Evaluation of methods for assessing visual function of infants

Pattern and sweep visual evoked potential in the objective determination of visual acuity

Purpose: To investigate the effects of pattern visual evoked potential (pVEP) and sweep visual evoked potential (sVEP) on the accurate visual acuity (VA) measurement in adults.  Methods: Medical files of 282 eyes of 141 patients who underwent VA measurement in our electrophysiology laboratory and did not undergo simulation were retrospectively analyzed. The VA was measured using the Snellen chart. Only those with a VA of higher than 1/10 on the Snellen chart were included in the study. The VA was assessed and reported by the pVEP (VA-pVEP) and sVEP test (VA-sVEP). The correlation analysis was performed using the Pearson correlation analysis. Results: Of 141 patients, 92 were males and 49 were females with a mean age of 37.7±18.4 years. There was a strong positive correlation between the VA measured by the Snellen chart and the VA measured by pVEP (VA-pVEP) (r=0.858, p<0.001). There was a weak positive correlation (r=0.267, p<0.001) between the VA measured by the Snellen chart and the VA measured by the sVEP (VA-sVEP). A weak positive correlation was found for the VA-pVEP and VA-sVEP (r=0.313, p<0.001). Conclusions: For the measurement of the degree of the VA, it seems reasonable to use pVEP initially, while sVEP should be used in cases with short attention span and those who are noncooperative and in infants. 

Cerebral visual impairment in CDKL5 deficiency disorder: vision as an outcome measure

AIM

To characterize the neuro-ophthalmological phenotype of cyclin-dependent kinase-like 5 (CDKL5) deficiency disorder (CDD) and assess visual acuity as a reproducible, quantitative outcome measure.

METHOD

We retrospectively analyzed clinical data from patients with CDD. Complete neuro-ophthalmological assessments, including visual acuity, were evaluated.

RESULTS

Of 26 patients (22 females, four males; median age 4y, interquartile range 2y 1mo-7y 10mo), cerebral visual impairment (CVI), defined as visual dysfunction in the absence of ocular or anterior visual pathway abnormalities, was diagnosed in all those over 2 years of age. Ophthalmological examinations revealed nystagmus in 10 patients and strabismus in 24 patients. Visual acuity was measured in 24 patients, by preferential looking in all and by sweep visual evoked potential in 13. Visual acuities were lower than age expectations and demonstrated improvement in the first 3 years. Adjusting for age and sex, average preferential looking visual acuity after 2 years of age was higher in patients with intact mobility than in those who were non-mobile.

INTERPRETATION

CVI was observed in patients with CDD. Visual acuity improved over time and correlated with mobility. Visual acuity, as a quantifiable measure of visual function, should be considered as an outcome measure in pre-clinical and clinical studies for CDD. What this paper adds Cerebral visual impairment is highly prevalent in cyclin-dependent kinase-like 5 deficiency disorder (CDD). Visual acuity is a measurable quantitative outcome measure in CDD. Visual acuity in CDD correlates with gross motor ability.

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.

VEP estimation of visual acuity: a systematic review

Purpose

Visual evoked potentials (VEPs) can be used to measure visual resolution via a spatial frequency (SF) limit as an objective estimate of visual acuity. The aim of this systematic review is to collate descriptions of the VEP SF limit in humans, healthy and disordered, and to assess how accurately and precisely VEP SF limits reflect visual acuity.

Methods

The protocol methodology followed the PRISMA statement. Multiple databases were searched using “VEP” and “acuity” and associated terms, plus hand search: titles, abstracts or full text were reviewed for eligibility. Data extracted included VEP SF limits, stimulus protocols, VEP recording and analysis techniques and correspondence with behavioural acuity for normally sighted healthy adults, typically developing infants and children, healthy adults with artificially degraded vision and patients with ophthalmic or neurological conditions.

