Electroretinography: application to clinical studies of infants

The Effects of Brain Damage on Visual Functioning in Children

This article reviews the research literature on the direct effects of brain damage on the visual functioning of children and the electrodiagnostic tests used to diagnose them. Although the studies documented that brain damage affects visual functioning, they suggested that the prognosis for good functional vision after remedial intervention is more optimistic than was previously thought. They also found that electrodiagnostic testing is a valuable tool, but that the use of a combination of tests yields a more complete picture of the effects than does any single test.

Congenital Nystagmus and Its Congeners

In recent years, we have made enormous strides in elucidating the phenomenology of congenital nystagmus. The purpose of this review is to briefly summarize our current understanding of congenital nystagmus in terms of its clinical symptomatology, pathophysiology, differential diagnosis, and ancillary testing, and clinical management. Finally, this discussion provides the reader with an armamentarium of clinical pearls to facilitate diagnosis of the numerous sensory visual disorders that can underlie congenital nystagmus.

Electroretinographic Changes during Childhood and Adolescence

Electroretinogram (ERG) changes with age have been studied widely, but there is no general agreement about the age at which ERG parameters reach adult values. We studied 296 eyes from 148 healthy subjects, divided into 14 age groups, ranging from 1 week to 21 years. Although most of the maturational changes or ERG take place during the first six months, the a wave completes development at three years of age and the b component shows a smooth increase in latency between 3 and 18–21 years. The latter component also shows an increase in amplitude from 7–8 to 12–14 years. During the first period of maturation the b wave parameters follow a multiplicative model. These data are discussed in relation to previously reported findings on ERG maturation and to morphological and functional eye changes with age.

Development of rod function in term born and former preterm subjects

PURPOSE

To provide an overview of some of our electroretinographic (ERG) and psychophysical studies of normal development of rod function and their application to retinopathy of prematurity (ROP).

METHODS

ERG responses to full-field stimuli were recorded from dark adapted subjects. Rod photoreceptor sensitivity (SROD) was calculated by fit of a biochemical model of the activation of phototransduction to the ERG a-wave. Dark adapted psychophysical thresholds for detecting 2 degrees spots in parafoveal (10 degrees eccentric) and peripheral (30 degrees eccentric) retina were measured and the difference between the thresholds, Delta10-30, was examined as a function of age. SROD and Delta10-30 in term born and former preterm subjects were compared.

RESULTS

In term born infants, (1) the normal developmental increase in SROD changes proportionately with the amount of rod visual pigment, rhodopsin, and (2) rod-mediated function in central retina is immature compared with that in peripheral retina. In subjects born prematurely, deficits in SROD persist long after active ROP has resolved. Maturation of rod-mediated thresholds in the central retina is prolonged by mild ROP.

CONCLUSIONS

Characterization of the development of normal rod and rod-mediated function provides a foundation for understanding ROP.

Flash electroretinography: normative values with surface skin electrodes and no pupil dilation using a standard stimulation protocol

OBJECTIVES

To demonstrate the clinical feasibility of using surface electrodes for recording flash electroretinography (ERG), using the stimulation standards of the International Society for the Clinical Electrophysiology of Vision (ISCEV), without pupillary dilation.

METHODS

Eighteen physiologically normal volunteers were tested. Surface recording electrodes were placed over the middle third of the lower eyelid of each eye, and the reference electrode placed on the temple. The recording filters and method of stimulation for the standard flash cone, 30 Hz flicker, rod, standard combined and oscillatory responses were those recommended by the ISCEV. Four patients with a history of visual dysfunction were also examined.

RESULTS

The amplitudes of the responses were noted to have a high signal to noise ratio, allowing us to average only a few responses. The waveform configurations were almost identical to those published using other recording methods. Patients with retinitis pigmentosa and early onset retinal dystrophy had abnormal responses, whereas patients with Stargardt's Syndrome and spasm of accommodation had responses within normal limits.

CONCLUSIONS

This study has established the clinical feasibility of performing flash ERG using surface skin electrodes, with no pupillary dilation and using the stimulation standards of the ISCEV.

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.

