Electrophysiologic testing techniques for children

Retinal Dysfunction in a Mouse Model of HCN1 Genetic Epilepsy

Pathogenic variants in HCN1 are associated with a range of epilepsy syndromes including a developmental and epileptic encephalopathy. The recurrent de novo HCN1 pathogenic variant (M305L) results in a cation leak, allowing the flux of excitatory ions at potentials where the wild-type channels are closed. The Hcn1M294L mouse recapitulates patient seizure and behavioral phenotypes. As HCN1 channels are highly expressed in rod and cone photoreceptor inner segments, where they shape the light response, mutated channels are likely to impact visual function. Electroretinogram (ERG) recordings from male and female mice Hcn1M294L mice revealed a significant decrease in the photoreceptor sensitivity to light, as well as attenuated bipolar cell (P2) and retinal ganglion cell responses. Hcn1M294L mice also showed attenuated ERG responses to flickering lights. ERG abnormalities are consistent with the response recorded from a single female human subject. There was no impact of the variant on the structure or expression of the Hcn1 protein in the retina. In silico modeling of photoreceptors revealed that the mutated HCN1 channel dramatically reduced light-induced hyperpolarization, resulting in more Ca2+ flux during the response when compared with the wild-type situation. We propose that the light-induced change in glutamate release from photoreceptors during a stimulus will be diminished, significantly blunting the dynamic range of this response. Our data highlight the importance of HCN1 channels to retinal function and suggest that patients with HCN1 pathogenic variants are likely to have a dramatically reduced sensitivity to light and a limited ability to process temporal information.SIGNIFICANCE STATEMENT Pathogenic variants in HCN1 are emerging as an important cause of catastrophic epilepsy. HCN1 channels are ubiquitously expressed throughout the body, including the retina. Electroretinogram recordings from a mouse model of HCN1 genetic epilepsy showed a marked decrease in the photoreceptor sensitivity to light and a reduced ability to respond to high rates of light flicker. No morphologic deficits were noted. Simulation data suggest that the mutated HCN1 channel blunts light-induced hyperpolarization and consequently limits the dynamic range of this response. Our results provide insights into the role HCN1 channels play in retinal function as well as highlighting the need to consider retinal dysfunction in disease caused by HCN1 variants. The characteristic changes in the electroretinogram open the possibility of using this tool as a biomarker for this HCN1 epilepsy variant and to facilitate development of treatments.

An alternative electroretinography protocol for children: a study of diagnostic agreement and accuracy relative to ISCEV standard electroretinograms

PURPOSE

To assess the diagnostic accuracy and agreement between a paediatric electroretinography protocol used at Great Ormond Street Hospital (GOSH-ERG) and the 'gold standard' international protocol (ISCEV-ERG) in health and disease.

METHODS

Patient databases between 2010 and 2020 were screened to identify children with an ISCEV-ERG recorded within four years of a GOSH-ERG. Electroretinogram (ERG) component peak times and amplitudes were re-measured, and data were analysed in terms of absolute abnormality and proportional deviation from respective reference ranges. Abnormality was defined by the retinal system affected and by individual ERG a- and b-wave component analysis.

RESULTS

A total of 59 patients were included: 38 patients had retinal disease defined by an abnormal ISCEV-ERG and 21 had normal ISCEV-ERGs. When absolute abnormality was defined by combined retinal systems, the GOSH-ERG showed an excellent overall sensitivity of 95% (accuracy 86%). Individual retinal systems showed good-excellent sensitivity (67%-100%) and specificity (68%-97%). Electroretinogram (ERG) component sensitivities ranged between 60% and 97% and specificities between 79% and 97% dependent upon the protocol step. The proportional relationship appeared mostly linear between protocols. Electroretinogram (ERG) morphology was comparable for both protocols in a range of retinal diseases including those with pathognomonic ERGs.