Results

A total of 155 studies are included. Commonly used stimulus, recording and analysis techniques are summarised. Average healthy adult VEP SF limits vary from 15 to 40 cpd, depend on stimulus, recording and analysis techniques and are often, but not always, poorer than behavioural acuity measured either psychophysically with an identical stimulus or with a clinical acuity test. The difference between VEP SF limit and behavioural acuity is variable and strongly dependent on the VEP stimulus and choice of acuity test. VEP SF limits mature rapidly, from 1.5 to 9 cpd by the end of the first month of life to 12–20 cpd by 8–12 months, with slower improvement to 20–40 cpd by 3–5 years. VEP SF limits are much better than behavioural thresholds in the youngest, typically developing infants. This difference lessens with age and reaches equivalence between 1 and 2 years; from around 3–5 years, behavioural acuity is better than the VEP SF limit, as for adults. Healthy, artificially blurred adults had slightly better behavioural acuity than VEP SF limits across a wide range of acuities, while adults with heterogeneous ophthalmic or neurological pathologies causing reduced acuity showed a much wider and less consistent relationship. For refractive error, ocular media opacity or pathology primarily affecting the retina, VEP SF limits and behavioural acuity had a fairly consistent relationship across a wide range of acuity. This relationship was much less consistent or close for primarily macular, optic nerve or neurological conditions such as amblyopia. VEP SF limits were almost always normal in patients with non-organic visual acuity loss.

Conclusions

The VEP SF limit has great utility as an objective acuity estimator, especially in pre-verbal children or patients of any age with motor or learning impairments which prevent reliable measurement of behavioural acuity. Its diagnostic power depends heavily on adequate, age-stratified, reference data, age-stratified empirical calibration with behavioural acuity, and interpretation in the light of other electrophysiological and clinical findings. Future developments could encompass faster, more objective and robust techniques such as real-time, adaptive control.

Registration

International prospective register of systematic reviews PROSPERO (https://www.crd.york.ac.uk/PROSPERO/), registration number CRD42018085666.

A survey on stimuli for visual cortical function assessment in infants

Visual processing, as a significant and complex functionality of the human brain, changes during the life span with the most developmental changes in the infancy. Different types of visual stimuli are needed for evaluating different functionalities of the infants' visual system. Selecting appropriate visual stimuli is an important issue in evaluating visual cortical functions in infants. Properties of stimulation influence responses of visual system and must be adjusted according to the age and specific function which is going to be investigated. In this review, the most commonly used stimuli to elicit visual evoked potentials (VEPs) are evaluated and characteristics of VEPs extracted by these stimulations are studied. Furthermore, various studies investigating different functionalities such as selectivity for orientation and directional motion are presented. Valuable results regarding emerging and maturation times of different functions and normative data for clinical diagnosis are provided by these studies.

Similarities and differences between behavioral and electrophysiological visual acuity thresholds in healthy infants during the second half of the first year of life

PURPOSE

Behavioral and electrophysiological methods for visual acuity estimation typically correlate well in children and adult populations, but this relationship remains unclear in infants, particularly during the second half of the first year of life. It has been suggested that the agreement between both methods mostly relies on age and/or subjective acuity factors. The present study aimed at comparing acuity thresholds obtained with both approaches in a sample of healthy infants in a relatively narrow age range, that is 6-10 months old.

METHODS

Acuity thresholds were assessed in 61 healthy infants aged between 6 and 10 months using the Teller acuity cards (TAC) and sweep visual evoked potentials (sVEP). The TAC stimuli (stationary vertical gratings displayed on laminated cards) ranged from 0.31 to 38 cycles per degree (cpd). The TAC acuity threshold was estimated according to the highest spatial frequency scored by the experimenter as seen by the infant. The sVEP stimuli (high-contrast vertical gratings counter-phased at 12 reversals/s) ranged from 13.5 to 1 cpd. sVEP were recorded at Oz and acuity threshold was estimated using regression linear fitting.

RESULTS

Considering the entire sample, sVEP acuity thresholds (8.97 ± 2.52 cpd) were significantly better than TAC scores (5.58 ± 2.95 cpd), although the difference was within 1 octave for 64% of the infants. Neither Pearson nor intra-class correlations between the two methods were significant (0.18 and 0.03, respectively). While age at assessment was not related to any dependent variable (TAC, sVEP, sVEP-TAC difference score), subjective (behavioral) acuity was found to underlie the difference between the two methods. The difference between sVEP and TAC scores decreased as a function of subjective acuity, and at the highest subjective acuity level (>10 cpd), TAC acuity slightly exceeded sVEP acuity.

CONCLUSIONS

The superiority of sVEP acuity often reported in the literature was evident in our infant sample when subjective acuity (TAC) was low or moderate, but not when it was high (>10 cpd). The relationship between the two estimation methods was not dependent on age, but on subjective acuity.

