Search PubMed⌕ Search

Biomedical subjects

C Schor

Publications and source records attributed to C Schor.

35 records · Page 2Linked to original sources
PubMed1986

Combined effects of spatial frequency and retinal eccentricity upon fixation disparity.

The variations in fixation disparity (FD) with spatial frequency and retinal locus of fusion locks were examined in two groups of subjects having either steep or flat forced-duction FD curves. FD for subjects with flat curves was unaffected by either spatial frequency or diameter of fusion locks. FD of observers with steep forced-duction curves increased with both the coarseness and eccentricity of fusion locks. Panum's horizontal fusion range increased markedly with target spatial period but only modestly with retinal eccentricity. These results indicate that factors other than the dimensions of Panum's fusional area (PFA) result in the increase of FD found in some observers with peripheral fusion locks.

Convergence, Ocular↗
PubMed1984

Binocular sensory fusion is limited by spatial resolution.

Binocular sensory fusion which was previously thought to have a maximum spatial extent at the fovea of 1 deg is at least 600% larger when stimulated by low spatial frequency (coarse) detail. This upper limit for sensory fusion has a constant phase disparity limit of 90 deg which corresponds to the monocular Rayleigh criterion for spatial resolution of two diffraction patterns. At low spatial frequencies the sensory fusion limit equals the upper disparity limit for stereoscopic depth perception which suggests that a common mechanism underlies these two phenomena.

Depth Perception↗
PubMed1983

Spatial characteristics of static and dynamic stereoacuity in strabismus.

The spatial and temporal organization of stereoscopic depth perception were compared in normal and strabismic observers. The minimum and maximum disparities for stimulating static and dynamic stereopsis in strabismus were examined as a function of spatial separation of disparate stimuli. Disparities and their spacing were produced by spatial modulation of two vertical lines viewed haploscopically. Most strabismics had normal upper disparity limits but elevated static and dynamic stereothresholds. Moderate stereothreshold elevations (100 arc sec) were constant for spatial separations greater than 15 arc min. Two new types of spatial crowding effects upon stereopsis were observed. The first type resulted from the constant elevation of the disparity threshold. The second type consisted of a reduced maximum disparity limit for stereopsis. In both cases, the constriction of the range of perceivable depth produced a reduction in the spatial and temporal frequency limits for depth perception. Clinical tests of stereoacuity that crowd stimuli closer than 0.25 degree underestimated the strabismic patients' potential stereoacuities by a factor of 2 to 4. Similarly, tests of dynamic stereopsis that use temporal frequencies greater than 1 Hz will underestimate optimal dynamic stereoacuity.

Depth Perception↗
PubMed1983

Rotating grating treatment of amblyopia with and without eccentric fixation.

Treatment of amblyopia with and without eccentric fixation using short term occlusion and rotating gratings was analyzed in a controlled study. A control group (n = 18) viewed a blank rotating disc for 15 minutes once a week for ten weeks while the treatment group (n = 20) observed rotating gratings for the same time period. Both groups performed visually guided tasks to maintain treatment interest. Visual acuity was analyzed before and after each treatment session using a multiple Landolt ring chart. Data were gathered in a double masked manner. Analysis did not reveal a statistically significant improvement of visual acuity with rotating grating therapy for treating amblyopia with or without eccentric fixation.

Adolescent↗
PubMed1982

Oculomotor functions in reading disability.

Oculomotor functions and information processing systems from a complex interaction in the achievement of reading skills, This study was designed to determine the relation between oculomotor functions and reading ability in fourth and sixth grade children. Four oculomotor functions were measured during the reading of digits and prose. The oculomotor functions were used independently and collectively to predict reading ability under both reading conditions. These relations were then examined with and without removal of the influence of verbal intelligence. The results indicate that when examined collectively, oculomotor functions are related to reading ability, but when oculomotor functions are examined independently, only marginally significant relations appear. Similar relations were found for both age groups. Verbal intelligence influenced some of the individual relations. The individual oculomotor functions that appeared responsible for the collective relation were frequency of fixations and lag of accommodation. A reciprocal-causation model between reading ability and oculomotor functions is proposed.

Accommodation, Ocular↗
PubMed1981

The use of rotating gratings for the treatment of amblyopia: a clinical trial.

The use of rotating gratings for the treatment of amblyopia was subjected to a controlled clinical trial. A treatment group (N = 19) observed rotating gratings for 15 min per week for 10 weeks and a control group (N = 19) observed a blank rotating disk for the same period. Both groups of amblyopes performed visually guided tasks to maintain their interest during treatment. Data were acquired in a double-masked manner. A second control group (N = 4) underwent weekly acuity evaluation without any form of treatment. Visual acuity was evaluated before and after each session and analyzed with a linear regression fit to a probit transform by a minicomputer. By using a criterion change in acuity of 10% Snell Sterling, we found no significant change of acuity in any group or between groups. These results demonstrate that rotating gratings are an insignificant variable in the treatment of amblyopia.

Adolescent↗
PubMed1980

Introduction to the Symposium on Basic and Clinical Aspects of Vergence Eye Movements.

The basic aspects of vergence eye movements revolve about a central theme of a critique of the Maddox classification. Topics include interactions between accommodation and convergence in the absence of visual stimuli, dynamic properties of accommodative and fusional vergence, interactions between vergence eye movements and other visual motor systems, violations of Hering's law associated with specific components of vergence, and sources of fixation disparity. The clinical reports examine the effectiveness of disparate and accommodative stimuli for driving vergence eye movements in strabismus with normal or anomalous binocular correspondence. Effectiveness of dynamic and static tests of vergence eye movements is compared for detection of general binocular dysfunction. The Symposium is concluded with an open discussion of the basic and clinical reports.