Infant vision and retinal function in studies of dietary long-chain polyunsaturated fatty acids: methods, results, and implications

Animal and human studies have documented several effects of different dietary and tissue concentrations of long-chain polyunsaturated fatty acids (LCPUFAs) on retinal function and vision. The enhanced visual development associated with increased intakes of LCPUFAs, particularly docosahexaenoic acid (DHA), provides the strongest evidence for the importance of these fatty acids in infant nutrition. The 2 primary visual measures used to assess the efficacy of infant formula LCPUFA supplementation are the electroretinogram and visual acuity. This review briefly describes the methodology, neural basis, and interpretation of these measures, as well as other measures of visual development that may be used to extend the functional evaluation of infants fed formulas with different fatty acid compositions.

Oscillatory potentials in the retina: what do they reveal

This chapter is an overview of current knowledge on the oscillatory potentials (OPs) of the retina. The first section describes the characteristics of the OPs. The basic, adaptational, pharmacological and developmental characteristics of the OPs are different from the a- and b-waves, the major components of the electroretinogram (ERG). The OPs are most easily recorded in mesopic adaptational conditions and reflect rapid changes of adaptation. They represent photopic and scotopic processes, probably an interaction between cone and rod activity in the retina. The OPs are sensitive to disruption of inhibitory (dopamine, GABA-, and glycine-mediated) neuronal pathways and are not selectively affected by excitatory amino acids. The earlier OPs are associated with the on-components and the late OPs with the off-components in response to a brief stimulus of light. The postnatal appearance of the first oscillatory activity is preceded by the a- and b-waves. The earlier OPs appear postnatally prior to, and mature differently from, the later ones. The second section deals with present views on the origin of the OPs. These views are developed from experimental studies with the vertebrate retina including the primate retina and clinical studies. Findings favor the conclusion that the OPs reflect neuronal synaptic activity in inhibitory feedback pathways initiated by the amacrines in the inner retina. The bipolar (or the interplexiform) cells are the probable generators of the OPs. Dopaminergic neurons, probably amacrines (or interplexiform cells), are involved in the generation of the OPs. The earlier OPs are generated in neurons related to the on-pathway of the retina and the later ones to the off-channel system. Peptidergic neurons may be indirectly involved as modulators. The individual OPs seem to represent the activation of several retinal generators. The earlier OPs are more dependent on an intact rod function and the later ones on an intact cone system. Thus, the OPs are good indicators of neuronal adaptive mechanisms in the retina and are probably the only post-synaptic neuronal components that can be recorded in the ERG except when structured stimuli are used. The last section describes the usefulness of the oscillatory response as an instrument to study the postnatal development of neuronal adaptation of the retina. In this section clinical examples of of the sensitivity of the OPs for revealing early disturbance in neuronal function in different retinal diseases such as pediatric, vascular and degenerative retinopathies are also given.

Rod photoresponses in 6-week and 4-month-old human infants

Rod-only electroretinograms (ERGs) were recorded from 6-week and 4-month-old normal human infants. The leading edge of the rod a-wave was fitted with a model of the activation phase of phototransduction to provide estimates of S (a sensitivity parameter) and RmP3 (the maximum saturated photoreceptor response) at each of the investigated ages. Both S and RmP3 increased over the first postnatal months but followed different developmental time courses with S approaching adult-like values sooner than RmP3. The changes in S and RmP3 can be interpreted within the context of a model incorporating the combined effects of increased levels of rhodopsin and the changing structure of the rod outer segment during development.