CONCLUSION

We demonstrate the high diagnostic accuracy of a paediatric ERG protocol (GOSH-ERG) relative to ISCEV standard ERGs. The close proportional deviation and similar waveform morphology indicate ERGs from each protocol are similarly affected in disease. This encourages the use of the GOSH-ERG protocol in the screening, diagnosis and monitoring of retinal disease in children who are unable to comply with the rigorous ISCEV-ERG protocol.

Subclinical maculopathy and retinopathy in transcobalamin deficiency: a 10-year follow-up

INTRODUCTION

Transcobalamin (TC) transports cobalamin (vitamin B₁₂) from plasma into cells. Its congenital deficiency is a rare autosomal recessive disorder due to mutations in the TCN2 gene. It causes intracellular cobalamin depletion with early onset in the first months of life, failure to thrive with pallor due to megaloblastic anemia. It can be associated with pancytopenia, gastrointestinal symptoms with vomiting, diarrhea, and neurological complications with myelopathy. Aggressive vitamin B12 parenteral therapy must be instituted early and continuously. Retinopathy and maculopathy are rarely associated with this condition.

SUBJECT

We report the electrophysiological results of one TC-deficient patient diagnosed at the age of 4 months immediately and continuosly treated by hydroxocobalamin IM. Her visual function was followed by eight ophthalmological assessments, eight flash-ERG, six EOG, one mf-ERG, and seven P-ERG recordings over a 10-year period, between the age of 2y 9 m and 12y 6 m.

RESULTS

Her ophthalmological assessment including visual acuity, fundi, optical coherent tomography (OCT), and retinal nerve fiber layer (RNFL) remained normal. From the age of 2y 9 m to 5y, dark-adapted and light-adapted flash-ERGs, EOGs and pattern-ERG were normal. From the age of 6y 4 m to 12y 6 m, dark-adapted flash-ERGs and EOGs remained normal. Cone a-wave amplitudes remained normal, whereas cone b-wave and flicker-response amplitudes were decreased. At the age of 12y 6 m, mf-ERG N1P1 amplitudes on the central 30° were decreased. From the age of 7y 4 m to 12y 6 m, P-ERG P50 amplitudes were decreased with no N95.

COMMENTS

While clinical and anatomical assessments remained normal over a 10-year period, patient's electrophysiological results suggested the progressive onset of a subclinical retinopathy of inner-cone dystrophy type, and a subclinical maculopathy on the central 30° including the ganglion cell layer deficiency on the central 15°, despite continuous intramuscular treatment, RPE and scotopic system remaining normal. The origins of such subclinical retinopathy and maculopathy are unknown and independent of early disease identification and aggressive intramuscular hydroxocobalamin therapy.

Evolution of the retinal function by flash-ERG in one child suffering from neuronal ceroid lipofuscinosis CLN2 treated with cerliponase alpha: case report

INTRODUCTION

Neuronal ceroid lipofuscinoses (CLN) are neurodegenerative disorders among the most frequent, inherited as an autosomal recessive trait. Affected patients can present with progressive decline in cognitive and motor functions, seizures, a shortened life span and visual deficiency. CLN2 is one of the rare CLN that benefits from treatment by cerliponase alpha an enzyme replacement therapy. Preliminary results on treated animal models have shown delayed neurological signs and prolonged life span. However, cerliponase alpha did not prevent vision loss or retinal degeneration in those animal models. Cerliponase alpha has currently been delivered to a few CLN2-affected patients. We report the case of one patient suffering from CLN2 treated with intracerebroventricular infusions of cerliponase alpha 300 mg every two weeks. Evolution of his retinal function was assessed by three successive flash-ERG and flash-VEP recordings throughout his treatment over a 4-year period.

RESULTS

Before treatment at the age of 4 years 5 months, patient's retinas were normal (normal fundi and normal flash-ERG). After 29 infusions at the age of 6 years 10 months, a-wave combined response was absent, while cone and flicker responses were normal. After 80 infusions at the age of 8 years 9 months, a-wave cone response was absent with b-wave peak time increased, and no combined response.

