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PubMed2006

[Multifocal visual evoked potential in retinitis pigmentosa and its comparison with visual field].

PURPOSE: To investigate the characteristics of the multifocal visual evoked potential (mfVEP) and to evaluate the potential of mfVEP as a way of objective perimetry in retinitis pigmentosa (RP). METHODS: The mfVEPs were obtained by using VERIS 4.9 visual evoked response imaging system for 12 RP patients (19 eyes) and 15 normal control subjects (30 eyes). The stimulative field consisted of 60 sectors in a dartboard configuration, the visual angle of one side was 26 degrees. The amplitude sums of P1 wave of the first slice of the second order kernel from patients with RP were compared with values from control subjects. The central 30 degrees visual fields were obtained in the RP patients. Correlation between sensitivity sums of visual field and amplitude sums of P1 wave was performed in the same area. RESULTS: The amplitude sums of P1 wave decreased significantly at all rings in RP group compared with those of normal control group (P < 0.05). Except for inferior ring 1 and inferior ring 2, there was correlation between sensitivity sums of visual field and amplitude sums of P1 wave at the other rings (P < 0.05). CONCLUSION: There was a certain correlation between visual field and mfVEP. The mfVEP can be a method to evaluate visual function objectively in RP.

Adult↗
PubMed1991

[Disorders of the afferent visual pathway in HIV infection. 1. Optic nerve and 2. Visual pathways/visual cortex].

Up to now little involvement of the afferent visual pathway (optic nerve and optic radiation and visual cortex) in HIV infection has been apparent. These results are based on our prospective investigations of 538 HIV-infected individuals, among them 261 patients with full-blown AIDS carried out by the same examiner over a 6-year period (1984-1990). Diseases of the optic nerve were observed in 22/261 (8.4%) of Aids patients but in only 1/227 (0.4%) of patients with earlier stages of HIV infection. Optic neuritis was the most common disease (in 14/261 = 5.4% of Aids patients), for the most part occurring in the course of CMV (cytomegalovirus) retinitis. For this form the prognosis was primarily good under virustatic therapy with ganciclovir in contrast to primary CMC papillitis. Furthermore, a few cases of optic perineuritis, optic neuropathy in basal meningitis, ischemic optic neuropathy and papilloedema with increased intracranial pressure were observed, most of them caused by opportunistic infections of the central nervous system. In single cases the HIV might hypothetically have played a role in the etiology. Visual impairment of the patients varied from subtle disturbances to blindness. Often optic atrophy resulted. Homonymous hemianopsia was the principal sign in diseases of the visual pathway between the lateral geniculate body and the visual cortex (in 10/261 = 3.8% of Aids patients). This symptom resulted from cerebral toxoplasmosis in 7 cases, progressive multifocal leukoencepalopathy (PML) in 2 cases and primary intracerebral malignant lymphoma in 1 case. The visual fields and neuroradiological findings are demonstrated. In 3 cases the homonymous hemianopsia was the first clinical appearance of Aids. Involvement of the afferent visual pathway in HIV infection may be a cause of blindness or visual disturbances despite normal findings on examination of the eyes themselves.

Fluorescein Angiography↗
PubMed1985

Dynamic topography of visual evoked potential in children: a study of the development of the visual system.

To study the development of the visual system, the dynamic topography of the visual evoked potential (VDT) was investigated in 30 normal children aged from two weeks to four years. Twenty-three of the 30 children (77%) showed reliable VDT. The results showed three steps in the development of the visual system in these young children. The first step was seen during the first 4 months after birth, and it was represented by a shortening of duration and an increasing of amplitude in N70 in the occipital region. The second step was seen between 9 months and 2 years of age, and it was represented by a shortening of duration and an increasing of amplitude in P100 and P150 over a widespread area in the occipito-parieto-temporal region. The third step was not clearly seen until 3 years of age, and was represented by the appearance of P200, the so called "vertex potential", around the occipitoparietal region. These three steps in the development of the visual system seemed to be closely related to the time-course of the development in the myelination and maturation of the neuron synapses in the visual pathway and visual cortex. With the aid of VDT, it was possible to clarify that the visual system in children develops step by step from a low level to a high level of the visual function.

Aging↗
PubMed1981

The visual claustrum of the cat. II. The visual field map.

Physiological and anatomical methods were used to study the representation of the visual field in the cat's dorsocaudal claustrum. In one set of experiments, the visual receptive fields of claustral neurons were plotted in multiple electrode penetrations. In another set of experiments, the termination of the corticoclaustral pathway was examined autoradiographically after the injection of [3H]proline at retinotopically defined sites in the visual cortex. Results obtained by the two methods were in close agreement. The claustrum was found to contain a single, orderly map of the contralateral hemifield and a small part of the ipsilateral field. High elevations are represented caudally and ventrally, low elevations rostrally and dorsally. The surface of the claustrum represents the periphery of the visual field, while the vertical meridian lies more ventrally, where the visual claustrum abuts the non-visual part of the nucleus. Visual field lines (isoazimuths or isoelevations) are represented as planes in the claustrum. The map is unusual in that isoazimuth planes are strongly curved and nested within each other, with peripheral ones enclosing those closer to the vertical meridian. This arrangement permits an expanded representation of the periphery compared with what is seen in visual cortex. The inputs from areas 17, 18, 19, 21a, and PMLS (posteromedial lateral suprasylvian area) are convergent, each projection retinotopically to the entirety of the claustral map.

