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PubMed1995

High resolution magnetic resonance imaging of the anterior visual pathway in patients with optic neuropathies using fast spin echo and phased array local coils.

High resolution MRI of the anterior visual pathways was evaluated using frequency selective fat suppressed fast spin echo (FSE) sequences in conjunction with phased array local coils in patients with optic neuropathies. Fifteen normal controls and 57 patients were examined. Coronal T2 weighted fat suppressed FSE images were obtained in 11 minutes with an in plane resolution of 0.39 x 0.39 mm. The optic nerve and its sheath containing CSF were clearly differentiated. Central retinal vessels were often visible. In demyelinating optic neuritis and in anterior ischaemic optic neuropathy high signal within the nerve was readily delineated. Meningiomas and gliomas involving the optic nerve were precisely visualised both in the orbit and intracranially. Extrinsic compression of the optic nerves was readily visualised in carotid artery ectasia and dysthyroid eye disease. Enlarged subarachnoid spaces around the optic nerves were demonstrated in benign intracranial hypertension. High resolution MRI of the anterior visual pathway represents an advance in the diagnosis and management of patients presenting with optic neuropathy.

Adult↗
PubMed1984

Abnormal central visual pathways in the brain of an albino green monkey (Cercopithecus aethiops).

The visual pathways of an albino green monkey have been studied electrophysiologically and by autoradiographic methods. The monkey had a white coat and pink eyes; it had a strabismus and a nystagmus. When comparisons were made with normal macaque and green monkeys, several abnormalities could be defined. In the retina there was no foveal pit. A whole mount preparation showed a central area of high ganglion cell density in which the ganglion cells were significantly larger than the most central ganglion cells of a normal monkey. More peripheral retinal areas showed an apparently normal distribution of ganglion cell sizes and packing densities. Within the optic tract the number of uncrossed retinofugal fibers was less than normal, the part of the tract that represents central vision showing almost no uncrossed component. The uncrossed input to the lateral geniculate nucleus and to the superior colliculus was similarly reduced. Regions normally receiving ipsilateral afferents from the central retina were innervated exclusively by crossed afferents. The pathways to the magnocellular geniculate layers showed a more extensive abnormality than did the pathways to the parvicellular layers. Not only were the afferents to the geniculate layers abnormal, but the laminar pattern in the nucleus was also clear than normal in some parts of the nucleus, and there were a number of abnormal laminar fusions. Within the visual cortex it was possible to demonstrate a normal mapping of the contralateral visual field through the contralateral nasal retina and through the peripheral parts of the ipsilateral temporal retina. The central parts of the temporal retina mapped abnormally in the contralateral visual cortex, so that there was a monocular map of the central parts of the visual field forming as a mirror reversal of the normal map. The normal map of the contralateral hemifield formed columns that alternated with the abnormal map of the ipsilateral hemifield. The peripheral parts of the visual field were represented as ocular dominance columns, demonstrable electrophysiologically and also by the transneuronal transport of 3H-proline.

Animals↗
PubMed1995

Dysfunction of visual pathways in HIV-1 infection.

Foveal and conventional full field pattern-shift visual evoked potentials (f-VEPs and c-VEPs) were recorded bilaterally in 100 HIV seropositive homosexual men (HIVs) and in 40 age-matched healthy controls. In HIVs, both f-VEPs and c-VEPs revealed a significant mean increase in P100 latency (p < 0.001). In stage WR2 early conduction changes were detected in 17% of the stimulated eyes by f-VEPs and in 3% by c-VEPs. In patients with CD4 cell counts below 100/microliters a 33% reduction in the mean c-VEP amplitude was found (ANOVA p < 0.01). Multivariate analyses (MANCOVA) revealed that CD4 cell depletion was independently associated with lower (p < 0.01) and zidovudine treatment with higher c-VEP amplitudes (p < 0.05). Also patients with severe CD4 cell depletion showed a trend towards higher c-VEP amplitudes (p = 0.09) and lower f-VEP latencies (p = 0.08) after long lasting zidovudine treatment (Kruskal-Wallis test). Our data suggest that f-VEPs are a sensitive measure of subclinical optic fiber dysfunction in early HIV-1 infection and that axonal loss of optic fibers emerges with manifest immune deficiency. The inverse correlation of VEP changes and zidovudine treatment merits further studies on the question, whether inhibition of HIV replication may preserve visual pathway function.

Adult↗
PubMed1983

Inhibition of non-neuronal cell proliferation in the goldfish visual pathway affects the regenerative capacity of the retina.

