The electroretinogram in strabismic amblyopia

Summary Neither the studies reported in the literature nor the studies presented in this paper have given evidence of significant or reliable differences in electrical response between the amblyopic and the normal fellow eye. There either are, in fact, no differences, or our technical means are inadequate to uncover them. However, only electrophysiologic studies would seem to be capable of deciding the question whether the retina is or is not involved in the mechanism under-lying amblyopia. It would seem, therefore, worthwhile to attempt further refinements in technique to seek a definitive answer.

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Zusammenfassung Ein zuverl?ssiger Unterschied zwischen dem normalen und dem amblyopischen Auge in Hinsicht auf ihre elektrische Reizbeantwortung konnte in der hier berichteten Untersuchung nicht gefunden werden, noch ergibt sich ein solcher Unterschied aus der diesbezüglichen Literatur. Dies bedeutet entweder, da? Unterschiede tats?chlich nicht bestehen, oder da? wir nicht im Stande sind, sie mit den uns zur Verfügung stehenden Methoden aufzudecken. Die Frage der Mitbeteiligung der Retina an den der Amblyopie zu Grunde liegenden Prozessen kann aber im Prinzip nur durch objektive, elektrophysiologische Methoden gel?st werden. Es ist daher angezeigt, weitere Verfeinerungen der Untersuchungstechnik anzustreben, um die referierten Resultate zu sichern.

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Résumé Ni les travaux rapportés dans la littérature, ni les travaux présentés ici ne mettent en évidence des différences significatives ou valables dans la réponse électrique entre l'oeil amblyope et son congénère normal. Ou bien il n'y a vraiment pas de différences, ou bien nos moyens techniques sont inadéquats à les découvrir. Cependant, seuls des examens électrophysiologiques semblent susceptibles de trancher la question: la rétine est-elle impliquée ou non dans le mécanisme qui est à la base de l'amblyopie? Il semble donc qu'il vaille la peine de rechercher des perfectionnements plus poussés dans la technique pour obtenir une réponse décisive.

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From the ERG laboratory of the Department of Ophthalmology and the Neurosensory Center (Paper No. 78) of the College of Medicine of the University of Iowa. The work of the ERG laboratory is supported by Grant No. B-349; the Neurosensory Center, by Program Project Grant B-3354 of the National Institute of Neurologic Diseases and Blindness, National Institutes of Health, Bethesda, Maryland.     

Image segregation in strabismic amblyopia

Humans with naturally occurring amblyopia show deficits thought to involve mechanisms downstream of V1. These include excessive crowding, abnormal global image processing, spatial sampling and symmetry detection and undercounting. Several recent studies suggest that humans with naturally occurring amblyopia show deficits in global image segregation. The current experiments were designed to study figure-ground segregation in amblyopic observers with documented deficits in crowding, symmetry detection, spatial sampling and counting, using similar stimuli. Observers had to discriminate the orientation of a figure (an "E"-like pattern made up of 17 horizontal Gabor patches), embedded in a 7x7 array of Gabor patches. When the 32 "background" patches are vertical, the "E" pops-out, due to segregation by orientation and performance is perfect; however, if the background patches are all, or mostly horizontal, the "E" is camouflaged, and performance is random. Using a method of constant stimuli, we varied the number of "background" patches that were vertical and measured the probability of correct discrimination of the global orientation of the E (up/down/left/right). Surprisingly, amblyopes who showed strong crowding and deficits in symmetry detection and counting, perform normally or very nearly so in this segregation task. I therefore conclude that these deficits are not a consequence of abnormal segregation of figure from background.     

Atropine occlusion in the treatment of strabismic amblyopia and its effect upon the non-amblyopic eye

A total of 189 cases with amblyopia, where atropine sulphate 1% had been used as a method fo unilateral occlusion, were reviewed. The results show that after atropine had been appropriately applied, permanent reversal of amblyopia is rare, and unwanted side-effects are few and of minor nature. Pupil size, light reflex and accommodation of the atropinized eye appear to be unaffected. The angle of squint was unaffected and fixation of the amblyopic eye either remained unchanged or shifted to a more central point.     

