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At least 145 records · Page 8Linked to original sources
PubMed1989

Prediction of visual function behind cataract using displacement threshold hyperacuity.

Visual acuity and displacement threshold hyperacuity were measured in a group of patients awaiting cataract extraction, and this was repeated several weeks subsequent to surgery. In addition, measurements were made on a group of patients with various ocular pathologies but without the presence of cataract. Displacement thresholds in the cataract group increased only slightly with the severity of the opacity. On the other hand, displacement thresholds for the pathology group showed a marked dependence upon visual acuity--the worse the acuity, the higher the threshold. This results in a clear distinction between vision loss due to optical factors (cataract) and retinal/neural factors. There was a good correlation between pre- and post-operative displacement thresholds in the cataract group, with post-operative thresholds being slightly better than pre-operative thresholds. The results suggest that this technique may offer patients a good indication of the likely quality of vision achieved following cataract extraction.

Aged↗
PubMed1978

Modification of visual functions of the parietal lobe at early age in the monkey.

In addition to the visual pathway ending in the visual cortex, visual information is also processed in the associative areas of the cortex. We have studied the posterior parietal association area (Brodmann's area 7), and in our sample about 40% of the neurons were influenced by visual stimulation or ocular movements. The visually activated neurons in this region in normal adult monkeys have large, binocular receptive fields and they respond well to all moving visual stimuli near the animal. They do not differentiate between different patterns of visual stimuli but respond well to objects of interest, such as food, drinks, new objects, etc. Many visual neurons also respond to somatic stimulation. Preliminary experiments on two young monkeys suggest that the visual input into area 7 is strongly modified by early visual deprivation. In one monkey monocular deprivation lead to total absence of any influence from the deprived eye to area 7. No deprivation effect was observed in the lateral geniculate nucleus of the thalamus and the effect in area 7 was stronger than in the visual cortex (area 17). One monkey raised with bilateral eye closure was behaviourally blind after the opening of the eyes and remained so for the observation period of one month. In area 7 of this monkey the proportion of recording sites responsive to visual stimulation was sharply reduced. In kittens binocular deprivation is known to effect the function of the visual cortex much less than monocular deprivation. It seems possible that at early age inputs representing different sensory systems compete for influence in the associative cortical areas in the same way as there is competition between inputs from the two eyes to the visual cortex.

Age Factors↗
PubMed1990

[Reduced visual function in relation to compensation questions].

In cases of visual impairment due to an accident it is the ophthalmologist's task to assess the functional loss. For the purposes of legal equality norms have been established for functional loss. Differences in the assessment of disability and loss of integrity in various countries are discussed.

Blindness↗
PubMed1990

[Dynamics of visual functions in the conditions of glow and sodium lighting. II. Time of conscious reaction and visual space-hand localization].

The authors present the results of investigations performed in 20 young persons with normal sight. A trial of evaluation of the strain of the central nervous system in conditions of various kind of lighting was carried out basing on its close connection with the visual hand localization as well as with the time of the conscious reaction. Analyzed was the behaviour of the quoted functions as the time passed during the morning hours and the results of the examinations obtained in conditions of glow and sodium illumination were compared. They suggest a favourable influence of the sodium light on the discussed functions.

Adolescent↗
PubMed1975

Use of the ERG and EOG in evaluating the effect of sleep deprivation on visual function in flying personnel.

The electroretinogram (ERG) and electrooculogram (EOG) are electrophysiological tests employed in ophthalmology to diagnose degeneration or injury to the outer half of the retina, including the rods and cones of the visual system. This pilot study was undertaken to determine if sleep deprivation of more than 24 h in rated flying personnel may show an abnormality in retinal function as measured by the ERG and/or EOG. This may give insight to the visual function in flying personnel on deployment or other long missions where uninterrupted sleep may be a problem. The results of this study showed that some subjects deprived of sleep exhibited a statistically significant variance in their EOG ratios as compared to a nondeprived control group. No significant changes in ERG were detected. Principles and theory of electrophysiological testing in ophthalmology are presented.

Adult↗
PubMed1989

[Automatic evaluation of visual functions using a computer].

