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PubMed1984

Component specificity in albino VEP asymmetry: maturation of the visual pathway anomaly.

The existence of an isolated albino asymmetry component was investigated in the visual evoked potential (pattern appearance/disappearance response) of 96 albinos ranging in age from 3 months to 65 years. Misrouted optic pathway projections in albinism produce VEP asymmetry across the left and right occiput upon monocular whole field stimulation of a checkerboard pattern (element size, 55'). Our results indicate that the asymmetry which reflects the albino feature is contralateral and is restricted to an early period of the appearance response corresponding to the latency of the CI component. Further support for CI component specificity in albino asymmetry is provided by half-field stimulation in non-albino controls and by the results of a component maturation study in children under 6 years of age.

Age Factors↗

PubMed2000

Neurofibromatosis type 1 and precocious puberty.

Since neurofibromatosis type 1 (NF1) is a well known cause of precocious puberty (PP), we reviewed 412 NF1 pediatric patients to evaluate the prevalence of PP, the association with optic pathway tumors (OPT), and other clinical, auxological and hormonal data. Thirty-one of 412 patients had OPT (7.5%), 10/412 PP (2.4%), and in seven of these PP was associated with OPT (7/31, 22.6%). OPT in patients with PP involved the chiasm in four patients, and the optic nerves alone in three patients. The age at the onset of puberty (or better at diagnosis) ranged from 5.2 to 7.5 yr in girls (n=6) and from 7.9 to 8.9 yr in boys (n=4). LHRH agonist therapy was used in only three children because in the others the predicted height at diagnosis was good, treatment was refused or the patients were referred to us too late. The three treated patients attained a final height within the familial range. In the untreated patients the progression of puberty was not too rapid and final height was slightly below the genetic target in four patients; however, three patients had a final height markedly below the familial range. In conclusion, the prevalence of PP is increased in children with NF1, and frequently but not exclusively is associated with OPT. Moreover, sexual precocity does not seem to be necessarily bound to chiasmatic OPT. Treatment seems to be useful in the children with younger age at the onset of puberty or with a progressive decline in predicted final height.

Adolescent↗

PubMedDate not supplied

Anterior visual pathway gliomas: The last 30 years.

Modern neuroimaging provides excellent characterization of anterior visual pathway gliomas, often obviating the need for biopsy of the tumor. Management remains controversial, but if there is progression, chemotherapy is preferred for young patients. Stereotactically guided conformal radiotherapy and proton beam radiotherapy allow smaller, more precise doses of radiation to be administered and can be considered in older children with progressive disease. A mouse model of NF-1 with optic pathway gliomas has the potential to provide important insights into the development of gliomas as well as serving as a model for their effective treatment.

Animals↗

PubMed1987

Primary cerebral lymphoma presenting as steroid-responsive chiasmal syndrome.

A case of multiple primary cerebral lymphoma presenting with bitemporal hemianopsia due to a large suprasellar lesion is described; the visual symptoms improved after corticosteroid treatment. Involvement of the optic pathways is very unusual in primary central nervous system lymphomas; the visual symptoms can be due to lymphomatous uveitis or to infiltration of the optic nerves by leptomeningeal lymphoma, whereas bitemporal hemianopsia due to chiasmal compression has not been reported as first symptom of a cerebral lymphoma. The CT finding of multiple hyperdense well-enhanced lesions and their symmetrical distribution in the basal ganglia and frontal horns suggest the diagnosis of lymphoma. Improvement of neurological deficits during corticosteroid treatment is another feature typical of cerebral lymphomas.

Adult↗

PubMed1985

Evidence for differential effects of terminal and dendritic competition upon developmental neuronal death in the retina.

