Measurement of vernier and motion sensitivity with the rapid-sweep-VEP

Author(s): Norcia, A. M., Manny, R. E.

Journal/Book: Klin Monatsbl Augenheilk. 1996; 208: Postfach 30 03 66, D-70443 Stuttgart, Germany. Ferdinand Enke Verlag. 11-17.

Abstract: Background The visual abilities of infants and small children, who are unable to communicate verbally, can be determined with ''objective'' visual acuity tests as, e.g., preferential looking (PL) or visual evoked potentials (VEP). Both methods provide an estimate of grating visual acuity, but are unable to determine optotype visual acuity. Grating acuity, however, is not an optimum indicator for visual performance, as it is less affected than optotype acuity by pathological changes. The diagnostic relevance of objective methods may be improved by testing visual functions that are more strongly degraded by a malfunction of the fovea than is grating acuity. Visual functions such as vernier acuity and relative motion sensitivity are potential candidates. Methods Characteristic properties of vernier- and motion-VEP have been determined on adult subjects with a rapid-sweep-technique at various eccentricities. Results Both vernier and motion stimuli elicited VEP-responses at the 2nd harmonic (F2) of the stimulus frequency. A VEP-response at the fundamental frequency (F1) could be recorded with the vernier stimulus only. Foveal VEP-thresholds were very similar to psychophysical thresholds lying in the range from 11 to 25 arcsecs. The eccentricity dependence of the VEP-threshold recorded with vernier- and motion stimuli shows different cortical magnifications and supports the notion that the Fl response is related to the detection of the vernier offset, whereas the F2 response is generated by motion components of the stimuli. Conclusions Vernier and relative motion-related VEP thresholds can be recorded with the steady-state VEP. They may provide more sensitive tests of foveal vision loss than grating visual acuity tests.

Note: Article W Wesemann, Grimmelschausenstr 9, D-50996 Cologne, Germany

Keyword(s): VEP; objective measurement of visual functions; cortical magnification; foveal vision loss; VISUAL-ACUITY; CORTICAL MAGNIFICATION; CONTRAST SENSITIVITY; HYPERACUITY; THRESHOLDS; PERCEPTION; RESOLUTION; SENSE

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