Proliferating cells associated with the visual pathway were found in the present study to affect the regenerative capacity of the goldfish retina following optic nerve injury. The contribution of these cells to the process of regeneration was investigated in the goldfish visual system by reducing their proliferation in the optic tract and tecta, using X-irradiation. The regenerative ability of the retina was then evaluated by the following parameters: sprouting from retinal explants, protein synthesis in the retina and accumulation of radiolabeled transported components in the tectum. X-irradiation of the visual system at an early stage of the regeneration process had a promoting effect whereas irradiation at a later stage resulted in a reduced capacity to regenerate. The results are discussed with respect to the possibility that proliferating cells, possibly glia, exert two contradictory contributions: an inhibitory effect at the site of injury, whereas distal to it, a supportive, perhaps trophic effect.

Animals↗
PubMed1990

Phylogeny of putative cholinergic visual pathways through the pretectum to the hypothalamus in teleost fish.

Three patterns of pretectal organization can be discerned morphologically in teleosts. The taxonomic distribution of these pretectal patterns suggests that the intermediately complex pattern (seen in most teleost groups) has given rise to both the elaborate pattern (seen in percomorphs) and the simple pattern (seen in cyprinids). Two pretectal patterns (intermediately complex and elaborate) form part of similar, homologous visual pathways to the hypothalamus; the third pattern is involved in a nonhomologous pathway to the hypothalamus. Acetylcholinesterase (AChE) histochemistry was used in the present study in order to characterize these pretectal patterns further. It is demonstrated that AChE is a highly selective and reliable interspecific marker for all divisions of the superficial pretectum, the nucleus corticalis, the posterior pretectal nucleus (or nucleus glomerulosus) and portions of the inferior lobe. Therefore, the histochemical data support the hypothesis of a homology between the three patterns of pretectal organization in teleosts. Furthermore, the present data provide a basis for more specific investigations regarding the involvement of acetylcholine as a neurotransmitter within the visual pathways to the hypothalamus in teleosts.

Acetylcholinesterase↗
PubMed1994

Dolphin peripheral visual pathway in chronic unilateral ocular atrophy: complete decussation apparent.

Components of the peripheral visual pathway were examined in two bottlenose dolphins, Tursiops truncatus, each with unilateral ocular degeneration and scarring of 3 or more years' duration. In both animals, the optic nerve associated with the blind eye (right eye in Tg419 and left eye in Tt038) had a translucent, gel-like appearance upon gross examination. This translucency was also evident in the optic tract contralateral to the affected eye. In Tg419, myelinated axons of varying diameters were apparent in the left optic nerve, whereas the right optic nerve, serving the blind eye, appeared to be devoid of axons. In Tt038, myelinated axons were associated with the right optic nerve (serving the functional eye) and left optic tract but were essentially absent in the left optic nerve and right optic tract. Examined by light microscopy in serial horizontal sections, the optic chiasm of Tt038 was arranged along its central plane in segregated, alternating pathways for the decussation of right and left optic nerve fibers. Ventral to this plane, the chiasm was comprised of fibers from the left optic nerve, whereas dorsal to the central plane, fibers derived from the right optic nerve. Because of this architectural arrangement, the right and left optic nerves grossly appeared to overlap as they crossed the optic chiasm with the right optic nerve coursing dorsally to the left optic nerve. At the light and electron microscopic levels, the optic nerves and tracts lacking axons were well vascularized and dominated by glial cell bodies and glial processes, an expression of the marked glial scarring associated with postinjury axonal degeneration. The apparent absence of axons in one of the optic tract pairs (right in Tt038 and left in Tg419) supports the concept of complete decussation of right and left optic nerve fibers at the optic chiasm in the bottlenose dolphin.

Animal Diseases↗
PubMed1977

Aspects on the treatment of gliomas of the anterior visual pathway.

Partial excision of the glioma of the anterior visual pathway seemed to have no effect on the vision in 7 patients and had a negative effect in 2. These results support the opinion that no excision should be made in such tumours. However, the course of the disease in one exceptional patient raises doubts about the general validity of this rule. In this case the postulated chiasmal glioma proved to be an exophytic glioma arising in one intracranial optic nerve and compressing the other. Excision of the exophytic portion caused rapid and considerable improvement of vision in both eyes. Direct visualization by craniotomy was needed to separate this mode of growth from the common intrinsic growth of such tumours.

Adolescent↗
PubMed1989

Preliminary studies of cytokine-induced functional effects on the visual pathways in the rabbit.

Epidural visual evoked potentials (VEP) were used to study the role of cytokines in the induction of pathophysiologic changes associated with inflammation in the central nervous system (CNS) of the rabbit. In normal rabbits, intraocular injection of human recombinant interferon-gamma (IFN-gamma) and tumor necrosis factor (TNF) increased the peak latency of the cortical VEP by more than 2 ms within 3 h of injection; equal volume injections of control substances had no effect. Alterations in conduction induced by IFN-gamma and TNF reversed within 24 h and could be reinduced by reinjection. Intraocular injection of recombinant human interleukin-1 beta (IL-1) induced a more progressive delay in conduction that peaked 24 h after intraocular challenge and reversed over the ensuing 48 h. Pathologic examination of the tissues indicated that the primary effect of these cytokines is on the vasculature and induces changes associated with inflammation. The results suggest that the acute reversible effects of cytokines on CNS function are associated with vascular events; further they support the sensitivity of the 'rabbit eye model' for studies on the pathophysiologic effect of inflammatory mediators on the CNS in vivo.

