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M C Flom

Publications and source records attributed to M C Flom.

At least 19 recordsLinked to original sources
PubMed1990

Fixational drift and nasal-temporal pursuit asymmetries in strabismic amblyopes.

This study evaluated to what extent inaccurate and asymmetric smooth pursuit in strabismic amblyopic eyes is attributable to abnormally high-velocity eye drifts that these eyes exhibit during monocular fixation. Smooth pursuit gains (peak eye velocity/peak target velocity) were determined in the amblyopic and nonamblyopic eyes of 11 strabismics for nasalward and temporalward motion; the target oscillated across 6 degrees of the horizontal meridian at frequencies ranging from 0.0625 to 1 Hz. In general, pursuit gains were higher for nasalward than temporalward motion, for both amblyopic and nonamblyopic eyes. Correction for each eye's mean velocity of fixational drift eliminated this nasal-temporal pursuit asymmetry for most of the nonamblyopic eyes, but not for the amblyopic eyes. Compared to the nonamblyopic eyes, corrected pursuit gains of the amblyopic eyes averaged about 0.2 lower nasalward and about 0.4 lower temporalward, but substantial variation occurred among individuals. We suggest that the overall reduction of pursuit gain in strabismic amblyopic eyes (after correction is made for fixational drift bias) stems from the use of a nonfoveal (eccentric fixation) locus for tracking; the further reduction of temporalward gain may result from a nasal-temporal asymmetry in processing motion signals.

Adult↗
PubMed1988

Does impaired contrast sensitivity explain the spatial uncertainty of amblyopes?

We investigated the possibility that the spatial imprecision of amblyopic eyes can be accounted for by the relative insensitivity to contrast that has been documented for these eyes. Thresholds for the discrimination of spatial misalignment, a measure of spatial uncertainty, were determined for three amblyopes and one normal for targets ranging in contrast from detection threshold to 99%. We found that spatial uncertainty was greater in amblyopic eyes than non-amblyopic eyes for targets equally above contrast threshold, and when the targets were presented at threshold contrast to the nonamblyopic eyes and at 99% contrast to the amblyopic eyes. Our results fail to support the possibility that the spatial imprecision of amblyopic eyes can, in general, be attributed to reduced contrast sensitivity. Different neural abnormalities are presumed to limit amblyopes' performance on different spatial tasks.

Amblyopia↗
PubMed1987

Effects of luminance on the visual acuity of strabismic and anisometropic amblyopes and optically blurred normals.

Evidence is accumulating to suggest fundamental differences between strabismic and anisometropic amblyopia. We explored differences in these amblyopes by assessing the effects of luminance on optotype acuity, using targets that ranged from photopic to low mesopic levels. Our results show that reducing luminance has less of a detrimental effect on the acuity of strabismic than anisometropic amblyopic eyes. Furthermore, the effect of decreasing luminance on the acuity of optically blurred normal eyes mimicked the effect we found for anisometropic amblyopic eyes. These results are consistent with the hypothesis that the fundamental deficit in anisometropic amblyopia is impaired resolution while in strabismic amblyopia the fundamental deficit is impaired spatial directionalization.

Amblyopia↗
PubMed1985

Bilateral oculomotor abnormalities in strabismic amblyopes: evidence for a common central mechanism.

The preferred eyes of strabismic amblyopes, generally presumed to be normal, have been implicated by recent studies as manifesting oculomotor abnormalities. We sought to determine whether these motor abnormalities occurred together and, if so, whether they could be related to a single underlying deficit. Occurring together in the preferred eyes of our strabismic amblyopes were: unsteady fixation (consisting of nasal drifts alternating with temporal saccades), minute fixational eccentricity (as indicated by eccentric directionalization of the Maxwell spot) and asymmetries of pursuit tracking. These motor abnormalities of the preferred eye are attributable to the presence of high-velocity nasal drifts. Since nasal drifts also account for several qualitatively similar motor abnormalities exhibited under monocular conditions by the fellow amblyopic eye, we conclude that a centrally-generated nasal drift bias is responsible for anomalous oculomotor behaviors of both eyes of strabismic amblyopes.

