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Results for “OPTIC PATHWAY”

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PubMed2006

Meyer's loop and the optic radiations in the transsylvian approach to the mediobasal temporal lobe.

OBJECTIVE: In the transsylvian approach to the mediobasal temporal structures, the temporal horn is approached through the floor of the sylvian fissure. The anterior bundle of the optic radiations (Meyer's loop) courses between the floor of the sylvian fissure and roof of the temporal horn and could be damaged in this approach. This study was designed to define the route through the floor of the sylvian fissure least likely to damage the optic pathways. METHODS: Meyer's loop was dissected by applying Klingler's fiber dissection technique in 10 formalin-fixed human hemispheres. Several measurements quantified the relationship of the Meyer's loop to surgically important structures. RESULTS: This study identified a triangular safe area below the floor of the sylvian fissure through which the temporal horn could be accessed in the transsylvian approach with a low risk of damaging the optic radiations. An incision in the floor of the sylvian fissure directed downward at the level of limen insula and the adjacent 5 mm of the inferior insular sulcus would avoid the optic radiations. An incision directed straight downward 10, 15, and 20 mm behind the limen in the inferior insular sulcus would cross Meyer's loop and would need to be directed downward and medially as much as 80 degrees from the sagittal plane to avoid Meyer's loop. CONCLUSION: In the transsylvian approach to the temporal horn, incisions at the level of the limen, or adjacent 5 mm of the inferior insular sulcus, are less likely to damage Meyer's loop and the optic radiations than more posterior incisions along the inferior insular sulcus. Incision at this safe level commonly opens into the amygdala, a portion of which is removed to provide entry into the temporal horn for removal of the mediobasal structures.

Cadaver↗

PubMed1994

The return of phosphorylated and nonphosphorylated epitopes of neurofilament proteins to the regenerating optic nerve of Xenopus laevis.

Neurofilament proteins of mammalian axotomized peripheral axons, which regenerate effectively, resemble those of embryonic axons. However, injured centrally projecting mammalian axons, which fail to regenerate, have very different neurofilament compositions than during development. If changes in neurofilament composition after injury reflect the ability of axotomized neurons to regenerate effectively, then the neurofilaments of centrally projecting axons that can regenerate should more closely resemble those of developing axons. In this study, the neurofilament compositions of injured optic axons of the frog, Xenopus laevis, were examined, since these axons can regenerate a fully functional projection. Antibodies to phosphorylated and nonphosphorylated forms of neurofilament proteins that had been used previously to study the neurofilament composition of newly developing X. laevis optic axons were used in immunocytochemical studies to examine the return of neurofilaments to the optic nerve after an intraorbital nerve crush. Intraocularly injected wheat germ agglutinin conjugated to horseradish peroxidase was used to label the regenerating axons independently of their neurofilaments. Neurofilament immunoreactivities disappeared rapidly from crushed axons during the first week after surgery. By nine days after surgery, antibodies to nonphosphorylated forms of middle (NF-M) and low molecular weight (NF-L) neurofilament proteins and the Xenopus neuronal intermediate filament protein (XNIF) began to stain the nerve just beyond the lesion. By this time, however, growing axonal terminals had reached the optic chiasm. Antibodies to phosphorylated epitopes of NF-M began to stain axons at 15 days, just as growing axons began to arrive at the optic tectum. Nonphosphorylated high molecular weight neurofilament protein (NF-H) began to appear in axons between 18 and 21 days after surgery. Thus, the reappearance of neurofilaments during optic axon regeneration resembled the general pattern seen during development. The chief difference between development and regeneration was that neurofilament epitopes took longer to emerge during regeneration. One possibility is that cues encountered along the optic pathway influence the neurofilament composition of retinal ganglion cell axons. Then, the greater distances travelled by regenerating axons could account for the longer time taken for their neurofilament compositions to mature.

Animals↗

PubMed1988

Normal visual pathway routing in dissociated vertical deviation.

Flash visually evoked cortical potentials have been recorded in three groups of age- and sex-matched subjects; one comprised of subjects with dissociated vertical deviation, one comprised of subjects with oculocutaneous albinism and one group of controls. The latency of the major positive (P2) component did not show statistically significant contralateral lateralization on monocular stimulation in either the dissociated vertical deviation group or the control group. Contralateral lateralization was found in the albino group at a statistically significant level (P less than 0.01). It is concluded that subjects with dissociated vertical deviation do not possess the typical albino optic pathway misrouting that has been reported.

