VEP-based acuity assessment in low vision
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Objective assessment of visual acuity (VA) is possible with VEP methodology, but established with sufficient precision only for vision better than about 1.0 logMAR. We here explore whether this can be extended down to 2.0 logMAR, highly desirable for low-vision evaluations.
Based on the stepwise sweep algorithm (Bach et al. in Br J Ophthalmol 92:396–403, 2008) VEPs to monocular steady-state brief onset pattern stimulation (7.5-Hz checkerboards, 40% contrast, 40 ms on, 93 ms off) were recorded for eight different check sizes, from 0.5° to 9.0°, for two runs with three occipital electrodes in a Laplace-approximating montage. We examined 22 visually normal participants where acuity was reduced to ≈ 2.0 logMAR with frosted transparencies. With the established heuristic algorithm the “VEP acuity” was extracted and compared to psychophysical VA, both obtained at 57 cm distance.
In 20 of the 22 participants with artificially reduced acuity the automatic analysis indicated a valid result (1.80 logMAR on average) in at least one of the two runs. 95% test–retest limits of agreement on average were ± 0.09 logMAR for psychophysical, and ± 0.21 logMAR for VEP-derived acuity. For 15 participants we obtained results in both runs and averaged them. In 12 of these 15 the low-acuity results stayed within the 95% confidence interval (± 0.3 logMAR) as established by Bach et al. (2008).
The fully automated analysis yielded good agreement of psychophysical and electrophysiological VAs in 12 of 15 cases (80%) in the low-vision range down to 2.0 logMAR. This encourages us to further pursue this methodology and assess its value in patients.
KeywordsVisual acuity Objective assessment Visual evoked potentials Low vision Sweep VEP Step VEP
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Conflict of interest
All authors certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent–licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge or beliefs) in the subject matter or materials discussed in this manuscript.
Statement of human rights
All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee and with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards.
Statement on the welfare of animals
This article does not contain any studies with animals performed by any of the authors.
Informed consent was obtained from all individual participants included in the study.
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