The development of monocular and binocular VEP acuity

The development of monocular and binocular grating acuity was measured in 87 infants, 2-52 weeks of age, using the sweep VEP technique. Average monocular and binocular acuity growth functions were nearly identical, with a small (less than 0.2 octaves) binocular acuity superiority occurring only under 6 months. Interocular acuity differences were small (averaging less than 1/4 octave, unsigned, with a 95% confidence interval of less than +/- 0.6 octaves) and were not significant at any age. These characteristics make the sweep VEP technique a potentially sensitive tool for the detection of monocular visual losses in the early stages of amblyopia.     

Sensitivity and specificity of the step VEP in suspected functional visual acuity loss

Background/aim

Early and accurate diagnosis of functional visual loss (FVL) allows optimum management. Visual evoked potentials (VEPs) offer a means of objectively estimating acuity and therefore could assist with early and accurate diagnosis. The aim of this study was to assess the sensitivity and specificity of the step VEP in diagnosing FVL.

Methods

A retrospective audit was conducted in 36 school-aged children presenting with reduced visual acuity and clinical suspicion of FVL. All had undergone step VEP testing as part of their investigation. Medical notes were reviewed, and where necessary, referring centres, general practitioners or electronic clinical portals were consulted to obtain longer-term outcome data.

Results

Twenty-seven of the 36 patients (75 %) were classified as having had FVL: all had a normal step VEP spatial threshold. Nine patients (25 %) had an organic cause for their acuity loss, of whom seven had abnormal step VEP spatial thresholds: the other two patients had some functional overlay to their organic disease. The step VEP sensitivity was 78 % (95 % confidence interval 40–96 %), and specificity was 100 % (95 % confidence interval 84–100 %).

Conclusion

The high specificity of the step VEP for FVL warrants increased suspicion of an organic cause should the step VEP spatial threshold be abnormal.     

Conducting shorter VEP tests to estimate visual acuity via assessment of SNR

Introduction

The estimation of visual acuity (VA) via visual evoked potentials (VEP) is a valuable measure for all preverbal and non-verbal subjects whether adults or children. The aim of this study is to introduce a novel technique of VEP acquisition based on estimates of signal-to-noise ratio (SNR) and comparison to a predefined detection threshold. We aim to demonstrate the reduction in total study time without compromising the accuracy of the VEP-determined acuity estimate.

Methods

The VEP-determined acuity of twelve normal subjects was assessed via a spatial frequency (SF) sweep. A pattern reversal checkerboard stimulus utilised SFs ranging from 0.1 to 28 cycles per degree (cpd). Using linear extrapolation and Bland–Altman analysis, VEP-acquired acuity was compared to a conventional Snellen Acuity measurement. An SNR test, Fsp, assessed signal quality to determine the minimum amount of sweep data required for VEP-based VA estimation.

Results

VEP acuity estimates correlated strongly (r ² = 0.91, SD = 0.06), leading to a VA limit via extrapolation. Bland–Altman analysis revealed agreement between tests is statistically valid (95 % CI ?0.11 to 0.42 logMAR). The Fsp statistic indicated SFs 1.3–3.6 cpd yielded Fsp >3.1 within 15 s of acquisition with frequencies >3.6 cpd being sub-threshold. The Kruskal–Wallis statistic compared final Fsp values for SFs as groups, where F = 208.82 ranking each frequency, with frequencies >7.2 cpd ranking lowest.

Discussion

The Fsp as an SNR measurement shows that rapid, quality-driven clinical tests for VEP-based acuity estimates can be conducted without compromising accuracy.     

Development of VEP Vernier acuity and grating acuity in human infants.