Temporal instability in the perception of strabismic amblyopia

Amblyopia is a developmental disorder of spatial vision resulting from an abnormal visual stimulation in early childhood. The aim of our study was to investigate the spatial and temporal distortions that occur in strabismic and anisometropic amblyopic vision. The main focus was on the temporal instability of amblyopic perception of low and high spatial frequencies. Our results indicate that temporal instability is perceived mainly by strabismic and strabismic-anisometropic amblyopes and occurs only at high spatial frequencies. We found two categories of temporal distortions in high spatial frequency patterns: a) the whole pattern is perceived as jittering, b) single lines or parts in a pattern are perceived as moving. Our data suggest that strabismus, in addition to amblyopia, is needed to elicit significant temporal distortions.     

斜视性弱视发病机制的研究进展

随着脑科学的蓬勃发展,弱视神经机制的研究进入到一个崭新阶段。研究证实:发育早期异常视觉经验可影响皮层神经元的空间特性,弱视视功能损害涉及多个脑区并与皮层神经元空间特性的异常密切相关,弱视是视觉神经通路多方位、多层次损害的综合。在此我们对斜视性弱视发病机制的研究进展作一综述。     

Orientation-based texture segmentation in strabismic amblyopia.

Texture segmentation of 'target' Gabors from an array of 'background' Gabors was measured in terms of the difference in orientation between the two regions, as well as the difference in orientation within each region. Segmentation was shown to occur on the basis of local orientation differences at the boundary between the target and background regions (Nothdurft, H.C. (1992). Feature analysis and the role of similarity in preattentive vision. Perception and Psychophysics, 52, 355-375.). We obtained similar results for both the amblyopic and non-amblyopic eye of three strabismic amblyopes, and showed also that the effects of texture undersampling and positional jitter were similar for the two eyes. This pattern of results is consistent with intact mechanisms of texture perception in amblyopic cortex, and suggests also that any amblyopic deficits in first-order cortical units (undersampling and/or positional uncertainty) do not limit higher-order texture segmentation processes. Therefore, first- and second-order processes involved in perceptual grouping of oriented elements (that appear to be abnormal in amblyopic cortex; Kovács, I., Polat, U., Norcia, A.M. (1996). Breakdown of binding mechanisms in amblyopia. Association for Research in Vision and Ophthalmology Abstracts; Mussap, A.J., Levi, D.M. (1995). Amblyopic deficits in perception of second-order orientation. Investigative Ophthalmology and Visual Science (Supplement), 36, S634; Mussap, A.J., Levi, D.M. (1998). Amblyopic deficits in perceptual grouping. Vision Research, submitted) do not contribute to texture perception based on orientation contrast.     

Two-dimensional spatial distortions in human strabismic amblyopia

Two-dimensional space perception was measured in the central visual field of amblyopic subjects under special consideration of spatial distortions and spatial uncertainty. The subjects had to construct circles with different radii around a given fixation point. Subjects with deep strabismic amblyopia were showed to exhibit considerable distortion in the amblyopic eye. Each subject exhibited an individual distortion pattern. The dominant eye showed distortions similar to those seen in normal observers. Subjects with mild strabismic amblyopia, strabismic alternators and anisometropic amblyopes did not exhibit any significant spatial distortions. Data from dichoptic localization experiments indicate that anomalous retinal correspondence might contribute to monocular spatial distortions.     

Epidemiologic study of strabismic amblyopia in Tunisia

The authors study 202 strabismus cases and evaluate the strabismic epidemiology of Tunisia: 58% of squint children have amblyopia. The low vision is important, and getting worse with age. The treatment is simple, consisting of occlusion of the good eye, but it become longer and more difficult after six years. The best results are obtained in the first four years. Good cooperation from the parents is required. The authors insist on the necessity of early detection through testing, the prevention of recurrence and, above all, on preventing the advent of amblyopia as soon as strabismus appears.