Analysis of Retinal Layer Thicknesses and Their Clinical Correlation in Patients with Traumatic Optic Neuropathy

The aims of this study were 1) To evaluate retinal nerve fiber layer (fRNFL) thickness and ganglion cell layer plus inner plexiform layer (GCIPL) thickness at the fovea in eyes affected with traumatic optic neuropathy (TON) compared with contralateral normal eyes, 2) to further evaluate these thicknesses within 3 weeks following trauma (defined as “early TON”), and 3) to investigate the relationship between these retinal layer thicknesses and visual function in TON eyes. Twenty-nine patients with unilateral TON were included. Horizontal and vertical spectral-domain optical coherence tomography (SD-OCT) scans of the fovea were taken in patients with unilateral TON. The main outcome measure was thickness of the entire retina, fRNFL, and GCIPL in eight areas. Thickness of each retinal layer was compared between affected and unaffected eyes. The correlation between the thickness of each retinal layer and visual function parameters, including best corrected visual acuity, color vision, P100 latency, and P100 amplitude in visual evoked potential (VEP), mean deviation (MD) and visual field index (VFI) in Humphrey visual field analysis in TON eyes was analyzed. Thicknesses of the entire retina, fRNFL, and GCIPL in SD-OCT were significantly thinner (3–36%) in all measurement areas of TON eyes compared to those in healthy eyes (all p<0.05). Whereas, only GCIPL in the outer nasal, superior, and inferior areas was significantly thinner (5–10%) in the early TON eyes than that in the control eyes (all p<0.01). A significant correlation was detected between retinal layer thicknesses and visual function parameters including color vision, P100 latency and P100 amplitude in VEP, MD, and VFI (particularly P100 latency, MD, and VFI) (r = -0.70 to 0.84). Among the retinal layers analyzed in this study, GCIPL (particularly in the superior and inferior areas) was most correlated with these five visual function parameters (r = -0.70 to 0.71). Therefore, evaluation of morphological change of each retinal layer using SD-OCT can help in understanding TON pathophysiology and indirectly assessing visual function. Moreover, evaluation of the morphological change of the GCIPL in TON eyes may be useful to assess visual function in patients with early TON.

Contribution of sVEP visual acuity testing in comparison with subjective visual acuity

AIMS

Visual acuity determination is an important task in ophthalmology and optometry practices. Visual acuity can be examined objectively or subjectively. The objective examination method, sVEP, allows for quick objective measurements of patient's visual acuity. Previous studies have not demonstrated the repeatability of this objective sVEP method. This study aims to evaluate the sVEP method and compare it to a subjective method.

METHODS AND RESULTS

The sample was divided into two groups. For the first group, visual acuity was measured with sVEP and Snellen methods on only one patient twelve times. In the second group, visual acuity was measured twice with sVEP followed twice with the Snellen method with Landolt's rings and logMAR modification on 32 non-pathological patients. Results showed significant differences between average values of visual acuity obtained with both methods (sVEP and Snellen) in both samples (T-test, P < 0.01; Wilcoxon test, P = 0.02 in second group). In the second group, significant correlations between repeated sVEP measurements (Spearman test, P < 0.05, r = 0.69) were found but no significant correlation between average sVEP measurement and average Snellen measurement (Spearman test, P > 0.05, r = 0.15) was found.

CONCLUSION

Objective measurement of visual acuity with sVEP is a valid and reliable method, but is recommended only when it is not possible to use a subjective method for measuring visual acuity, e.g. children, patients with mental retardation or simulating/dissimulating patients.

The Parameters of Pattern Visual Evoked Potential in the Severe Visual Loss Patients in Korean

Purpose

To compare the characteristics of the pattern visual evoked potential (PVEP) in patients with severe visual loss and normal controls, and to demonstrate the range of PVEP parameters in normal Koreans.

Methods

The patients were divided into three groups according to visual acuity: group 1, ranging from no light perception to less than 0.02; group 2, ranging from 0.02 to 0.1; and group 3, ranging from 0.125 to 0.25. Group 4 was established as a healthy control group. The 95% confidence intervals (CIs) of the PVEP parameters were calculated for group 4. The PVEP parameters were compared among these four groups, and the amplitudes were evaluated with respect to the 95% CIs. We used the area under the curve to integrate the sensitivity and the specificity of the PVEP parameter quantitative values (7.01 to 9.57 µV and 6.75 to 10.11 µV).

