Scotopic b-wave stimulus/response (S/R) functions are abnormal in several human retinal degenerative disorders. However, the mechanisms by which diseases affect the S/R parameters are not yet fully known. Three experiments were done to simulate functional pathologies known to occur in retinal degenerations: 1) attenuated sensitivity of retinal units, 2) loss of rhodopsin, 3) loss of sensitivity with little or no loss of rhodopsin. None of the experimental perturbations of normal function replicated the pattern of S/R abnormalities caused by retinal degenerations. Thus, in the retinal degenerative disorders intrinsic abnormalities of cellular processing must affect the organization of distal retinal function indexed by the b-wave.

Adult↗

PubMedDate not supplied

Electroretinogram responses and refractive errors in patients with a history of retinopathy prematurity.

Ametropias, particularly myopia, and mild retinal dysfunction are found in eyes with a history of retinopathy of prematurity. The retina is an important controller of refractive development. The aims of this study were to find out whether altered measures of retinal function and ametropias are associated and to consider mechanisms by which the retina might control refractive development. Nine infants and children with a history of stage 1, 2 or 3 retinopathy of prematurity and known courses of refractive development were studied. Spherical equivalents at the time of the electroretinogram ranged from +5.50 to -9.00 diopters. Rod photoresponse characteristics were derived from the a-wave, and postreceptoral components were also analyzed with calculation of the sensitivity and saturated amplitude of the b-wave, the sensitivity of oscillatory wavelet OP2, and average amplitudes of OP3 and OP4. In hyperopic and myopic patients alike, the saturated amplitude and gain of the rod cell response were attenuated. In all patients, b-wave sensitivity was low, but in most there was little effect on saturated b-wave amplitude. In patients with courses toward myopia, the amplitude of OP4, an 'OFF' signal, is relatively more attenuated than that of OP3, an 'ON' signal. OP4 is relatively larger in patients with courses toward hyperopia. The OP results suggest that an imbalance of 'ON' and 'OFF' activity in the retina is associated with development of ametropias in retinopathy of prematurity.

Child↗

PubMedDate not supplied

Measuring visual acuity in infants.

This paper reviews the course of development of visual acuity in human infants and young children. Researchers have devised methods based on optokinetic nystagmus, visually evoked cortical potentials and preferential looking to assess visual acuity in infants and preverbal youngsters. During the first postnatal year and early childhood, acuity, measured by any of these methods, improves with increasing age. Each of these methods, has now been applied to the evaluation of clinical cases. Also presented are the results of a quick and simple test based on preferential looking, which has been incorporated into our clinical evaluation of infants. The data so far indicate that infants with normal eyes pass the test while infants with ocular problems which would interfere with vision fail. For evaluation of large numbers of infants this test appears to have the potential to assist nonspecialized personnel in the early identification of ophthalmic abnormalities.

Age Factors↗

PubMedDate not supplied

The VEP thresholds for full-field stimuli in dark-adapted infants.

Dark-adapted adults' electroretinographic b-wave thresholds are approximately 2 log units below a-wave thresholds and approximately 3 log units above the perceptual threshold, and their perceptual and the visually evoked cortical potential (VEP) thresholds are similar. Dark-adapted infants' scotopic a- and b-wave thresholds for full-field stimuli are both about 0.5 log units above those of adults, but their scotopic VEP thresholds for such stimuli have not been studied. We obtained scotopic VEP thresholds for brief, full-field stimuli from dark-adapted, infants and adults to consider the relationships of the cortical responses to the responses of more distal structures, namely the rod photoreceptors (scotopic a-wave) and ON-bipolars (scotopic b-wave). The median VEP threshold of infants is 0.5 log unit above that of adults. Thus, the relationships of a- and b-wave and VEP thresholds in infants are similar to those in adults. These results are consistent with rod cell immaturities being the primary determinant of the difference between infants' and adults' thresholds.