Adolescent↗

PubMed1976

Malignant optic glioma in a 70-year-old patient.

In a 70-year-old man with glioma of the optic nerves and tracts, the initial symptom was a unilateral loss of vision that progressed rapidly and was followed by amaurosis of both eyes. All diagnostic radiological procedures were negative. Four months after the onset of the disease, the patient developed hemiplegia, became comatose, and died. Post-mortem examination revealed a glioblastoma multiforme of both optic nerves, chiasma, and optic tracts that extended posteriorly into the left thalamus and medial geniculate body. The tumoral thickening of the optic nerves was absent in the intracanalicular part, a finding that concurred with the normal radiological appearance of the optic foramen. Glioblastoma multiforme of the optic pathways should be included in the differential diagnosis of acute visual failure in elderly people, even though the final diagnosis may be possible only at postmortem examination.

Aged↗

PubMedDate not supplied

Synchronous optic and pineal pilocytic astrocytomas in a paediatric patient with neurofibromatosis type 1.

A 12-year-old girl with neurofibromatosis type 1 presented with headache, visual acuity and visual field disturbance. Computed tomography and magnetic resonance imaging revealed an enhanced solid mass involving her right optic nerve and optic chiasm, and a cystic lesion in the pineal region that had resulted in obstructive hydrocephalus. An open biopsy of the right optic nerve tumour was performed, and it was histologically identified as a pilocytic astrocytoma. Local irradiation of 50 Gy to the optic pathway tumour was performed, and the tumour has remained stable for more than 29 months. On the contrary, the pineal cystic mass that was also histologically identified as a pilocytic astrocytoma showed marked enlargement within 5 months after a subtotal resection. Chemotherapy with cisplatin and vincristine was performed after a second surgery, and the pineal tumour has not re-grown in 18 months. To our knowledge, this is the first case report to describe synchronous optic and pineal pilocytic astrocytomas associated with neurofibromatosis type 1.

Astrocytoma↗

PubMed1988

[Homonymous hemianopsia in brain tumors].

Homonymous hemianopsia may be caused by tumors in the region of the optic tract, the lateral geniculate body, the optic radiation, and the visual cortex. Tumors are responsible for about two-thirds of the temporal lesions and about one-half to one-third of the parietal and occipital lesions. With brain tumors a chronological sequence of two groups of signs and symptoms is the rule: first the focal symptoms corresponding to the tumor lesion in a defined cerebral area, later the distant effects of the increasing volume of the tumor, which lead to the general signs of increased intracranial pressure. The different types of homonymous hemianopia in tumor lesions along the suprachiasmatic pathway (optic tract, lateral geniculate body, temporal lobe, parietal lobe, occipital lobe) are described and discussed. The general neurological signs and symptoms are briefly reviewed. Demonstration of important cerebral diagnostic examination methods (plain X-ray, electroencephalogram, computer tomogram, nuclear magnetic resonance, angiography). Differential diagnosis of brain tumors (hematomas, abscesses, granulomas, parasites etc.).

Brain Mapping↗

PubMed1991

Lens fluorometry: light-attenuation effects and estimation of total lens transmittance.

Front-face fluorometry of the axial fluorescence profile of the lens is influenced by attenuation of light along the optical pathways leading to and from the detection volume. The resulting distortion is evident when the curve is compared with the intrinsic profile that can be recorded by direct measurement on the transected lens. Assuming that attenuation of light by scatter and absorption is proportional to fluorescence, the intrinsic profile can be reconstructed from the non-invasive fluorescence profile. The calculations involve the deduction of total lens transmittance and fluorescence-related absorptivity, parameters that provide essential information about the optical quality of the lens. The method was applied to human lens fluorometry in vivo and in vitro (excitation 430-490 nm, fluorescence 530-630 nm). Even the most anterior lens fluorescence measurements were found to be markedly affected by attenuation of light in the lens. Lens transmittance estimates agreed within +/- 12% with direct measurements of lens transmittance. The differences were due in part to inter-individual variations in the shape of the intrinsic fluorescence profile of the lens.

Absorption↗

PubMed1993

Neurofibromatosis type 1: magnetic resonance imaging findings.

