Visual Evoked Potential Acuity Research Articles

Assessment of Human Visual Acuity Using Visual Evoked Potential: A Review.

Visual evoked potential (VEP) has been used as an alternative method to assess visual acuity objectively, especially in non-verbal infants and adults with low intellectual abilities or malingering. By sweeping the spatial frequency of visual stimuli and recording the corresponding VEP, VEP acuity can be defined by analyzing electroencephalography (EEG) signals. This paper presents a review on the VEP-based visual acuity assessment technique, including a brief overview of the technique, the effects of the parameters of visual stimuli, and signal acquisition and analysis of the VEP acuity test, and a summary of the current clinical applications of the technique. Finally, we discuss the current problems in this research domain and potential future work, which may enable this technique to be used more widely and quickly, deepening the VEP and even electrophysiology research on the detection and diagnosis of visual function.

Maternal supplementation with docosahexaenoic acid during pregnancy does not affect early visual development in the infant: a randomized controlled trial

The docosahexaenoic acid (DHA) intake of pregnant women is lower than estimates of the DHA accretion by the fetus, and recommendations were made to increase the DHA intake of pregnant women. The objective of this study was to determine whether the supplementation of pregnant women with DHA improved the visual acuity of infants at 4 mo. We conducted a blinded assessment of a subset of healthy, full-term infants born to women enrolled in a double-blind, randomized controlled trial called the DHA for Maternal and Infant Outcomes (DOMInO) trial. Women were randomly assigned to consume DHA-rich fish-oil capsules (≈800 mg DHA/d in the treatment group) or vegetable oil capsules (control group) from midpregnancy to delivery. The primary outcome was the sweep visual evoked potential (VEP) acuity at 4 mo. The VEP latency at 4 mo was a secondary outcome. Mean (±SD) VEP acuity did not differ between treatment and control groups [treatment group: 8.37 ± 2.11 cycles per degree (cpd), n = 89; control group: 8.55 ± 1.86 cpd, n = 93; P = 0.55]. VEP latencies also did not differ between groups. Irrespective of the group, maternal smoking in pregnancy was independently associated with poorer VEP acuity in the infant. DHA supplementation in women with singleton pregnancies does not enhance infant visual acuity in infants at 4 mo of age. Visual acuity in infancy is adversely associated with maternal smoking in pregnancy. This trial was registered at www.anzctr.org.au as ACTRN12606000327583. The DOMInO trial was registered at www.anzctr.org.au as ACTRN12605000569606.

Early Visual-Evoked Potential Acuity and Future Behavioral Acuity in Cortical Visual Impairment

Cortical Visual Impairment (CVI) is bilateral visual impairment caused by damage to the posterior visual pathway. Both preferential looking and sweep visual-evoked potential (VEP) can be used to measure visual acuity. The purpose of this study was to determine if an early VEP measure of acuity is related to a young patient's future behavioral acuity. The visual acuity of 33 patients with CVI was assessed using the sweep VEP and a behavioral measure on two occasions. The median age of the patients at the initial visit was 4.8 years (range: 1.3 to 19.2 years), and they were followed for an average of 6.9 years (SD: 3.5 years). The mean initial VEP acuity was 20/135 (0.735 logMAR), and the mean initial behavioral acuity was 20/475 (1.242 logMAR). The average difference between the two initial measures of acuity was 0.55 log unit, with the behavioral measure reporting a poorer visual acuity in all patients. However, the mean final behavioral acuity was 20/150 (0.741 logMAR), and the average difference between the initial VEP acuity and the final behavioral acuity was only 0.01 log unit. Therefore, the initial VEP measure was not statistically different from the final behavioral measure (t = 0.11; dF = 32; p = 0.45). Even though the initial VEP measure was much better than the initial behavioral measure, the initial VEP measure was similar to the behavioral visual acuity measured approximately 7 years later. Sweep VEP testing can be used as a predictive tool for at least the lower limit of future behavioral acuity in young patients with CVI.

Sweep Visual Evoked Potential Testing as a Predictor of Recognition Acuity in Albinism

To determine if sweep visual evoked potential (VEP) acuity is predictive of recognition acuity in children with albinism. A retrospective review was performed in children with albinism who underwent sweep VEP testing from 1992 to 2003. All patients had a complete ophthalmologic examination with either binocular or monocular sweep VEP testing and at least 5 years of follow-up. Positive predictability of sweep VEP acuity was defined as final recognition acuity within 1 Snellen line of initial sweep VEP acuity. Of the 13 patients included in the study, 11 had nystagmus, iris transillumination defects, and foveal hypoplasia at initial examination. The mean age at initial sweep VEP testing was 3.1 years (range, 0.1-10.0 years). Five of 13 patients had initial sweep VEP acuity that was predictive of final recognition acuity. Five additional patients had final recognition acuity, which surpassed initial sweep VEP acuity by 2 to 3 lines. Of these 10 patients, the mean duration for recognition acuity to reach VEP acuity was 5.4 years. There was no correlation between predictive VEP acuity and foveal pigmentation, refractive error, strabismus, nystagmus, or longer follow-up. Sweep VEP testing can be used as a predictive tool for recognition acuity in children with albinism. Predictability was found in a clinical spectrum of albinism.

