Electronic retinoscopy: special considerations in the aphakic patient.
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Accommodation, Ocular↗
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[Examination for essential strabismus].
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Accommodation, Ocular↗
Emmetropisation and accommodation in hypermetropic children before they show signs of squint--a preliminary analysis.
1119 hypermetropic children have been followed from the age of 6 months to 3 1/2 years. Observations are reported on (i) the changes in their refraction and (ii) their accommodation. Children who eventually had either a convergent squint or a microtropia were significantly (i) less likely to have spontaneously reduced their hypermetropia, and (ii) more likely to have problems with their accommodation, than those who had no squint. These abnormalities were demonstrated in both the fixing and the non-fixing eyes. There was no obvious difference between the findings for children who had microtropia and squint. We suggest that there was a basic defect in the function, and/or the development, of the visual systems relating to both fixing and non-fixing eyes of children who had squint or microtropia; and that this defect was present before squint or microtropia were diagnosed. The question of whether this defect had a congenital or an acquired (form vision deprivation) cause is discussed.
Accommodation, Ocular↗
The diagnosis of amblyopia and strabismus: a programmed approach.
A simplified method of recording and analyzing amblyopic and strabismic examinations is presented. With this new form, the average practitioner is provided with a relatively standardized set of tests in a logical, organized sequence. Programming the patient's responses into meaningful categories facilitates the formation of a differential diagnosis and also provides valuable insight into the eventual outcome of each case.
Adaptation, Ocular↗
[Detection of resting state of accommodation by accommodative microfluctuation].
Accommodative microfluctuations were recorded when the subjects were looking at a stable target. The waves of the accommodative microfluctuation were analyzed by fast Fourier transform. When accommodation was in a resting state, the high frequency components were minimized. This suggested that the resting state of accommodation might be measured when the subject was looking at a target. At a little distance from the resting state of accommodation, the high frequency components were maximized. This might suggest a negative accommodation.
Accommodation, Ocular↗
[Sensory-motor and distinguishing ability of the eye in adolescents with normal central visual acuity].
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Accommodation, Ocular↗
Normal heterophoric changes: 20 years' follow-up.
BACKGROUND: Evaluation of changes in the heterophoric condition of 100 normal individuals over a 20-year period. METHODS: A retrospective study was undertaken. Charts of 100 normal men were reviewed. Individual changes in the heterophoric status were recorded over a 20-year period. The average value of the phoria at age 18-22 years was compared with the average value at age 34-38 years. Measurements were taken for near and distance fixation. No one was heterotropic. Changes in convergence and accommodation were also calculated. RESULTS: A 0.9 +/- 1.7 prism diopter increase in esophoria for distance fixation and a 0.6 +/- 2.5 prism diopter increase in exophoria for near fixation were found. These changes were statistically significant (P < 0.001 and P < 0.02 respectively). The near point of convergence receded by 0.5 +/- 1.1 cm (P < 0.001), and a decrease in accommodation over time of 2.8 +/- 1.4 diopters was found (P < 0.001). CONCLUSION: An increase in esophoria for distance fixation and a exophoria for near fixation was found in a 20-year follow-up of 100 normal subjects.
Accommodation, Ocular↗
Fixation disparity and nonius bias.
Fixation disparity, i.e. the vergence error within Panum's area, can be measured psychophysically with two nonius (vernier) lines that are presented dichoptically, i.e. one to each eye. The observer adjusts these nonius lines to subjective alignment; the resulting physical nonius offset indicates the amount of fixation disparity. The present experiments investigate the relation between fixation disparity and the nonius bias, which is the physical offset of the nonius lines that is adjusted by the observer in order to perceive them as aligned when both nonius lines are presented to both eyes (binocular nonius bias) or both to the left or both to the right eye (monocular nonius bias). It was found that (1) the fixation disparity is correlated with the binocular nonius bias in the horizontal and vertical meridian and (2) the binocular nonius bias can be predicted from the average of the right eye and left eye monocular nonius bias. To remove the influence of the nonius bias on measured fixation disparity it is possible to calculate the fixation disparity relative to the individual binocular nonius bias, rather than to the physical coincidence of the nonius lines. This procedure tends to increase the correlation between fixation disparity and the tonic resting position of vergence. We discuss the clinical relevance of the dichoptic nonius method for measuring fixation disparity and its limitations as compared to physical recordings of eye position.