Retinal ganglion cells with ipsilaterally projecting axons were labelled with horseradish peroxidase injected unilaterally along the optic pathway in adult rats. Unoperated controls were compared with three groups of animals operated at birth, given (a) contralateral enucleation, (b) contralateral lesion to the optic tract or (c) both lesions simultaneously. The numbers of ipsilaterally projecting cells were increased in all three operated groups, presumably because of a reduction in natural neuronal death following diminished terminal and dendritic competition. The pattern of increase of labelled cell density varied with the type of lesion: enucleation led to a major increase within lower temporal retina; optic tract lesion caused its major increase in upper temporal retina, centred at the location of the area centralis; and the double lesion combined both effects above. The distribution of cell-body sizes was differentially affected by the lesions: enucleation led to a shift in the distribution towards the small cell side of the spectrum, when compared with the controls; optic tract lesion shifted the distribution towards the large cell side of the spectrum, but only outside the temporal crescent; and the double lesion led to a shift towards small cells within the temporal crescent and towards large cells outside the crescent, again combining the effects of the single lesions. Large alpha-like neurones with ipsilateral axons were common in the nasal retina of both groups given optic tract lesions but they were rare in the nasal retina of unoperated and, especially, of enucleated rats. The limits of the temporal crescent were unchanged, notwithstanding the large numbers of cells outside the crescent in operated rats. It is suggested that postnatal competitive interactions at the level of terminals and of dendrites control natural neuronal death in the rat retina with different requirements regarding retinal topography and ganglion cell types. The postnatal regulation of neuronal numbers is not responsible for the generation of the nasotemporal division but may be involved in the development of differential distributions of specific ganglion cell types across the retina.

Animals↗

PubMed2002

Differential responses of temporal and nasal retinal neurites to regional-specific cues in the mouse retinofugal pathway.

Retinal explants of mouse embryos were cultured together with explants of different regions in the retinofugal pathway in order to investigate whether ventral temporal (VT) and dorsal nasal (DN) retinal neurites showed differential responses to regional-specific cues in the pathway. In the presence of the chiasm, biased outgrowth of retinal neurites was found in explants of both retinal regions, which was accompanied by a reduction in total neurite growth in the VT but not the DN retina. Such differential responses to the diffusible negative influence were also observed when explants of two retinal origins were cocultured with the ventral diencephalon, but were not found with the dorsal diencephalon that contains targets of the optic axons. Indeed, extensive neurite invasion was found in the dorsal diencephalic explants and this ingrowth was more prominent for VT than DN neurites, showing a difference in axons from a distinct position in the retina to contact-mediated stimulatory activity within the target nuclei. We conclude that neurites from different regions of the retina show differential responses to the regional-specific cues in the diencephalon. These cues exist in both diffusible and contact-mediated forms that may shape the characteristic course and organization of retinal axons in decision regions of the optic pathway and the visual targets.

Animals↗

PubMed1984

Fiber-fiber interaction and tectal cues influence the development of the chicken retinotectal projection.

The development of the retinotectal projection has been studied by a new experimental approach combining antibodies against the nerve cell adhesion molecule (NCAM), and techniques for mapping neuronal pathways using rhodamine B isothiocyanate (RITC) crystals. Anti-NCAM Fab', which specifically inhibits neurite fasciculation, was injected into the eye cup of 4-day-old chicken embryos. After 4-6 days of development, a small RITC crystal was placed on the neural retina to stain selectively axons arising from a localized region. One day later the retina, optic nerve, and tectum were examined and the paths of the fluorescent retinal ganglion cell axons were traced. These studies have led to four observations: (i) The presence of anti-NCAM Fab' causes the axons to form a disordered nerve bundle at the optic fissure. (ii) Disorder produced in the optic nerve persists throughout the optic pathway up to the tectum. (iii) Many of the misrouted fibers growing on or near the tectal surface can at least partially correct their position. (iv) Late axons grow in straight tracks along other fibers and do not correct their position. Together the results suggest that formation of the retinotectal projection involves both reading of positional cues on the tectum by growth cones of early arriving retinal axons and the tracking of growth cones along preexisting fibers that normally belong to neighboring retinal ganglion cells.