Long chain polyunsaturated fatty acids and visual function in preterm infants

Electroretinograms (ERG) were recorded at 40 weeks post-conceptual age (PCA) in 18 infants born prematurely (25-32 weeks gestation). Fatty acid composition of plasma and red cell phospholipids was measured within 4 days of birth and at time of ERG testing, and detailed record was kept of dietary intake. Correlations were seen between percentage intake of breast milk and docosahexaenoic acid (DHA) in both plasma (r = 0.818, P < 0.0001) and red cells (r = 0.534, P = 0.035) and significant differences in fatty acid profiles were seen between infants receiving > 50% and < 50% breast milk. No difference was seen in retinal sensitivity between infants receiving > 50% or < 50% breast milk. A positive correlation was seen between scotopic (rod) b-wave implicit time on ERG and DHA in both plasma (r = 0.733, P = 0.001) and red cells (r = 0.502, P = 0.04). A positive correlation was seen between arachidonic acid and rod ERG amplitude (r = 0.565, P = 0.022) which may reflect the higher AA/DHA ratio in the developing retina. These data did not support our hypothesis that increased dietary DHA results in enhanced retinal maturation. Visual acuity measured at 40 weeks PCA and again 3 months later was similar between groups. While subtle relationships were demonstrated between long chain polyunsaturated fatty acids and visual function, all infants were felt to be within age-appropriate normal range at expected date of delivery and at 3 months corrected age.

Maturation of electroretinograms and visual evoked potentials in preterm infants

Electroretinograms (ERGs) and visual evoked potentials (VEPs) to flash stimulation were recorded from 51 infants (gestational age 26 to 42 weeks; post-conceptional age (PCA) 31 to 47 weeks) to give cross-sectional data on the maturation of these responses. Sequential recordings were taken from a separate group of 24 preterm infants (gestational age 28 to 33 weeks) to give longitudinal data. There was a significant decrease in ERG a-wave latency and increase in a-b amplitude with increasing PCA in both groups. For the VEPs there was a significant decrease in latency of the early negative component (N1) and the major positive component (P2). Comparison between recordings made on preterm infants with those from term infants at an equivalent PCA suggested faster maturation of VEPs in the extra-uterine environment, but no difference in maturation of the ERG.

Postnatal retinal development as measured by the electroretinogram in premature infants

Light-adapted and dark-adapted electroretinograms were obtained in 27 premature infants who were screened for retinopathy of prematurity shortly after birth. Thirteen showed no retinopathy and 13 had mild to moderate retinopathy, which ranged from stage I, zone III (International Classification) to stage III, zone II. Measurements were made during the first 16 months of life. The configuration of the waveforms under both photopic and scotopic conditions changed during this period showing increased amplitudes of both the a- and the b-waves. A scotopic intensity series was performed and the b-wave amplitudes and implicit times were measured. The b-wave amplitude data were averaged for three adult control subjects, for infants without retinopathy of prematurity measured at 3-4 and at 6-7 months and for infants with retinopathy of prematurity measured at 3-4 and at 6-7 months. The Naka-Rushton function was fitted to the average data. The Rmax increased from 3 to 6 months and from 6 months to adulthood, and the Isat values decreased over this age range. The b-wave implicit times were within normal range in the 6-month data. There was no difference in Rmax or Isat for infants with and without ROP.

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.

The role of n-3 fatty acids in visual and cognitive development: current evidence and methods of assessment

Low levels of dietary n-3 fatty acids during development lead to changes in the electroretinogram and visual acuity in rats, monkeys, and human infants. Additional aspects of vision can be measured in infants and may provide further useful information about the nature of the changes induced by n-3 fatty acid deficiency and their potential long-term relevance for formula-fed human infants. Several tests are available to assess the development of specific cognitive functions such as visual recognition and short-term memory. These measures can provide information that is not now available to test the hypothesis that n-3 fatty acids are important for other aspects of neural function, including intellectual or cognitive development.

An electrophysiological study on children and young adults with Alport's syndrome

Alport's syndrome is characterised by progressive haematuric nephritis and high tone sensorineural hearing loss. Ocular signs are variable, the most consistent findings being anterior lenticonus and retinal flecks in the macula and mid peripheral areas. Previous electrophysiological studies on patients with Alport's syndrome have mostly been on adult patients undergoing haemodialysis, or after renal transplantation. A group of young patients with Alport's syndrome were studied to assess if early electrophysiological changes were detectable. A total of 20 patients (15 males and five females) between the ages of 3.5 and 22 years (mean 12.7 (years) were examined and compared with control subjects. Visual evoked potentials and electroretinograms were obtained following flash and pattern reversal stimulation. Electro-oculograms were also recorded. No significant electrophysiological changes were found in any of the 20 patients, including four who had visible fundus changes.

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).

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.