Results

A total of 101 eyes were investigated. The 95% CIs of the P100 and N135 amplitudes of group 4 were 7.01 to 9.57 µV and 6.75 to 10.11 µV, respectively. The amplitudes of P100 and N135 were significantly higher in group 4 (p < 0.001). The P100 and N135 amplitude were below the 95% CI in all group 1 patients. The area under the curve of the P100 amplitude was the highest (0.789).

Conclusions

No legally blind patient in the present study exhibited a value within the 95% CI of the controls. The P100 amplitude may be the best parameter for defining blindness in patients.

Visual cognitive function in infants with intractable epilepsy before and after surgery

PURPOSE

One purpose of pediatric epilepsy surgery is to improve psychomotor development. However, few methods are available for evaluating cognitive function in infants with severe developmental delays. We used the following battery of tests to evaluate visual cognitive function of infants following surgery for intractable epilepsy.

METHODS

The following battery of tests were used to evaluate eight patients before and 1 month after surgery: (1) Erhardt Developmental Vision Assessment (EDVA); (2) evaluation of ocular pursuit for a flashing LED toy; (3) three visual acuity tests preferential looking procedure, optokinetic nystagmus, and Sheridan's Test for Young Children and Retarded balls vision test; and (4) existing developmental test.

RESULTS

EDVA scores and ocular pursuit score with a flashing LED toy showed the same trends with developmental age as the existing developmental tests. However, in some patients, the EDVA score and ocular pursuit score improved greatly, whereas the developmental age changed very little.

CONCLUSIONS

These tests are suitable for patients with intractable epilepsy and severe developmental delay. By performing these tests before and after surgery, small cognitive changes occurring soon after the surgery may be detected.

Meta-analysis of LCPUFA supplementation of infant formula and visual acuity

BACKGROUND AND OBJECTIVE

Long-chain polyunsaturated fatty acids (LCPUFAs) are hypothesized to affect visual acuity development in infants. Randomized controlled trials (RCTs) have been conducted to assess whether supplementation of LCPUFAs of infant formulas affects infant visual acuity. This meta-analysis was conducted to evaluate whether LCPUFA supplementation of infant formulas improves infants' visual acuity.

METHODS

PubMed and PsycInfo were searched for RCTs assessing the efficacy of LCPUFA supplementation of infant formulas on infant visual acuity. RCTs assessing the effects of LCPUFA supplementation on visual acuity (by using either visual evoked potential or behavioral methods) in the first year of life were included in this meta-analysis. Our primary outcome was the mean difference in visual resolution acuity (measured in logarithm of minimum angle of resolution [logMAR]) between supplemented and unsupplemented infants. We also conducted secondary subgroup analyses and meta-regression examining the effects of LCPUFA dose and timing, preterm versus term birth status, and trial methodologic quality.

RESULTS

Nineteen studies involving 1949 infants were included. We demonstrated a significant benefit of LCPUFA supplementation on infants' visual acuity at 2, 4, and 12 months of age when visual acuity was assessed by using visual evoked potential and at 2 months of age by using behavioral methods. There was significant heterogeneity between trials but no evidence of publication bias. Secondary analysis failed to show any moderating effects on the association between LCPUFA supplementation and visual acuity.

CONCLUSIONS

Current evidence suggests that LCPUFA supplementation of infant formulas improves infants' visual acuity up to 12 months of age.

Reliability of acuities determined with the sweep visual evoked potential (sVEP)

sVEPs are generally used to rapidly obtain visual acuity. Several studies have determined the reliability of acuity measurements with psychophysical techniques. The aim of this study was to determine the intersession and intrasession variabilities of sVEP measurements. Twenty-four normal, adult subjects took part in this project. Stimulus production and data analyses were done using an Enfant 4010. Standard VEP recording techniques were employed. Data were collected on two separate days (at least 1 week apart). At each visit, two complete sets of sVEP data were collected and averaged. A logMAR acuity chart was also used to determine the acuity at each visit. Paired t tests, 95% confidence intervals, intraclass correlation coefficients, and coefficients of repeatability were used to determine whether there was a difference in the intrasession and intersession acuities. The mean acuity difference and coefficient of repeatability were +0.01 and 0.191 for visit 1 and -0.019 and 0.186 for visit 2, respectively. The mean acuity difference and coefficient of repeatability across visits were +0.008 and 0.176 for the first acuity and-0.02 and 0.170 for the second acuity, respectively. Paired t tests did not find a significant difference between any set of data or the average for visits one and two (all P values > 0.05). The intraclass correlation coefficients comparing the average sVEP data and the logMAR data for visits 1 and 2 were 0.71 and 0.88, respectively. The coefficients of repeatability for the averaged sVEP acuity and the logMAR acuity for the two visits were 0.11 and 0.07, respectively. The repeatability of the sVEP acuity estimate in a large population of adults is similar to that of previous published reports on infants and is nearly as high as that of logMAR acuity chart data. The repeatability is the same for single best estimates of acuity and averaged estimates of acuity across visits.