Accommodation, Ocular↗
PubMed1980

Fixation of disparity: a steady state error of disparity-induced vergence.

Fusional vergence eye movements are controlled by a fast-acting mechanism that aligns the eyes in response to retinal image disparity and a slow-acting mechanism that sustains binocular alignment. These two control mechanisms are distinguished by their decay time constants and stimuli. Fast fusional vergence responds to retinal image disparity, and slow fusional vergence responds to the effort or output of the fast control mechanism. Fixation disparity is modeled as a steady-state error of fast fusional vergence. Fixation disparity is shown to be inversely related to prism adaptation, a manifestation of slow fusional vergence, in normal but not abnormal binocular vision. Sensory factors such as interocular suppression influence the magnitude of fixation disparity in strabismus. Clinical implications concerning the relation between fixation disparity and heterophoria in normal and abnormal binocular vision are discussed.

Adaptation, Ocular↗
PubMed1978

Zero retinal image disparity: a stimulus for suppression in small angle strabismus.

Suppression was examined with binocular perimetry in patients with small angle strabismus. Suppression stimuli were presented to the fovea of the fixating eye or 5 degrees nasal or temporal from the fovea. Suppression was found in the deviating eye of patients with normal or anomalous correspondence at retinal points corresponding to the retinal locus of the suppression stimulus. Suppression was demonstrated on both the nasal and temporal hemiretina of the deviating eye. Results indicate that zero retinal disparity is a strong stimulus for suppression in the central and peripheral visual field of patients with small angle strabismus.

Adolescent↗
PubMed1978

Introduction to the symposium on functional amblyopia: sensory or motor disorder?

The theme of the symposium is identified by 2 questions: (1) is the mechanism that underlies functional amblyopia sensory or motor? and (2) How do sensory and motor factors contribute to the loss of acuity in amblyopic eyes? The answers to these questions as well as to several questions about clinical diagnosis and treatment of amblyopia are provided in the following 7 papers and panel discussion that comprise this symposium.

Amblyopia↗
PubMed1978

A motor theory for monocular eccentric fixation of amblyopic eyes.

A motor theory is proposed to explain monocular eccentric fixation of amblyopic eyes. Clinical observations that suggest the involvement of a motor anomaly related to strabismus are cited. The model proposes that potentiation (after discharge) of the agonist muscle in strabismus results in a nonregistered error of monocular fixation of the amblyopic eye. The position error goes undetected as a result of reduced sensitivity of the amblyopic eye. Evidence is cited for normal muscle potentiation in nonamblyopic eyes. A suggestion is made that amblyopia be considered both a sensory and a motor disorder. The sensory disorder is the reduced acuity at the fovea of the amblyopic eye. The motor disorder is muscle potentiation that causes the amblyopic eye to fixate with an eccentric retinal region that has lower acuity than the fovea. A distinction is made between motor anomalies that have a sensory basis, such as unsteady fixation in anisometropic amblyopia, and motor anomalies that have a motor basis, such as eccentric fixation in strabismic amblyopia.

Amblyopia↗
PubMed1978

Slow control of eye position in strabismic amblyopia.

Unsteady and eccentric monocular fixation were examined in subjects with strabismic amblyopia. Records of horizontal components of unsteady fixation by amblyopic eyes were characterized by abnormally large saccades and a nasalward bias for slow drifts. Typically, these fixational movements aligned the retinal image on an eccentric nasal retinal region. The presence of a slow control mechanism for eye position in amblyopia was examined by teaching subjects to voluntarily suppress fixation saccades. In the absence of saccades, amblyopic eyes continued to fixate eccentrically, using slow drifting movements. When attempting to fixate in the dark, fast drifts moved an amblyopic eye several degrees from its usual eccentric fixation posture, and large saccades were necessary to control eye position. Results demonstrate the operation of a slow control mechanism for eye position in amblyopia.

Adult↗
PubMed1976

Contour interaction and temporal masking in strabismus and amblyopia.

Visual acuity of amlyopic eyes, measured under binocular viewing conditions, was improved by reducing the contrast of targets presented to the normal eye. Improvement was also obtained by adjusting the temporal relationship between inputs to the normal and amblyopic eye. Optimal acuity was obtained by alternately presenting targets to the two eyes at rates centered about 2 and 7 Hz. These results are interpreted in terms of binocular contour interaction and metacontrast suppression. They suggest that a portion of the amblyope's acuity loss during binocular viewing conditions results from excessive masking by the dominant normal eye.

Amblyopia↗
PubMed1975

A directional impairment of eye movement control in strabismus amblyopia.

Saccadic and pursuit tracking movements were elicited to determine the ability of the amblyopic eye to sense and respond to position and motion of the retinal image. Amblyopic eyes were found to initiate saccades as rapidly as normal eyes (200 to 300 msec.), however, the amblyopic eye's saccades were reduced in amplitude, highly variable, and required refinement by subsequent saccades, particularly in response to nasalward displacements of the retinal image. Pursuit responses of amblyopic eyes to both constant and sinusoidal velocity targets contained brief periods of abnormally slow following movements interrupted by position-corrective saccades. As with the saccadic response, the amblyopic eye's pursuit movements were more accurate for temporal than for nasal retinal image motion. Abnormal saccadic and pursuit eye movements in amblyopia result from reduced monocular position and velocity sensitivity probably associated with binocular suppression scotomas normally found in amblyopia.

Amblyopia↗