Animals↗
PubMedDate not supplied

Representation of the visual field in the striate cortex: comparison of MR findings with visual field deficits in organic mercury poisoning (Minamata disease).

PURPOSE: To compare MR imaging findings of the striate cortex with visual field deficits in patients with Minamata disease and to reestimate the classical Holmes retinotopic map by using the data obtained from comparing visual field abnormalities with degree of visual cortex atrophy. METHODS: MR imaging was performed in eight patients with Minamata disease who had been given a full neuroophthalmic examination, including Goldmann dynamic perimetry. The atrophic portions of the calcarine area were measured in the sagittal plane next to the midsagittal image and represented as a percentage of atrophy of the total length of the calcarine fissure. MR findings were compared with results of a visual field test. RESULTS: The visual field test revealed moderate to severe concentric constriction of the visual fields, with central vision ranging from 7 degrees to 42 degrees (mean, 19 degrees). The ventral portion of the calcarine sulcus was significantly dilated on MR images in all patients. A logarithmic correlation was found between the visual field defect and the extent of dilatation of the calcarine fissure. The central 10 degrees and 30 degrees of vision seemed to fill about 20% and 50% of the total surface area of the calcarine cortex, respectively. CONCLUSION: Visual field deficits in patients with Minamata disease correlated well with MR findings of the striate cortex. Our data were consistent with the classical Holmes retinotopic map.

Atrophy↗
PubMed1995

Oculo-manual coordination control: respective role of visual and non-visual information in ocular tracking of self-moved targets.

We evaluated the role of visual and non-visual information in the control of smooth pursuit movements during tracking of a self-moved target. Previous works have shown that self-moved target tracking is characterised by shorter smooth pursuit latency and higher maximal velocity than eye-alone tracking. In fact, when a subject tracks a visual target controlled by his own arm, eye movement and arm movement are closely synchronised. In the present study, we showed that, in a condition where the direction of motion of a self-moved visual target was opposite to that of the arm (same amplitude, same velocity, but opposite direction of movement), the resulting smooth pursuit eye movements occurred with low latency, and continued for about 140 ms in the direction of the arm movement rather than in the direction of the actual visual target movement. After 140 ms, the eye movement direction reversed through a combination of smooth pursuit and saccades. Subsequently, while arm and visual target still moved in opposite directions, smooth pursuit occurred in pace with the visual target motion. Subjects were also submitted to a series of 60 tracking trials, for which the arm-to-target motion relationship was systematically reversed. Under these conditions subjects were able to initiate early smooth pursuit in the actual direction of the visual target. Overall, these results confirm that non-visual information produced by the arm motor system can trigger and control smooth pursuit. They also demonstrate the plasticity of the neuronal network handling eye-arm coordination control.

Adult↗
PubMed2006

Visual rehabilitation of children with visual impairments.

Visual rehabilitation, consisting of visual stimulation and visual training, is a common practice in the education of children with visual impairments. Ferrell and Muir have stated that scientific research into the effects of visual stimulation and training is ambiguous and that therefore stimulation and training should be abandoned. The support for this statement is reviewed by describing the scientific relevance and plausibility of the aims and presuppositions of visual stimulation and training programs as well as the results of 10 empirical intervention studies. The review results are in strong agreement with the claim of Ferrell and Muir to abandon noncontingent visual stimulation. It is hypothesized that it is possibly counterproductive for the adaptive functioning of the brain to show strong visual stimuli in artificial surroundings, which are noncontingent on the behavior of the child. Training of visual functions seems fruitful whenever skills that are ecologically valid and adapted to the individual needs and task demands of the child are trained. However, the empirical evidence is still too sparse to draw convincing conclusions. There is an urgent need for good randomized controlled trials with dependent variables that are relevant to everyday life.

Adaptation, Psychological↗
PubMed1984

Response properties of neurons in posterior parietal cortex of monkey during visual-vestibular stimulation. I. Visual tracking neurons.