Amblyopia↗
PubMed1985

Identifying amblyopia using associated conditions, acuity, and nonacuity features.

Reduced visual acuity is the most notable feature of functional amblyopia--so much so that it is common to think that it is the only, main, or even the fundamental defect. To identify all amblyopic eyes by acuity alone would require an acuity criterion of 6/6 (20/20) or somewhat better acuity--a criterion that would necessarily include more normal than amblyopic eyes. The association of amblyopia with strabismus and anisometropia is sufficiently specific to make these two nonacuity features useful in identifying amblyopia. The diagnosis of amblyopia derives from a syndrome of features, most of which are nonacuity features. Two recently quantified nonacuity features--spatial uncertainty and distortion--are not only clinically useful but they may be the fundamental defects in strabismic amblyopia, with impaired resolution being fundamental in anisometropic amblyopia.

Amblyopia↗
PubMed1985

Spatial aberrations and acuity in strabismus and amblyopia.

Spatial uncertainty and distortion were quantified from judgement of the horizontal position of a flashed 0.5 deg vertical line with respect to a flanking reference target in strabismics with and without reduced acuity. Spatial uncertainty was outside the range of 30 normal eyes in all of 23 strabismic amblyopic eyes (visual acuity = 20/40 or worse) and in 20 of 22 squinting eyes with 20/30 or better acuity. Abnormal spatial distortion was found in 16 amblyopic and 10 squinting eyes. In the deviated eyes of the strabismics, the extent of spatial uncertainty and distortion correlated with visual acuity. Spatial aberrations were not accounted for by strabismics' unsteady or eccentric fixation, nor were they mimicked in normal eyes when visual acuity was artifically reduced. The authors suggest that spatial uncertainty and distortion represent the primary abnormalities in strabismics and produce deficits of visual acuity according to their severity.

Amblyopia↗
PubMed1983

Normal and abnormal space perception.

The mononuclear spatial judgments made by normal adults are quite accurate and precise. Although relatively little is known about how the spatial sense develops, it is likely that it can be compromised by abnormal visual experience as provided, for example, by strabismus. Previously, we reported that the spatial sense of strabismic amblyopic eyes is distorted, having quantified these distortions as marked inaccuracies in equating spatial extents in the nasal and temporal field and specifying when one target is vertically aligned with another. Distortions--localized "expansions" and "compressions" of spatial values and "bending" of direction lines--characterize the amblyopic eyes of strabismics but not non-squinting anisometropes. Thus, according to our previously published hypothesis, spatial distortions can account for the reduced acuity and abnormal oculomotor behavior of strabismic (but not anisometropic) amblyopic eyes. In the present paper, we provide quantification of another spatial measures--spatial precision--and show that extensive imprecision characterizes the space sense of the strabismic amblyopic eye. We now add spatial imprecision to our original hypothesis as a significant element in accounting for the abnormal sensory and motor behaviors of strabismic amblyopic eyes.

Adolescent↗
PubMed1981

Monocular spatial distortion in strabismic amblyopia.

We examined monocular spatial vision of strabismic amblyopes by measuring errors of relative directionalization (specifying whether or not two targets are in vertical alignment) and partitioning (equating left- and right-field spaces). Abnormally large errors were made when fixation occurred with the amblyopic eye; these errors did not attributable to reduced acuity, unsteady fixation, or eccentric fixation. From the results we infer that monocular space perception of strabismic amblyopic eyes is severely distorted and is characterized by "bending" of vertical lines of direction and by local "compressions" and "expansions" of horizontal spatial values. Such distortions can readily account for many of the oculomotor abnormalities of the amblyopic eye as well as for the strabismic subject's phenomenological description of the difficulties experienced in using this eye--difficulties that are typically much worse than the reduced acuity would predict.

Amblyopia↗
PubMed1980

Corresponding and disparate retinal points in normal and anomalous correspondence.

