Bach M, Maurer JP, Wolf ME (2008) **Visual evoked potential-based acuity assessment in normal vision, artificially degraded vision, and in patients**. Brit J Ophthalmol 92:396–403

Aims: To assess visual acuity (VA) objectively using visual evoked potentials (VEPs), avoiding subjective trace evaluation and providing an acuity estimate with associated confidence limits.

Methods: 40 normal subjects and 24 patients (with corneal and retinal diseases, decimal VA range 0.15–1.1 ( = 0.8_{logMAR} to −0.04_{logMAR})) participated in the study. Checkerboard stimuli with six check sizes covering 0.05–0.4° (or 0.09–0.8° for visual acuities below 0.35 ( = 0.46_{logMAR}) were presented in brief-onset mode (40 ms on, 93 ms off) at 7.5 Hz. In normal subjects, the stimuli were also optically degraded by frosted occluders resulting in a decimal VA range of 0.13–2.8 ( = 0.9_{logMAR} to −0.45_{logMAR}). Altogether, 108 steady-state VEPs were recorded with a Laplacian montage (2×Oz−(RO+LO)). Fourier analysis yielded the magnitude (A) at the stimulus frequency, and the average of the two neighboring frequencies as noise estimate (N). A and N determine the significance level p of the response, and from their ratio the non-noise-contaminated response (A*) can be calculated. Tuning curves were obtained by plotting A* vs the dominant spatial frequency of the corresponding checkerboard. A fully automatic algorithm used the significance level (p<5%) and A* to automatically select an appropriate region in the high spatial-frequency range on which a linear regression was performed, yielding a zero-amplitude extrapolated spatial frequency SF_{0}. Subjective VA was obtained with the automated “Freiburg Acuity Test”.

Results: The brief-onset presentation evoked high VEP amplitudes; however, many tuning curves displayed the well-known “notch” at intermediate check sizes. The fully automated analysis algorithm succeeded in 107 of 108 cases and effectively ignored the notch, if present. The relation between logVA and log(SF_{0}) was a constant factor throughout the range tested: logVA = log(SF_{0})/17.6 cpd. In more than 95% of all cases, the acuity predicted from SF_{0} coincided within a factor of two (up and down, or ±0.3 logMAR) with subjective VA with a coefficient of correlation of 0.90.

Conclusion: The fully automated analysis avoided subjective problems in peak-trough assessment. The results provide quantitative limits to assess patients with possible malingering.