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

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

Electrophysiological assessment of visual pathway function in infants

The flash ERG and VEP have conspicuous immature features during the first 4 months following birth. The most marked maturational changes occur in ERG amplitude and VEP latency. Concurrent recording of the skin ERG and VEP provides information which is very useful in helping to arrive at a diagnosis in the young infant with nystagmus who appears to be blind and has a fundus of normal appearance. ERG and VEP features associated with Leber's Amaurosis, congenital cone dysfunction, albinism, optic nerve hypoplasia and unilateral hemisphere dysfunction are described.

A computational model of the amplitude and implicit time of the b-wave of the human ERG

To improve the usefulness of the ERG in identifying the sites and mechanisms of adaptation, development, and disease processes, a theoretical framework based upon Granit's analysis of the ERG was evaluated. The framework assumes that the ERG is the sum of two potentials, one, P3, generated by the receptors and the other, P2, generated by the cells of the INL. Hood and Birch (1990a, b) demonstrated that the leading edge of the a-wave can be quantitatively described by a model used to describe the response from single rod receptors. This model provides P3(t), a theoretical receptor response as a function of time, for any given flash intensity. The ERGs from normal observers and patients with retinal diseases were analyzed in this framework, first by deriving P2 by computer subtracting the predicted P3(t) responses. This analysis was successful and a computational model of the ERG was then derived. The model of P2(t) was constructed with linear filters and a static nonlinearity and using P3(t) as the input. The ERG for any given flash intensity is then P3(t) + P2(t). The model describes (1) the change both in implicit times and in trough-to-peak b-wave amplitudes with flash intensity for the normal, dark-adapted observers; and (2) the changes in b-wave implicit times and amplitudes for three patients with retinal diseases. Among the implications drawn from these analyses were as follows: (1) The fits of the Naka-Rushton equation to trough-to-peak b-wave amplitudes must be interpreted with great care. (2) When the INL is affected by retinal disease, the b-wave may be a very poor reflection of INL activity. (3) The implicit time of the b-wave can provide a measure of receptor sensitivity.

Full-field electroretinograms in patients with the carbohydrate-deficient glycoprotein syndrome

We examined five patients who had carbohydrate-deficient glycoprotein syndrome with full-field electroretinograms. Only two of the patients showed fundus changes typical for retinitis pigmentosa, whereas abnormal electroretinograms were seen in all patients. There was no recordable rod response; however, a delay in the cone b-wave implicit time was noted. All patients had nyctalopia. These observations suggest that patients with the carbohydrate-deficient glycoprotein syndrome have a progressive tapetoretinal degenerative disorder of the retinitis pigmentosa type with defined alterations in the electroretinogram.

Electroretinographic assessment of background adaptation in 10-week-old human infants

Full field, scotopic b-wave stimulus/response functions of 10-week-old infants and adults were measured in the dark-adapted condition, and in the presence of steady backgrounds. Dark adapted b-wave sensitivity (log sigma) differed significantly between infants and adults; the median dark adapted sensitivity of infants was 0.50 log unit less than that of adults. The median eigengraus of infants (-1.32 log scot. td) and adults (-1.55 log scot. td) did not differ significantly. The median slope of the linear portion of the background adaptation function was about 0.9 for infants and adults. These results argue for post-receptoral immaturities, but do not rule out receptoral immaturities.

Temporal summation in dark-adapted 10-week old infants

The effect of stimulus duration on the b-wave and psychophysical responses of dark-adapted 10-week-old infants and adult control subjects is reported. Both infant and adult b-wave sensitivities vary with stimulus duration, show summation for brief duration stimuli, critical durations estimated at 88-155 msec, and little variation in sensitivity for longer durations. There are however, substantial differences between the infant and adult psychophysical temporal summation functions. The infant function is described by a straight line, slope about -0.5, across all flash durations while adults show summation at durations less than 100 msec and critical durations of 136 to 151 msec. Adult, but not infant, b-wave integration times and b-wave rise and fall times show duration-dependent changes. Thus, both ERG and psychophysical measures demonstrate immaturities in the rod mediated function of the infant retina.