Many different tests for visual acuity, glare and contrast sensitivity, even by computer, are known. We developed a new computer system that is directed by the patient who works with a joystick. A special overlay computer program receives the answers given by the joystick, calculates the information on the screen and provides a new combination of background illumination, optotype position, color, contrast and enlargement. With this automatic test we examined cataract patients before and after the operation. After the operation the patients have better visual acuity and less sensitivity to glare- and contrast in both the dark and light.

Cataract↗
PubMed1990

Simple clinical techniques to evaluate visual function in patients with early cataract.

Among the 80 subjects who were recruited with normal retinal and neural function, 54 had cataract and a visual acuity (VA) better than 6/24. The 26 age-matched subjects had clear media. Contrast sensitivity (CS) at low and intermediate spatial frequencies was measured using the Pelli-Robson letter chart. Two measures of glare disability (GD) were obtained using the Mentor Brightness Acuity Tester (BAT) in conjunction with a logMAR VA chart and the Pelli-Robson chart. Although CS is predominantly affected at high spatial frequencies in early cataract, we found that some subjects had reduced scores on the Pelli-Robson chart. This CS loss could not be predicted from VA measurements and was particularly found in subjects with posterior subcapsular cataract. High GD scores were found in a number of subjects with relatively good VA and could not be predicted from results of VA or CS. We suggest that CS and GD measurements using the Pelli-Robson chart and the BAT provide valuable information regarding the management of patients with early cataract.

Aged↗
PubMed1985

Functional visual effects of lesions located near the optic nerve head.

Three patients with retinal lesions near or impinging on the optic nerve head are presented. Three different functional disruptions are demonstrated by quantitative layer-by-layer perimetry. In one, a patient who primarily exhibited subretinal neovascularization, inner retinal functions were anomalous; but the overlying nerve fiber bundle was as yet not affected. In the second patient, an individual with possible histoplasmosis causing an outer retinal/choroidal lesion, the overlying nerve fiber bundle was affected causing apparent retrograde changes in inner retinal function at remote visual field locations; but another aspect of optic nerve function (time-dependent response) was not anomalous. These apparently retrograde changes were essentially identical to functional changes previously demonstrated in patients with established open-angle glaucoma. In the third patient, with presumed toxoplasmosis, there were clear-out time-dependent anomalous responses consistent with optic nerve involvement, as previously reported in patients with optic neuritis. There were also modest, time-stable, nerve fiber bundle defects present in this third patient. Together, these results demonstrate that lesions in the area of the disc can have very different functional consequences, and that quantitative psychophysical techniques can elucidate these differences.

Adult↗
PubMed1987

Influence of vasospasm on visual function.

In a number of patients with etiologically unexplained visual field loss, a vasospastic syndrome could be found with the help of a capillaroscopic local cooling test on the fingers. In the patients with proven vasospastic syndrome, the visual field defects were increased after a cold water test and decreased after a therapy with calcium entry blockers. General aspects of the physiology and pathophysiology of the circulation and especially of the circulation in the eye are presented.

Calcium Channel Blockers↗
PubMedDate not supplied

[The effect of anti-glaucoma surgery on the visual function in patients with primary glaucoma].

Examinations of the visual field in 25 patients with Stages I and II primary open-angle glaucoma have shown that in the majority of cases surgery results in improvement of stabilization of the visual field status in respect of all its parameters (retinal sensitivity threshold, deficiency of the field and sensitivity). Increase of the number of defects and reduction of the retinal ability to discern light were observed in 5 patients: in 2 with postoperative hypotension and 3 with progressive cataracts.

Adult↗
PubMed1990

[Postnatal development of visual functions in primates].

The author presents the results of experimental investigations performed in apes in which he evaluated the development of the visual system. Immediately after the birth the animal's lids were stitched together, first in one eye than in the second one; at the same time the first one was opened. Electrodes were then introduced surgically to the region of the lateral geniculate bodies and to the brain cortex. The function of the visual pathways and of the visual cortex were evaluated by using differential visual stimuli. Greatest changes were seen by the author in the visual cortex. He feels that the process of formation of the visual reaction in apes is finished around the second month of life. On the basis of these investigations he discusses the mechanisms of origination of amblyopia ex anopsia in children. He encourages the earliest possible examination of the visual acuity in babies and the undertaking of treatment of amblyopia before the 1st year of life.

Animals↗
PubMedDate not supplied

A study of visual function in the premature infant.