PURPOSE: To compare the developmental sequences of two basic measures of pattern vision, Vernier acuity and grating acuity, using steady state visual-evoked potentials (VEPs) and an analysis designed to isolate pattern-specific responses from those due to motion in the Vernier stimulus. METHODS: The authors recorded VEPs from 57 healthy full-term infants and 4 adults. The grating acuity stimulus was a sinusoidal grating, temporally modulated (appearance-disappearance) at a rate of 3 Hz, with spatial frequency decreasing in linear steps during each 10-second trial. The Vernier acuity stimulus was a vertical square-wave grating with portions of each bar temporally modulated to make offsets appear and disappear at a rate of 3 Hz. Vernier offset size changed in log steps from small to large offsets. The authors recorded each observer's electroencephalogram (EEG) during multiple presentations of each stimulus type, and the EEG was digitized and filtered to obtain the amplitude and phase of the response at the first two harmonics of the stimulus temporal frequency. Thresholds were estimated with an extrapolation technique that took into account the signal-to-noise ratio and phase of the response. RESULTS: VEP Vernier acuity and grating acuity develop at different rates, with grating acuity approaching adult levels earlier than Vernier acuity. The within-subject relationship between VEP Vernier acuity and grating acuity follows the same developmental trajectory established by previous psychophysical studies of humans and monkeys. CONCLUSIONS: This VEP technique provides a rapid estimate of Vernier acuity in infants. VEP Vernier acuity remains strikingly immature throughout the first year of life, similar to behavioral Vernier acuity. Because Vernier acuity is a sensitive measure of amblyopia, this VEP test may be useful in the future to identify amblyopia and to follow its treatment progress in pediatric patients.     

Spatial frequency sweep VEP: visual acuity during the first year of life

The grating acuity of 197 infants from 1 week to 53 weeks of age was measured using the visual evoked potential (VEP) in response to counterphase grating stimulation. The gratings were presented as a 10 sec spatial frequency sweep which spanned the acuity limit. The amplitude and phase of the second harmonic response were extracted by discrete Fourier analysis. The VEP amplitude versus spatial frequency function showed narrow spatial frequency tuning with amplitude peaks at one or more spatial frequencies. The phase of the response at medium to high spatial frequencies was generally constant at a spatial frequency peak, followed by a progressive phase lag with increasing spatial frequency. Grating acuity was estimated by linear extrapolation to zero microvolts of the highest spatial frequency peak in the VEP amplitude versus spatial frequency function. This visual acuity estimate increased from a mean of 4.5 c/deg during the first month to about 20 c/deg at 8-13 months of age. The VEP acuities at 1 month are a factor of three to five higher than previously reported for pattern reversal or pattern appearance stimuli. By 8 months VEP grating resolution was not reliably different from adult levels in the same apparatus.     

Measurement of position acuity in strabismus and amblyopia: specificity of the vernier VEP paradigm

PURPOSE: An objective measure of positional acuity is desirable in the nonverbal clinical population. This study was conducted to investigate the specificity of the vernier VEP as a measure of positional acuity, evaluating the potential confound of asymmetric motion responses that may be present in some groups of patients. These motion responses could masquerade as position-specific responses, since they occur at the same response frequency as the vernier-related response. METHODS: Twelve observers with early-onset esotropia (EOE), 30 children with untreated amblyopia, and 15 control children underwent swept vernier VEP acuity testing accompanied by a swept motion control stimulus. The control condition was used to detect the presence of artifactual responses not related to position sensitivity. The patients with EOE were selected for high levels of motion asymmetry as documented with oscillating gratings presented monocularly. As a measure of motion confound (penetration), the proportion of first-harmonic responses recorded in the control condition was determined. RESULTS: The penetration rate in the vernier condition in each study group (EOE: 0.93%; amblyopes: 4.26%; normal subjects: 2.40%) and the entire group (2.85%) was acceptably low. The level of penetration was not significantly influenced by the presence of amblyopia. CONCLUSIONS: The vernier VEP paradigm, when applied in the manner described, can be interpreted as a measure of position sensitivity. The presence of motion asymmetry or untreated amblyopia does not affect the validity of vernier measurements made.     

应用视觉诱发电位技术评估视力

目的:将诱发电位技术应用于视力的客观评定。方法:以最小信号视角、P100波幅和潜伏期作为受检眼的检测指标,运用模式翻转视觉诱发电位(PRVEP)技术检测与记载各受检眼各不同信号视角条件下的结果(包括P100波幅和潜伏期的变化)。应用SPSS软件对收集数据作统计学处理和分析。结果:确定最小信号视角是客观评估视力的基础,选定P100波幅作为视力量化评价指标,建立了最小信号视角条件下P100波幅与视力间的回归方程,运用该方法对180眼视力的客观评估与国际标准视力表筛查结果比较无显著性差异。结论:应用在最小信号视角条件下P100波幅与视力的回归方程对受检者视力的评估切实可行、简便且能达到量化分析的目的。     