COMMENTS

Despite treatment, our patient's retinas showed a progressive abnormal and inhomogeneous function. Rods function was altered first, then the scotopic system and afterward, the cones. This result differs from those recorded in animal models. The relative preservation of cone functioning for a while could not be unequivocally attributed to enzyme replacement therapy as we lack comparison with the evolution of flash-ERGs recorded in untreated subjects.

Repeated measurements of ERGs and VEPs using chloral hydrate sedation and propofol anesthesia in young children

PURPOSE

Sedation with chloral hydrate or anesthesia using propofol allow ocular examination and testing in young children, but these drugs may affect electrophysiologic recordings. We compared the flash and pattern ERGs and VEPs recorded with each drug in a cohort of young children enrolled in a prospective study of optic nerve hypoplasia (ONH) syndrome.

METHODS

ERGs and VEPs to light-adapted, standard, full-field flashes, to standard and steady-state pattern-reversal (PR) were recorded with cycloplegia in 9 participants. Age range at the first session, with chloral hydrate was 8-23 mo; at the second session with propofol it was 20-29 mo. Examiners masked to the drug and clinical conditions measured the waveforms for longitudinal, paired comparisons between the sessions.

RESULTS

Flash ERG amplitudes did not differ between sessions; peak times were longer at the second session (propofol) by clinically insignificant amounts (< 2 ms, p = 0.002). Standard PERGs had larger amplitudes and later peaks in the second session (propofol) than with chloral hydrate (P50 2.9 vs 4.7 μV, p = 0.016 and 43 vs 52 ms, p < 0.001; N95 4.0 vs 6.1 μV, p = 0.003 and 91 vs 98.5 ms p = 0.034.). These differences were present for those with an interval of  > 10 mo between sessions (n = 5, 10 eyes) but not for those with a shorter inter-test interval (< 8 mo, p > 0.05, n = 4). Magnitudes of the steady-state PERGs did not differ between tests but the waveforms had earlier peaks at the second test with propofol. Flash VEP waveforms were present in 10/18 eyes and showed 72% agreement for recordability between sessions. Standard pattern VEPs were recordable in only a few eyes in this cohort with ONH.

CONCLUSIONS

Light-adapted flash ERG waveforms were generally similar with chloral hydrate and with propofol. Larger PERGs with later peaks, found in the second session (propofol) could reflect maturation of the PERG generators, as the differences found were associated with a greater age difference between the sessions, but we do not rule out that small differences in the waveforms may be drug-related. There are insufficient VEP data from these children with ONH to identify drug-related or maturational effects on VEPs.

Long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD) deficiency and progressive retinopathy: one case report followed by ERGs, VEPs, EOG over a 17-year period

BACKGROUND

LCHAD (long-chain 3-hydroxyacyl-CoA dehydrogenase) deficiency is a rare genetic disorder of mitochondrial long-chain fatty acid oxidation inherited as a recessive trait. Affected patients can present with hypoglycaemia, rhabdomyolysis and cardiomyopathy. About half of the patients may suffer from retinopathy.

CASE REPORT

A 19-year-old girl was diagnosed as suffering from LCHAD deficiency with recurrent rhabdomyolysis episodes at the age of 7 months by an inaugural coma with hypoglycaemia and hepatomegaly. Appropriate dietary management with carnitine supplementation was initiated. Retinopathy was diagnosed at age two. Ophthalmological assessments including visual acuity, visual field, OCT, flash ERGs, P-ERG, flash VEPs and EOG recordings were conducted over a 17-year period.

RESULTS

Visual acuity was decreased. Fundi showed a progressive retinopathy and chorioretinopathy. Photophobia was noticed 2 years before the decrease in photopic-ERG amplitude with normal scotopic-ERGs. Scotopic-ERG amplitude decreased 10 years after the decrease in photopic-ERG amplitude. No EOG light rise was observed. Flash VEPs remained normal. These results suggest that the cone system dysfunction occurs largely prior to the rod system dysfunction with a relative preservation of the macula function.

