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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↗
PubMed1996

Visual function with monofocal versus multifocal IOLs.

PURPOSE: To assess visual outcome in four groups: one multifocal intraocular lens (IOL), one monofocal IOL, and two phakic, one older and one younger. SETTING: Department of Ophthalmology, National Health Service, Puerta de Hierro University Clinic, Madrid, Spain. METHODS: This prospective study comprised 70 aphakic eyes, 42 with a multifocal and 28 with a monofocal IOL, and 42 phakic eyes, 21 older than 60 years and 21 younger than 60 years. The phakic groups served as a double control. Main outcome measures were corrected and uncorrected distance and near visual acuities, contrast and glare sensitivity, and clinical and subjective complications. RESULTS: There were no significant differences between the monofocal and multifocal IOL groups in uncorrected or corrected distance visual acuity. Near visual acuity in the multifocal group, with and without distance correction, was significantly better than in the monofocal group. Near vision with addition was similar between the two IOL groups. There were no significant differences between the monofocal and multifocal IOL groups in contrast sensitivity at the 96 and 50% thresholds. Between-group differences of less than one Regan line were found at the 25 and 11% thresholds. The phakic groups had better contrast sensitivity. The older phakic group's results were closer to those of the IOL groups. There were no significant complications. CONCLUSION: Distance acuity and contrast sensitivity were similar in the monofocal and multifocal IOL groups; however, the multifocal group had significantly better near acuity. The younger phakic group had significantly better contrast sensitivity than the other groups.

Adult↗
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↗
PubMed1998

Effects of migraine on visual function.

BACKGROUND: Data is reported from an ongoing trial considering whether visual loss associated with migraine is consistent with a selective deficit in M- or P-cell functioning. METHODS: The psychophysical tests used include spatio-temporal contrast thresholds and luminance increment thresholds for a spot drifting across a spatially or temporally modulated background. A migraineur and 15 non-headache controls participated in the present study. Measurements were made foveally and at 10 degrees in the superior field. Static and flicker perimetry were conducted. RESULT/CONCLUSION: Regionalized losses occurred for stimuli with moderate temporal frequencies (16 Hz), which is consistent with M-cell dysfunction.

Adult↗
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↗
PubMed1999

Characteristics of discrepancies between self-reported visual function and measured reading speed. Salisbury Eye Evaluation Project Team.

PURPOSE: Visual impairment is a risk factor for morbidity in the elderly and is often screened for by self-report. This study evaluates whether there are subsets for whom there is a discrepancy between self-reported and measured function. METHODS: The prevalence of a discrepancy between self-reported difficulty reading a newspaper and measured reading speed was determined in 2520 community-based men and women, aged 65 to 84 years, and the discrepant group characterized by polychotomous regression. RESULTS: Of subjects who reported minimal difficulty reading a newspaper, 10.8% (227/2107) read newsprint-sized text (0.21 degrees) more slowly than 80 words/min, a level previously shown to be necessary for sustained reading. Poor visual acuity, presence of psychiatric symptoms, and less satisfaction with vision were associated with being in the group that read slowly and reported difficulty with reading. Better cognition, better visual acuity, more years of education, white race, and fewer psychiatric symptoms were associated with being in the group that read more quickly and reported minimal difficulty. When reading the text size at which subjects read their fastest, only 2.6% of those with minimal difficulty remained discrepant. These individuals were more likely to have less education, be male, be African American, and have poorer cognitive status than those who did not remain discrepant. CONCLUSIONS: A subset of the elderly population have a substantial discrepancy between self-reported reading difficulty and measured reading speed. In some, this discrepancy may be based on underlying expectations and experiences, and in others it may represent a transition from no visual impairment to visual impairment.

Aged↗
PubMed1993

Early postnatal development of visual function in ganglion cells of the cat retina.

1. Spontaneous and visually evoked action potentials were recorded from single retinal ganglion cells in superfused retina-eyecups prepared from cats between postnatal day 5 (P5) and adulthood. The development of functional responses was studied quantitatively with contrast-modulated spots and sinusoidal grating stimuli. Some functionally characterized cells were impaled and injected intracellularly with horseradish peroxidase to permit direct structure-function comparisons during the period of synaptogenesis and the expression of transient morphological features. 2. Around the time of eye opening at postnatal day 7-postnatal day 10, the spontaneous discharge of ganglion cells was characterized by bursts of action potentials separated by periods of no activity lasting up to tens of seconds. This "burst-type" pattern gradually changed to a more regular spontaneous discharge during the first 2-3 postnatal wk. The burst-type discharge was completely blocked by 10 mM Mg2+, but was largely unaffected by bath application the excitatory amino acid receptor antagonist 6-cyano-7-nitroquinoxaline-2,3- dione at concentrations that eliminated both spontaneous and light-driven activity of cells that had developed a regular spontaneous discharge. DL-2-amino-7-phosphonoheptanoic acid, a competitive antagonist of the N-methyl-D-aspartate (NMDA) receptor, also had little effect on the burst-type discharge but did block the depolarizing effects of exogenous NMDA. These results demonstrate that the burst-type spontaneous discharge is a calcium-dependent process but probably is not mediated by synapses utilizing receptors for excitatory amino acids. 3. On P5, a minority of ganglion cells responded to a light stimulus delivered to the retina at the electrode tip. The percentage of responsive cells increased over time so that all cells responded by P10. During this transition period, the light responses were often weak, fatigued with repeated stimulation, and displayed poor temporal resolution. There was a rapid increase in the briskness of the response to a standard light stimulus during the second through fourth postnatal weeks. However, cells that responded sluggishly to visual stimulation were observed at all ages studied. 4. Both ON- and OFF-type receptive field (RF) centers were observed in approximately equal numbers as soon as the light response developed, and the proportion of the two types was independent of age. Three percent (10/342) of visually responsive ganglion cells had ON-OFF RFs, and the incidence of this type also appeared to be invariant with age.(ABSTRACT TRUNCATED AT 400 WORDS)

