Impaired vision in children prenatally exposed to methadone: an observational cohort study

BACKGROUND/OBJECTIVES

To examine prevalence of failed visual assessment at 8-10 years in children born to methadone-maintained opioid dependent (MMOD) mothers and relate this to known in utero substance exposure.

SUBJECTS/METHODS

Follow up of observational cohort study of methadone-exposed and comparison children matched for birthweight, gestation and postcode of residence at birth. Participants were 144 children (98 exposed, 46 comparison). Prenatal drug exposure was previously established via comprehensive maternal and neonatal toxicology. Children were invited to attend for visual assessment and casenotes were reviewed. Presence of acuity poorer than 0.2 logMAR, strabismus, nystagmus and/or impaired stereovision constituted a 'fail'. Fail rates were compared between methadone-exposed and comparison children after adjusting for known confounding variables.

RESULTS

33 children attended in person: data were also derived from casenote review for all children. After controlling for maternal reported tobacco use, methadone-exposed children were more likely to have a visual 'fail' outcome, adjusted odds ratio 2.6, 95% CI 1.1-6.2; adjusted relative risk 1.8 (95% CI 1.1-3.4). Visual 'fail' outcome rates did not differ between methadone-exposed children who had (n = 47) or had not (n = 51) received pharmacological treatment for neonatal abstinence/opioid withdrawal syndrome (NAS/NOWS); fail rate 62% vs 53% (95% CI of difference-11-27%).

CONCLUSIONS

Children born to MMOD mothers are almost twice as likely as unexposed peers to have significant visual abnormalities at primary school age. Prenatal methadone exposure should be considered in the differential diagnosis of nystagmus. Findings support visual assessment prior to school entry for children with any history of prenatal opioid exposure.

TRIAL REGISTRATION

The study was prospectively registered on ClinicalTrials.gov (NCT03603301), https://clinicaltrials.gov/ct2/show/NCT03603301 .

Visual evoked potentials in infants exposed to methadone in utero

We investigated the effects of maternal drug misuse on neonatal visual evoked potentials (VEPs). Flash VEPs were recorded within 4 days of birth from 21 term infants of mothers misusing drugs and prescribed substitute methadone and 20 controls. Waveforms were classified as typical, atypical, immature or non-detectable, and amplitude and latencies were measured. VEPs from drug-exposed infants were less likely to be of typical waveform and more likely to be immature or non-detectable (p<0.01) than those of control infants. They were also smaller in amplitude (median 10.8 vs 24.4 microV, p<0.001). VEPs of drug-exposed infants had matured after 1 week but remained of lower amplitude than VEPs of newborn controls (p<0.01) and were non-detectable in 15%. Flash VEPs differ between maternal drug-exposed and non-drug-exposed newborns. Future research should address the specific effects of maternal methadone and/or other illicit drug misuse on infant VEPs, and associations between neonatal VEPs and subsequent visual development.

A visual skills inventory for children with neurological impairments

Children with neurological impairments often have visual deficits that are difficult to quantify. We have compared visual skills evaluated by carers with results of a comprehensive visual assessment. Participants were 76 children with mild to profound intellectual and/or motor impairment (33 males, 43 females; age range 7mo-16y; mean age 5y 1mo [SD 4y 2mo]) who completed a visual skills inventory before attending a special vision clinic. The inventory included 16 questions about visual skills and responses to familiar situations. Responses were augmented by taking a structured clinical history, compared with visual evoked potential (VEP) and/or acuity card measures of visual acuity, and examined using exploratory factor analysis. Acuity ranged from normal to no light perception, and was positively associated with responses to individual questions. After excluding four uninformative questions, an association between the remaining questions and two significant independent factors was found. Factor 1 was associated with questions about visual recognition (e.g. 'Does your child see a small silent toy?') and these items were correlated with both the VEP and acuity card thresholds. Factor 2 was associated primarily with questions about visually mediated social interactions (e.g. 'Does he/she return your silent smile?'). Evaluation of visual skills in children with neurological impairment can provide valid information about the quality of children's vision. Questions with the highest validity for predicting vision are identified.