Fusional (disparity) vergence requires that the ocular images fall on noncorresponding (disparate) retinal points. Study of the distribution of corresponding retinal points is accomplished by analyzing the locus of object points in space that are seen either singly or in the same direction for each eye. This locus, a horopter, is easily determined for persons with binocular fixation but requires a special tangent plane apparatus (which is described) for persons with strabismus. The identical visual direction horopter for the intermittent exotrope under conditions of bifixation passes through the fixation point and curves sharply toward the eyes, a phenomenon that may produce disparity conflicts between the central and peripheral fields. For squinters with normal anomalous correspondence (where the two foveas correspond), the horopter passes through the intersection of the visual axes, for squinters with anomalous correspondence, it does not; instead, it courses through the space between the visual axes, which indicates correspondence between opposite occipital hemispheres. Additionally, these horopters exhibit a localized central convexity toward the eyes (a notch) that implies correspondence being less anomalous centrally than peripherally. In validating the presence of this horopter notch, a three-light test was developed. Irregular fusional vergence movements of squinters may be attributed in part to their irregular horopters.

Esotropia↗
PubMed1980

Control of unsteady, eccentric fixation in amblyopic eyes by auditory feedback of eye position.

A technique for providing amblyopes with auditory feedback signals of eye position errors is described. With auditory cues, 12 adult eccentrically fixing amblyopes with strabismus and/or anisometropia have been able to maintain steady and foveal fixation with the amblyopic eye. The changes observed in fixation patterns with auditory feedback were both quantitative and qualitative; with such feedback, amblyopes often exhibited sequences of normal-appearing fixation. Some of our subjects have been successful in maintaining steady foveal fixation for short periods of time after feedback is turned off, apparently using visual error signals. For two subjects, feedback also promoted major improvements in smooth tracking performance. We conclude that the use of auditory feedback of eye position has significant value for basic studies of the mechanisms underlying amblyopia and potentially for the clinical treatment of this condition.

Acoustic Stimulation↗
PubMed1978

Marijuana, alcohol, and combined drug effects on the time course of glare recovery.

The time course of light adaptation after intense light exposure is significantly delayed by alcohol, marijuana, and a combined dose of alcohol and marijuana. These effects were found in a double blind experiment, using 10 subjects. The experimental treatments were placebo, 0.75 ml/kg of 95% ethanol, 8 and 15 mg of delta9 tetrahydrocannabinol (THC). and 0.75 ml/kg of 95% ethanol together with 15 mg of THC. The marijuana-induced delay in recovery is doserelated. Both drugs produce delayed recovery for at least 2 h after drug ingestion. The combined alcohol and marijuana treatment produces little more than the effect produced by either drug alone, suggesting some antagonism between the drugs--a suggestion supported by a significantly lower blood alcohol level for the alcohol dose when combined with marijuana than when taken alone.

Adaptation, Ocular↗
PubMed1978

Visual acuity at different retinal loci of eccentrically fixating functional amblyopes.

Visual acuity was measured in eccentrically fixating amblyopic subjects to determine the contribution of sensory (inhibitory) and motor (retinal-locus) components of the acuity loss. A unique aspect of this research involved the subjects' use of auditory feedback to control their unsteady and eccentric fixation while responding to flashed (800 msec) or continuously presented targets at various eccentricities in the visual field. All 4 amblyopic eyes had maximum visual acuity at the fovea; from there, the acuity declined approximately symmetrically into the nasal and temporal periphery. Foveal acuity for these amblyopic eyes was depressed from the acuity at the fovea of the normal eye. We conclude that Worth's explanation of eccentric fixation (eccentric fixation develops in an attempt by the amblyopic eye to fixate with a peripheral retinal locus having higher acuity than the fovea) cannot apply to our amblyopes. The acuity losses exhibited by the amblyopic eyes studied have a sensory (inhibition) component and a motor (retinal-locus) component, the sensory component being greater for small degrees of eccentric fixation and the motor component being greater for large amounts of eccentric fixation.

Acoustic Stimulation↗