COMMENTS

This dysfunction of cones prior to the dysfunction of rods was not reported previously. This could be related to mitochondrial energy failure in cones as cones are greater consumers of ATP than rods. This hypothesis needs to be further confirmed as other long-chain fatty oxidation defective patients (VLCAD and CPT2 deficiencies) do not exhibit retinopathy.

Full-field electroretinograms in infants with hereditary tapetoretinal degeneration

Full-field electroretinograms were recorded from four infants (under the age of 12 months), with different types of tapetoretinal degeneration. Some of these patients, appear to have normal fundi. This article stresses the clinical usefulness of evaluation with electroretinography in young children.

Comparison of ERGs recorded with skin and corneal-contact electrodes in normal children and adults

PURPOSE

Compare electroretinogram (ERG) responses to full-field stimuli recorded with corneal-contact and skin electrodes in healthy children and adults.

METHOD

ERGs were recorded independently in two laboratories in children (aged 4-14 years) and adults (aged 20-62 years). A Burian-Allen (BA) electrode were used to test both children and adults in one laboratory. A Gold Foil (GF) electrode was used to test adults and skin electrodes to test children and adults in the other laboratory. Responses were recorded to full-field stimuli similar to those specified in the ISCEV Standard. Dark-adapted responses were also recorded over a 5 log unit range of stimulus energies.

RESULTS

All ISCEV rod and cone responses were recorded in every subject with skin electrodes as well as with eye-contact electrodes. BA and GF amplitudes and latencies were similar for the majority of ISCEV responses. The waveform morphology of rod and cone skin electrode responses was similar to corneal electrode responses in children and adults. GF electrode responses were on average 4 to 5 times larger than skin electrode responses recorded in the same laboratory. After scaling skin electrode responses by 4.5 the distribution of response amplitudes was found to be similar to that for the eye-contact electrodes in both children and adults. Dark-adapted responses were recorded to all stimulus intensities in every subject with each type of electrode. B-wave S-R functions were evaluated by fitting the Naka-Rushton equation. Vmax was similar for BA and GF electrode responses and this was about 4 times greater than for skin electrode responses. Log (sigma) was similar for GF and skin electrodes but these differed significantly from the BA electrode. Vmax and log(sigma) were similar in adults and children for BA and skin electrode responses.

CONCLUSION

ERGs to full-field stimuli can be recorded successfully with either eye-contact or skin electrodes.

Standard full-field electroretinography in healthy preterm infants

The purpose of this study was to determine electroretinographic parameters according to the standard protocol from the International Society for Clinical Electrophysiology of Vision (ISCEV) in healthy preterm infants with normal fundus. Seventeen healthy preterm infants with normal fundus were recruited and divided in two age groups: 3-week group, nine infants with mean adjusted age at test = 2.67 +/- 0.92 weeks and 8-week group, eight infants with mean adjusted age at test = 7.92 +/- 1.72 weeks. Full-field ERGs were obtained with a Burian-Allen bipolar contact lens electrode from the anesthetized cornea in one eye, through a fully dilated pupil after 30 min of dark adaptation. The standard ISCEV protocol was used and the following responses were recorded: rod, maximal, oscillatory potentials, cone and 30 Hz flicker. Median values and 1st, 5th, 95th and 99th percentiles for amplitude and implicit time are described for both age groups. There was statistically larger amplitude for 30 Hz flicker (t = 2.191; p = 0.046) and for cone response (t = 2.307; p = 0.044) in the 8-week-old group. Statistically shorter implicit times were found in 8-week group for rod response (t = 3.219; p = 0.015), cone response (t = 2.839; p = 0.016) and flicker response (t = 3.326; p = 0.005). Shortening of implicit time was evident in the older group of preterms and this finding is consistent with other maturational studies confirming the anatomical and functional development of the photoreceptors. Medians and ranges between the 1st and 99th and the 5th and 95th percentiles can be used as a baseline for future comparisons with infants with ROP.