The purpose of this study was to determine the locations and characterize the types of brain abnormalities noted on brain magnetic resonance imaging in patients with probable and definite neurofibromatosis type 1. Patients with definite neurofibromatosis type 1 (n = 17) were studied when clinically indicated, and patients with probable neurofibromatosis type 1 (n = 9) were studied to evaluate for asymptomatic optic pathway glioma. Of the 26 patients evaluated, 14 (53%) had high-intensity signal abnormalities and 11 (42%) had significant structural abnormalities. Subsequent clinical follow-up has confirmed conversion to a definite neurofibromatosis type 1 diagnosis in three of the four cases of probable neurofibromatosis type 1 who had high-intensity signal abnormalities. The most common locations of high-intensity signal lesions were in the globus pallidus of the basal ganglia and cerebellar white matter. Tortuous or thickened optic nerves and/or optic chiasm were seen in eight cases. Brain magnetic resonance imaging scans frequently reveal high-intensity signal lesions and structural abnormalities in selected patients with both probable and definite neurofibromatosis type 1. These findings may allow for a definitive diagnosis in clinically probable cases.

Adolescent↗

PubMed1984

Enzyme histochemical changes in retinal ganglion cells and the optic nerve after goldfish optic nerve lesion. A regenerative and hypertrophic phenomena study.

After sectioning of the goldfish optic nerve a number of enzyme histochemical changes are observed in the hypertrophied retinal ganglion cells and in the optic nerve. Between one and eighteen days postoperatively an increase in the amount of acid phosphatase reaction product is noted. The enhanced activity decreased to normal first in the optic nerve, followed by the optic tract and tectum. Four days postoperatively higher levels of activity were noted in the hypertrophic retinal ganglion cells for the enzymes NADH tetrazolium reductase, cytochrome oxidase, glutamate dehydrogenase and lactate dehydrogenase. The same enzymes also showed an activity increase in the lesioned optic nerve after four to ten days postoperatively, beginning at the cut and gradually spreading towards the optic tectum. Between fifteen and eighteen days the activity dropped to normal in the hypertrophic retinal ganglion cells, while in the lesioned nerve raised levels of reaction products could be seen till days thirty-five and/or forty-five. It was concluded that the degeneration of the optic pathway is marked by the increase of acid phosphatase activity, whereas the process of regeneration is characterized by an increase of NADH tetrazolium reductase, cytochrome oxidase, glutamate dehydrogenase and lactate dehydrogenase activities. The possible functional implications of these enzymes in the regenerative phenomena are discussed.

Animals↗

PubMed1992

Suprasellar and sellar tumors in childhood and adolescence.

Suprasellar and sellar region tumors in children constitute a diverse group of lesions. We advocate an aggressive surgical approach to these tumors for diagnostic and therapeutic purposes. With detailed knowledge of the microneurosurgical anatomy of this region, the neurosurgeon can choose from a number of operative approaches on the basis of tumor size and location. The benefits of radiation therapy for craniopharyngiomas and optic chiasmatic/hypothalamic tumors must be carefully weighted against the substantial long-term risks associated with irradiation of the developing brain in this region. During the next decade, the role of primary chemotherapy for germinoma and adjuvant chemotherapy for optic pathway gliomas will be determined. Also, the role of stereotactic radiation therapy, of great value to some children with recalcitrant tumors in the suprasellar region, may be better defined.

Adolescent↗

PubMedDate not supplied

Cerebral N-acetylaspartate is low in patients with multiple sclerosis and abnormal visual evoked potentials.

PURPOSE: Our purpose was to compare cerebral proton MR metabolite changes in patients with multiple sclerosis (MS) and abnormal visual evoked potentials (VEPs) with those in MS patients with normal VEPs. METHODS: Seventeen subjects with clinically definite MS were studied with VEPs and MR spectroscopic imaging. Proton MR metabolites were measured using a fast spectroscopic imaging technique called proton echo-planar spectroscopic imaging (PEPSI). Kurtzke's Expanded Disability Status Scale (EDSS) score was also ascertained for each subject to obtain a clinical rating. Twelve regions of interest within the visual pathway of the cerebrum were evaluated for levels of N-acetylaspartate (NAA), choline, creatine, and the presence or absence of MR-detectable lesions. RESULTS: PEPSI NAA values (water-normalized, CSF-corrected) were significantly lower in MS subjects with abnormal VEPs than in subjects with normal VEPs. MR-detectable lesion fractions and EDSS scores were also significantly different between the two VEP groups, but NAA comparison had a P value 100 times less than either of these measures. CONCLUSION: In patients with MS, NAA measurements in the optic pathways of the brain were sensitive to VEP abnormalities. NAA was more sensitive to VEP changes than were choline, creatine, MR-detectable lesions, and EDSS score.