Animals↗
PubMed1994

Selective suppression of the magnocellular visual pathway during saccadic eye movements.

Visual scientists have long sought to explain why the world remains stable during saccades, the ballistic eye-movements that continually displace the retinal image at fast but resolvable velocities. An early suggestion was that vision may be actively suppressed during saccades, but experimental support has been variable. Here we present evidence that saccadic suppression does occur, but that it is selective for patterns modulated in luminance at low spatial frequencies. Patterns of higher spatial frequency, and equiluminant patterns (modulated only in colour) at all spatial frequencies were not suppressed during saccades, but actually enhanced. The selectivity of the suppression suggests that it is confined to the colour-blind magnocellular stream (which provides the dominant input to motion centres and areas involved with attention), where it could dull the otherwise disturbing sense of fast low-spatial-frequency image motion. Masking studies suggest that the suppression precedes the site of contrast masking and may therefore occur early in visual processing, possibly as early as the lateral geniculate nucleus.

Color Perception↗
PubMed1990

The visual pathways of eutherian mammals and marsupials develop according to a common timetable.

Data from cats, ferrets, hamsters, macaques, mice, rabbits and rats concerning the time of occurrence of 26 developmental events involved in the establishment of the retinofugal, geniculocortical, corticogeniculate and corticocollicular pathways were analysed. For each species the timing of developmental events was expressed as a proportion of the period between conception and eye opening ('caecal period'). For 6 of these events, the values for all species fell within a range of 1-5% of the caecal period, the values for 11 other events fell within a range of 6-10% of the caecal period, 4 events had ranges of 11-15% of the caecal period, and only 5 events were spread over more than 15% of the caecal period. The 26 events had an overall mean variation of about 11% of the caecal period, suggesting that the visual pathways of eutherian mammals develop according to a common 'timetable' that is related to the duration of the caecal period. One of the roles of this common timetable may be to assist the establishment of orderly interconnections between the visual centres. Relatively few data are available concerning the timing of developmental events in marsupial visual pathways. However, it is apparent that, during the first half of the caecal period, most events occur much earlier in marsupials than in eutherians, whereas during the second half of the caecal period most events occur at the same stages of the caecal period in both marsupials and eutherians. The accelerated rate of visual development during the first half of the caecal period in marsupials may be related to the precocious development that they undergo prior to their very early birth.

Animals↗
PubMed1985

Gliomas of visual pathways and hypothalamus in children--a preliminary report.

26 children with gliomas of the visual pathway and hypothalamus were seen during 5 years. 4 of them had intraorbital tumors, in 22 children tumors were localized in the chiasmal/hypothalamic regions. In 25 patients the tumors were surgically explored. All 4 intraorbital gliomas were radically removed using a transcranial approach. Exploration without biopsy was performed 7 times, exploration plus limited biopsy in 3 cases. In the remaining 11 operated children partial or subtotal removal of the tumor was possible. One of the 18 histologically verified tumors was an anaplastic glioma, the others were typical pilocytic astrocytomas. 12 children had hydrocephalus. 7 patients died, 19 are still alive. The operative mortality was 4 out of our 25 operated cases (16%). All of these patients had large tumors with posterior spread into the hypothalamus. In future, surgery in these children should be confined to exploration and limited biopsy followed by radiotherapy. We advocate exploration and biopsy in all chiasma/hypothalamic tumors. The growth potential of these tumors is individually variable. We recommend to follow-up all patients at 3 months' intervals by means of visual evoked potentials, visual acuity, fundoscopy and visual field testing. CT scans and X-rays of the optic canals should be performed once a year. Surgery should only be considered if clinical and/or neuroradiological progression has been documented.

Adolescent↗
PubMed1979

Computed tomography of the visual pathways.

Many articles have discussed the anatomy and pathology of the orbits. Although this area is exquisitely visualized via computed tomography, the bulk of the visual apparatus lies behind the optic canal. A variety of pathologic conditions will manifest themselves by changes in the visual fields. This article demonstrates the normal anatomy of the visual pathways within the brain by CT scanning and correlates various changes that cause visual field defects.

Adult↗
PubMed1991

N-acetylaspartylglutamate immunoreactivity in neurons of the monkey's visual pathway.