Pattern ERG and VEP maturation in schoolchildren

OBJECTIVE

The maturation of the visual system has been studied with pattern electroretinograms (PERG) and pattern visual evoked potentials (PVEP) mostly in children under the age of 6 years. To address the question of maturation of the visual system in childhood and adolescence we investigated age-dependent PERG and PVEP changes in children aged 7-18 years.

METHODS

PERG were recorded with skin electrodes attached to the lower eyelid, and PVEP were recorded with 5 electrodes. Visual stimuli, consisting of pattern-reversal 50' checks to full-field and to half-field stimulation, were applied to obtain macular (N70, P100, N145) and paramacular waves (P80, N105, N135).

RESULTS

We found an age-dependent decrease (linear regression P<0.05) of PERG P50 amplitude and full-field PVEP P100 latency to monocular right and left eye stimulation, indicating central retinal and postretinal changes. In addition, waveform changes were found in responses to half-field stimulation. The paramacular wave N105 was typically enhanced in younger schoolchildren and diminished with age. The age-dependent decrease (linear regression P<0.01) of paramacular N105 amplitude indicated the increasing predominance of the macular structures of the visual system.

CONCLUSIONS

Our findings suggest that central retinal and postretinal electrophysiological maturation persists throughout childhood. Age-dependent PVEP changes seem to correlate with the morphological and metabolic findings that maturation of the visual cortex continues until puberty and even later.

Mechanism of binocular interaction in refraction errors: study using pattern-reversal visual evoked potentials

In this study we sought to determine whether a natural condition involving fine discrimination, for example moderately severe myopia, might yield interesting information regarding the binocular interaction expressed by visual evoked potentials (VEPs). We studied ten normal subjects with a mild refraction deficits. Transient VEPs were elicited by monocular and binocular stimulation under conditions of natural and lens-corrected vision. The visual stimulus was a pattern-reversal checkerboard consisting of 15' and 40' checks. VEPs in response to binocular stimulation were compared with monocular VEPs. We plotted the monocular 'better-VEP' and 'worse-VEP' response, since significant differences between individual eye stimulations were present. We found no significant difference between the mean N75 and P100 latencies of the binocular VEP and the better monocular VEP, regardless of the check size used and of natural or corrected vision. Under all stimulus conditions, the mean amplitude of the N75-P100 of the binocular VEPs was also larger than the better monocular VEP response. The difference proved more significant when we stimulated our subjects with smaller squares and left vision uncorrected. The mean P100-N145 amplitude obtained with binocular stimulation was larger than the better monocular VEP response only when using small checks (15') and uncorrected vision. Overlapping latencies are consistent with an earlier hypothesis that monocular and binocular VEPs originate postsynaptically from the binocular neurons in the primary visual cortex. The gain in amplitude achieved by binocular stimulation may depend upon the removal of 'tonic interocular inhibition' and/or on a cortical modulatory mechanism.

Time courses for maturation of electroretinogram responses from infancy to adulthood

The purpose of this study was to determine how responses in the normal human electroretinogram (ERG) change with subject age. We studied 62 children, 10 days to 15 years old, and 30 subjects 15-37 years old, using the standard protocol established by the International Society for Clinical Electrophysiology of Vision, with Burian-Allen bipolar contact-lens electrodes. We measured rod response, maximal response, oscillatory potentials (OPs), cone response, flicker response, and b-wave amplitude/log intensity (V/log I) curve. A logistic growth curve was used to describe the developmental changes. Dark- and light-adapted ERG a- and b-wave amplitudes reached adult levels by three to five years of age. although b-wave amplitudes of scotopic rod-mediated responses were slower to reach maturity than mixed rod-cone mediated responses. In early infancy OPs were the most immature of the ERG responses, although the rate of development thereafter exceeded that of the other responses such that OP amplitudes were within adult levels by two years of age. Amplitudes of the ERG responses in 21 children sedated with chloral hydrate did not differ significantly from 21 who had not been sedated. ERG responses developed at varying rates, reflecting different developmental stages in photoreceptors, middle retinal layers and more proximal retina.

