Objective assessment of spatial vision using the visual evoked potential

Abstract

Early assessment of the visual function is very important, as many congenital and acquired visual anomalies may lead to permanent visual loss, if not detected and effectively treated within the critical period of visual system development. Any tests employed to assess vision in infants should be objective and give a valid result quickly.The visual evoked potential (VEP) does not require active responses from the patient. It is recorded in relation to a time‐locked stimulus, typically a grating that reverses in phase (pattern reversal VEPs). Reversal VEPs have been used to estimate visual acuity. A more complete psychophysical description of the visual function is obtained with the contrast sensitivity function (CSF) which determines visibility not only of the finest detail, but also of a wide range of spatial frequencies. However, the VEP amplitude versus spatial frequency function does not accurately reflect the normal CSF when reversing gratings are employed. Reduced VEP responses are obtained in the middle spatial frequency range where stimulus visibility is highest.Here we show that 16 Hz on‐off modulation of a grating elicits a VEP versus spatial frequency plot which is similar to the CSF in a group of normal adults. When compared with reversal modulation, the test was more predictive of spatial vision defects in a group of amblyopes, thus demonstrating its clinical utility. We have shown that the same technique can be used to monitor age‐related changes in spatial vision in a group of infants whose ages ranged from 5 weeks to 14 months. The test promises to be a useful clinical tool in paediatric ophthalmology.Supported by a grant from the North Western Regional Health Authority.