Adult↗

PubMed1988

Regenerated optic fibers in goldfish reestablish a crude sectoral order in the visual pathway.

The goldfish optic pathway is regenerated after an optic nerve crush. We have examined the axonal topography of the regenerated pathway by labeling, with horseradish peroxidase (HRP), axons originating from retinal sectors or annuli. The positions of the labeled axons in the cross section of the pathway were compared to the normal and related to the factors that may influence axonal pathfinding. The positions of retinal axons in the cross section of the normal pathway are predictable from the retinal addresses of the ganglion cells described by the polar coordinates r (the distance from the optic disc) and theta (the sectoral or clockface position). The two coordinates map orthogonally onto the cross section of the pathway; r varies monotonically along one axis; theta varies along a perpendicular axis. The normal r-order, present in the nonregenerated stump of the experimental nerve, was severely degraded and perhaps lost entirely in the regenerated optic nerve, tract, and brachia. Sectoral order was also lost as the axons passed the crush site, but it was reestablished, albeit crudely, in the regenerated tract and brachia where axons tended to occupy positions appropriate to their dorsal, ventral, nasal, and temporal retinal origins. The exit sequence of the regenerated axons from the stratum opticum into the tectal neuropil was normal: temporal first, nasal last. These results suggest that the regenerating fibers followed some theta-specific cue located in the nonaxonal environment. It seems likely that the original axons probably followed the same cue. In contrast, the absence of r-order suggests that there is no r-specific cue for the regenerates to follow. It seems likely that the original r-order was a consequence of nonspecific influences--the orderly spatiotemporal growth of the retina and the existence of a permissive region for axonal growth.

Animals↗

PubMed1986

Electrophysiological and pathological studies on Creutzfeldt-Jakob disease with retinal involvement.

In a case of Creutzfeldt-Jakob disease in a 59-year-old female, multifocal degeneration from the cerebral cortex through the visual pathway to the retina was detected clinically, electrophysiologically, and pathologically. Visual evoked cortical potentials (VECPs) showed a peculiar huge negative wave in the early stage but the amplitude reduced gradually. The a- and b-waves of the ERG were detectable in the final stage. Dynamic topography of VECPs revealed a delay of excitation in the visual cortex in the early stage, but a complete defect of the cortical potential and diminished reactivity of the brain stem were apparent in the later stage. Pathological findings were the spongy degeneration of the cerebral cortex, demyelination of the white matter and the optic pathway, and the degeneration of the nerve fiber layer and ganglion cell layer of the retina.

Brain↗

PubMed1979

The eye of the soldier beetle Chauliognathus pulchellus (Cantharidae).

The soldier beetle eye is unusual in having large optically isotropic corneal cones which project inwards from a thick isotropic cornea. Refraction is mainly at the corneal surface. Calculation shows that the first focal plane is near the tip of the cone, from which the optical pathway continues as a crystalline tract. At the distal end of the crystalline tract, 3 micrometer in diameter, the four cone cells enclose the proximal tip of the corneal cone; at the proximal end they enclose the distal tip of a long fused rhabdom rod. The eye is remarkable in that there are two classes of retinula cells; four cells contribute to the long thin axial rhabdom, 2 micrometer in diameter and 120 micrometer long, and the other four cells form two rounded rhabdoms, 10 x 4 micrometer in cross-section and 20 micrometer deep, which lie to one side of the optical axis. The physiological properties of individual retinula cells were measured by intracellular recording. The retinula cells are of three spectral types with peaks near 360, 450 and 520--530 nm. Except by the criterion of spectral sensitivity, the retinula cells sampled could not be sorted into more than one class. The measured value of the acceptance angle, near 3 degrees in the dark-adapted state, is consistent with the hypothesis that all sampled cells were of the anatomical type that participate in the central rhabdom rod. A calculation of the theoretical field size of individual retinula cells from measurments of refractive index and lens dimensions predicts that cells which participate in the central rhabdom will have acceptance angles near 3 degrees. The conclusion, therefore, is that only one anatomical type of cell has so far been sampled.