Extracellular recordings were obtained from 163 visual tracking neurons in area 7a or PG (24) of alert monkeys. The firing patterns were observed during movements of the chair in which the monkey was seated with its head fixed and of a visual target that the monkey was trained to fixate continuously. Horizontal visual tracking neurons were classified into three groups, A, B, and C, on the basis of the following two discharge characteristics: directional preference for visual tracking and response to horizontal sinusoidal oscillation of the chair in the dark. Those neurons that did not respond to chair oscillations in the dark were classified as type A (26/53). Of the remainder, those that responded with the same directional preference as during visual tracking were classified as type B (19/53), and those that showed the opposite directional preference were classified as type C (8/53). When the target and the chair were oscillated together and the monkey canceled the vestibuloocular reflex (VOR) (combined eye and head tracking), most of the visual tracking neurons (types A and B, 32/38) continued to respond in the same way as during visual tracking when the chair was stationary. Type C neurons showed only weak responses. When the monkey fixated an earth-fixed target while the chair was oscillated sinusoidally (VOR target task), responses of the types A and B neurons were much smaller than during visual tracking, while type C neurons were clearly modulated. The results suggest that visual tracking neurons receive information concerning the smooth-pursuit command during combined eye and head (gaze) movements; some also receive vestibular information in addition to the pursuit command information.

Animals↗
PubMed1983

Effects of lateral suprasylvian visual cortex lesions on visual localization, discrimination, and attention in cats.

Experiments were carried out to begin to define the behavioral functions of the lateral suprasylvian (LS) visual area of the cat's cortex. Behavioral tasks were chosen for analysis on the basis of previous suggestions in the literature concerning possible functions of LS cortex and its afferent pathways. These tasks included the ability of cats to orient the head and eyes to a stimulus presented in particular locations in the visual field, the ability to learn successive reversals of a two-choice visual pattern discrimination, and the ability to maintain or shift attention between relevant or irrelevant visual form and brightness cues. Eight cats were trained on each of these tasks. Four of the cats then received bilateral lesions of LS cortex, including the AMLS and PMLS regions, and the remaining 4 cats were used to assess normal retention. The LS cortex lesions had no significant effect upon performance of any of the behaviors tested. Thus, this region of cortex appears to play no essential role in simple brightness, form, and pattern discrimination performance, visual reversal learning, maintaining and shifting visual attention, or orienting the head and eyes to stimuli in the visual field. These results are discussed in relation to previous lesion studies involving large regions of the cat's extrastriate cortex and studies in other species. Possible functions of LS cortex, based upon recent electrophysiological studies, are suggested.

Animals↗
PubMed1993

Organization of visual corticostriatal projections in the cat, with observations on visual projections to claustrum and amygdala.

Electrophysiological mapping criteria were employed to identify visual areas 20a, 20b, 21a, 21b, PMLS, AMLS, ALLS, PLLS, DLS, VLS, and PS in the cat, and to guide placement of tracer deposits. Anterograde tracer methods were used to study the corticostriatal projections of these extrastriate visual areas. The experiments demonstrate that all 11 extrastriate areas send projections to two distinct regions within the striatum, an extensive longitudinal zone within the caudate nucleus, and a more compact region within the posterolateral putamen. Cortical visual projections to the putamen terminate in relatively compact sheets or slabs, and appear to overlap extensively, while those to the caudate nucleus are irregularly patchy and more widely dispersed. Retrograde tracer deposits into the visual recipient zone of the caudate nucleus reveal substantial convergence of other cortical inputs to this same domain. Aspects of visuotopic organization are preserved in the visual projections to both the putamen and the caudate nucleus, but unequivocal retinotopic organization could not be inferred from the available material. Ten of the eleven extrastriate visual area also project topographically onto the visual zone of the claustrum. Area PS does not appear to contribute to the corticoclaustral projections. Five of the extrastriate visual areas (ALLS, PLLS, DLS, VLS, PS) also send sparse projections to the amygdaloid complex.

Amygdala↗
PubMed2004

Visual stimulation, 1H MR spectroscopy and fMRI of the human visual pathways.

The purpose was to assess changes in lactate content and other brain metabolites under visual stimulation in optical chiasm, optic radiations and occipital cortex using multiple voxel MR spectroscopy (MRS). 1H chemical shift imaging (CSI) examinations of transverse planes centered to include the above structures were performed in four subjects at an echo time of 135 ms. Functional MRI (fMRI) was used to confirm the presence of activity in the visual cortex during the visual stimulation. Spectral maps of optical chiasm were of poor quality due to field disturbances caused by nearby large blood vessels and/or eye movements. The optic radiations and the occipital lobe did not show any significant MR spectral change upon visual stimulation, i.e., the peak areas of inositol, choline, creatine, glutamate and N-acetylaspartate were not affected. Reproducible lactate signals were not observed. fMRI confirmed the presence of strong activations in stimulated visual cortex. Prolonged visual stimulation did not cause significant changes in MR spectra. Any signal observed near the 1.33 ppm resonance frequency of the lactate methyl-group was artifactual, originating from lipid signals from outside the volume of interest (VOI). Previous claims about changes in lactate levels in the visual cortex upon visual stimulation may have been based on such erroneous observations.

Adult↗