PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Visual Pathways”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources
PubMed1997

Anterior visual pathway gliomas.

The benign anterior visual pathway glioma undoubtedly is the most controversial subject in neuro-ophthalmology. Although we are persuaded by the evidence that they are true neoplasms rather than hamartomas, the controversy over their biological nature seems moot, as they have a low growth potential. That is not to say that serious visual loss is not common or that, in some cases (especially among those lesions arising in the chiasmalhypothalamic region), tumor-related death and disability cannot occur. These posteriorly located lesions may cause hydrocephalus, and shunting is required if that occurs. The need for shunting in such cases may be the only point on which experts agree. What has yet to be established is whether any of the forms of therapy now available for anterior visual pathway gliomas without hydrocephalus is better than no treatment. Surgery, radiation, and chemotherapy all carry risks. A randomized, controlled study, if feasible, would be apt to settle the issue. The low incidence of these tumors might frustrate attempts to complete such an investigation in a reasonable period. A team of physicians should manage patients with benign anterior visual pathway gliomas. Radiologists, neurologists, neurosurgeons, radiation oncologists, pediatricians, endocrinologists, and oncologists all have a role, but the neuro-ophthalmologist should be the leader. Neuro-ophthalmologists are in the unique position of being able to recognize and document changes in the patient's visual function. Furthermore, neuro-ophthalmologists, being disinterested, are free to choose without bias from among the various management options. The malignant anterior visual pathway glioma is not a subject of controversy. The clinical features at presentation are apt to be misinterpreted as evidence of an inflammatory or ischemic neuropathy rather than the announcement of a fatal brain tumor. Though these patients receive radiotherapy and chemotherapy, these measures have not improved survival significantly, and the outcome is uniformly fatal. The only positive thing that can be said about the malignant gliomas of the anterior visual pathway is that they are so rare.

Adolescent↗
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↗
PubMed2005

Factors determining the precision of the correlated firing generated by a monosynaptic connection in the cat visual pathway.

Across the visual pathway, strong monosynaptic connections generate a precise correlated firing between presynaptic and postsynaptic neurons. The precision of this correlated firing is not the same within thalamus and visual cortex. While retinogeniculate connections generate a very narrow peak in the correlogram (peak width < 1 ms), the peaks generated by geniculocortical and corticocortical connections have usually a time course of several milliseconds. Several factors could explain these differences in timing precision such as the amplitude of the monosynaptic EPSP (excitatory postsynaptic potential), its time course or the contribution of polysynaptic inputs. While it is difficult to isolate the contribution of each factor in physiological experiments, a first approximation can be done in modelling studies. Here, we simulated two monosynaptically connected neurons to measure changes in their correlated firing as we independently modified different parameters of the connection. Our results suggest that the precision of the correlated firing generated by strong monosynaptic connections is mostly determined by the EPSP time course of the connection and much less by other factors. In addition, we show that a polysynaptic pathway is unlikely to emulate the correlated firing generated by a monosynaptic connection unless it generates EPSPs with very small latency jitter.

Animals↗
PubMed2006

Congenital absence of optic chiasm: demonstration of an uncrossed visual pathway using monocular flash visual evoked potentials.

A 35 month old child was referred for electrophysiology testing with pendular nystagmus, corresponding head oscillations and reduced vision. Flash visual evoked potential (VEP) revealed large responses at the right occiput (but not the left occiput) from the right eye and similar large responses at only the left occiput from the left eye, indicating absent/deficient crossover at the chiasm. A magnetic resonance imaging (MRI) scan subsequently confirmed absence of the optic chiasm. There was no other evidence of midline brain defects. Her subsequent development to age 11 has been followed. The nystagmus has remained mainly horizontal but a torsional component was noted from age 5 years and described as see-saw at age 6 years. A small right esotropia was noted at 6 years and spectacles prescribed for low hypermetropic refractive error. Bilateral superior rectus recessions at age 7 years produced an improved head posture. Her visual acuity has remained stable at around 6/24 from age 4 years. No binocularity nor stereopsis has been demonstrated over subsequent visits.

Child, Preschool↗
PubMed2006

Comparison of shape encoding in primate dorsal and ventral visual pathways.

