Miniature fiber-optic pattern-reversal stimulator for determination of the visual evoked potential threshold; comparison with Snellen acuity

Abstract

In this report we recommend the estimation of visual acuity by detection of the visual evoked potential (VEP) threshold, defined by the smallest visual angle of a constant check size that evokes potentials. This approach was implemented using a fiber-optic pattern-reversal stimulator placed at measured, increasing distances from the examined eye. Snellen visual acuity as determined in 113 subjects was correlated with the VEP detection threshold. A highly significant correlation was found between visual acuity and the threshold visual angle of check size in subjects whose vision was impaired due to opacity in ocular media. For any given visual acuity a somewhat wide range of threshold check sizes, typically 5-10 min of arc was observed. Technical difficulties that need to be overcome to improve these results are discussed.

Pattern visual evoked potentials in the assessment of objective visual acuity in amblyopic children

“…Unlike the electroencephalogram or electrocardiogram, the interpretation of PVEP results is dependent on the individual examiner [5]. A There are several ways to determine the VA using PVEP: (1) determine the smallest stimulus check size at which the PVEP is recordable [3,13,14]; (2) identify a spatial frequency at which the peak response is recorded [4]; (3) use the extrapolation technique from the PVEP amplitude-check size function [5,6,13]. The relationship between PVEP amplitude and stimulus pattern element size has elicited a strong interest in using PVEP acuity testing as an objective assay of VA.…”

Snellen Visual Acuity versus Pattern Reversal Visual-Evoked Response Acuity in Clinical Applications

“…There are several ways to determine PVER acuity. One is an estimation of the VA from the smal lest check size providing a reproducible vi sual-evoked response [6,[13][14][15][16][17], PVER acui ty can also be estimated from the amplitudes taken at different spatial frequencies by iden tifying where the peak response lies [18,19]. An alternative approach is that the regression line of the curve is extrapolated to zero ampli tude or the noise level, then the check size coinciding with this intercept is assumed to indicate the detail resolution ability of the eye [2-4, 20, 21], Another less precise method of estimating the PVER acuity is by comparing the amplitude of a patient's visual-evoked response to that of a normal group.…”

Assessment of patients with suspected non-organic visual loss using pattern appearance visual evoked potentials

“…However, although pattern reversal and pattern onset VEPs have been reported to be useful in the objective assessment of VA both in children and in patients with unexplained visual loss, there is little consensus regarding the methodology or interpretation of VA assessment [16,35,40]. Previous paradigms have included VEP amplitude-spatial frequency function curves [25,36], extrapolation to zero from VEP spatial tuning curves [1,28,38] or the highest spatial frequency to give a recognisable VEP [18,30,34].…”

“…Previous studies have utilised the pattern VEP in attempts to assess visual acuity objectively [1,2,15,30,38,43]. However, although pattern reversal and pattern onset VEPs have been reported to be useful in the objective assessment of VA both in children and in patients with unexplained visual loss, there is little consensus regarding the methodology or interpretation of VA assessment [16,35,40].…”

“…This was compared with visual acuity in both normal subjects [15] and patients with visual acuity reduction [17]. The test protocols in the current study were initially established by selecting stimulus contrast and check size parameters that were likely to give just-detectable VEPs over a wide range of visual acuities; testing protocols were subsequently refined and shortened in preliminary experiments (Arden GB, unpublished data) Although pattern reversal VEPs are more commonly used [1,30,41] in diagnostic VEP practice, pattern onset VEPs offer certain advantages in objective VA assessment; the spatio-temporal tuning function is less complex [19,29]; the spatial frequency function of PappVEP correlates closely with contrast sensitivity [17,29]; the responses are of higher amplitude compared to reversal [29]; and a short duration pattern onset not only matches the integration time for achromatic VEPs [22,32,37], but also greatly reduces the ability of the patient to influence the results by voluntary defocus [17]. Pattern reversal VEPs elicited using similar spatial parameters are probably less effective and allow less precise acuity appraisal [14].…”