The luminance-response function of the human photopic electroretinogram: a mathematical model

The luminance-response function of the brief flash full-field photopic electroretinogram (ERG) rises to a peak before falling to a sub-maximal plateau -- the 'photopic hill'. The combination of on- and off-responses inherent in the brief flash photopic ERG suggests that this luminance-response function could be modelled by the sum of a Gaussian function and a logistic growth function. Photopic ERGs to a luminance series of brief flashes against three different background luminances recorded from seven healthy adults showed the characteristic 'photopic hill' function for b-wave amplitudes which were satisfactorily fitted with the sum of a Gaussian curve and a logistic growth curve. As background luminance increased, both components shifted to the right on the luminance axis. The Gaussian component increased in amplitude while the logistic growth function component decreased in amplitude. The luminance-response function of a complete congenital stationary night blindness patient had almost no logistic growth component.

Retinal function in infants with optic nerve hypoplasia: electroretinograms to large patterns and photopic flash

AIMS

Optic nerve hypoplasia (ONH), which is defined as a congenital deficiency of retinal ganglion cells, may also involve more distal layers of the retina. We investigated electrophysiological function of the retina in ONH using electroretinograms (ERGs).

METHODS

ERGs were recorded from 48 subjects (3.5-35 months) with unilateral or bilateral ONH. Pattern reversal (4 degrees checks) was presented under chloral hydrate sedation, using an optical system to correct a cycloplegic refraction. A photopic flash stimulus was also used. Fundus photographs were used to measure the disk diameter/disk macula ratio (DD/DM), and to document other clinical signs. Eyes were classified as moderate (0.15-0.3) or severe (<0.15) ONH, and those with DD/DM greater than 0.3 were used as reference eyes.

RESULTS

Pattern ERG recording was completed in 89 eyes and was detectable in 80% of eyes with ONH (61/76 tested) and in all 13 reference eyes. Photopic flash ERGs were of good quality in all eyes. The severity of ONH correlates with the amplitude of the photopic flash b-waves and with the amplitude of the N95 component of the pattern ERG (P<0.01). However, the ERGs to large patterns were well preserved (>3.5 microV) in 10 of 35 eyes with severe ONH. Tortuous retinal vessels in eyes with either moderate or severe ONH were associated with smaller amplitude photopic b-waves and markedly diminished or undetectable pattern ERGs.

CONCLUSIONS

This study supports the hypothesis that retinal dysfunction distal to the ganglion cells is common in ONH, but is not predictable on the basis of ONH severity alone. Additionally, tortuous retinal vessels in ONH may be a sign associated with retinal dysfunction.

Maternal docosahexaenoic acid supplementation during pregnancy and visual evoked potential development in term infants: a double blind, prospective, randomised trial

AIM

To test the hypothesis that maternal docosahexaenoic acid (DHA) supplementation during pregnancy enhances maturation of the visual evoked potential (VEP) in healthy term infants.

METHODS

One hundred women were supplemented with either fish oil capsules rich in DHA (n = 50) or placebo capsules (n = 50) from week 15 of pregnancy until delivery. Total fatty acids in red blood cells and plasma were measured at weeks 15, 28, and 40 of pregnancy and at delivery in umbilical cord blood. Infant visual pathway development was assessed using VEPs recorded to flash stimuli shortly after birth and to both flash and pattern-reversal stimuli at 50 and 66 weeks post-conceptional age (PCA).

RESULTS

Maternal supplementation did not significantly elevate the level of DHA in umbilical cord blood. Moreover, there were no significant differences in any of the VEP measures observed between supplementation groups. However, maturity of the pattern-reversal VEP at 50 and 66 weeks PCA was associated with DHA status of the infants at birth. Infants with higher DHA status, both as a concentration and as a percentage of total fatty acids, showed shorter P100 peak latencies of the pattern-reversal VEP than those with lower DHA status.

CONCLUSIONS

Maternal DHA supplementation during pregnancy did not enhance VEP maturation in healthy term infants. However, these results show an association between the DHA status of infants at term and early postnatal development of the pattern-reversal VEP, suggesting that DHA status itself may influence maturation of the central visual pathways.