Convergence, Ocular↗
Spontaneous fluctuations in pupil size are not triggered by lens accommodation.
Fluctuations in pupil size and lens accommodation are measured concurrently under open loop conditions, constant illumination and far fixation. In 12/17 trials no correlation was measured between the fluctuations in pupil size and lens accommodation. For the remaining 5/17 trials no lag was observed between the changes in pupil size and lens accommodation indicating that this correlation does not arise as a consequence of a near response. These observations suggest that under conditions of constant illumination and far fixation, the supranuclear centers controlling the near response are not active.
Accommodation, Ocular↗
Objective measurement of binocular fixation misalignment.
The amount of deviation from central fixation during binocular fusion of a vertical border was compared with conventional fixation disparity measured at the same time, forced convergence serving as the independent variable. Fixation eccentricity was measured objectively by monitoring a scleral blood vessel with a video camera and by analyzing the movement, greatly magnified, on a video screen. Fixation disparity was measured conventionally by interocular nonius alignment of vertically dissociated line segments. The results agree well with previous comparisons of these responses, in which the fixation eccentricity was measured by using a technique based on the effect of retinal stimulus location on border enhancement. As in the previous experiment, the fixation misalignment was found to be many times larger than the corresponding disparity for most forced convergence values. The large discrepancy between actual fixation misalignment and fixation disparity has thus been documented objectively as well as subjectively.
Convergence, Ocular↗
Effect of induced aniseikonia on fixation performance.
The purpose of the study was to determine to what extent induced aniseikonia affects fixation performance. Aniseikonia was induced in the vertical meridian only, whereas fixation alignment was monitored in the horizontal meridian. A previously developed technique based on the dependency of border enhancement bandwidth on fixation eccentricity was used to monitor deviations from central fixation during fusion. Stress on the fusion mechanism was supplied by controlled increments of forced horizontal vergence. It was found that deviation from central fixation in the horizontal meridian generally increases with increasing amounts of vertical aniseikonia. The effect is particularly pronounced for small amounts of aniseikonia.
Aniseikonia↗
Modern tests of vestibular function, with special reference to their value in clinical practice.
The many vestibular tests now available provide the means of accurate localization of lesions at all levels of the vestibular pathways. The value of the test procedures described has been well established in the examination of very many patients over the past twenty years, and though other forms of tests are available only those have been included which have proved to give consistently useful information.Most of these tests can be undertaken by the clinician without the use of any costly equipment, and together with a careful history and examination the diagnosis can in most cases be arrived at. Recognition of the highly important role of optic fixation and ocular deviations on vestibular nystagmus, together with recent facilities to demonstrate this electronystagmographically, may provide additional valuable and more precise information.
Adult↗
Fixation disparity vs. binocular fixation misalignment.
Conventional fixation disparity was compared with the corresponding foveal fixation misalignment measured by a recently developed method based on the effect of retinal eccentricity on the width of the border enhancement band. Unlike procedures using binocular nonius alignment, the method is not subject to adaptive changes in perceived direction. Forced convergence and divergence stimulation served as the independent variable. It was found that conventional fixation disparity represents only a small, constant fraction of the misalignment through the greater portion of the vergence range. However, when the misalignment is restricted to a small, central portion of the foveola, this relation changes drastically, and the fixation disparity can then be much larger than the fixation misalignment. During perfect fixation alignment of the foveal centers, there is always a significant amount of fixation disparity present. It is suggested that the large differences between fixation disparity and fixation misalignment are due to a fundamental, perceptual mechanism that is always at work during binocular vision, changing the relation between retinal location and perceived visual direction.
Convergence, Ocular↗
Neuroanatomical and neurophysiological consequences of strabismus: changes in the structural and functional organization of the primary visual cortex in cats with alternating fixation and strabismic amblyopia.