Binocular interaction in normal vision studied by pattern-reversal visual evoked potential (PR-VEPS)

Monocular and binocular visual evoked potentials (VEPs) in response to different check size (15-21-38-84 minutes or arc) were studied in 14 subjects with normal visual acuity and stereopsis. The binocular VEP amplitude is slightly higher than the VEP amplitude on stimulation of the "better eye" and significantly higher than the VEP amplitude on stimulation of the "worse eye"; this effect is observed using small checks and almost exclusively involved N75-P100. Both the N75 and P100 peaks occur earlier after binocular than monocular stimulation. The shortening of the N75 mean latency is significantly greater than that of the P100 mean latency when larger check sizes are used. The mean latency of the N145 potential is not significantly different in monocular and binocular stimulus conditions. The slight summation effect and latency shortening in the binocular VEPs are not consistent with the hypothesis that it is the sum of separate monocular signals originating from the visual cortex that gives rise to the response. The early components of both monocular and binocular VEPs are thought to be of post-synaptic origin (outside layer 4c of area 17), where the inputs become mixed so that most cells receive information from both eyes. The amplitude enhancement of binocular VEPs, which mainly occurs when using small checks, may be related to the increase in the total amount of cortical activity representing the macular region; this may account for binocular superiority in fine spatial resolution. The latency shortening in binocular conditions can be explained by considering that the critical determinant of the latency is the fundamental spatial frequency of the pattern. When coarse patterns are used, their effectiveness in parafoveal stimulation may affect the VEPs, with a significant contribution coming from the more peripheral retina. The enlargement of the visual field when the eyes see simultaneously may therefore further reduce the latency of the response when using the larger checks suitable for eccentric stimulation.

Prognostic value of visual evoked potentials (VEP) in infants with visual inattentiveness

Visual evoked potentials elicited by strobe flash (fVEPs) were recorded in 56 infants (3 months to 15 months of age) with visual inattentiveness but without prechiasmal problems. Their visual status was reexamined one or more years later when 41 children were found to be visually competent (Group NB) and 15 were blind (Group B). We also evaluated a group of 32 age-matched children who had no visual symptoms (Group C). It was found that well organized VEP waveforms over one or both hemispheres (Types U and S), or those with a characteristic negative shift (Type N) suggest favorable prognosis. Integrated voltage of the VEP correlated well with long-term prognosis for visual recovery. The vertex VEP also (had) provided some predictions for visual prognosis. Overall results indicate good prognosis if related to sufficient voltage and complexity of the VEP components.

Infant visual development: an overview of studies using visual evoked potential measures from Harter to the present

Studies of sensory and perceptual abilities in infants require creative, innovative techniques. Although the young infant's response repertoire may appear limited to the naive individual, a number of highly refined procedures have been developed and implemented with these non-verbal humans over the last twenty years. The most successful protocols for evaluating visual development rely either on behavioral responses or on electrophysiological recordings. The first published report using visual evoked potentials to study the development of pattern vision in human infants was presented by M. Russell Harter. This work provided the impetus for a wealth of studies exploring issues of visual information processing abilities in early infancy. The available range of data and experimental techniques are now sufficiently refined that many clinical issues are currently being addressed. The purpose of this review is to document the evolution of scientific studies since Harter's seminal work. The selection of protocols presented focuses on those with either current clinical applications or those which hold promise for future applications in the evaluation and treatment issues of abnormal visual development.