Animals↗

PubMed1994

[Dosimetric studies using glass fibers].

PURPOSE: Ionizing radiation may cause discolouring of glasses by creation of colour centers. So radiation induced optical loss is a measure of absorbed dose. With a doped glass fiber a small volume optical dosimeter is developed for clinical purposes providing real time dosimetry with high spatial resolution. MATERIALS AND METHODS: Discolouring of glass by ionizing radiation is dose dependent and can be measured as light attenuation at a fixed wavelength. Light power of usual light emitting diodes (LED) is sufficient for this purpose. The readout light is conducted through a transmission fiber of arbitrary length. Concurrent measurements were performed at several wavelengths (660 to 850 nm) using a time multiplexing technique. We investigated the radiation induced light attenuation of a lead doped silica fiber with 60 Wt-% PbO2, diameter < 0.5 mm, and length < 0.1 m. The fiber was exposed to high energy photons of cesium-137, cobalt-60, 12-MV-photons, and 18-MV-photons generated by a linear accelerator, respectively. The influence of various temperatures, doses, and dose rates was tested. When sensor fiber is termed by a mirror reflected light can be detected with one transmission fiber and optical pathway is doubled. RESULTS: In a wide dose range (0 to 112 Gy) radiation induced loss represents absorbed dose in a linear manner without saturation effects. Optical loss is diminished by partial recovery of radiation damage depending on time and temperature. In order to compensate fading a phenomenological model was fitted to experimental data. Temperature dependence may be corrected by measurements with several readout wavelengths. Above 1 MeV there is merely a slight dependence on photon energy. At a size of the glass fiber reflection sensor of L = 2 cm doses of 0.04 Gy may be detected. The reproducibility at 1 Gy is about 4%. CONCLUSION: Lead doped silica fiber is suitable for radiation dosimetry in a dose range interesting for clinical practice. Fading may be compensated during irradiation using a phenomenological model. The size of a reflection sensor is comparable to thermoluminescence dosimeters. In contrast to TLD glass fiber provides real time dose measurements. By this means optical glass fiber dosimeter may be appropriate for in-vivo dosimetry in radiation therapy.

Glass↗

PubMed2006

Attempts to restore visual function after optic nerve damage in adult mammals.

Retinal ganglion cells (RGCs) and their axons, i.e., optic nerve (ON) fibers, provide a good experimental model for research on damaged CNS neurons and their functional ecovery. After the ON transection most RGCs undergo retrograde and anterograde degeneration but they can be rescued and regenerated by transplantation of a piece of peripheral nerve (PN). When the nerve graft was bridged to the visual center, regenerating RGC axons can restore the central visual projection. Behavioral recovery of relatively simple visual function has been proved in such PN-grafted rodents. Intravitreal injections of various neurotrophic factors and cytokines to activate intracellular signaling mechanism of RGCs and electrical stimulation to the cut end of ON have promoting effects on their survival and axonal regeneration. Axotomized RGCs in adult cats are also shown to survive and regenerate their axons through the PN graft. Among the cat RGC types, Y cells, which function as visual motion detector, tend to survive and regenerate axons better than others. X cells, which are essential for acute vision, suffer from rapid death after ON transection but they can be rescued by intravitreal application of neurotrophins accompanied with elevation of cAMP. To restore visual function in adult mammals with damaged optic pathway, the comprehensive and integrative strategies of multiple approaches will be needed, taking care of functional diversity of RGC types.

Animals↗

PubMed1998

Morphological dissociation between visual pathways and cortex: MRI of visually-deprived patients with congenital peripheral blindness.

MRI was used to study possible morphological changes in the visual system in 12 patients suffering from congenital blindness of peripheral (ocular) origin. While their optical pathways showed degeneration, hypoplasia or atrophy in 7 out of 12 cases, the occipital cortex appeared normal in all cases. This dissociation between afferent pathways and the cortex is contrary to the assumption that visually deprived cortex may undergo degeneration. The finding is congruent with evidence that the occipital cortex is used for other, nonvisual functions.