Aging↗
PubMed1997

Regenerating ganglion cell axons in the adult rat establish retinofugal topography and restore visual function.

The mechanisms of neuronal network response to axotomy are poorly understood. In one of the favoured models used to study the fate of injured neurons in the adult rat visual system, appreciable numbers of retinal neurons survive optic nerve injury under conditions of microglia-targeted neuroprotection. Rescued neurons can regenerate their axons and become target-dependently stabilised after reconnection with their natural visual centres by means of a peripheral nerve graft, which, in addition to guidance, actively supports axonal growth. The mechanisms that control regenerative axonal growth and resynaptogenesis include coordinated cell-cell interactions between growing neurites and target cells in order to establish a meaningful reconnectivity. Here the function of the regenerating visual circuitry was first studied by monitoring the ability of animals to discriminate spatial patterns, and second by recording visual evoked cortical potentials (VEPs) in the same animals. These functions were correlated with neuroanatomical studies of the retinotopic organisation of regenerating axons. To achieve these goals, adult rats were behaviourally trained in a Y-maze to discriminate between vertical and horizontal stripes. Both optic nerves were transected, and the regenerating axons of one optic nerve were guided into the area of optic tract with a peripheral nerve graft according to the protocols of neuroprotection and simultaneous grafting, in order to enable large numbers of axons to reinnervate the major visual targets in the midbrain and thalamus. Postoperative testing of the animals showed a marked improvement of visual perception and behaviour. The VEPs of the same animals were measurable indicating a restoration of the visual circuitry including the ascending corticopedal connections. Neuroanatomical assessment of the fibre topography within the graft and the area of termination revealed a rough topographic organisation that may account for restoration of the function. These results suggest that interrupted central pathways can be functionally reconnected by providing a neuroprotective environment in combination with peripheral nerve grafts to bypass lesions.

Animals↗
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↗
PubMedDate not supplied

Perceptual and cognitive visual functions of parietal and temporal cortices in the cat.

We used reversible cooling deactivation to compare the functions of cortices lining the middle suprasylvian (MS) sulcus and forming the ventral portion of the posterior suprasylvian (vPS) gyrus. A battery of attentional, motion and mnemonic processing tasks were used and performance was examined during deactivation of each region. The results show a clear dissociation of functions. Deactivation of MS cortex resulted in profound deficits on a visual orienting task and on the discrimination of direction of motion, whereas deactivation of vPS cortex severely impaired both retention and learning of novel and overlearned object discriminations. In addition, deactivation of either MS or vPS cortex impaired discrimination of learned patterns when components of the patterns were in motion, whereas only deactivation of vPS cortex impaired the discrimination when all components were static. Together, these results show that a region of parietal cortex contributes to the processing of visual motion and to attentional processes, whereas a region of temporal cortex contributes to the learning and recognition of three-dimensional objects and two-dimensional patterns. This functional dissociation is linked to differences in underlying visual pathways, which have many features in common with the parietal and temporal visual processing streams previously identified in monkeys and humans. Furthermore, the broad similarity in neural operations carried out in parietal and temporal cortices of cats, monkeys and humans suggests the existence of a common plan for cortical processing machinery within mammals with well developed cerebral cortices.

Animals↗
PubMed1983

Visual function in the ventral lateral geniculate nucleus of the cat.

The visual receptive fields of 293 single units in the ventral lateral geniculate nucleus of the cat were studied. In addition to the wide variety of types described by others, a group of units responding differentially to color was identified that included units responding particularly to blue and others with opponent color properties. Some units with spontaneous firing and without definite visual receptive fields were inhibited by stimulation of the optic chiasm (OX). A study of latency of firing to OX stimulation suggested that these cells were driven by retinal ganglion cells of the W type. One-third of all units studied were binocularly driven.

Afferent Pathways↗
PubMed1984

Developmental aspects in the assessment of visual function in young children.

The developmental aspects in the assessment of visual acuity in the preverbal child have been reviewed. Several investigative techniques indicate that visual acuity of infants increases significantly between birth and age 6 months. Transient oculomotor deviation in infancy must be differentiated from pathologic ocular conditions. Changes in refraction of the developing eye that occur normally and as a result of an ocular disorder must be recognized and managed early in the infant's life.

Age Factors↗
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↗