Within the first week of life visual tracking and pattern differentiation were tested in 34 out of 47 premature infants born between 28--34 weeks of gestation. Positive results were achieved from 30 weeks onwards. Pattern differentiation was tested as soon as infants could be taken out of the incubator. Preference could be observed from 31 weeks post-conceptional age. Both functions showed comparable maturation to full-term controls by 34 weeks gestation.

Fixation, Ocular↗
PubMed1991

[Pulvina-lateralis posterior nucleus complex of mammals and the visual function].

It is now well established that the lateral posterior-pulvinar (LP-P) complex of mammals is involved in visual processing. However, the actual function of these large nuclei of the thalamus remains unknown. In contrast to the nearby lateral geniculate nucleus, the LP-P complex does not receive any substantial direct projections from the retina. Its main visual inputs come from the mesencephalon and the neocortex. Most cells in the LP-P complex behave like cortical units. They are tuned to the orientation, direction, spatial and temporal frequencies of the visual stimulus. In addition, most units are binocular and sensitive to relative retinal disparity. Despite their multiple inputs, the LP-P complex cells form an homogeneous population and their overall properties do not reflect those of a given cortical or subcortical area. On the basis of its afferent and efferent connectivity, it has been proposed that the LP-P complex may serve as a relay of an extrageniculate ascendant pathway which originates from the superior colliculus, and/or provide another route for the geniculo-striate input to reach the extrastriate areas. Despite the fact that there is some electro-physiological evidence of such functions, it is now often suggested that the LP-P complex may integrate its multiple inputs and be involved in functions which go beyond those of a simple thalamic relay. Recent findings suggest that the LP-P complex might play a role in visual spatial attention.

Animals↗
PubMed1992

Isoluminant stimuli may not expose the full contribution of color to visual functioning: spatial contrast sensitivity measurements indicate interaction between color and luminance processing.

Visual performance is greatly impaired when tested with heterochromatic isoluminant stimuli. It is thus concluded that the chromatic system contribution to many visual tasks is limited. We suggest that unless color and luminance are shown to be processed independently, such experiments do not demonstrate shortcomings of the chromatic system but rather the inadequacy of using isoluminant stimuli for isolating that system. We hypothesize that color vision has evolved not only to encode color per se but also to enhance luminance-based visual processing, so that for color information to be fully effective, luminance as well as chromatic variations should be present in the stimulus. The hypothesis was tested by studying the contribution of color to spatial vision. The human contrast sensitivity function (CSF) was studied using luminance, isoluminance (color) and combined luminance/color sinusoidal gratings. It is found that luminance contrast sensitivity is enhanced when luminance contrast is accompanied by color contrast and vice versa. The nature of the interaction is best described by an additive single analyzer model. Color opponent cells which respond to both chromatic and achromatic stimuli may be identified as the analyzer.

Color Perception↗
PubMed1992

Structural modeling of functional visual pathways mapped with 2-deoxyglucose: effects of patterned light and footshock.

This paper describes the first application of structural modeling to the visual system. Structural modeling, or path analysis, is a mathematical method that allows for the quantification of the functional strengths of anatomical connections between the structures that form a neural system. The objective was to demonstrate how structural modeling can be used to determine the functional interrelationships between brain structures that form the visual system and how these interrelationships change under different conditions. Data were obtained from measures of 2-deoxyglucose uptake in the visual system of rats presented with either patterned light or darkness. The effects of arousing footshock on visual system operations were also investigated. Models based on the anatomical connections and the interregional correlations between metabolic activity data were used to determine path coefficients representing the magnitude of the influence of each directional path. Statistical evaluation of the models revealed that the dominant positive influences on visual system activity in the darkness were the tectocortical subsystem and the descending connections from secondary visual cortex. In the patterned light model, the total influence of the geniculocortical subsystem was higher than in the dark, and the tectocortical pathways showed both a reduction and a shift in the direction of effects. The models also revealed that the effects of footshock-induced arousal on visual system operations depended upon the visual environment and on extra-visual influences. The footshock led to an increase in the interaction of the two main subsystems at the level of connections between primary visual cortex and the lateral posterior nucleus, and a descending negative influence from the secondary visual cortex became dominant. The models are discussed in the context of conventional analyses to show how structural modeling allows for the determination of much more information about the functional interactions within the visual system of subjects under different experimental conditions.

Animals↗