The effects of maternal supplementation of polyunsaturated Fatty acids on visual, neurobehavioural, and developmental outcomes of the child: a systematic review of the randomized trials

Polyunsaturated fatty acid (PUFA) use in pregnancy has been promoted as beneficial for visual and neurobehavioural development in the fetus. However, no systematic review of the randomized trials has been conducted. The objective of this review was to evaluate potential advantages of this regiment by reviewing all randomized trials in pregnancy. Methods. Systematic review of randomized controlled studies comparing cognitive and visual achievements among infants whose mothers were treated and untreated with PUFA during gestation. Results. Nine studies met the inclusion criteria, three focusing on visual and six on neurobehavioural development. Due to differing outcome measurements in the infants, the studies could not be combined into a formal meta-analysis. Synthesizing the existing data, for both visual and neurobehavioural development, most studies could not show sustained benefits to infant cognition or visual development. Conclusion. At the present time a recommendation to change practice and supplement all expecting mothers with PUFA to improve offspring vision or neurobehavioural function is not supported by existing evidence.

Keep your eyes on development: the behavioral and neurophysiological development of visual mechanisms underlying form processing

Visual form perception is essential for correct interpretation of, and interaction with, our environment. Form perception depends on visual acuity and processing of specific form characteristics, such as luminance contrast, spatial frequency, color, orientation, depth, and even motion information. As other cognitive processes, form perception matures with age. This paper aims at providing a concise overview of our current understanding of the typical development, from birth to adulthood, of form-characteristic processing, as measured both behaviorally and neurophysiologically. Two main conclusions can be drawn. First, the current literature conveys that for most reviewed characteristics a developmental pattern is apparent. These trajectories are discussed in relation to the organization of the visual system. The second conclusion is that significant gaps in the literature exist for several age-ranges. To complete our understanding of the typical and, by consequence, atypical development of visual mechanisms underlying form processing, future research should uncover these missing segments.

Achieving definitive results in long-chain polyunsaturated fatty acid supplementation trials of term infants: factors for consideration

Numerous randomized controlled trials (RCTs) have been undertaken to determine whether supplementation with long-chain polyunsaturated fatty acids (LCPUFAs) in infancy would improve the developmental outcomes of term infants. The results of such trials have been thoroughly reviewed with no definitive conclusion as to the efficacy of LCPUFA supplementation. A number of reasons for the lack of conclusive findings in this area have been proposed. This review examines such factors with the aim of determining whether an optimal method of investigation for RCTs of LCPUFA supplementation in term infants can be ascertained from previous research. While more research is required to completely inform a method that is likely to achieve definitive results, the findings of this literature review indicate future trials should investigate the effects of sex, genetic polymorphisms, the specific effects of LCPUFAs, and the optimal tests for neurodevelopmental assessment. The current literature indicates a docosahexaenoic acid dose of 0.32%, supplementation from birth to 12 months, and a total sample size of at least 286 (143 per group) should be included in the methodology of future trials.

Early visual-evoked potential acuity and future behavioral acuity in cortical visual impairment

PURPOSE

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.

METHODS

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).

RESULTS

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).

CONCLUSIONS

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.

Threshold determination in sweep VEP and the effects of criterion

In order to develop criteria for the range of data points used for regression line fitting in sweep visually evoked potential (sVEP), which would be objective, clearly specified and give good repeatability and validity, and in order to investigate the effect of luminance on sVEP measurement, visual acuity (VA) and contrast sensitivity (CS) were measured with sVEP in adults aged 17-30 years and children aged 6-8 years. Six to ten participants took part in each experiment. Five criteria (C0-C4) for fitting the regression line were implemented. Test-retest repeatability and validity against psychophysical thresholds at three luminance levels were considered for thresholds and the number of acceptable readings. There were significant effects of criteria (repeated measures ANOVAs, P < 0.05). The criteria, C2 and C3 (based on the range over which the signal-to-noise ratio >or=1), consistently gave better VA and CS, more viable readings, better agreement with psychophysical thresholds in adults and better repeatability than the other criteria. In the case of adults, C2 gave thresholds that were not significantly different from the psychophysical thresholds (P > 0.05). There was little effect of luminance over the 25-100 cd/m(2) range used. Overall, C2 performed the best and would be the criterion of choice, giving better repeatability, better validity and more viable plots.