The visual evoked potential in the mouse—Origins and response characteristics

The visual evoked potential (VEP) in the mouse is characterized and compared to responses obtained with the electroretinogram (ERG). The results indicate that: 1, the VEP originates in the visual cortex; 2, the rod and cone pathways contribute separately to the VEP; 3, temporal tuning functions for rod and cone ERGs are low pass and band pass, respectively; VEP tuning functions are both band pass; and 4, VEP acuity is 0.62 ± 0.156 cycles/degree. The differences in the spatial and temporal tuning functions obtained from the retina and visual cortex provides a tool to investigate signal processing through the visual system.

Development of Visual Acuity in Children With Cerebral Visual Impairment

To study the development of visual acuity in term-born children with cerebral visual impairment and a history of neonatal hypoxic-ischemic encephalopathy. We studied 19 term-born children, aged 6 months to 6 years, with moderate to severe neonatal hypoxic-ischemic encephalopathy and behaviors indicative of cerebral visual impairment. Longitudinal measures of grating acuity were obtained using preferential looking (PL) and visual evoked potential (VEP) procedures. Visual acuities at first and last visits were compared. The courses of acuity development in the 9 children who underwent both VEP and PL acuity assessment at 4 or more ages were compared with normal development. All children had measurable PL and VEP acuity, despite poor visual behavior. In nearly all, both PL and VEP acuity were below normal for age. For both PL and VEP measures, acuity at the last visit was, on average, 1 octave better than at the first visit, with a rate of improvement lower than normal. Although parallel courses of PL and VEP development occurred in many, substantial disparities in PL and VEP acuity were observed in others. Modest increases in PL and VEP grating acuity occur during early childhood in many of these patients. The rate of increase is lower than normal.

Visual maturation of term infants fed long-chain polyunsaturated fatty acid–supplemented or control formula for 12 mo

Several studies found a benefit of long-chain polyunsaturated fatty acid (LCP) supplementation for visual or mental development, but others found no benefit. Likely contributors to differences among studies are the amount of LCP supplementation, functional outcomes, and sample size. We evaluated LCP supplementation in amounts typical for human milk (based on local and worldwide surveys) in a large cohort of infants by using sweep visual evoked potential (VEP) acuity as the functional outcome. The study was a double-masked, randomized, controlled clinical trial in 103 term infants. By age 5 d, infants were randomly assigned to receive either formula with no docosahexaenoic acid (DHA) or arachidonic acid (ARA) or formula supplemented with DHA and ARA as 0.36% and 0.72%, respectively, of total fatty acids. Sweep VEP acuity was the primary outcome. Random dot stereoacuity, blood lipid profile, growth, and tolerance were secondary outcomes. VEP acuity in the LCP-supplemented group was significantly better than that in the control group at ages 6, 17, 26, and 52 wk. Stereoacuity in the LCP-supplemented group was significantly better than that in the control group at age 17 wk but not at ages 39 and 52 wk. By ages 17 and 39 wk, the red blood cell DHA concentration in the LCP-supplemented group was more than double and more than triple, respectively, that in the control group. Growth of infants fed LCP-supplemented and control formulas did not differ significantly, and both diets were well tolerated. LCP supplementation of term infant formula during the first year of life yields clear differences in visual function and in total red blood cell lipid composition.

Maturation of Visual Acuity Is Accelerated in Breast-Fed Term Infants Fed Baby Food Containing DHA-Enriched Egg Yolk