Ventral and dorsal visual pathways perform fundamentally different functions. The former is involved in object recognition, whereas the latter carries out spatial localization of stimuli and visual guidance of motor actions. Despite the association of the dorsal pathway with spatial vision, recent studies have reported shape selectivity in the dorsal stream. We compared shape encoding in anterior inferotemporal cortex (AIT), a high-level ventral area, with that in lateral intraparietal cortex (LIP), a high-level dorsal area, during a fixation task. We found shape selectivities of individual neurons to be greater in anterior inferotemporal cortex than in lateral intraparietal cortex. At the neural population level, responses to different shapes were more dissimilar in AIT than LIP. Both observations suggest a greater capacity in AIT for making finer shape distinctions. Multivariate analyses of AIT data grouped together similar shapes based on neural population responses, whereas such grouping was indistinct in LIP. Thus in a first comparison of shape response properties in late stages of the two visual pathways, we report that AIT exhibits greater capability than LIP for both object discrimination and generalization. These differences in the two visual pathways provide the first neurophysiological evidence that shape encoding in the dorsal pathway is distinct from and not a mere duplication of that formed in the ventral pathway. In addition to shape selectivity, we observed stimulus-driven cognitive effects in both areas. Stimulus repetition suppression in LIP was similar to the well-known repetition suppression in AIT and may be associated with the "inhibition of return" memory effect observed during reflexive attention.

Action Potentials↗
PubMed1989

Detection and recognition of visual field defects resulting from lesions involving the visual pathways.

A prospective study of visual field defects associated with lesions of the visual pathway was carried out using kinetic and suprathreshold static stimuli with a view to establishing the most effective screening method for these field defects. The 215 abnormal fields so obtained showed that all field defects due to lesions of the visual pathways are detectable within 30 degrees of fixation and that not only is central field testing mandatory in excluding such a field defect, but more peripheral field testing alone is ineffective. This study also revealed that when kinetic fields are charted, it is probably not worthwhile searching for scotomata other than within the most central part of the field. Furthermore, where outer and inner isopter depression is not coextensive, inner isopters are always depressed more than outer isopters when the field defect is due to a lesion of the visual pathway.

Central Nervous System Diseases↗
PubMed1988

Intracranial visual pathway gliomas in children with neurofibromatosis.

The association between neurofibromatosis and visual pathway gliomas is well documented. The introduction of computed tomography and magnetic resonance imaging has heralded a new era in the understanding of visual pathway gliomas. Both of these noninvasive neuroinvestigative techniques have demonstrated extensive abnormalities throughout the visual pathway in children with visual pathway gliomas, especially in those with neurofibromatosis. The clinical significance of these abnormal areas of brain, especially in asymptomatic patients, is unknown. In an attempt to clarify the incidence, natural history, and clinical course of patients with neurofibromatosis and visual pathway lesions, we reviewed our experience with 24 patients managed consecutively at Children's Hospital of Philadelphia over the past 12 years. The patients in this series were compared to 29 children with visual pathway gliomas without neurofibromatosis who were evaluated at our institution over the same period of time. Visual pathway gliomas in children with neurofibromatosis differ from those in children without neurofibromatosis. In general, lesions tended to be more extensive in patients with neurofibromatosis and the clinical course of these patients is more variable. Twelve of the 24 patients with neurofibromatosis in our series had symptoms of progressive disease at the time of diagnosis and underwent treatment with variable results. Twelve children with neurofibromatosis and visual pathway lesions had static lesions at the time of diagnosis and, to date, 3 have developed progressive disease. From our review we can make some recommendations concerning the management of children with neurofibromatosis and visual pathway gliomas, but many questions remain unanswered. Sequential follow-up of a large cohort of both asymptomatic and symptomatic children with neurofibromatosis and visual pathway lesions is needed to more definitively outline the best management approach for these patients.

Adolescent↗
PubMed1981

Radiation therapy in and about the retina, optic nerve, and anterior visual pathway. Psychophysical assessment.

Visual changes may develop in patients receiving radiation therapy for malignant neoplasms in and about the optic nerve and anterior visual pathway. Cases have been studied using a series of psychophysical tests, including kinetic perimetry, increment threshold determinations, Flashing Repeat Static Test, and sustained- and transient-like functions. A characteristic time-dependent reduction in sensitivity has been identified in these patients. This finding, in addition to the presence of nerve fiber bundle defects, appears to place the pathologic changes in the axon of the ganglion cell posterior to the lamina cribrosa. Any change in the sustained- and transient-like functions, the organization of which appears to be in the neural retina, was seen only if a concomitant radiation retinopathy was identified.

Adenocarcinoma↗
PubMed1999

A possible selective impairment of magnocellular function in compression of the anterior visual pathways.