Adult↗

PubMed1997

Development of primary visual projections occurs entirely postnatally in the fat-tailed dunnart, a marsupial mouse, Sminthopsis crassicaudata.

We have examined the development of retinal projections in a diminutive polyprotodont marsupial, the fat-tailed dunnart, Sminthopsis crassicaudata. Here, we document the most immature mammalian visual system at birth described to date. At postnatal day (P) 0, the retinal ganglion cell layer has yet to form, and axons have not entered the optic stalk. By P4, the retinal ganglion cell layer could be distinguished at the posterior pole, and the front of growing axons extended one-third the length of the optic stalk, a distance of approximately 150 microm; a few pioneer growth cones had grown beyond the main axon group but had still to reach the midline. Axons had decussated at the optic chiasm by P10 to penetrate the base of the contralateral optic tract and, by P15, had reached the dorsal lateral geniculate nucleus (dLGN), superior colliculus (SC), and accessory optic system (AOS); ipsilaterally projecting axons matured slightly later. From P20, axons had reached the caudal SC both contralaterally and ipsilaterally and terminated throughout the depth of the retinorecipient layers. After P30, the projections gradually refined. Within the rostral dLGN, segregation into four contralateral and four ipsilateral bands occurred by P50, approximately 5 days after eye opening. The projection to the ipsilateral SC underwent refinement by P50, becoming restricted to its rostral pole, and presented as discrete patches within the stratum opticum. At birth, the dunnart visual system is comparable to early to midembryonic stages [embryonic day (E) 12, E14, E19, E24, and E30, respectively] in the mouse, rat, ferret, cat, and monkey. The extreme immaturity of the neonatal dunnart together with the observation that the entire development of the primary optic pathway occurs postnatally over a protracted period make this marsupial especially valuable for investigating factors that control pathway formation in the early developing mammalian primary visual system.

Age Factors↗

PubMed2004

Immunohistochemical localization of cocaine- and amphetamine-regulated transcript peptide in the central nervous system of the frog Rana esculenta.

The distribution of cocaine- and amphetamine-regulated transcript peptide (CARTp)- like immunoreactivity was studied only in the rat central nervous system (CNS). In mammals, CART peptides occur among others in brain areas that control feeding behavior. We mapped CARTp-immunoreactive structures in the CNS of the frog Rana esculenta and assumed that differences may exist in the CARTp-containing neuronal populations between the frog, which does not feed in winter, and the rat. In the forebrain, immunoreactive cells and fibers were found in the olfactory bulb, nucleus accumbens, amygdala, medial pallium, septum, striatum, the preoptic nuclei, ventromedial nucleus, central thalamic nucleus, and the hypothalamus. The optic pathway was free of immunoreactivity. The neurohypophysis showed intense immunostaining. In the mesencephalon, many cells were stained in the Edinger-Westphal nucleus, and a few in the optic tectum, where fibers were stained in all plexiform layers. In the retina, some cells in the inner nuclear layer contained CARTp. In the rhombencephalon, cells were stained in the raphe nuclei, central gray, nucleus of the solitary tract, and the vicinity of motor nuclei. Neurons of the motor cranial nerves were densely innervated by CARTp-positive fibers originating from the spinal cord. In the spinal cord, preganglionic cells were stained, and motoneurons were surrounded by immunoreactive varicose axon terminals. Major differences were found between the frog and the rat brains in the distribution of CARTp in the visual system, olfactory bulb, preoptic area, and the motor nuclei. Some of these differences may be related to feeding behavior of these animals.

Animals↗

PubMedDate not supplied

Dural ectasia of the optic nerve sheath in neurofibromatosis type 1: CT and MR features.