Between 6 and 12 mo of age, blood levels of the (n-3) long-chain PUFA, docosahexaenoic acid (DHA), in breast-fed infants typically decrease due to diminished maternal DHA stores and the introduction of DHA-poor solid foods displacing human milk as the primary source of nutrition. Thus, we utilized a randomized, clinical trial format to evaluate the effect of supplemental DHA in solid foods on visual development of breast-fed infants with the primary outcome, sweep visual-evoked potential (VEP) acuity, as an index for maturation of the retina and visual cortex. At 6 mo of age, breast-fed infants were randomly assigned to receive 1 jar (113 g)/d of baby food containing egg yolk enriched with DHA (115 mg DHA/100 g food; n = 25) or control baby food (0 mg DHA; n = 26). Gravimetric measures were used to estimate the supplemental DHA intake which was 83 mg DHA/d in the supplemented group and 0 mg/d in controls. Although many infants in both groups continued to breast-feed for a mean of 9 mo, RBC DHA levels decreased significantly between 6 and 12 mo (from 3.8 to 3.0 g/100 g total fatty acids) in control infants, whereas RBC DHA levels increased by 34% from 4.1 to 5.5 g/100 g by 12 mo in supplemented infants. VEP acuity at 6 mo was 0.49 logMAR (minimum angle of resolution) and improved to 0.29 logMAR by 12 mo in controls. In DHA-supplemented infants, VEP acuity was 0.48 logMAR at 6 mo and matured to 0.14 logMAR at 12 mo (1.5 lines on the eye chart better than controls). At 12 mo, the difference corresponded to 1.5 lines on the eye chart. RBC DHA levels and VEP acuity at 12 mo were correlated (r = -0.50; P = 0.0002), supporting the need of an adequate dietary supply of DHA throughout 1 y of life for neural development.

A randomized trial of different ratios of linoleic to α-linolenic acid in the diet of term infants: effects on visual function and growth

There are nutritional recommendations that the ratio of linoleic to alpha-linolenic acid (LA:ALA) in formula for term infants be between 5:1 and 15:1. These recommendations were made in the absence of data on functional or clinical outcomes. We compared the fatty acid status, visual evoked potential (VEP) acuity, and growth of term infants fed formula containing an LA:ALA of 10:1 or 5:1 with those of a breast-fed reference cohort. Formula-fed infants were allocated randomly in a double-blind fashion to receive formula with an LA:ALA of either 10:1 (16.9:1.7; n = 36) or 5:1 (16.3:3.3; n = 37) from near birth to 34 wk of age. Increased ALA was attained by replacing soy oil with low-erucic acid cannola oil. A parallel group of breast-fed infants was also recruited. Infant growth and fatty acid status were assessed at 6, 16, and 34 wk of age. VEP acuity was assessed at 16 and 34 wk. Infants fed the 5:1 formula had greater docosahexaenoic acid (DHA) concentrations in plasma and erythrocyte phospholipids than did infants fed the 10:1 formula, but DHA concentrations of infants fed the 5:1 formula remained less than those in breast-fed infants. The VEP acuity of all formula-fed and breast-fed infants was not significantly different at 16 and 34 wk of age. At birth, infants fed the 5:1 formula were heavier, were longer, and had a greater head circumference than infants assigned to the 10:1 formula group; this differential was maintained throughout the trial. The rate of gain in weight, length, and head circumference was not significantly different between the 2 formula-fed groups, although breast-fed infants had lower weight and length gains than did formula-fed infants between 16 and 34 wk of age. Lowering the LA:ALA in formula from 10:1 to 5:1 by using low-erucic acid canola oil resulted in a modest increase in plasma DHA but had no effect on VEP acuity or growth rate.

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.

Visual and brain function measurements in studies of n-3 fatty acid requirements of infants

Dietary n-6 or n-3 fatty acid deficiencies result in changes in brain and retinal phospholipid composition that can affect cell membrane and organ function. An n-3 fatty acid deficiency has been associated with altered electroretinograms and reduced visual acuity in animals. Other promising methods for assessing the effects of fatty acid deficiencies on brain and retinal maturation include visual-evoked potential acuity, sleep-wake cycle, auditory brain stem-evoked response, somatosensory-evoked potential measurements, and the Fagan and forced-choice preferential looking acuity tests. Preterm infants fed a formula low in alpha-linolenic acid (18:3n-3) had significant electroretinographic changes at discharge from the nursery, indicating a delay in rod photoreceptor maturation. However, infants fed human milk or supplementary n-3 fatty acids as marine oil had electroretinogram indexes like those of infants of comparable age tested soon after birth. Visual cortex function, measured by pattern reversal visual-evoked potential and forced-choice preferential looking visual acuity response, was also better in infants fed human milk or marine oil-supplemented formula than in infants fed formulas without docosahexaenoic acid (22:6n-3). Studies of term infants suggest that visual acuity is more mature in breast-fed than in formula-fed infants [corrected] at 4 months and 3 years of age.

Forced-Choice Preferential Looking and Visual Evoked Potential Acuities of Visually Impaired Children

In the authors’ previous study, the success rate for forced-choice preferential looking (FPL) with preverbal visually impaired children was higher than that with pattern visual evoked potential (VEP). The current study sought to increase the VEP success rate and to improve agreement between the FPL and the VEP acuity estimates using horizontal-bar stimuli for children with nystagmus and steady-state presentation for those without nystagmus.

