Evaluation of the "Freiburg Acuity VEP" on Commercial Equipment

To assess the implementation and outcome quality of the Freiburg Acuity VEP methodology (Bach et al. in Br J Ophthalmol 92:396-403, 2008) on the Diagnosys Espion Profile and E3 electrophysiology systems.

We recorded visual evoked potentials (VEPs) from both eyes of 24 participants, where visual acuity (VA) was either full or reduced with scatter foils to approximately 0.5 and 0.8 LogMAR, resulting in a total of 144 recordings. Behavioral VA was measured in each case under the same conditions using the Freiburg Acuity Test (FrACT); VEP-based acuity was assessed with the "heuristic algorithm," which automatically selects points for regression to zero amplitude.

Behavioral VA ranged from - 0.2 to 1.0 LogMAR. The fully automatic heuristic VEP algorithm resulted in 8 of 144 recordings (6%) that were scored as "no result." The other 136 recordings (94%) had an outcome of - 0.20 to 1.3 LogMAR (which corresponds to a range of 20/12.5-20/400, or 6/3.8-6/120, in Snellen ratios; or 1.6-0.1 in decimal acuity). The heuristic VEP algorithm agreed with the behavioral VA to within ± 0.31 LogMAR (95% limits of agreement), which is equivalent to approximately three lines on a VA chart.

The successful implementation of the Freiburg Acuity VEP "heuristic algorithm" on a commercial system makes this capability available to a wider group of users. The limits of agreement of ± 0.31 LogMAR are close to the original implementation at the University of Freiburg and we believe are clinically acceptable for a fully automatic, largely objective assessment of visual acuity.