Visual acuity measurement using evoked potentials and fast Fourier transform.

Visual evoked cortical potentials (VECP) were recorded from 10 subjects with normal visual acuity (VA) 1.0. Reversing square-wave gratings of 16 different spatial frequencies were used as stimuli. In all 10 subjects significant increase in power at the stimulation frequency was observed in the Fourier spectrum. The VA, calculated from the Fourier spectra, ranged from 0.4 to 1.0. The described method for VA measurement is entirely objective, and the examination can be performed very rapidly and conveniently with the aid of a computer. However, the results indicate that the reliability of the measurement in individual cases may be doubtful.