Emmetropisation following preterm birth

BACKGROUND/AIMS

Even in the absence of retinopathy of prematurity (ROP), premature birth signals increased risk for abnormal refractive development. The present study examined the relation between clinical risk factors and refractive development among preterm infants without ROP.

METHODS

Cycloplegic refraction was measured at birth, term, 6, 12, and 48 months corrected age in a cohort of 59 preterm infants. Detailed perinatal history and cranial ultrasound data were collected. 40 full term (plus or minus 2 weeks) subjects were tested at birth, 6, and 12 months old.

RESULTS

Myopia and anisometropia were associated with prematurity (p<0.05). More variation in astigmatic axis was found among preterm infants (p<0.05) and a trend for more astigmatism (p<0.1). Emmetropisation occurred in the preterm infants so that at term age they did not differ from the fullterm group in astigmatism or anisometropia. However, preterm infants remained more myopic (less hyperopic) than the fullterm group at term (p<0.05) and those infants born <1500 g remained more anisometropic than their peers until 6 months (p<0.05). Infants with abnormal cranial ultrasound were at risk for higher hyperopia (p<0.05). Other clinical risk factors were not associated with differences in refractive development. At 4 years of age 19% of the preterm group had clinically significant refractive errors.

CONCLUSION

Preterm infants without ROP had high rates of refractive error. The early emmetropisation process differed from that of the fullterm group but neither clinical risk factors nor measures of early refractive error were predictive of refractive outcome at 4 years.

Pattern-reversal visual evoked potentials in infants: gender differences during early visual maturation

This paper investigates gender differences in the peak latency and amplitude of the P1 component of the pattern-reversal visual evoked potential (pattern-reversal VEP) recorded in healthy term infants. Pattern-reversal VEPs in response to a series of high contrast black and white checks (check widths 120', 60', 30', 24', 12', 6') were recorded in 50 infants (20 males, 30 females) at 50 weeks post-conceptional age (PCA) and in 49 infants (22 males, 27 females) at 66 weeks PCA. Peak latency of the major component, P1, was considerably shorter in female compared with male infants. Differences in head circumference do not entirely account for the gender differences in peak latency reported here. A gender difference in P1 amplitude was not detected. These findings stress the importance of considering gender norms as well as age-matched norms when utilizing the pattern-reversal VEP in clinical investigations. Studies including a wider range of ages are clearly necessary in order to establish whether the earlier peak latencies in female infants represents a difference in the onset or rate of visual maturation.

Spatial summation of peripheral Gabor patches

Previous studies have specified the foveal pattern that is seen most efficiently, with the assumption that the waveform of the best pattern matches the impulse response of the most sensitive visual filter. We measured the threshold contrast for circular, collinear, and orthogonal Gabor stimuli of 6 Hz temporal frequency presented 7 deg above the fixation point. We found that the threshold contrast energy is minimal for a class of stimuli whose Fourier-spectra bandwidth is less than approximately 1 octave. These findings suggest that an energy algorithm might underlie spatial summation of peripheral Gabor patches. The different behavior of spatial summation in fovea and periphery might reflect the differences in pattern detectability across space in the central and peripheral visual fields. It is also possible that a coherent (cross-correlation) algorithm is employed in detection of foveal stimuli and that an incoherent (energy) algorithm is employed in detection of peripheral stimuli.

A VEP investigation of parallel visual pathway development in primary school age children

Different features of visual function mature along unique timescales through infancy and early childhood. It is not clear which functions continue to mature in school age children. Functions believed to be mediated by the Magnocellular (M) and Parvocellular (P) pathways were compared in five- (n=25), eight- (n=21) and eleven-year-old children (n=21) and young adult controls (n=20). Steady-state visual evoked potentials were recorded from occipital electrodes in response to very low spatial frequency gratings, at a series of contrasts (M), and to high contrast gratings at a series of spatial frequencies (P). No evidence was found to indicate M pathway development across these age groups. However, the youngest children demonstrated elevated VEP thresholds to the high contrast gratings compared with either the adults or eleven-year-olds. This difference in threshold implies an immaturity of the high contrast, high spatial frequency stream, i.e. the putative P pathway.