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.

Frequency domain analyses of neonatal flash VEP

A battery of frequency-dependent measures was made for high-density electroencephalographic recording measured in response to a flash stimulus in 12 normal term infants within 2 d of birth. Significant changes recorded in posterior electrodes in the same time window as the visual evoked potential (VEP) included increased local synchrony at approximately 40 Hz, increased power at approximately 16 Hz, the emergence of nonlinear coupling of lower (approximately 2 Hz) and higher frequency oscillations, and phase locking over a wide range of frequencies. This research provides evidence of neural synchrony and nonlinear coupling in response to a simple visual stimulus. These mechanisms are functional in early development. It is proposed that the frequency domain metrics of this study may augment current diagnostic measures of cortical function at birth.

Longitudinal Quantitative Assessment of Vision Function in Children with Cortical Visual Impairment

PURPOSE

Cortical visual impairment (CVI) is bilateral visual impairment caused by damage to the posterior visual pathway, the visual cortex, or both. Current literature reports great variability in the prognosis of CVI. The purpose of this study was to evaluate change in vision function in children with CVI over time using a quantitative assessment method.

METHODS

The visual acuity and contrast sensitivity of children with CVI were retrospectively assessed using the sweep visual evoked potential (VEP). Thirty-nine children participated in the visual acuity assessment and 34 of the 39 children participated in the contrast threshold assessment. At the time of the first VEP, the children ranged in age from 1 to 16 years (mean: 5.0 years). The time between measures ranged from 0.6 to 13.7 years (mean: 6.5 years).

RESULTS

Forty-nine percent of the children studied showed significant improvement of visual acuity. The average improvement was 0.43 log unit (mean change: 20/205 to 20/76) in those who improved. The initial visual acuity was worse in those who improved compared with those who did not improve (p < 0.001). Forty-seven percent of the children studied showed significant improvement of contrast threshold. In those who improved, the average amount of improvement was 0.57 log unit (10 to 2.6% Michelson). The initial contrast threshold was significantly worse in those who improved compared with those who did not improve (p = 0.001). Also, the change in contrast threshold was related to age of the child (p = 0.017).

CONCLUSIONS

Significant improvement in vision function can occur over time in children with CVI. In the present study, approximately 50% of the children improved and the remainder remained stable. No relation was found between etiology and improvement. Further investigation is warranted to better understand the prognosis for visual recovery in children with CVI.

A new visual evoked potential system for vision screening in infants and young children

INTRODUCTION

With a prevalence of 3-5%, amblyopia represents a major public health problem. Effective treatment depends on early detection, and a broad consensus of professional opinion supports vision screening of infants and young children. No single method of screening has been demonstrated to be superior in detecting amblyopia and all methods have significant limitations.

METHODS

We assessed a new, "child-friendly" visual evoked potential (VEP) system (ENFANTtrade mark II, Diopsys Corp., Metuchen, NJ) for use in screening. We studied 122 children, aged 6 months to 5 years, comparing test results in a masked fashion to results of standard ophthalmologic examinations. A statistical program analyzed VEP differences between fellow eyes to determine a "pass" or "fail" for each child. For verbal patients, clinical amblyopia was defined as an interocular difference of two or more lines in best-corrected visual acuity. For preverbal patients, clinical amblyopia was defined by the clinician's decision to treat with occlusion or atropine penalization. Preverbal children with significant refractive errors or structural eye pathology were also considered clinically abnormal.

RESULTS

The test was completed by 94% of the study group, each child requiring an average of 10 minutes to complete testing of both eyes. The sensitivity was 0.973, the specificity 0.808, the positive predictive value 0.706, and the negative predictive value 0.984.

CONCLUSION

With its easy electrode placement and rapid, attractive stimulus, the new system overcomes technical difficulties which were associated with older VEP techniques. The test shows promise as a screening tool for detecting amblyopia and other visual deficits in young children.