Two parallel visual systems, the magnocellular (M) and parvocellular (P) pathways, originate from different types of retinal ganglion cells, and are known to be segregated in different portions of the pregeniculate visual pathways. Their relative contribution to two main cortical streams, dorsal and ventral, is still under discussion, but it is reasonable to suppose that selective damage to the M or P subcortical system might interfere with specific aspects of processing within one or the other cortical system. Using two different apparent-motion tasks, we compared the performance of patients affected by compression of the ventral part of the pregeniculate visual pathways with that of normal controls. In the first task, observers detected small displacements of a low-contrast vertical bar, while in the second task they estimated the visible persistence of moving dots. In the first task, patients were impaired with parafoveal displays, especially in the temporal portion of the visual field. In the second task, patients showed reduced suppression of visible persistence at long, but not at short, exposure durations. Three considerations support the hypothesis that these results represent a selective impairment of the M system. First, M axons are more likely to suffer from compression, particularly in the case of a mass growing from below since they are known to occupy a ventral subpial position in the optic chiasm and tract. Second, the performance of patients with a ventral compression is consistent with the characteristics of the response properties of P ganglion cells, which have previously been shown to exhibit elevated and unmodulated thresholds for displacement detection in the macaque monkey. Third, such patients are less sensitive to the inhibitory signals that suppress visible persistence, which probably originate in the M system.

Adenoma↗
PubMed1995

Receptive-field dynamics in the central visual pathways.

Neurons in the central visual pathways process visual images within a localized region of space, and a restricted epoch of time. Although the receptive field (RF) of a visually responsive neuron is inherently a spatiotemporal entity, most studies have focused exclusively on spatial aspects of RF structure. Recently, however, the application of sophisticated RF-mapping techniques has enabled neurophysiologists to characterize RFs in the joint domain of space and time. Studies that use these techniques have revealed that neurons in the geniculostriate pathway exhibit striking RF dynamics. For a majority of cells, the spatial structure of the RF changes as a function of time; thus, these RFs can be characterized adequately only in the space-time domain. In this review, the spatiotemporal RF structure of neurons in the lateral geniculate nucleus and primary visual cortex is discussed.

Animals↗
PubMed1983

Higher functions and plasticity in visual pathways.

A summary of the visual pathways in the brain is presented as a basis for considering abnormalities in this system. The role of the cortical associative regions in visual function is briefly delineated. A short summary of experiments describing plastic properties of the visual pathways at early age is also presented, and experiments describing neural and behavioural changes after binocular deprivation are reviewed. It is concluded that early visual deprivation leads to a profound alteration of the associative systems of the brain and that in monkeys and humans these changes are difficult to remedy later. Therefore early detection and correction of visual abnormalities is very important as well as early compensation using other forms of sensory communication.

Adult↗
PubMed2004

Intracranial pathology of the visual pathway.

Intracranial pathologies involving the visual pathway are manifold. Aligning to anatomy, the most frequent and/or most important extrinsic and intrinsic intracranial lesions are presented. Clinical symptoms and imaging characteristics of lesions of the sellar region are demonstrated in different imaging modalities. The extrinsic lesions mainly consist of pituitary adenomas, meningeomas, craniopharyngeomas and chordomas. In (asymptomatic and symptomatic) aneurysms, different neurological symptoms depend on the location of aneurysms of the circle of Willis. Intrinsic tumors as astrocytoma of any grade, ependymoma and primary CNS-lymphoma require the main pathology in the course of the visual pathway. Vascular and demyelinating diseases complete this overview of intracranial lesions.

Astrocytoma↗
PubMed1980

The incidence and nature of visual pathway involvement in Friedreich's ataxia. A clinical and visual evoked potential study of 22 patients.