Visual event-related potentials in children with phenylketonuria

Visual event-related potentials (ERPs) were examined in 16 children (aged 5-14 y) with phenylketonuria (PKU) and 16 age- and sex-matched controls. Lifetime median measures of phenylalanine (Phe) were 230-460 micromol/l. The most recent Phe levels were 56-624 micromol/l. ERPs were recorded whilst the children performed a discrimination task. All stimuli were square wave gratings degree, which appeared for 33 ms. A response to an infrequent grating that differed in orientation or spatial frequency was required. The older children with PKU had a delay in the first peak (P1) of the ERP, and age-related changes in the amplitude of P1. There was attenuation of the second peak across age groups in PKU. There was no evidence of reduced response accuracy or longer reaction times in children with PKU. Latencies of the cognitive P3 were not delayed in PKU. The delayed early peaks are consistent with previous studies that have shown delayed visual evoked potentials in PKU. The lack of differences in reaction time and P3 may be due to relatively good Phe control in children with PKU, or to the simplicity of the task. Suggestions are made for future ERP studies of PKU.

Maturation of the pattern-reversal VEP in human infants: a theoretical framework

Visual evoked potentials to pattern reversal (PR-VEPs) are used to assess the integrity and maturation of the visual pathways in infants and young children. To establish normal ranges and to facilitate interpolation, we consider the maturation rate of PR-VEPs using published normative data. Curves based on the logistic function (a sigmoid model) are introduced and compared with three other models: (1) the power law function; (2) the sum of two decaying exponentials; and (3) a two-stage linear model. Although methods vary somewhat, remarkable consistency among laboratories is found for the maturation of the major positivity (P1) of PR-VEP. The P1 occurs at approximately 260 ms in neonates and is quite variable. It matures rapidly before 12-14 weeks of age and becomes much less variable. The logistic model provides a parsimonious description of P1 maturation with most rapid maturation at around 6 weeks of age for large patterns and around 9 weeks for small patterns. As inter-laboratory agreement is generally good, the normal ranges based on this model could be used in centres, which do not have their own normative databases for infant VEPs.

Prognostic value of flash visual evoked potentials in preterm infants

This paper investigates the prognostic value of flash visual evoked potentials (VEPs) recorded in preterm infants at birth and at term age with respect to severe neurological outcome. Flash VEPs were recorded in 81 preterm infants at birth (i.e. <35 weeks' gestation) and repeated in 56 of these infants at term age. The preterm infants were assigned to either a healthy or at-risk subgroup based on clinical birth factors. Normal ranges of flash-VEP latencies, amplitudes, and number of components present were obtained from the subgroup of healthy preterm infants and from 68 term infants tested postnatally. The flash-VEP results of the entire preterm group were compared with the normal ranges and any abnormalities noted. Seven preterm infants in the at-risk group died, six of whom had abnormal flash VEPs before term age. Of the five infants from the at-risk group diagnosed with cerebral palsy (CP), three had abnormal flash VEPs before term age. Thus the sensitivity and specificity of the flash VEP with respect to survival was 86% and 89% respectively, and with respect to the development of CP was 60% and 92%. The abnormal features of the flash VEP associated with adverse outcomes comprised a delayed N3 component before term age and the absence of a positive component (P2) at term age.

Comparisons of contact lens, foil, fiber and skin electrodes for patterns electroretinograms

Pattern electroretinograms are small physiologic signals that require good patient cooperation and long recording times, particularly when conditions are not optimal. Six electrodes were compared to evaluate their efficacy. Pattern electroretinograms were recorded in eight healthy volunteers to high-contrast, pattern-reversal checks (40' width) with Burian-Allen, DTL fiber, C-glide, gold foil, HK loop and skin electrodes. Raw data for 320 reversals were analyzed off-line to evaluate signal amplitude, quality, P50 and N95 peak times, artifact rate and electrical noise. Insertion time, impedance and subjective comfort were also assessed. The Burian-Allen contact lens electrode gave the largest signal and lowest impedance but was the least comfortable and had the highest artifact rate (p < 0.01). A skin electrode on the lower eyelid produced the smallest pattern electroretinogram with the poorest quality (p < 0.05). The four other electrodes were foil or fiber electrodes in contact with the tear film, conjunctiva and/or the inferior cornea. The signal from these showed only minor differences. When electrodes are compared for pattern electroretinograms recording, the foil and fiber electrodes do not differ substantially but contact lens and skin electrodes show substantial disadvantages.