Skin ERGs: their effectiveness in paediatric visual assessment, confounding factors, and comparison with ERGs recorded using various types of corneal electrode

Comparison of scotopic and photopic ERGs recorded using a variety of ERG electrodes show that contact lens electrodes produce the largest ERGs, and these are about 30-50% larger compared with those recorded with foil or thread electrodes, which contact a smaller part of the cornea. Flash ERGs recorded from infra-orbital skin electrodes are about one eighth the size of those recorded with contact lens electrodes, and around one quarter the size of those recorded with foil or fibre corneal electrodes. Reliable ERGs can be obtained in young children from infra-orbital electrodes sited centrally, within 1 cm of the rim of the eyelid, when signal averaging is used. Stimulation under fully darkened laboratory conditions with red and dim blue flashes permit assessment of cone and rod function, respectively. Factors such the recording electrode position, electrode derivation, upward rotation of the eye, eyelid closure and markedly constricted pupils can degrade the skin ERG. There are strong diagnostic advantages in recording the VEP concurrently with the skin ERG, particularly in young children. Examples of recordings in Leber's amaurosis, delayed visual maturation, albinism, optic nerve hypoplasia, achromatopsia add X-linked congenital stationary nightblindness are shown to demonstrate how ERG/VEP recordings can help in distinguishing between these conditions.

Full-field electroretinograms during general anesthesia in normal children compared to examination with topical anesthesia

Full-field electroretinograms were obtained from 20 normal children during general anesthesia and compared with electroretinograms obtained with topical anesthesia. Disoprofol and fentanyl induced a reduction in the b-wave amplitudes and an increase in the cone b-wave implicit time, but the changes were small and fall within the range limits seen with topical anesthesia (i.e., average +/- 2 SD).

A comparison of flash electroretinograms recorded from Burian Allen, JET, C-glide, gold foil, DTL and skin electrodes

Single flash scotopic and photopic electroretinograms (ERGs) were recorded from the same subjects using six types of corneal electrode, in order to assess their relative effectiveness. In addition, the ERG from a lower eyelid skin electrode was recorded to give an indication of the degree of attenuation to be expected from a skin electrode. On average, the scotopic ERG recorded from the Burian Allen electrode measured 471 microV (100%), and relative to this the b-waves recorded using other electrodes were as follows: JET (89%), C-glide (77%), gold foil (56%), DTL (46%) and skin (12%). Under photopic conditions the order was the same and the interelectrode proportions similar. The b-wave amplitude recorded using the Burian Allen electrode was 125 microV (100%), and with other electrodes was as follows: JET (93%), C-glide (78%), gold foil (60%), DTL (60%) and skin (14%).

Effects of halothane on children's electroretinograms

BACKGROUND

At times, anesthesia is necessary to test children's electroretinographic (ERG) responses. Halothane, an anesthetic commonly used for pediatric patients, affects some aspects of ERG responses, but it is unknown if halothane affects ERG parameters evaluated by contemporary clinical protocols.

METHODS

Scotopic and photopic ERG responses were recorded from children when awake and then under halothane.

RESULTS

Halothane has no effect on scotopic b-wave stimulus/response parameters, including amplitude, sensitivity, and implicit time. Scotopic a-wave amplitudes, implicit times, model parameters, and ratio of a- to b-wave amplitudes are unaffected by halothane. The amplitudes and implicit times of photopic responses to red flashes and 30 Hz flickering white light are not altered by halothane. Halothane causes no significant change in amplitudes and implicit times of the oscillatory potential wavelets.

CONCLUSION

These results suggest that significant departures of ERG responses (studied with the protocol described herein) from a laboratory's normal values cannot be attributed to halothane.

Electrophysiologic evaluation of the visual pathway in children. Case reports

Clinical findings and results of electrophysiologic evaluation of the visual pathway were studied in seven children ranging in age from 10 months to 13 years. Using skin electrodes for electroretinographic and visual evoked potential testing, we obtained reliable results without sedation or pupil dilation. The half-field stimulation was indispensable for localizing lesions along the visual pathway and thus for specific diagnosis.