A quantitative measure of the electrical activity of human rod photoreceptors using electroretinography

An electrical potential recorded from the cornea, the a-wave of the ERG, is evaluated as a measure of human photoreceptor activity by comparing its behavior to a model derived from in vitro recordings from rod photoreceptors. The leading edge of the ERG exhibits both the linear and nonlinear behavior predicted by this model. The capability for recording the electrical activity of human photoreceptors in vivo opens new avenues for assessing normal and abnormal receptor activity in humans. Furthermore, the quantitative model of the receptor response can be used to isolate the inner retinal contribution, Granit's PII, to the gross ERG. Based on this analysis, the practice of using the trough-to-peak amplitude of the b-wave as a proxy for the amplitude of the inner nuclear layer activity is evaluated.

Development of visual sensitivity to light and color vision in human infants: a critical review

The recent literature on test threshold and color vision in human infants is critically reviewed. Test thresholds are higher in infants than in adults at the absolute threshold and at all adapting luminances, but approach adult values rapidly over the first six months of life. The spectral luminous efficiency function of infants is similar to V(lambda) above 1.0 log phot. cd/m2. For lights below about 1.0 log scot. cd/m2 and wavelengths shorter than 590 nm, the luminous efficiency function is similar to V'(lambda). The luminous efficiency of any given stimulus may differ markedly between infants and adults, especially when the adult data depend on the temporal and spatial parameters of the stimuli. Color vision improves greatly over the first three postnatal months, and most normal 3-month olds have at least some color vision. The overall insensitivity of infants to contrast is likely to provide a satisfactory explanation of the poor color vision of infants. The critical immaturity primarily responsible for the high thresholds and poor color vision of infants is probably after the site of visual adaptation, although lower-level factors may also play a role.

Electrophysiologic testing techniques for children

This practical article for clinical electrophysiologists discusses the evaluation of infant and child patients' visual systems using electroretinographic (ERG), electrooculographic (EOG), and visually evoked potential (VEP) techniques. These techniques not only help to secure specific diagnoses, but by systematic assessment of function along the visual pathways can also localize dysfunction underlying visual deficits of pediatric patients. Among children, development as well as disease can affect electrophysiological parameters. Therefore diagnosis of normal or abnormal depends critically on an adequate description of normal responses for age. Procedures that the authors have found feasible, reliable, and valid are summarized. Standardization of pediatric testing appears to be an important next step. The power of ERG, EOG and VEP recordings to demonstrate the neurophysiological basis for pediatric visual impairment is predicted to stimulate further research in this area.

Visual acuities and dark-adapted thresholds of children with Bardet-Biedl syndrome

We studied the visual acuities and dark-adapted sensitivities of 12 children with Bardet-Biedl syndrome. All except one child, who was seen only once, were tested serially. In the first decade of life, all visual acuities were within 2 octaves of normal. All but two final visual acuities obtained from patients in their second and third decades were more than 2 octaves poorer than normal. Dark-adapted sensitivities of all patients were, or became, significantly less than normal even in those patients whose period of follow-up was limited to the first decade of life. Of the 11 patients measured serially, seven showed decreases in dark-adapted sensitivities of at least 0.5 log unit during the follow-up period, and the last measured sensitivities of all patients were at least 2 log units less than the normal mean.

The electroretinogram in preterm infants

With the hope that the electroretinogram (ERG) in preterm infants could help clarify their vitamin A requirements, a technique for recording the full-field ERG in the neonate is described. One hundred seventy-seven ERGs were performed in 59 preterm and 52 term infants. An ERG was recorded as soon as 7 hours after birth and as early as 30 weeks after conception. In preterm infants the a-wave latency was longer and the amplitude less than in term infants of the same age. The amplitude of the ERG in preterm infants increased with the duration of light exposure. Longitudinal data on 15 preterm infants showed a reduction in a-wave latency. None of the ERG findings correlated with postconceptional age, which suggests that the duration of light exposure is a major determinant of the ERG pattern in preterm infants. Despite low circulating levels of retinol, no correlations with any of the ERG values were found.