Pattern-onset visual evoked potentials: more useful than reversal for patients with nystagmus

PURPOSE

The visual evoked potential is often used to assess visual function in neurologically impaired patients, a group in whom nystagmus is a common feature. Pattern-reversal stimuli are commonly used to produce visual evoked potentials in clinical practice. Previous reports have shown that this stimulus is not optimal when subjects have nystagmus. The present study aimed to compare the efficacy of pattern-onset and reversal stimuli when used to measure visual evoked potentials from subjects with idiopathic nystagmus.

METHODS

In five adults with congenital nystagmus and 10 visually normal adults, VEPs were recorded and reproduced for checkerboard stimuli of two sizes (120' and 60'). Each size was presented as both pattern-onset and reversal check.

RESULTS

Visually normal adults demonstrated similar visual evoked potential amplitudes and quality in response to pattern-reversal and pattern-onset. However, in the presence of nystagmus, visual evoked potentials recorded to pattern-reversal stimuli were significantly smaller and of poorer quality than those obtained to pattern-onset stimuli (analysis of variance p<0.05; Kendall's tau, p<0.05).

CONCLUSIONS

Pattern-onset stimuli produce larger and clearer visual evoked potentials in patients with nystagmus compared with those produced to pattern-reversal stimuli.

The infant patient

The infant patient presents a challenge to the optometrist who must structure an examination within the infant's limited capabilities and then manage a rapidly developing visual system. The present paper provides an overview of infant visual development and the visually guided behaviours expected during normal development. Techniques for assessing vision in infant are reviewed and a recommendation is given for the optometric examination of infants. Some important urgencies, emergencies and causes of visual impairment are highlighted.

A 'passive' event-related potential?

Event potentials (ERPs) were recorded in response to visual patterns in two conditions: (1) where no instructions were given to subjects; and (2) where subjects pressed a button whenever a rare stimulus was detected. P3 amplitudes for the No Instructions condition were smaller than for the Active condition, but the latency of the P3s did not differ across conditions. In both conditions, the P3 was either absent or significantly smaller for frequent stimuli than for rare stimuli. It appears a 'passive' visual P3 is measurable, and it occurs at the same latency as a P3 recorded in association with an active response. Thus, it may be possible to record P3s in response to visual stimulation in subjects who cannot follow instructions to respond to rare events.

Relation between neurological status, refractive error, and visual acuity in children: a clinical study

The aims of the present study were: (1) to determine the refractive status and visual acuity of a group of 75 neurologically impaired children (5 to 192 months of age); and (2) to investigate the relation between the visual and neurological status of these children. Refractive error was determined using non-cycloplegic near retinoscopy and visual acuity was estimated using acuity cards (Keeler or Cardiff) and pattern-onset visual evoked potentials (VEP). Subjects demonstrated a markedly different distribution of refractive error from that of a neurologically normal age-matched population. Refractive error anomalies were more prevalent in children older than 5 years, suggesting abnormal refractive development. A wide range of visual acuity was found with both tests (acuity cards, 0.07 to 2.08 logMAR; VEP, O.78 to 2.68 logMAR). Visual acuity and refractive status varied with level and type of physical impairment. Level of intellectual impairment exhibited a weak relation with visual status.

