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At least 721 records · Page 40Linked to original sources
PubMed1994

Gaze orientation in perception of reversible figures.

We hypothesized that during perception of reversible figures the direction of gaze toward a specific perceptual focal point plays a determining role in the identification of the images, i.e., when subjects are asked by the experimenter to perceive one of the two images, a displacement of the eyes toward a specific spatial area of the figure occurs. For each image we think there is a particular point of the figure which acts as perceptual organizer. The stimuli were the Hill and Boring, Ehrenstein, Rubin, and Schroeder reversible figures. Subjects were 47 undergraduate psychology students (32 women and 15 men). The number of ocular movements toward a different spatial direction were calculated for each suggested image of the reversing figure. Analysis showed that, in perceiving reversing figures, specific ocular displacements were present for each suggested image.

Adult↗
PubMedDate not supplied

Ophthalmologic features of Prader-Willi syndrome.

Forty-six patients with Prader-Willi syndrome were examined to determine the incidence and character of ocular abnormalities. All patients met clinical criteria for this syndrome including infantile hypotonia, hypogonadism, truncal obesity, intellectual impairment, dysmorphic facies, and short stature. Thirty-two patients had best corrected visual acuities between 6/6 and 6/9 in each eye. Seven patients (15%) had myopia greater than -3.75 diopters. Nineteen (41%) patients had astigmatism of 1.25 diopters or greater. Amblyopia of strabismic, anisometropic, or ametropic etiology was present in 11 (24%) of the patients. Strabismus was present in 25 (54%) patients: 22 (48%) patients had esotropia and three (7%) had exotropia. Nine patients either received or required strabismus surgery. Thirty-three percent of the patients examined for iris transillumination defects had this finding. This study represents the first large series of patients with Prader-Willi syndrome to undergo detailed ophthalmologic evaluation. Recognition of this syndrome is important because of the high incidence of potentially treatable ocular problems.

Adolescent↗
PubMedDate not supplied

Long-term stability of alignment in the monofixation syndrome.

From a collection of 328 patients with congenital esotropia, 80 patients were identified who had a minimum 4-year follow-up after surgical alignment within 8 prism diopters (pd) of orthophoria. These patients were subdivided into two groups: the M.S. group (38 patients) demonstrated the monofixation syndrome; the NO M.S. group (42 patients) did not have monofixation. The alignment of patients in each group was followed over time. After 17.5 years, 74% of patients in the M.S. group maintained alignment within 8 pd of orthophoria. In the NO M.S. group, only 45% were well aligned after 14 years. The mean time to loss of stability was significantly shorter for the NO M.S. group (P less than 0.005). Our findings suggest achievement of the monofixation syndrome improves but does not guarantee stability of ocular alignment.

Amblyopia↗
PubMed2005

Perceptual learning of Gabor orientation identification in visual periphery: complete inter-ocular transfer of learning mechanisms.

We combined the external noise paradigm, the Perceptual Template Model approach, and transfer tests to investigate the mechanisms and eye-specificity of perceptual learning of Gabor orientation in visual periphery. Coupled with a fixation task, discriminating a 5 from an S in a rapid small character string at fixation, contrast thresholds were estimated for each of eight external noise levels at two performance criteria using 3/1 and 2/1 staircases. Perceptual learning in one eye was measured over 10 practice sessions, followed by five sessions of practice in the new eye to assess transfer. We found that monocular learning improved performance (reduced contrast thresholds) with virtually equal magnitude across a wide range of external noise levels with no significant change in central task performance. Based on measurements of learning effects at two performance criterion levels, we identified a mixture of stimulus enhancement and external noise exclusion as the mechanism of perceptual learning underlying the observed improvements. Perceptual learning in the trained eye generalized completely to the untrained eye. We related the transfer patterns to known physiology and psychophysics on orientation direction coding.

Contrast Sensitivity↗
PubMed1984

Influence of peripheral vision upon vestibulo-ocular reflex suppression.

The effect of peripheral vision upon the suppression of caloric induced nystagmus has been studied in normal subjects and patients with Parkinson's disease and cerebellar lesions. In normal subjects, caloric responses in the presence of optic fixation upon a target light viewed in darkness are further suppressed by a factor of two when background illumination is introduced. In both patient groups background illumination had significantly less effect. Additionally, optokinetic and pursuit test have revealed specific abnormalities consistent with the notion of a peripheral retinal feed-back mechanism deranged by disease. These in turn appear to have particular relevance to certain visuo-vestibular disturbances characteristic of patients in both groups.

Adolescent↗
PubMed1991

Pathology of fixation fibrosis on intraocular lenses.