Infant and adult grating acuity estimated by VEPs and heart-rate change

Heart rate (HR) responses to onset of reversing (6 Hz) sine wave gratings of various spatial frequencies (SFs) and concurrent steady-state visual evoked potential (VEP) amplitudes were used to estimate the grating acuities of infants, ages 10 to 13 weeks, and adults. For infants, HR acuity was estimated at 14 c/deg as compared to VEP acuity at 9 c/deg. Conservative (95% confidence) estimates of infant VEP and HR acuities from the same trials using comparable criteria were both 6 c/deg. Adult psychophysical and HR acuities did not differ significantly, but both were greater than VEP acuity, although all three estimates were within one octave. Thus, adults and 3-month-old infants make HR responses to SFs at least as high as the striate cortex grating resolution limit as indicated by VEP acuity. The HR response to a grating apparently originates after SF information has reached temporal lobe substrates essential for pattern perception. Therefore, the relatively high SFs that are resolved at striate cortex in infants are not trapped there but are accessed by the higher cortical visual pattern-processing stream. This suggests that the comparatively low behavioral looking acuities of infants may be due to more conservative criteria or relatively slow maturation of parietal and, especially, frontal cortex neural substrates necessary to produce integrated, goal-directed overt orientation to visual stimuli.

The Clinical Utility of Visual-Evoked Potential Acuity Testing

We assessed the clinical utility of objectively measured acuity using visual-evoked potentials. The technique was first standardized in normal emmetropic subjects and then applied to uncorrected myopic subjects. We found that visual-evoked potential acuity could accurately indicate Snellen acuity in emmetropia and corrected myopia; however, the two measures were highly correlated only in those uncorrected myopic subjects with visual acuities of 20/100 or better. In subjects with poorer than 20/200 uncorrected visual acuity caused by myopia, estimates of visual-evoked potential acuity could not be obtained. The correlation between these two measures of visual acuity was also lower in patients with decreased Snellen acuity attributable to retinal or ocular disease. We found that patients with unexplainable claims of decreased visual acuity could be diagnosed as having functional visual loss based on objective visual-evoked potential acuities.

Visual Assessment of the Multiply Handicapped Patient

The visual capabilities of the multiply handicapped and/or developmentally delayed patient are difficult to assess with methods that depend on the patient's subjective responses. Fifty-nine patients with multiple neurological handicaps and unknown visual capabilities were examined using a modified ophthalmic examination which included visual acuity measures using visual evoked potential (VEP) and preferential looking (PL) techniques. Patients ranged in age from 3 to 33 years; median age 9 years. Significant refractive error (in 73%) and strabismus (in 71%) were the most common ocular disorders. Of the 43 patients with a significant refractive error, only 16 (37%) were wearing their proper correction (ranging from -21 to +20 D). In 27 patients the uncorrected refractive error ranged from -10 to +20 D. Binocular acuities (with refractive correction) could be obtained from 56 patients (95%) using a spatial frequency sweep VEP technique, and in 41 patients (70%) using PL grating acuity cards. The VEP and PL grating acuity measures agreed to within 1 octave (a factor of 2 in minimum angle of resolution) in 27 of 41 patients. VEP acuity was 1.1 to 2.7 octaves higher in 12 patients. Grating acuity of at least 6/12 (20/40) was estimated in 12 patients. Residual vision can be measured in "difficult to examine" multiply handicapped patients with VEP and PL techniques.

Infant VEP acuity measurements: Analysis of individual differences and measurement error

The reliability of visual evoked potential (VEP) measurements of acuity was determined by estimating acuity for sinewave luminance gratings which were counterphase modulated at either 12 or 20 reversals/sec (rps). Gratings were swept in spatial frequency beyond the acuity limit and acuity was estimated from an extrapolation based on the last peak in the VEP amplitude versus spatial frequency function. Twenty-five infants ranging in age from 17 to 25 weeks were studied. Individual 10 sec sweeps resulted in records with a criterion response in 65–75% of trials. The reliability of acuities obtained from individual 10 sec sweeps was ±0.54 octaves at 95% confidence across 12 and 20 rps recording conditions (RMS error of ±0.27 octaves). The best acuity attained by each infant on either a single sweep, or on their vector average, was reliable to ±0.38 octaves at 95% confidence (RMS error of ±0.19 octaves) compared to a range of individual acuities of about 2 octaves. Much of the variability of sweep VEP acuity in cross-sectional samples of infants is therefore attributable to reliable individual differences rather than to measurement error. In testing individual infants our analysis indicates that choice of temporal frequency accounts for only 14% of the variation in acuity estimates within subjects.