OBJECTIVE: Optic nerve glioma is a common finding in patients with neurofibromatosis type 1 (NF-1). Although dural ectasia of the optic nerve is encountered rarely, it has to be considered in the differential diagnosis. MATERIALS AND METHODS: Three patients affected by NF-1 were examined sequentially by CT and MRI. RESULTS: Computed tomography demonstrated nonprogressing enlargement of the anterior optic pathways. Magnetic resonance imaging displayed widening of the perioptic dural sheath without any suggestion of tumor. CONCLUSION: These findings are compatible with meningocele or dural ectasia of the optic nerve sheath. This entity represents a differential diagnosis to optic glioma in patients with NF-1.

Adolescent↗

PubMed1996

The pathways of light measured in fundus reflectometry.

We measured the spectral reflectance of the fovea of ten normal subjects in four conditions, i.e. under dark-adapted and bleached conditions and at two retinal angles of incidence. The objective was to study optical pathways through the photoreceptor layer, resulting in a model that simultaneously explains spectral, directional and bleaching properties of the fovea. On theoretical grounds, we propose that small reflections from the stack of discs in the cone outer segments are the origin of the directional component of foveal reflection. Non-directional reflection occurs at the inner limiting membrane and at all layers posterior to the outer segments. With four reflectance spectra as input, the model allows determination of the density of the photostable absorbers, the lens, macular pigment, melanin and blood. Because of the simplified modeling of the layers posterior to the photoreceptor layer, the values for the density of melanin and blood are not necessarily comparable to physiological data. The density of the visual pigment calculated with this model is consistent with psychophysical data, with estimates for the ten subjects ranging from 0.41 to 0.80. The long wavelength sensitive cone fraction is calculated as 0.56.

Blood↗

PubMed1987

Synapse formation in the olfactory cortex by regenerating optic axons: ultrastructural evidence for polyspecific chemoaffinity.

The optic nerve was severed at its entry into the optic chiasma and implanted into the striatal region of the ipsilateral cerebral hemisphere in adult frogs (Rana pipiens). Regenerating retinal ganglion cell axons, observed by the autoradiographic tracing method and by horseradish peroxidase (HRP) fiber filling, grew anteriorly along the olfactory tracts and posteriorly along the ipsilateral lateral forebrain bundle and stria medullaris. Many of the regenerating axons ultimately joined the ipsilateral optic tract. The optic axons formed terminal plexuses in the olfactory cortex, lateral geniculate complex, pretectum, tectum, and basal optical nucleus but not in the amygdala or other cerebral territories not postsynaptic to the olfactory bulb, nor in the cell groups associated with the lateral forebrain bundle or stria medullaris. Optic axon terminals labeled with HRP were observed by electron microscopy in the ipsilateral olfactory cortex and in the normal projection areas of the optic nerve, although they were misplaced to the ipsilateral side. They contained clear, spherical synaptic vesicles and pale mitochondria and made Gray type I, asymmetric contacts on dendrites. The retinal projection to the olfactory cortex was formed early in regeneration and was maintained to some degree for periods up to 39 weeks. It was absent in a specimen surviving 50 weeks. Retinal innervation appeared earlier in the lateral geniculate complex and pretectum than in the tectum. These observations suggest that regenerating retinal ganglion cell axons have an affinity for neurons in the olfactory cortex, as well as for the neurons in the optic pathway to which they are normally postsynaptic. Unless the apparent selectivity of the aberrant projection is regulated by principles other than those that bring about the reinnervation of the normal optic centers, the data further suggest that the nature of the molecular mechanisms conveying synaptic specificity must be broad enough to permit the formation of limited sets of alternative synaptic connections. The ability to innervate selectively targets other than those normally specified is termed, here, polyspecificity. Since polyspecificity refers to the the affinity of retinal ganglion axons, as a class, for target structures considered as unit aggregates, it is conceptually different from the graded affinity of ganglion cells in different regions of the retina for target neurons in different regions of the tectum.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1999

Radiation-induced bilateral optic neuropathy in cancer of the nasopharynx. Case failure analysis and a review of the literature.