Test-retest reliability of swept visual evoked potential measurements of infant visual acuity and contrast sensitivity

The aim of the study was to describe variations in swept visual evoked potential (SWEEP-VEP) assessment of visual acuity and contrast sensitivity in infants and to evaluate the best way to estimate visual performance from obtained SWEEP-VEP data. The visual performance of 92 infants (6-40 wk of age) was measured in two separate visits. Results were verified with repeated tests in seven adults. There was a strong association between the two measurements of infant visual acuity (r = 0.91, p < 0.001), with no constant bias and an inter-assay coefficient of variation of 8.4%. The intra-assay coefficient of variation was 17% and in repeated sessions all obtained acuity measures were normally distributed, indicating that the mean and not the maximum threshold best estimates visual acuity. This estimate of visual acuity also had lower test-retest variability than those calculated from the maximum threshold or threshold from the average EEG signals (p = 0.001). Test-retest measures of infant contrast sensitivity had a correlation coefficient of 0.72 (p < 0.001) and an inter-assay coefficient of variation of 23%. With the observed test-retest variability, SWEEP-VEP is less valid for estimating the visual performance of individual subjects, but it can give reliable group means. This method was well suited to describe visual development in the infants, which for acuity as well as contrast sensitivity increased by 0.64 octave per doubling in age. However, the variability of the SWEEP-VEP method can be a limiting factor, for example, in the assessment of the potential effect of dietary docosahexaenoic acid in a homogeneous group of infants.

Nutrient requirements for preterm infant formulas

Achieving appropriate growth and nutrient accretion of preterm and low birth weight (LBW) infants is often difficult during hospitalization because of metabolic and gastrointestinal immaturity and other complicating medical conditions. Advances in the care of preterm-LBW infants, including improved nutrition, have reduced mortality rates for these infants from 9.6 to 6.2% from 1983 to 1997. The Food and Drug Administration (FDA) has responsibility for ensuring the safety and nutritional quality of infant formulas based on current scientific knowledge. Consequently, under FDA contract, an ad hoc Expert Panel was convened by the Life Sciences Research Office of the American Society for Nutritional Sciences to make recommendations for the nutrient content of formulas for preterm-LBW infants based on current scientific knowledge and expert opinion. Recommendations were developed from different criteria than that used for recommendations for term infant formula. To ensure nutrient adequacy, the Panel considered intrauterine accretion rate, organ development, factorial estimates of requirements, nutrient interactions and supplemental feeding studies. Consideration was also given to long-term developmental outcome. Some recommendations were based on current use in domestic preterm formula. Included were recommendations for nutrients not required in formula for term infants such as lactose and arginine. Recommendations, examples, and sample calculations were based on a 1000 g preterm infant consuming 120 kcal/kg and 150 mL/d of an 810 kcal/L formula. A summary of recommendations for energy and 45 nutrient components of enteral formulas for preterm-LBW infants are presented. Recommendations for five nutrient:nutrient ratios are also presented. In addition, critical areas for future research on the nutritional requirements specific for preterm-LBW infants are identified.

Which ocular and neurologic conditions cause disparate results in visual acuity scores recorded with visually evoked potential and teller acuity cards?

PURPOSE

We investigated whether disparity between visually evoked potential (VEP) acuity scores and Teller Acuity Card (TAC) scores varied according to presence of ocular or neurologic conditions.

METHODS

Charts from 175 children (mean age, 34.8 months; range, 3 to 158 months) referred for visual acuity testing were examined. All children had been tested with pattern-alternation VEP and TAC and had undergone a complete eye examination. VEP and TAC acuity scores were relative to age-expected acuity scores for each acuity test. The absence and degree of macular abnormality, retinal abnormality, optic nerve hypoplasia, optic nerve atrophy, cortical visual impairment, developmental delay, cerebral palsy, seizures, and nystagmus were noted. Analysis of variance models were used to determine whether differences between VEP and TAC scores varied according to the presence of specific deficits. Logistic regression analysis determined whether degree of specific deficits was associated with a greater chance of inconsistency between VEP and TAC scores (>0.3 log unit difference).

RESULTS

Inconsistent scores were found in 48% of children. Developmental delay was associated with relatively poorer TAC than VEP score, and the chance of inconsistency increased with severity of developmental delay.

CONCLUSIONS

Diagnosis-dependent variability exists between TAC and VEP scores. Therefore knowledge of the clinical picture is necessary in interpretation of VEP and TAC scores. It is not clear which test is more useful when a disparity exists, either from this or previous studies. When visual acuity is assessed longitudinally in a given child, then consistency in method for acuity assessment is important.