Adolescent↗

PubMedDate not supplied

Dark-adapted thresholds at 10- and 30-deg eccentricities in 10-week-old infants.

We tested the hypothesis that the dark-adapted sensitivity of the near central retina is lower than that of peripheral retina in 10-week-old infants. A spatial two alternative forced-choice psychophysical method was used to estimate the threshold for 2-deg spots presented 10 deg and 30 deg from the center of a screen. Each 10-week-old infant (n = 11) and adult (n = 5) subject was tested at both eccentricities. Every infant's threshold at 10 deg is higher than that at 30 deg. The median difference between the infants' thresholds at 10 deg and 30 deg is about 0.5 log unit. Whereas the scotopic thresholds of adults at 10 deg and 30 deg are virtually identical, the thresholds of infants' near central retina are higher than those in more peripheral retina. Delayed maturation of the near central rod outer segments with consequent lower quantum catch may be the primary determinant of this infantile sensitivity pattern.

Adolescent↗

PubMedDate not supplied

Rod and rod mediated function in patients with beta-thalassemia major.

An electroretinographic (ERG) study was undertaken to test the hypothesis that scotopic retinal function is altered in transfused thalassemics on chronic Deferoxamine (DFO). ERG a- and b-wave responses and dark adapted visual thresholds were obtained from 11 patients with beta-thalassemia major, ages 7 to 38 (median 17) years. A quantitative model of the activation of phototransduction was fitted to the a-waves to estimate the gain of the transduction processes and the saturated amplitude of the rod photoresponse. From b-wave stimulus/response functions. the saturated b-wave amplitude and an index of b-wave sensitivity (log sigma ) were calculated. The patients' data were compared to those of normal subjects. The relations of the ERG parameters to age. average ferritin level, and duration of transfusion without DFO as well as other clinical parameters were examined. Longitudinal measures of b-wave responses and dark adapted visual thresholds. available for nine of the patients, were examined for significant change over time. For all patients both the gain and saturated amplitude of the rod response are normal. In two patients log sigma is below the 99% prediction interval for normal. One has low scotopic visual sensitivity. The duration of transfusion therapy unprotected by DFO chelation therapy was correlated with log a. These results suggest iron accumulation rather than DFO toxicity underlies scotopic dysfunction in older thalassemics. some of whom may have had extended periods of transfusion without the protection of chelation. Thus, monitoring of retinal function is recommended in such patients.

Adolescent↗

PubMedDate not supplied

Preferential looking vision testing: application to evaluation of high-risk, prematurely born infants and children.

We studied the application of preferential looking (PL) procedures to evaluation of visual performance of 59 prematurely born infants and young children. Neurological abnormalities were present in 29 of the 59 patients. Ophthalmic examination revealed normal eyes in 20 of the patients; retinopathy of prematurity (20 patients) and strabismus (13 patients) were the most prevalent ophthalmological disorders; the remaining 6 patients had a variety of ophthalmic anomalies. Results indicate that PL testing of such patients is best accomplished after age 2 months. Patients with developmental delays can be tested, but they may have poor PL performance that is not accounted for by ophthalmic abnormalities. Differences in PL acuities between right and left eyes were indicative of amblyopia in some of the strabismic patients; sequential PL acuities monitored occlusion therapy in these pre-verbal youngsters.

Birth Weight↗

PubMedDate not supplied

Electroretinography: application to clinical studies of infants.

The electroretinographic (ERG) responses of normal human infants have been studied in scotopic conditions. The relation of stimulus intensity to the amplitude of the b-wave of the ERG undergoes developmental changes during infancy. The maximum amplitude that can be obtained gradually increases to approach adult values by age 12 months. Sensitivity, however, is equivalent to that of adults at age five to six months. Latencies reach adult values at the end of the first year. Some results of ERG testing of infant patients with retinal disorders are compared to the normal results. As previously reported for animals and human adults with retinal disorders, amplitude, sensitivity and latency are not always equally compromised by the retinal diseases of infants.

Child Development↗