The acidic dipeptide N-acetylaspartylglutamate (NAAG) was identified immunohistochemically within neurons of the visual pathways of two adult macaque monkeys which had undergone midsagittal sectioning of the optic chiasm 6 or 9 years earlier. In both temporal and nasal retinae, amacrine cells, including some displaced amacrine cells, expressed NAAG immunoreactivity. In temporal but not nasal retina, retinal ganglion cells were stained, as were their dendrites in the inner plexiform layer, and their axons in the optic nerve fiber layer. In nasal retina, the ganglion cells had degenerated because they were axotomized by the optic chiasm section. In the target regions of the retinal ganglion cells, the superior colliculus and the lateral geniculate nucleus (LGN), both neuropil and cell bodies were stained. In LGN, staining was confined to layers 2, 3, and 5, that is, to the layers innervated by the intact ipsilateral pathway. Immunoreactivity was also seen in the cells of layers 2, 3A, 4B, 5, and 6 of area 17 and layers 3 and 5 of area 18. The neuropil was stained in all layers of area 17, but more heavily in layers 1, 2, 4B, the bottom of 4C beta, 5B, and 6B. Within 4C the staining was patchy; in tangential sections there were alternating bands of light and dark label which matched the ocular dominance bands demonstrated by cytochrome oxidase histochemistry in adjacent sections. This banding pattern is consistent with the presence of NAAG in geniculocortical terminals of the intact ipsilateral pathway and the absence of such terminals for the contralateral pathway, which had undergone transneuronal degeneration due to the optic chiasm sectioning. Overall, our results for monkey are very similar to those in cat and suggest that NAAG or a structurally related molecule may have a prominent role in the communication of visual signals at retinal, thalamic, and cortical levels.

Animals↗
PubMed1989

Spatial contrast sensitivity in unilateral cerebral ischaemic lesions involving the posterior visual pathway.

Contrast sensitivity function was studied in 16 patients with unilateral ischaemic lesions involving the posterior visual pathway. Sixty-two percent of the patients showed contrast sensitivity loss in at least one eye for horizontal or vertical stimulus orientation. Visual perception was distorted in a qualitatively different way according to the anteroposterior site of the lesion. Patients with occipital or occipitotemporal lesions showed high spatial frequency selective losses and patients with temporal or parietal lesions low frequency selective losses. Stimulus orientation selectivity was observed in patients with lesions of the primary visual cortex as well as in patients with lesions anterior to the striate cortex. Contrast sensitivity orientation-selective losses were demonstrated in 14 of the 17 'affected' eyes.

Aged↗
PubMed1987

Significance of abnormal pattern electroretinography in anterior visual pathway dysfunction.

The pattern electroretinogram (PERG) findings in 72 patients with disease of the anterior visual pathways are presented in relation to the site of dysfunction. Two components of the PERG are described which are selectively involved in different pathologies. In particular, the main positive P50 component is invariably affected in retinal/macular dysfunction, whereas the late negative N95 component is principally affected in optic nerve disease.

Adolescent↗
PubMed1967

Visual pathway mediating pineal response to environmental light.

Activity of the melatoninforming enzyme, hydroxyindole-O-methyltransferase, in rat pineal is increased when the animal is exposed to continuous darkness, and it is decreased by exposure to continuous light. Response to environmental light is initiated in the retina and transmitted to the pineal by way of the central nervous system and the cervical sympathetics. The central visual pathway essential for mediation of this response is the inferior accessory optic tract. Visual pathways to thalamus and tectum do not participate in this response.

Animals↗
PubMed1986

Interocular transfer in parallel visual pathways in pigeons.

Pigeons were trained to perform intensity, color and pattern tasks monocularly. After their training was completed, a unilateral electrolytic lesion was made either in the nucleus rotundus or in the nucleus opticus principalis thalami (OPT). The lesion was made in the trained hemisphere (contralateral to the trained eye) in half of the subjects and in the untrained hemisphere in the other half. After a 7-day recovery period the birds were retrained on the same tasks with the previously untrained eye. A rotundal lesion, on either side, resulted in the loss of interocular transfer of discrimination, whereas neither contralateral nor ipsilateral OPT lesions affected discrimination. These results suggest that the tectofugal visual pathway plays a crucial role in the interhemispheric transfer of visual information in pigeons.

Animals↗
PubMed1982

Pattern evoked cortical potentials and compressive lesions along the visual pathways.

It is stressed that not only demyelinating diseases, but also compressive lesions along the anterior visual pathways, may cause severely disturbed or clearly delayed occipital potentials to pattern reversal stimulation. Only tumors exerting real pressure on optic nerve fibres cause these relatively marked disturbances of the pattern responses. Such tumors are tumors of the optic nerve itself, those along the optic canal, at the base of the anterior fossa or around the chiasm, and not tumors of the orbit or those situated beyond the chiasm.

Adenoma, Chromophobe↗