Visual acuity assessment of children with neurological impairment using grating and vanishing optotype acuity cards

We have compared the testability and acuity thresholds achieved with vanishing optotype acuity cards and traditional grating acuity cards when used to examine children with neurological impairment. These children encompass a wide range of ages and abilities and it may be desirable to use the two types of cards for acuity assessment. Subjects were a diverse group of children (n = 91; 8 months-19 years) whose learning ability ranged from normal to severe disability. There was no significant difference between the individual success rates for the two sets of cards (grating 91% (n = 61) vanishing optotype 89% (n = 59)). Over a wide range of acuities (0 to 2.0 LogMAR) the mean difference between acuity thresholds did not differ significantly from zero (p = 0.24). Ninety-three percent of acuity estimates agreed to within +/- 0.50 LogMAR units. The results indicate that the two acuity tests could be used interchangeably in clinical populations of children with neurological impairment.

Vision care requirements among intellectually disabled adults: a residence-based pilot study

Intellectually disabled adults have an high incidence of visual problems and they are often unable to communicate their visual difficulties. At Lennox Castle and Waverley Park Hospitals, vision care is through referral by medical and nursing staff to designated optometrists and ophthalmologists. This practice has provided a good service when visual difficulties are noticed. The vision care requirements of all residents had not been comprehensively assessed and a new interdisciplinary procedure developed at Waverley Park Hospital had drawn attention to the fact that only 11% had been offered vision assessment within the previous 5 years. In this study, 63 residents without specific referral received a comprehensive visual and medical assessment. The residents ranged from age 20 to 85 years and included the full range of disabilities. Objective assessments, ophthalmoscopy and retinoscopy were generally successful for all levels of disability. Visual acuity and visual fields were tested using methods suitable for nonverbal subjects. Success rates for these subjects were generally good, except in the profoundly disabled group where less than 30% were able to respond. A high prevalence of visual impairment, refractive error, squint and other ocular conditions was found. Visual impairment was most common in the severe and profoundly disabled groups because of optic nerve or cortical dysfunction. New spectacles were recommended for 23 residents (seven others had adequate correction). Nine residents were referred for ophthalmologic consultation, mainly for cataract. Three required monitoring for visual conditions. Thirty-one residents (49%) required no immediate action beyond documentation of the visual status. This study has shown a high prevalence of visual difficulties which were not previously detected. Routine biennial vision assessment of all residents is recommended to allow timely intervention to correct vision problems, and also to provide the necessary information about vision to plan appropriate programmes of activity.

Visual evoked potentials in children with developmental coordination disorder

Children who demonstrate problems with skilled movement in the absence of physical handicap are formally designated as suffering from developmental coordination disorder (DCD). Diagnosis of DCD was confirmed by the 'movement assessment battery for children'. Visually evoked potentials (VEPs) were recorded to evaluate the integrity of the visual pathway and to rule out the presence of any neurological lesions affecting visual input. Binocular, pattern onset VEPs were recorded in 14 children with DCD aged between five and seven years, and an age-matched control group using pattern onset, high contrast, grating stimuli. Implicit times to the first and second peaks and troughs were measured, and results between the two groups were compared. Inattention and movement artefact meant that VEPs were more difficult to record within the DCD group, resulting in smaller amplitudes of the waveform, but no significant differences in the implicit times were observed between the DCD group and controls. Further research is required to determine the specific source of the neurological deficits in DCD but a problem with the integrity of the afferent visual pathway does not appear to be a causal factor.

The effect of motion on pattern-onset visual evoked potentials in adults and children

Visual evoked potentials can be elicited by a variety of visual stimuli, including pattern-onset and motion-onset. It may be desirable to combine pattern-onset with motion-onset stimuli, for example, to make a direct comparison between optokinetic nystagmus and visual evoked potential acuity thresholds. Both procedures employ grating stimuli; however, the gratings must be moving to produce optokinetic nystagmus. We compared pattern-onset visual evoked potentials with both a static and a moving pattern to investigate the effect of motion on the pattern-onset visual evoked potential waveform. Visual evoked potential recordings were made from 10 adults (aged 20-37 years) and 10 children (aged 5-7 years) with the active electrode at Oz. Stimuli consisted of onset of high-contrast vertical bars of three sizes (12', 30' and 60') both with and without motion (3 cycles/s). In a subgroup of subjects, visual evoked potentials were recorded to motion onset of constantly present gratings. Motion of the pattern had no significant effect on any of the latency components of the visual evoked potential waveform in adults or children. The amplitude of the C2-C3 component was significantly increased (p < 0.001) in adults. The motion appears to add a late negative component to the visual evoked potential similar to that produced by the motion-only stimulus. The latency of the early components of the pattern-onset visual evoked potential was unaffected by the presence of motion. Therefore, pattern-onset visual evoked potentials with moving gratings could be used to estimate visual acuity, and direct comparisons could be made between visual evoked potential and optokinetic nystagmus acuity thresholds with the use of the same stimulus parameters.

