Clinical significance of objective vision assessment using visually evoked cortical potentials induced by rapid pattern sequences of different spatial frequency

Abstract

In patients where reliable subjective assessment of visual acuity is impossible, further diagnostics should be enhanced by an objective method. A group of 34 patients was examined by objective assessment of visual acuity using visual evoked potentials (VEP) as described by Hajek and Zrenner in 1988. The presentation of five checkerboards with different spatial frequency in repetitive sequences on a TV-monitor elicits a series of transient visual evoked potentials. Shape and amplitude of each wavelet depends on check size and directly reflect a spatial tuning function with a low- and high-frequency cut-off. This amplitude is described by a polynomial fit (2nd order). The function's intersection with the x-axis at higher spatial frequencies leads to an estimation of the visual acuity. This result is compared to the subjectively determined visual acuity. In the majority of the presented cases the suspected malingering was confirmed. Patients with suspected malingering represent the primary indication of the described method.