Pattern-reversal visual evoked potentials (VEP) were recorded from 22 patients (mean age 33.7 years) with Friedreich's ataxia, 15 of whom also had a detailed neuro-ophthalmological assessment prior to the VEP examination. None had noted symptomatic visual impairment. Eleven of the 15 (73 per cent) examined clinically had one or more neuro-ophthalmic abnormality and 14/22 (64 per cent) had an abnormal VEP study which was always binocular and comprised absent responses, or most commonly, increased P100 component latencies. The maximum P100 latency was 143 ms and the group mean was 118 ms. The P100 amplitude was also generally reduced particularly in those patients with latencies less than 115 ms (upper limit of normal), while in those with latencies above the normal range there was a significant inverse correlation between the P100 amplitude and latency. The waveform, temporal dispersion and interocular differences were normal in almost all patients with identifiable responses, including those with prolonged VEP latencies. Electroretinograms recorded from three selected patients were either normal or minimally abnormal and suggested secondary rather than primary retinal involvement. The only VEP parameter to correlate with either the duration of the generalized disease or the visual acuity was the P100 amplitude. A good correlation was found between the VEP and the clinical neuro-ophthalmic findings. Temporal pallor of the optic disc was most often associated with an abnormal VEP result and impaired visual acuity or colour vision were uncommon in the absence of VEP abnormalities. The VEP changes and those obtained from 24 age- and acuity-matched cases of demyelinating optic neuritis are contrasted and the probable pathophysiology is discussed. Two main conclusions emerge from this study. First, there is a high incidence of asymptomatic visual pathway involvement in Friedreich's ataxia which can be demonstrated by both clinical and VEP examination. Secondly, the VEP changes in Friedreich's ataxia differ from those found in typical demyelinating optic neuropathy and are consistent with progressive nerve fibre loss and associated slowing of conduction, indicating that the visual pathway is affected by the same widespread process of axonal degeneration found throughout the nervous system.

Adult↗
PubMedDate not supplied

[Visual evoked potentials in cases of damage to visual pathways at different levels].

Visual potentials induced with a checker pattern were studied in a group of patients with damage to the visual pathways at different levels, and were compared with similar potentials in 10 adult subjects without diseases. A statistically significant prolongation of latency of the main deflections (N1, P max and N2) was observed in the group of 14 patients with optic nerve damage, while in 10 patients with lesions above the chiasma different, often normal responses were obtained. High-grade deformity of visual potentials was observed in 2 cases of visual agnosia. The study of visual evoked potentials may be in the opinion of the authors, useful in cases of damage to the optic nerve, retina and cortical visual centres.

Adult↗
PubMed1973

Genetic mechanisms determining the central visual pathways of mice.

Albino mammals have abnormal visual pathways. "Flecked" mice have a variegated pigment distribution, with roughly half the cells normally pigmented and half albino. They do not show the albino abnormality in the visual pathways. The gene at the albino locus, which determines the course of the visual pathways must, thus, have an extracellular action.

Albinism↗
PubMed1994

[A.R.G.U.S. A model for an interactive visual field and visual pathway atlas].

A.R.G.U.S. is a data base that connects visual field defects directly with possible lesion sites that are presented graphically. By means of a touch screen or "mouse," scotomata can be depicted on a VDU, while on a second monitor the computer program simultaneously shows the resulting defects in the visual pathway. It is possible to page through different sections of the visual pathway; the lesion is probably located in the section where the affected fibers lie the closest to each other and where the non-affected fibers are the farthest apart. Additionally, the VDU depicting the visual pathway can show the surrounding anatomic structures in the form of brain sections. Even in these sections, lesions can be superimposed interactively; the resulting scotomata are simultaneously depicted on the "visual field VDU." Anatomic and functional details can be displayed by touching the structure of interest. If necessary, a video clip can be activated in the same way. New anatomic findings can be considered by modifying the course of the fibers of the visual pathway. This new technique is especially helpful in distributing comprehensive neuro-ophthalmological knowledge.

Artificial Intelligence↗
PubMed1995

Effect of short term changes in blood glucose on visual pathway function in insulin dependent diabetes.

BACKGROUND: Visual pathway function is abnormal in patients with insulin dependent diabetes mellitus (IDDM) without retinopathy, yet the mechanism underlying this abnormality is unknown. It is hypothesised that short term changes in blood glucose level affect visual pathway function in IDDM. METHODS: Colour discrimination was measured in 10 uncomplicated aretinopathic IDDM patients during hyperinsulinaemic clamp, with the Farnsworth Munsell 100 hue test (100 hue test). After stable euglycaemia, patients were made hyperglycaemic (14 mmol/l), maintained euglycaemic (5 mmol/l), and rendered hypoglycaemic (2.5 mmol/l), in random order, on separate occasions at least 1 week apart. RESULTS: Short term (1-2 hours) changes in blood glucose did not affect colour discrimination: mean (SD) 100 hue error score at 2.5 mmol/l was 34 (22) compared with 35 (33) at 5 mmol/l, and 39 (28) at 14 mmol/l. CONCLUSION: These data suggest that short term (1-2 hours) changes in blood glucose are not the mechanism for visual pathway dysfunction in aretinopathic IDDM patients.

Adult↗