Visual function in Rett syndrome

The authors examined refractive error, pattern onset visual evoked potentials, ocular posture and they performed internal and external eye examinations in 11 subjects with Rett syndrome (aged between four and 24 years) and 18 normal controls (aged between six and 20 years). Substantial refractive errors were common in the Rett syndrome group. Spectacle correction had never previously been worn and glasses were provided where appropriate. No subjects had nystagmus or optic nerve pallor and only one was strabismic. All subjects had recognisable and reproducible pattern-onset VEPs and latencies and amplitudes did not differ significantly from those of the controls. All demonstrated VEP thresholds of at least 24'. In contrast to other populations with profound disabilities, people with Rett syndrome have good function of the afferent visual pathways and, in view of their substantial refractive errors, are likely to benefit from spectacle correction.

Assessment of visual acuity in multiply handicapped children

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Comparison of visual assessment tests in multiply handicapped children

The aims of this study were to compare acuity estimates achieved with visual evoked potential (VEP) and acuity card techniques and to examine the success rates of each test in a group of multiply handicapped children. Subjects were 52 children (3-183 months) with multiple handicaps associated with prematurity (n = 17), congenital anomalies (n = 16), hypoxic insult (n = 10) and other disorders (n = 9). Success rates for completing the tests were: VEP 88% and acuity cards 85% (Keeler or Cardiff). The acuity card tests were less likely to be successfully completed in the severely disabled (p < 0.05) and in those children with nystagmus (p < 0.05). When both acuity cards were successful, results agreed to within +/- 1.75 octaves. Acuity card thresholds were significantly correlated with VEP thresholds (p < 0.02), but thresholds achieved with VEPs were better in children with poor vision.

Pattern reversal visual evoked potentials following early treatment of unilateral, congenital cataract

OBJECTIVE

To describe the pattern reversal visual evoked potentials (VEPs) that were used to monitor and quantify early visual development following treatment for dense, unilateral, congenital cataract.

DESIGN

Longitudinal prospective study.

PATIENTS

Six infants who underwent surgery and contact lens correction before age 5 months and who had good compliance with occlusion therapy throughout the first 3 years of life.

RESULTS

Initially, VEPs from aphakic eyes showed marked abnormalities, including small amplitudes, prolonged latencies, missing components, and absent VEPs to small check sizes. Threshold check size was elevated by 3 octaves or more. With part-time occlusion of the opposite eye, VEPs normalized rapidly in the first year, but residual deficits remained to age 4 years when visual acuities were between 20/50 and 20/120 in aphakic eyes. Threshold check size clearly differentiated between aphakic and normal eyes and was the only VEP parameter that was correlated with single-letter visual acuity. Thus, threshold check size had greater clinical use than measures of pattern VEPs based on latency, amplitude, or waveform.

CONCLUSIONS

Patients treated for unilateral congenital cataract, who have early surgery and contact lens correction and comply with occlusion therapy, show a period of rapid VEP maturation and have a good visual prognosis.