Adaptation, Physiological↗

PubMedDate not supplied

Arrest of myelination and demyelination in rabbit retina induced by herpes simplex virus infection.

Herpes simplex virus was injected into the vitreous of suckling and adult rabbits. In the suckling rabbits the infection caused an arrested myelination of the strip. Further, the infected strips showed degenerative changes with splitting and distension of myelin sheaths which then disintegrated. Ultrastructurally, herpes simplex virus particles were found in both oligodendroglial cells and in astrocytes in the bundles. No increase in intraocular pressure was recorded during the inflammation. The infection spread along optic pathways to the opposite side. Inflammatory cells appeared at the surface and infiltrated the degenerating strip. Especially in the contralateral eye, an extensive inflammatory cell infiltration was seen among bundles of nerve fibres which showed partly well-preserved myelin and partly with signs of demyelination reminiscent of the picture of experimental allergic encephalomyelitis in the epiretinal strip.

Animals↗

PubMed1985

Retinal function in mucolipidosis IV.

In an 18-month-old girl affected by mucolipidosis IV (ML IV) with mild corneal clouding, normal retinal activity was documented by electroretinogram (ERG) and slightly delayed optic pathway conduction was revealed by visual evoked potential (VEP). Re-examination 9 years later disclosed severe retinal alterations resulting in atrophy with reduced photopic and missing scotopic ERG components and flat VEP. These fundoscopic and electrophysiologic deteriorations in ML IV suggest progressive rod-cone impairment similar to tapetoretinal dystrophy.

Corneal Opacity↗

PubMed2002

Specific heparan sulfate structures involved in retinal axon targeting.

Heparan sulfate (HS), a structurally diverse molecule comprising distinct sequences of sulfated disaccharide units, is abundant in the developing brain and binds to axon guidance molecules. Addition of HS to the developing Xenopus optic pathway causes severe targeting errors yet it is not known how the structural diversity of this molecule relates to its role in axon guidance. We have used an in vivo brain assay to identify the structural characteristics of HS that induce aberrant axon targeting. Inhibiting sulfation of endogenous HS with chlorate causes axons to bypass their target, the tectum, and treatment with chemically modified heparins reveals that 2-O- and 6-O-sulfate groups have potent bypass-inducing activity. Experiments with purified heparin saccharides show that bypass-inducing activity correlates with distinct structures, particularly those containing a combination of 2-O- and 6-O-sulfate groups. Taken together the results indicate that specific sequences, rather than gross structural composition, are critical for activity. In situ hybridisation revealed that HS 6-O-sulfotransferase is regionally expressed along the border of the dorsal optic tract whereas 2-O-sulfotransferase is expressed broadly. Our results demonstrate that specific HS sequences are essential for regulating retinotectal axon targeting and suggest that regionalised biosynthesis of specific HS structures is important for guiding axons into the tectum.

Animals↗

PubMed1992

A practical approach to albino diagnosis. VEP misrouting across the age span.

In addition to the genetic heterogeneity in albinism, widespread clinical heterogeneity frequently impedes albino detection and differential diagnosis. Further, several auxiliary ocular and/or cutaneous manifestations of this inherited error of pigmentary metabolism are neither pre-requisite nor specific to the albino condition. However, one feature that is specific to albinism regardless of genotype or phenotype is a unique pattern of abnormal visual pathway organization. With an appropriate test paradigm, the albino visual pathway can be revealed by the non-invasive recording of the visual evoked potential (VEP) distribution across the occiput which shows contralateral hemispheric asymmetry following full field monocular stimulation. As described in this report, the VEP albino misrouting detection test has been refined to yield extraordinarily high sensitivity and selectivity across the age span from the neonate to the elderly. As the VEP profile undergoes maturational changes, these changes have been taken into account in the development of an albino age-range VEP test recipe which includes the pattern onset paradigm for older albinos and a luminance flash paradigm for the albino infant. The age appropriate optic pathway misrouting test provides reliable albino detection and definitive differential diagnosis. Further, as the albino VEP signature of contralateral asymmetry is also age specific, the VEP misrouting test can be extended to the objective assessment of visual pathway maturation.

Adolescent↗