Visual acuity assessment from birth to three years using the acuity card procedure: cross-sectional and longitudinal samples

We used the Teller Acuity Cards (TAC) to test 7 groups of 20 healthy infants and children ranging in age from 1 week to 36 months. We also tested 27 of these children at least twice within their first year. We had two primary goals: (1) to provide normative data on the development of visual acuity as assessed with the new version of the TAC (Vistech, Inc.) and (2) to investigate the predictive value of the TAC. The results from the cross-sectional samples show that our estimates of visual acuity are consistent with those reported by other researchers who used earlier versions of the TAC. The longitudinal data indicate that, on the average, an early estimate of visual acuity was not predictive of a later estimate, at least within the first year. The results are discussed in terms of the usefulness of the TAC for testing normal and clinical populations.     

Validation study of VEP vernier acuity in normal-vision and amblyopic adults

PURPOSE: Vernier displacement thresholds can be measured with swept-parameter visual evoked potentials (sVEPs) and may therefore be useful in pre- or nonverbal subjects. This study was conducted to test whether sVEP vernier thresholds are valid measures of the visibility of vernier offsets in two different settings. METHODS: Vernier acuity thresholds were measured psychophysically and electrophysiologically using square-wave gratings containing vernier displacements modulated at 3.76 Hz. The detectability of the vernier alignment cue was degraded by introducing either gaps or standing offsets in the stimulus. These manipulations were performed in normal-vision observers. In a second experiment, psychophysical and sVEP vernier acuity were measured in amblyopic observers. RESULTS: sVEP thresholds and overall amplitudes in normal observers were strongly affected by the introduction of gaps or standing offsets, as were psychophysical thresholds. Psychophysical and sVEP vernier offset thresholds were significantly correlated in the amblyopic eyes, as were sVEP and optotype interocular threshold differences. sVEP amplitudes of patients with strabismus were lower than those of patients with anisometropic amblyopia, even though optotype acuities were the same in the two groups. CONCLUSIONS: Vernier acuity thresholds derived from the sVEP tap mechanisms that are specific for the relative position of stimulus elements, and they correlate with perceptual visibility in normal and amblyopic observers. Because of this correlation and because sVEP thresholds can be measured without the need for instruction or behavioral responses, they may be useful in assessing visual function in pre- and nonverbal patients.     

Age and binocular advantage: A VEP assessment

Monocular and binocular visual evoked potentials (VEP's) were recorded in response to contrast-reversing checkerboard patterns of 2 check sizes (14 and 28 min arc) and 2 contrast-reversal rates (1.88 and 7.50 rps) in children (10 and 11-year-olds) and young adults (20 to 30-year-olds). The magnitude of binocular advantage, expressed as the ratio of the binocular to the average monocular response, was assessed by amplitude measurements of the major positive peak. The overall VEP amplitudes were larger for children than for adults across all conditions. The VEP amplitudes for binocularly viewed patterns were also consistently larger than the VEP amplitudes for the monocularly viewed patterns for both age groups. However, when the binocular advantage was expressed as a ratio of binocular to monocular average (MAV), the amplitude difference between the age groups was no longer apparent; although the children's average VEP responses were of a larger amplitude, the binocular advantage remained the same regardless of age.     

The acuity card procedure: a rapid test of infant acuity

Forced-choice preferential looking (FPL) and operant preferential looking (OPL) procedures for testing infant acuity typically require 15-45 min to derive an acuity estimate. This article presents a new acuity assessment technique ("acuity cards") that combines FPL/OPL stimuli with an observer's subjective assessment of an infant's looking behavior. The infant is shown a series of gray cards that contain grating targets of various spatial frequencies. An observer watches the eye movement patterns and behavior of the infant and judges whether the infant can or cannot see the grating on each card in the series. Acuity is estimated as the highest spatial frequency that the observer judges the infant to be able to see. With this technique, the binocular acuity of normal infants can be estimated with reasonable accuracy in the laboratory setting in 3-5 min.     