Visual evoked potentials in infants and children

Visual evoked potential (VEP) studies are of great value in a wide variety of pediatric patients, including those with disorders of the sensory visual pathway and those at risk for visual pathway damage. VEPs are simple, non-invasive, and are particularly appropriate for infants and young children who cannot communicate visual symptoms or cooperate for standard vision assessment. VEPs in pediatric patients have the following main purposes: (1) detecting lesions causing dysfunction of the sensory visual pathways (the VEP is a sensitive indicator of subclinical lesions and can be used to differentiate visual impairment from visual inattention in young infants); (2) confirming functional loss when disorders of the visual system are present; (3) quantifying visual impairment in patients with known visual disorders, accomplished either empirically by noting the severity of the VEP abnormality to flash and pattern stimuli or by visual acuity estimation studies (early quantification of vision loss allows referral to early intervention programs, which can ameliorate the long-term consequences of the disability); (4) monitoring patients who are at risk for visual complications either from diseases (such as hydrocephalus or neurofibromatosis) or as a complication of therapeutic intervention (e.g., neurosurgery, chemotherapy) to help detect and avoid long-term sequelae of such therapies on the developing nervous system; (5) establishing prognosis for visual and systemic recovery based on flash VEPs for specific pediatric disorders including perinatal asphyxia in full-term neonates, acute-onset cortical blindness, and, to a fair extent, in comatose children; and (6) in some cases, contributing to the differential diagnosis. Abnormalities of flash and/or pattern VEPs are generally nonspecific to the type of exact location of the lesion, except in distinguishing prefrom postchiasmal lesions. However, in certain conditions, such as the hereditary ataxias of childhood, VEP abnormalities may help in the diagnosis. Similarly, deterioration in VEPs may help differentiate progressive from static encephalopathies. VEPs have become an indispensable tool in pediatric ophthalmology and neurology. They will probably play an increasingly important role in the future, primarily due to the difficulty in assessing visual system function in young or ill children and the VEP's sensitivity to subclinical damage in this aspect of the central nervous system.

Development of the human visual system: monocular and binocular pattern VEP latency

Pattern visual evoked potentials (P-VEPs) were recorded in 161 human infants who were between 3 weeks and 2 yr of age. The latency of the first reproducible positive peak in the P-VEP was measured monocularly and binocularly for five sizes of phase alterations checkerboard stimuli (range: 120' to 7.5' check widths). Rapid visual maturation in the first 6 months of life was shown by the development of reproducible P-VEPs to smaller check sizes and by a rapid decrease in the latency of the first reproducible positive peak. Monocular P-VEPs have slightly longer latencies than the binocular P-VEPs. This latency difference is invariant with age, but is significantly greater with larger check stimuli. Normal ranges for this large population are provided as a reference for clinical studies.

Prognostic value of VEPs in young children with acute onset of cortical blindness

Visual evoked potentials (VEPs) were recorded in 32 children (ages 4 months to 5 years) who were clinically diagnosed as being cortically blind. None of the children had visual or neurologic abnormalities prior to the precipitating insult which included surgery (N = 15), trauma (N = 3), infectious disease (N = 5), hypoxia (N = 3), and other causes (N = 6). VEPs were recorded during the acute stage of cortical blindness in all children and were repeated in 24 of them. Either flash or pattern stimulation was used, depending upon the age and visual status of the child. All but one of the children who had normal flash VEPs while cortically blind, recovered normal visual function. All patients with abnormal VEPs had permanent visual impairment or blindness and all but one of those with absent VEPs remained blind. The recovery period was highly variable, ranging from 5 days to 3 years. Thus, flash VEPs recorded during the period of blindness were useful in predicting visual outcome, regardless of etiology. Repeat studies using pattern VEPs were valuable in monitoring recovery in many of these patients.

Visual evoked potentials and visual prognosis following perinatal asphyxia

Twenty-five children born at term with perinatal asphyxia were studied at age 2.5 to 4.5 years to evaluate visual function and to determine the prognostic value of postnatal assessments of visual outcome. Postnatal assessments included several visual evoked potentials and electroretinograms in the first week of life. Follow-up assessments included flash and pattern visual evoked potentials, visual evoked potential threshold measurements, and clinical eye examinations. Nineteen children had normal visual function, three were visually impaired, and three remained blind. A strong association was found between normal, abnormal, or absent visual evoked potentials in the early postnatal period and long-term visual outcome (P less than .0001). Other perinatal indicators of asphyxia, including neurologic status, Apgar scores, and arterial pH values, were poor predictors of visual outcome. The risk of visual impairment was limited to those survivors with neurodevelopmental deficits.