Ocular tissues frequently form a special kind of reactive fibrosis with distinct cellular strands that anchors prominent surface irregularities of lens implants--haptics, manipulation holes, or borders--to adjacent ocular structures and helps fixate the implant in the eye. The strands originate in reactive proliferation of chemotactically attracted sessile macrophages on the surface of lens implants. They are cellular in their early stages and may undergo secondary fibrosis or hyalinization. The formation of these strands is called "fixation fibrosis." An initial description of the pathology of this complicated process is presented.

Aged↗
PubMed1977

Neuro-optometry: an evolving specialty clinic.

Neuro-optometry is evolving as an optometric clinical specialty focusing on neurological dysfunctions of the visual system. Initially, we focused upon abnormalities of ocular movements, and our investigations have now broadened to include static and dynamic measurements of eye movements, accommodation, and the pupil. We feel the clinic serves three fundamental purposes: (1) to provide service to the patient, (2) to perform clinical research, and (3) to broaden the scope of the students' clinical experience. Operation of the clinic, technical methods of measurement, the testing protocol, and examples of interesting clinical recordings are described.

Accommodation, Ocular↗
PubMed2003

Vestibular reflexes and positional manoeuvres.

Dizziness and vertigo are some of the more frequently encountered symptoms in neurology clinics. In turn, one of the most common causes of vertigo is benign paroxysmal positional vertigo (BPPV), accounting for a quarter of all patients with dizziness and vertigo. Reviewing the value of the positional manoeuvres available is relevant, particularly in the light of the efficient treatments available for BPPV. In this article I will deal with positional manoeuvres first, and then with how vestibulo-ocular reflexes (VOR) can be tested in the clinic. I will not discuss VOR suppression assessment.

Fixation, Ocular↗
PubMed1989

The effect of alcohol on the vestibulo-ocular reflex and gaze regulation.

To clarify the effect of the temporary decline in cerebellar function on the vestibulo-ocular reflex (VOR) and gaze functions, we examined 12 normal adults under passive rotations before and after they drank alcohol at dosages of 0.43 and 0.65 g/kg. Whereas spatial gaze fixation was maintained accurately with 0.65 g/kg administration (0.06% blood alcohol level), gaze fixation on a head-fixed target and smooth pursuit were impaired by the higher dosage of 0.43 g/kg (0.03% blood alcohol). The magnitude of the alteration in the VOR gain after drinking was correlated significantly with the VOR gain before drinking: while small values were enhanced by drinking, large values were suppressed. The present study indicates that the VOR in the dark is regulated by the balance between the amplifying and suppressing forces controlled by the cerebellum.

Adult↗
PubMed1983

Edrophonium test in Eaton-Lambert syndrome: quantitative oculography.

Accurate ocular motility recordings were made of the saccadic responses of five patients with Eaton-Lambert syndrome (ELS). It was found that, contrary to common belief, the ocular motor system is affected. The saccades of ELS patients mimicked those of patients with myasthenia gravis (MG). Both groups exhibited hypometria and multiple, closely spaced saccades. Two patients demonstrated both saccadic facilitation and positive edrophonium tests. The ELS patients had slow or normal saccadic velocities, not the "super-fast" velocities found in patients with ocular MG.

Aged↗
PubMed1992

Predictive mechanisms of head-eye coordination and vestibulo-ocular reflex suppression in humans.

Head and eye movements of human subjects have been recorded during head-free pursuit in the horizontal plane of a target executing sinusoidal motion at a frequency of 0.26 to 0.78 Hz and a peak velocity of +/- 96 degrees/s. The target was not presented continuously but was exposed for brief durations of 120 to 320 ms as it passed through the centre of the visual field at peak velocity. This technique allowed the timing of each response to be assessed in relation to the onset of target appearance. During the first 3 to 4 target presentations, there was a progressive buildup of both head velocity and the smooth component of gaze velocity, while, simultaneously, the responses became more phase-advanced with respect to target onset. In the steady state, similar temporal response trajectories were observed for head and gaze velocity, which were initiated approximately 500 ms prior to target onset, rose to a peak that increased with the duration of target exposure, and then decayed with a time constant of 0.5 to 1 s. Whenever the target failed to appear as expected, the gaze and head velocity trajectories continued to be made, indicating that predictive suppression of the vestibulo-ocular reflex (VOR) was taking place in darkness. In a further experiment, subjects attempted to suppress the VOR during whole body oscillation at 0.2 or 0.4 Hz on a turntable by fixating a head-fixed target that appeared for 10 to 160 ms at the time of peak head velocity. Again, VOR suppression was initiated prior to target appearance in the same manner as for natural head movements, and when the target suddenly disappeared but rotation continued, predictive VOR suppression was observed in darkness. The similarity of these predictive effects to those obtained previously for head-fixed pursuit provides further support for the hypothesis that both pursuit and visual suppression of the VOR are controlled primarily by identical visual feedback mechanisms.

Dark Adaptation↗