The development of scotopic retinal function in human infants

Scotopic retinal function undergoes age-related changes early in human infancy. Electroretinographic psychophysical, and pupillographic responses have been used in the study of normal development. Various components of the electroretinographic responses index distal and proximal retinal function. Changes in pupillary diameter, measurable in infants under carefully selected conditions, represent rhodopsin regeneration in the infants under carefully selected conditions, represent rhodopsin regeneration in the photoreceptor outer segment. From psychophysical data, inferences can be drawn about scotopic retinal control of visual performance. These data constrain theories about the determinants of sensitivity, about the flow of signals from the distal, rhodopsin-bearing, outer segments to the proximal retina, and about modulations of straight-through flow by feedback or inhibitory circuits. The results indicate that the post natal development of human scotopic function is due mainly to reorganization of processes central to the photoreceptors.

The relation of rhodopsin and scotopic retinal sensitivity in sector retinitis pigmentosa

We used reflection retinal densitometric, psychophysical, and electroretinographic techniques to study the scotopic retinal function of a mother and her three daughters who had clinical evidence of a sectoral type of retinitis pigmentosa. Retinal regions with, and those without, ophthalmoscopic signs of degeneration were investigated. During dark adaptation, the time courses of rhodopsin regeneration and recovery of scotopic sensitivity were similar to normal as was the relation of rhodopsin to scotopic threshold. In dark-adapted eyes, threshold increases were not proportional to rhodopsin loss. The results of psychophysical tests of background adaptation and temporal summation, and analysis of the relation of electroretinographic a- to b-wave amplitudes, led to the conclusion that abnormalities of photoreceptor cell function central to the rhodopsin-bearing outer segments accounted for the increased thresholds.

Special diagnostic and therapeutic modalities in pediatric ophthalmology

Ophthalmology is a specialty rich in instrumentation used for special diagnostic and therapeutic functions. Many of these special modalities are appropriate to pediatric ophthalmology, and this article discusses them in summary fashion for those who may wish to know about the procedures but who may not be involved directly in their use.

The relation of rhodopsin and scotopic sensitivity in choroideremia

We examined two patients who had clinical characteristics typical of choroideremia using psychophysical and reflection retinal densitometric techniques. In the dark-adapted state, sensitivity was more compromised than would be predicted on the basis of the modest losses of rhodopsin. In the dark-adapted state, studies of spatial and temporal summation suggested that postreceptoral processes are similar to normal. The kinetics of rhodopsin regeneration after bleaching exposures were abnormal in some retinal regions.

Oscillatory potentials of visually inattentive children

The oscillatory potentials (OPs) are probably generated in the proximal retina. The OPs of 20 visually inattentive infants and children were recorded. All 20 had evidence of abnormalities of the visual parts of the brain. The a- and b-waves, indices of distal retinal function, were normal in 10 patients, abnormal in the other 10. Among the patients with abnormal, attenuated a- and b-waves, OP amplitudes were more attenuated than among those with normal a- and b-waves. However, the timing of the OP wavelets was not correlated with distal retinal activity. These results suggest that in humans OP amplitude may be determined by inputs from the distal retina, but OP latency and periodicity are governed by processes within the proximal retina.

The relationship of retinal sensitivity and rhodopsin in human infants

During dark adaptation after full field, greater than or equal to 90% bleaches recovery of sensitivity and regeneration of rhodopsin were studied using electroretinographic and pupillographic techniques in both 10-week-old infants and adults. The courses of scotopic sensitivity recovery and rhodopsin regeneration of infants and adults were similar and were reasonably well fit by single exponentials having tau = 400 sec. For both infants and adults log scotopic sensitivity was linearly related to the proportion of rhodopsin present during dark adaptation. It is concluded that by age 10 weeks human distal retinal processes that occur after photolysis are equivalent to those of adults.

Background adaptation in human infants

Human infants' thresholds for detecting 10 degrees diameter 50 and 1000 msec stimuli in the dark adapted condition and in the presence of steady red backgrounds were determined using a preferential looking method. Dark adapted sensitivity and the slope of the linear portion of the increment threshold function increased with age. The slope was 0.5 at 4 weeks, but by 10 weeks it was not different from the adult value (approximately 1.0). At all ages the eigengrau was approximately the same as that of adults (-2.3 log scot. td). These results suggest that visual mechanisms involved in detection of flashes and adaptation to steady background lights mature postnatally.