reduced acuity from 1 to ca. 0.8, 0.6, 0.3, 0,2 and 0.1. The research followed the tenets of the Declaration of Helsinki.
Visual acuities (log MAR) measured using ETDRS and FrACT were highly correlated (r2=0.94, CV= 0.25), however values measured by FrACT were significantly lower than those of ETDRS (t-test; p< 0.001) by an average of 0.12. FrACT gave better correlations than ETDRS for all VEP acuity conditions. Acuities estimated from the transient VEP tended to overestimate high and underestimate low acuities (based on FrACT; r2 = 0.86 (CV=0.36) and 0.91(CV=1.06)). Laplace electrode placement did not improve transient VEP analysis. While VEP response amplitudes were higher for transient VEPs, a more objective analysis could be performed for the steady-state VEPs by calculating signal-to-noise ratios. Acuities estimated from steady state VEP were similar to those of FrACT. However, for both the variability was large.
VEP might be used to estimate the visual acuity in cases were VEPs responses show good signal/noise ratio. However, while we found a good overall correlation of the acuity estimates from VEP with those of FrACT, VEP estimates are generally beset by a significant variability and reduced repeatability, allowing only rough individual acuity estimates from VEP measurements.
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