CASE REPORT: A case history of unanticipated radiation-induced bilateral optic neuropathy, 18 months after induction chemotherapy and radiation therapy for a locally advanced nasopharyngeal carcinoma, is presented. Retrospective reanalysis of the radiation therapy technique, with emphasis on the doses received by the optic pathway structures, was performed. These re-calculations revealed unexpectedly high doses in the range 79 to 82 Gy (cumulative external and brachytherapy dose) at the level of the optic nerves, which explained the observed radiation injury. CONCLUSION: Routine implementation of computed tomography for 3D dose planning purposes is therefore advocated. Review of the current literature confirms the importance of 3D dose planning in avoiding this complication and high-lights the role of MRI in establishing the diagnosis of radiation-induced optic neuropathy.

Adult↗

PubMed1999

Visual recovery after a year of craniopharyngioma-related amaurosis: report of a nine-year-old child and a review of pathophysiologic mechanisms.

BACKGROUND: The probability of visual recovery in tumor-related optic neuropathy usually correlates with the severity and duration of optic pathway compromise. Recovery of visual acuity to normal levels is unexpected after profound loss of vision extending for a period of weeks and months. METHODS: A 9-year-old girl who had neurosurgical resection of a craniopharyngioma compressing the optic chiasm and optic tract was followed up serially with neuroimaging and clinical examinations over a 6-year period. RESULTS: Within 3 months of the diagnosis of craniopharyngioma, the girl's vision was reduced to no-light-perception blindness when she viewed with the more involved eye. The blindness correlated with an amaurotic (i.e., >3.6 log unit) relative afferent pupillary defect and an absence of any response when tested with visual field perimetry. After more than a year of total blindness and cessation of all neurosurgical and radiation therapy, visual acuity recovered to a normal level (20/25), the afferent pupillary defect improved, and sensitivity in a portion of the temporal hemivisual field was restored. In the follow-up that has extended for 5 years from the time of recovery, stability of the restored vision has been documented. CONCLUSION: Children who have tumor-related loss of vision due to damage to the anterior visual pathways may be capable of recovery after intervals of blindness that would be considered irreversible in adults. The mechanism of the recovery in our patient may have been decompression-related restoration of axoplasmic flow, followed by gradual remyelination of visual fibers, which allowed reorganization of connections to the lateral geniculate nucleus to optimize synaptic transmission.

Blindness↗

PubMed1978

The hypothalamic magnocellular system of the rhesus monkey: an immunocytochemical study.

The hypothalamic magnocellular system of the adult female rhesus monkey is studied here, using immunoperoxidase technique and antisera to estrogen stimulated neurophysin (ESN), nicotine stimulated neurophysin (NSN), oxytocin (OT) and vasopressin (VP). These observations confirm and enlarge previous descriptions by others using Gomori techniques. It is apparent from this study that the magnocellular system spreads through a broader area than is generally accepted. A group of cells ventral to the head of the caudate nucleus and medial to the internal capsule is described. The general orientation of the nuclei and their tracts can only be appreciated when coronal, horizontal and sagittal sections are compared. Our observations suggest that the supraoptic nucleus is made up of a single group of cells that straddles the optic pathways, and is not divided in three segments, as it is generally described. It is also shown that the rostral extensions of the paraventricular and supraoptic nuclei merge above the optic chiasm. Cells containing ESN/OT and NSN/VP are evenly dispersed in the paraventricular nucleus but a topographical arrangement is present in the supraoptic nucleus. The magnocellular nuclei project to the organum vasculosum of the lamina terminalis, zona externa of the median eminence and pars nervosa of the pituitary gland. Reactive fibers were also seen within islets of cells from the pars intermedia located inside the pars nervosa. A globular structure containing small blood vessels surrounded by positive fibers was noticed protruding into the floor of the third ventricle, at the level of the median eminence.

Animals↗