Michael S. Bradnam

Cortical visual dysfunction in children: a clinical study.

Damage to the cerebral cortex was responsible for impairment in vision in 90 of 130 consecutive children referred to the Vision Assessment Clinic in Glasgow. Cortical blindness was seen in 16 children. Only 2 were mobile, but both showed evidence of navigational blind-sight. Cortical visual impairment, in which it was possible to estimate visual acuity but generalised severe brain damage precluded estimation of cognitive visual function, was observed in 9 children. Complex disorders of cognitive vision were seen in 20 children. These could be divided into five categories and involved impairment of: (1) recognition, (2) orientation, (3) depth perception, (4) perception of movement and (5) simultaneous perception. These disorders were observed in a variety of combinations. The remaining children showed evidence of reduced visual acuity and/ or visual field loss, but without detectable disorders of cognitive visual function. Early recognition of disorders of cognitive vision is required if active training and remediation are to be implemented.

Ophthalmic, clinical and visual electrophysiological findings in children born to mothers prescribed substitute methadone in pregnancy

Background and aims There are growing concerns regarding visual outcome of infants exposed to opiates (including substitute methadone) and/or benzodiazepines in utero. We describe the combined ophthalmology and visual electrophysiology findings in 20 infants and children who had been exposed to substitute methadone and other drugs of misuse in utero. Methods This was a descriptive case series of 20 patients, all of whom had been referred to a paediatric visual electrophysiology service because of concerns regarding visual function, and all of whom had been exposed to methadone in utero. All children underwent a full ophthalmic and orthoptic examination as well as visual electrophysiology testing deemed appropriate on an individual basis. A review was undertaken of paediatric case notes and of maternal antenatal urine toxicology. Results Ophthalmic abnormalities included reduced acuity (95%), nystagmus (70%), delayed visual maturation (50%), strabismus (30%), refractive errors (30%), and cerebral visual impairment (25%). Visual electrophysiology was abnormal in 60%. A quarter of the children had associated neurodevelopmental abnormalities. The majority of children with nystagmus (79%) had been treated for neonatal abstinence syndrome (NAS). Conclusion Infants born to drug-misusing mothers prescribed methadone in pregnancy are at risk of a range of visual problems, the underlying causes of which are not clear. Those infants with NAS severe enough to receive pharmaceutical treatment may be at particular risk of developing nystagmus. The inclusion of visual electrophysiology in comprehensive visual assessment of children exposed to substance misuse in utero may help clarify the underlying causes by differentiating abnormalities of retinal and cortical origin.

Neonatal visual evoked potentials in infants born to mothers prescribed methadone.

OBJECTIVE: Drug misuse in pregnancy is associated with impaired infant visual development. Pilot data showed abnormal flash visual evoked potentials (VEPs) in neonates exposed to methadone in utero, but results were confounded by intrauterine growth restriction, gestation, and ongoing drug misuse. This large cohort study aimed to clarify the effects on neonatal flash VEPs of maternal drug misuse in pregnancy, including prescription of substitute methadone and subsequent development of neonatal abstinence syndrome. METHODS: This was a prospective cohort study. Flash VEPs were recorded within 3 days of birth from 100 healthy infants of drug-misusing mothers prescribed substitute methadone during pregnancy and 50 comparison infants matched for birth weight, gestation, and socioeconomic deprivation. VEP morphology was classified as mature, typical, or immature, and amplitudes and implicit times of the major waveform components measured. Drug exposure was determined by maternal history, maternal and infant urine, and meconium toxicology. RESULTS: VEPs from maternal drug-exposed infants were more likely to be of immature waveform (P < .001) and were smaller in overall amplitude (median 27 µV vs 39 µV, P < .001) compared with non–drug-exposed infants. Most infants were exposed to illicit drugs in addition to prescribed methadone; differences in VEP parameters were independently associated with maternal prescribed methadone and persisted after correcting for birth weight, cigarette smoking, and excess in utero alcohol exposure. CONCLUSIONS: In utero exposure to prescribed substitute methadone is associated with altered flash VEPs in the newborn period and these infants may warrant early clinical visual assessment.