In recent years, evidence has accumulated indicating that long-ranging neuronal connections within the primary visual cortex (area 17) mediate the influences of context and experience, possibly also those of expectation. After early onset strabismus, the layout of these connections is massively modified: in strabismic but not in normally raised cats, horizontal connections extend primarily between neurons activated by the same eye. As a possible consequence of the modified circuitry, neuronal synchronization between different ocular dominance domains is also massively reduced. Thus, the inability of strabismics to combine the signals arriving from the two eyes into a single percept may be caused by these structural and functional changes. Strabismic amblyopia is also accompanied by significant modifications of intracortical associational interactions: corresponding to the psychophysical deficits, neurons driven by the normal eye displayed stronger synchronization of their responses than neurons dominated by the amblyopic eye.(1) These data demonstrated for the first time a clear neurophysiological correlate of strabismic amblyopia in area 17. They suggest that - similar to our observations in divergent squinters - at least some of the perceptual deficits of amblyopic patients are due to experience-dependent changes in intracortical circuitry. We analyze this question by combining optical imaging of intrinsic signals with 3-D reconstructions of neuronal circuitry.
Amblyopia↗
Periodic alternating esotropia.
Periodic alternating esotropia (PAE) is a rare ocular motility disturbance observed in association with periodic alternating gaze deviation (PAG) or periodic alternating nystagmus. We examined a 9-month-old developmentally delayed girl who showed PAE occurring synchronously with PAG. The ocular motility disorder consisted of rhythmic alternating fixation with the right eye in abduction, a left face turn and esotropia of the left eye (90 seconds), a changeover phase (10 to 15 seconds) during which the eyes are straight and the head is upright, then fixation with the left eye in abduction, a right face turn, and esotropia of the left eye (90 seconds). There was no spontaneous jerk nystagmus present. These findings continued incessantly during a follow-up period of 18 months. Magnetic resonance imaging revealed pronounced cerebellar vermis hypoplasia. Only three clinically similar cases have been previously reported, but none had been studied with modern neuroimaging techniques.
Atrophy↗
Follow-up study of electronystagmographic findings in Friedreich's ataxia patients and evaluation of their relatives.
Fourteen Friedreich patients (F group) who had undergone a first electronystagmogram (E.N.G.) reported in 1978, had the same test 12 to 24 months after the first one. In the second study, there are more patients with bilateral hypoactive caloric nystagmus failure of fixation suppression, ocular dysmetria, irregular pendulum tracking and ocular flutter. These signs are probably most representative of the progression of the disease. Nineteen unaffected relatives of these patients (H group) also had an electronystagmogram but no special "familial" electronystagmographic pattern could be identified. Irregular ocular poursuit, nearly invariable in the F group but absent in the H group, was one of the most important differences between patients and their relatives.
Electronystagmography↗
The relationship between cerebral T2 hyperintensity and fixation suppression of vestibulo-ocular reflex in elderly patients with dysequilibrium symptoms.
OBJECTIVES: To evaluate the relationship between cerebral T2 hyperintensity on MRI and visual suppression of vestibulo-ocular reflex (VOR) in elderly patients with dysequilibrium symptoms. METHODS: Eighty-nine elderly patients with no MRI abnormalities in the infratentorial region aged 60-89 years complaining dysequilibrium symptoms were studied. Cases with whom a definitive diagnosis of peripheral or central disease could be established were not included. T2 hyperintense lesions in the cerebrum: basal ganglia, subcortical white matter and periventricular white matter were evaluated. VOR in darkness and fixation-suppressed VOR using pseudo-sinusoidal rotation stimuli were recorded to calculate visual suppression rate. Correlation between visual suppression rate and semi-quantitative scores for severity of T2 hyperintensity in the cerebrum was investigated. RESULTS: Patients with T2 hyperintensity in the cerebrum exhibited significantly lower visual suppression rate than those without lesions in the cerebrum. Multiple regression analysis showed that visual suppression rate was significantly and negatively correlated with severity of lesions in the basal ganglia, but not with patient age, severity of subcortical white matter lesions, or that of periventricular white matter lesions. CONCLUSIONS: In elderly patients with dizziness with a non-specific history and otoneurological findings, fixation suppression of vestibular nystagmus was associated with T2 hyperintensities in the basal ganglia.
Aged↗