Clinical validation of a novel web-application for remote assessment of distance visual acuity

Background/ObjectivesOphthalmic disorders cause 8% of hospital clinic attendances, the highest of any specialty. The fundamental need for a distance visual acuity (VA) measurement constrains remote consultation. A web-application, DigiVis, facilitates self-assessment of VA using two internet-connected devices. This prospective validation study aimed to establish its accuracy, reliability, usability and acceptability.Subjects/MethodsIn total, 120 patients aged 5–87 years (median = 27) self-tested their vision twice using DigiVis in addition to their standard clinical assessment. Eyes with VA worse than +0.80 logMAR were excluded. Accuracy and test-retest (TRT) variability were compared using Bland–Altman analysis and intraclass correlation coefficients (ICC). Patient feedback was analysed.ResultsBias between VA tests was insignificant at −0.001 (95% CI −0.017 to 0.015) logMAR. The upper limit of agreement (LOA) was 0.173 (95% CI 0.146 to 0.201) and the lower LOA −0.175 (95% CI −0.202 to −0.147) logMAR. The ICC was 0.818 (95% CI 0.748 to 0.869). DigiVis TRT mean bias was similarly insignificant, at 0.001 (95% CI −0.011 to 0.013) logMAR, the upper LOA was 0.124 (95% CI 0.103 to 0.144) and the lower LOA −0.121 (95% CI −0.142 to −0.101) logMAR. The ICC was 0.922 (95% CI 0.887 to 0.946). 95% of subjects were willing to use DigiVis to monitor vision at home.ConclusionsSelf-tested distance VA using DigiVis is accurate, reliable and well accepted by patients. The app has potential to facilitate home monitoring, triage and remote consultation but widescale implementation will require integration with NHS databases and secure patient data storage.Subject terms: Diagnosis, Health services, Eye manifestations     

Yves Le Grand and the assessment of retinal acuity using interference fringes

Just over sixty years ago, Yves Le Grand's article 'Sur la mesure de I'acuité visuelle au moyen de franges d'interference' (C. R. Acad. Sci. Paris 200: 490–491; 1935) was published. A translation of this important article into English is given and a commentary discusses the application of the interference fringe method to the study of the ocular modulation transfer function, the spatial arrangement of retinal receptors and the potential acuity of cataract patients.     

The effects of luminance on FPL and VEP acuity in human infants.

Grating acuity was measured in 16-week-old human infants. Three measurement techniques were used: forced-choice preferential-looking (FPL), and two visual-evoked-potential (VEP) techniques. The stimuli were counterphase flickering sinewave gratings with a space-average luminance of -1.0 or 2.0 log cd/m2. Slightly different luminance-dependent changes occur between FPL and VEP acuities, suggesting that some factor influences the two methods differently as stimulus luminance varies. A comparison between FPL acuities and VEP acuities within infants suggests a quantitative relationship between techniques. Infant's acuity for sinewave gratings with a space-average luminance of -2.0, -1.0, 0.0, 1.0 and 2.0 log cd/m2 was also measured using a single VEP paradigm. The results are compared to the same measurements in adults and to infant and adult ideal observers. VEP acuity in this group of infants improves by about 0.5 log units between -2.0 and 0.0 log cd/m2 and remains asymptotic between 0.0 and 2.0 log cd/m2. This result suggests that luminance-dependent changes in infant acuity cannot be fully accounted for by immaturities in the optics and photoreceptor spacing and efficiency.     

Comparison of Snellen acuity and objective assessment using the spatial frequency sweep PVER

Background: We compared the vision objectively assessed by spatial frequency sweep pattern-reversal visual-evoked response (SPVER) with the Snellen acuity in patients. Methods: SPVER acuity and Snellen acuity were measured in 100 patients with various ocular pathologies, including macular diseases, diffuse retinal degeneration, optic nerve diseases, glaucoma, and high myopia. For SPVER, 10 sinusoidally modulated vertical gratings were presented as stimuli. The responses were averaged and displayed through the discrete Fourier transform on the monitor display. The PVER acuity was determined by extrapolating the SPVER amplitude-spatial frequency function to baseline. Results: Vision ranged from 20/15 to 20/400 with Snellen acuity, and from 20/25 to 20/190 with SPVER. The overall correlation between the two acuities wasr=0.666. The correlation varied fromr=0.895 in eyes with glaucoma tor=0.436 in eyes with optic nerve disease. Seventy-seven eyes (77%) had a visual acuity agreement of within 1.0 octave between the two measurements. Conclusion: The SPVER acuity and the Snellen acuity correlated to a certain degree. Discrepancies were found in certain diseases, with the highest disparity in patients with optic nerve disease. We conclude that the SPVER is effective in estimating vision objectively, particularly in patients in whom the standard Snellen test is impossible to perform or yields unreliable results.This study was presented in part at the American Academy of Ophthalmology Annual Meeting, San Francisco, November 1994     