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 μV, 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.

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.

Vitamin A Supplementation Improves Retinal Function in Infants at Risk of Retinopathy of Prematurity

OBJECTIVEnPreterm infants show reduced retinal sensitivity at term corrected age compared with newborn term infants. We tested the hypothesis that retinal sensitivity in preterm infants is improved by early, high-dose vitamin A.nnnSTUDY DESIGNnWe report a double-blind, randomized controlled trial of infants <32 weeks gestation and/or <1501 g birth weight. Supplemented infants received additional intramuscular vitamin A 10xa0000 IU 3 times weekly from day 2 for a minimum of 2 weeks or until establishment of oral feeding. Hepatic stores were assessed by relative dose response (RDR). The primary outcome measure was cone-corrected dark-adapted retinal rod sensitivity measured by electroretinogram at 36 weeks postmenstrual age (PMA).nnnRESULTSnEighty-nine infants (42 supplemented and 47 controls) were recruited. Plasma retinol was higher in supplemented infants at 7 and 28 days (median, 1.0 vs 0.5 μmol/L and 0.7 vs 0.6 μmol/L; P < .001 and .03, respectively). Neither plasma retinol nor RDR differed between groups at 36 weeks PMA. Retinal sensitivity was greater in supplemented infants (-0.81 vs -0.61 log cd • s • m(-2); P < .03) and was not related to RDR.nnnCONCLUSIONSnEarly high-dose intramuscular vitamin A supplementation for infants at risk of retinopathy of prematurity improves retinal function at 36 weeks PMA.

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 childrens vision. Questions with the highest validity for predicting vision are identified.

Contact lens electroretinography in preterm infants from 32 weeks after conception : a development in current methodology

AIM To assess the feasibility of using a contact lens electrode to record the electroretinogram (ERG) in preterm infants less than 35 weeks after conception. METHODS The ERG was recorded from seven very low birthweight preterm infants on a total of 14 occasions using an infant monkey contact lens electrode. Age at recording the first ERG ranged from 23 to 51 days (gestational age 32–34 weeks), and weight ranged upwards from 1100 g. RESULTS No complications were observed. With advancing age and maturity the dark adapted rod threshold decreased, indicating increased retinal sensitivity. CONCLUSIONS Contact lens recording of the ERG from extremely small immature preterm infants is a practicable and well tolerated procedure. This method of recording the ERG will enable further evaluation of retinal development in this vulnerable population.

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.

Abnormal visual evoked potentials in newborn infants of drug-misusing mothers: is prescription of substitute methadone to blame?

Background/aim Abnormal neonatal visual evoked potentials (VEPs) have been documented following in utero exposure to methadone and other illicit drugs: these pilot data were however confounded by intrauterine growth restriction, social deprivation and gestation.1 We now report a larger controlled study of the effects of maternal drug misuse upon neonatal VEPs. Methods Flash VEPs were recorded from 100 term infants of drug-misusing mothers prescribed substitute methadone, and 50 control infants matched for birthweight, gestation and socio-economic group. Drug exposure (including excess alcohol consumption) was determined by history, maternal and infant urine and meconium toxicology. VEPs were classified according to waveform, and amplitude and latencies measured. Results VEPs were recorded from all infants at a median age of 24 h (IQR 13–44). Gestation, birthweight and socio-economic group did not differ between groups. VEPs from drug-exposed infants were more likely to be of immature waveform (p<0.001) and were smaller in amplitude (median 27 μV vs 39.5 μV, p<0.001) compared to controls. Differences persisted after correcting for excess in utero alcohol exposure. The majority of infants were exposed to additional drugs of misuse: regression analysis indicated that differences in VEPs were due to methadone exposure and not to other illicit drugs. There was no association between VEP parameters and subsequent onset or severity of neonatal abstinence syndrome. Conclusion In utero exposure to prescribed substitute methadone and other illicit drugs is associated with alterations in neonatal visual electrophysiology. These changes appear to be due to methadone rather than alcohol or other associated drugs of misuse.