Visual evoked potential-based acuity assessment: overestimation in amblyopia
- 317 Downloads
When visual acuity (VA) is assessed with spatially repetitive stimuli (e.g., gratings) in amblyopes, VA can be markedly overestimated. We evaluated to what extent this also applies to VEP-based objective acuity assessment, which typically uses gratings or checkerboards.
Seventeen subjects with amblyopia (anisometropic and strabismic) participated in the study; decimal VA range of their amblyopic eye covered 0.03–1.0 (1.5–0.0 logMAR). Using the Freiburg Acuity VEP (FrAVEP) method, checkerboard stimuli with six check sizes covering 0.02°–0.4° were presented in brief-onset mode (40 ms on, 93 ms off) at 7.5 Hz. All VEPs were recorded with a Laplacian montage. Fourier analysis yielded the amplitude and significance at the stimulus frequency. Psychophysical VA was assessed with the Landolt-C-based automated Freiburg Visual Acuity Test (FrACT).
Test–retest limits of agreement for both FrACT and FrAVEP were ±0.20 logMAR. In all but two dominant eyes and high-acuity amblyopic eyes (VA <0.3 logMAR), FrACT and FrAVEP agreed within the expected limits of ±0.3 logMAR. However, the VEP-based acuity procedure overestimated single Landolt-C acuity by more than 0.3 logMAR in 9 of 17 (53 %) of the amblyopic eyes, up to 1 logMAR. While all subjects had a psychophysical acuity difference >0.2 logMAR between the dominant and amblyopic eye, only three of them showed such difference with the FrAVEP.
Both measurements of visual acuity with the VEP and FrACT were highly reproducible. However, as expected, in amblyopia, acuity can be markedly overestimated using the VEP. We attribute this to the use of repetitive stimulus patterns (checkerboards), which also lead to overestimation in psychophysical measures. The VEP-based objective assessment never underestimated visual acuity, but needs to be interpreted with appropriate caution in amblyopia.
KeywordsVisual acuity Objective assessment Visual evoked potentials Amblyopia
- 3.Ghasia F, Brunstom J, Tychsen L (2009) Visual acuity and visually evoked responses in children with cerebral palsy: gross motor function classification scale. Br J Ophthalmol 93:1068–1072Google Scholar
- 16.Bach M, Joost W (1989) VEP vs spatial frequency at high contrast: subjects have either a bimodal or single-peaked response function. In: Kulikowski J, Dickinson C, Murray I (eds) Seeing contour colour. Pergamon Press, Oxford, pp 478–484Google Scholar
- 20.Bach M, Strahl P, Waltenspiel S, Kommerell G (1990) Amblyopia: reading speed in comparison with visual acuity for gratings, single Landolt Cs and series Landolt Cs. Fortschr Ophthalmol 87:500–503Google Scholar
- 27.Bach M (1996) The Freiburg Visual Acuity Test: automatic measurement of visual acuity. Optom Vis Sci 73:49–53Google Scholar
- 30.Loumann Knudsen L (2003) Visual acuity testing in diabetic subjects: the decimal progression chart versus the Freiburg Visual Acuity Test. Graefes Arch Clin Exp Ophthalmol 241:615–618Google Scholar
- 31.Wesemann W (2002) Visual acuity measured via the Freiburg Visual Acuity Test (FVT), Bailey Lovie chart and Landolt Ring chart. Klin Monbl Augenheilkd 219:660–667Google Scholar
- 35.Bach M (2007) Freiburg evoked potentials. http://www.michaelbach.de/ep2000.html. Accessed 19 Aug 2013
- 37.Fahle M, Bach M (2006) Basics of the VEP. In: Heckenlively J, Arden G (eds) Principles and practice of clinical electrophysiology of vision. MIT Press, Cambridge, pp 207–234Google Scholar
- 40.R Development Core Team (2006) R: a language and environment for statistical computing. http://www.R-project.org. Accessed 26 Oct 2013
- 52.Heinrich SP, Marhöfer D, Bach M (2010) “Cognitive” visual acuity estimation based on the event-related potential P300 component. Clin Neurophysiol 121:1464–1472Google Scholar