The International Council of Ophthalmology 360-degree assessment tool: development and validation

Background

The Accreditation Council for Graduate Medical Education and other organizations recommend 360-degree assessments for evaluation of interpersonal and communication skills, professional behaviours, and some aspects of patient care and system-based practice. No such tool has been developed for ophthalmology or received international content validation.

Effects of sweep VEP parameters on visual acuity and contrast thresholds in children and adults

Background  

There are many parameters that may impact the thresholds obtained with sweep visually evoked potentials (sVEP), yet a number of these parameters have not been systematically studied, and there is no recognised standard for sVEP recording. In this study, the effects of electrode placement, temporal frequency, sweep direction, presence of a fixation target, stimulus area, and sweep duration on visual acuity (VA) and contrast thresholds of the sVEP were investigated. Additionally, the effect of these parameters on the number of viable threshold readings obtained from five active electrodes was investigated.     

The technique, validity and clinical use of the sweep VEP

Vision scientists have concentrated on studying two visual functions when it comes to assessing the sensory visual development in human: visual acuity and contrast sensitivity. The methods used to measure these visual functions can be either behavioral or electrophysiological. A relatively new technique for measuring the visual acuity and contrast sensitivity electrophysiologically is the sweep visual evoked potential (sVEP). This paper is a review of the literature on the sVEP technique: stimulus parameters, threshold determination, validity and reliability of sVEP are discussed. Different studies using the sVEP to study the development of visual acuity, contrast sensitivity, and vernier acuity are presented. Studies have demonstrated that the sVEP is a potentially important tool for assessing visual acuity and contrast sensitivity in non-verbal individuals with disorders affecting their visual system.     

Reproducibility of visual acuity assessment in normal and low visual acuity

PURPOSE: To assess the reproducibility of measurements of visual acuity in both the upper and lower range of visual acuity. MATERIALS AND METHODS: The retroilluminated ETDRS 1 and ETDRS 2 charts (Precision Vision) were used for measurement of visual acuity. Both charts use the same letters. The sequence of the charts followed a pseudorandomized protocol. The examination distance was 4.0 m. When the visual acuity was below 0.16 or 0.03, then the examination distance was reduced to 1 m or 0.4 m, respectively, using an appropriate near correction. Visual acuity measurements obtained during the same session with both charts were compared. A total of 100 patients (age 8-90 years; median 60.5) with various eye disorders, including 39 with amblyopia due to strabismus, were tested in addition to 13 healthy volunteers (age 18-33 years; median 24). At least 3 out of 5 optotypes per line had to be correctly identified to pass this line. Wrong answers were monitored. The interpolated logMAR score was calculated. In the patients, the eye with the lower visual acuity was assessed, and for the healthy subjects the right eye. Differences between ETDRS 1 and ETDRS 2-acuity were compared. RESULTS: The mean logMAR values for ETDRS 1 and ETDRS 2 were -0.17 and -0.14 in the healthy eyes and 0.55 and 0.57 in the entire group. The absolute difference between ETDRS 1 and ETDRS 2 was (mean +/- standard deviation) 0.051 +/- 0.04 for the healthy eyes and 0.063 +/- 0.05 in the entire group. In the acuity range below 0.1 (logMAR > 1.0), the absolute difference (mean +/- standard deviation) between ETDRS 1 and ETDRS 2 of 0.072 +/- 0.04 did not significantly exceed the mean absolute difference in healthy eyes (p = 0.17). Regression analysis (|ETDRS 1 - ETDRS 2| vs. ETDRS 1) showed a slight increase of the difference between the two values with lower visual acuity (p = 0.0505; r = 0.18). DISCUSSION: Assuming correct measurement, the reproducibilty of visual acuity measurements in the lower acuity range is not significantly worse than in normals.