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At least 235 records · Page 13Linked to original sources
PubMed1984

Cupping of the optic disc with compressive lesions of the anterior visual pathway.

Cupping of the optic nerve, classically a sign of glaucoma, was demonstrated in 16 patients with lesions compressing the anterior visual pathway. Color contrast determinations of the cup/disc ratio demonstrated a ratio greater than 0.49 in 31 eyes. Further evaluation by stereobiomicroscopy showed cavernous degeneration by contour changes in 25 of the optic nerves. None of the patients had intraocular pressures greater than 22, and seven had normal tonography. Visual fields demonstrated bitemporal field defects in most patients and none were typical of glaucoma. Snellen acuity loss, out of proportion to the extent of optic disc cupping was found in 12 patients. This study indicates that diseases other than glaucoma can cause significant cupping of the optic nerves. Detailed evaluation of the disc changes and the visual fields will prevent confusion between compressive lesions of the optic nerves or chiasm and glaucoma.

Adolescent↗
PubMed1980

Statokinetic dissociation in lesions of the anterior visual pathways. A reappraisal of the Riddoch phenomenon.

With standard Goldmann perimetry, physiologic dissociation of kinetic and statis stimuli was first investigated in 15 normal subjects. Variable degrees of statokinetic dissociation (SKD) occurred for white and for red (achromatic perception) targets, but not for chromatic recognition of red. To analyze relative sensitivity of these stimuli in defining field defects, a set of "isopter equivalents," eg, white I2e, red II4c (achromatic perception), and red V4e (chromatic recognition) was empirically established in normal and in pathologic fields of 11 patients with compression of the anterior visual pathways. The "Riddoch phenomenon" (SKD) was documented in defective fields in all patients with tumors; SKD occurred for white or for red achromatic perception. The most sensitive technique for elaborating field defects proved to be static presentation of white or red stimuli (achromatic perception) and chromatic recognition of static or kinetic red. As a rapid, sensitive screening method, especially for subtle defects, we suggest the addition of chromatic recognition of kinetic red stimuli to the application of standard kinetic white stimuli. Our findings are discussed in light of current concepts of retinal ganglion cell physiology.

Brain Neoplasms↗
PubMed1980

Effect upon eye movements of rabbits induced by severance of mossy fiber visual pathway to the cerebellar flocculus.

In albino rabbits the visual mossy fiber pathway to the cerebellar flocculus was interrupted by placing lesions in the nucleus reticularis tegmenti points (NRTP). After recovery of more than 3 days, eye movements were tested by means of a television eye tracking system. The optokinetic response (OKR) in one eye was induced by sinusoidally moving a vertical slit light on the horizontal plane(2.5 degrees peak-to-peak amplitude) at 0.17-0.033 Hz in front of that eye. In rabbits with unilateral NRTP lesions, the OKR gain was reduced significantly in the eye contralateral to lesions, whereas that in the ipsilateral eye did not differ from control rabbits. The horizontal vestibulo-ocular reflex (HVOR) exhibited no change attributable to NRTP lesions. The operated rabbits were rotated (5 degrees peak-to-peak amplitude) at 0.1 Hz continuously for 3h, while the slit light was presented to the eye contralateral to the NRTP lesions. During the rotation, the HVOR gain in the test eye increased adaptively as in control rabbits. It is concluded that the visual mossy fiber pathway to the flocculus contributes to the OKR, but not to visually-guided adaptive modification of the HVOR.

Animals↗
PubMed1998

Connexin50, a gap junction protein of macrogliaP6n the mammalian retina and visual pathway.

Reverse transcriptase-polymerase chain reaction (RT-PCR), Western blotting and immunocytochemistry were used to study the expression of gap junction proteins (connexins; Cx) in the rat and rabbit retina. RT-PCR of rabbit total retinal RNA using primers selected for the human Cx50 (alpha 8 Cx) DNA template yielded cDNA fragments of the predicted base pair size. Western blots of rat and rabbit retinal membrane preparations probed with a monoclonal antibody which recognizes Cx50 in the lens of several mammalian species revealed a single band (MW 50 kD), identical to that recognized in lens membrane extracts. In frozen retinal sections of both species, the same monoclonal antibody as well as two polyclonal antisera raised against a synthetic peptide from the C-terminal region of the human Cx50 polypeptide labeled Müller cells and astrocytes. In Müller cells, labeling was strongest in the endfeet and in the filamentous processes ensheathing the photoreceptors. Extending from the neural retina, Cx50-like immuno-reactivity was detected in astrocytes of the optic nerve and along retinal projections within the CNS. Our data indicate that Müller cells and astrocytes of mammalian retinas and throughout the visual pathway are coupled through gap junctions composed of connexin50.

Animals↗
PubMed1999

Fate of oligodendrocytes during retinal axon degeneration and regeneration in the goldfish visual pathway.

Retinal axons in goldfish regenerate after optic nerve lesion, restore synaptic connections, and become myelinated by oligodendrocytes. The fate of oligodendrocytes during these events is not known and may require generation of new oligodendrocytes or dedifferentiation and redifferentiation of the existing ones. To determine the reaction of oligodendrocytes to optic nerve lesion, we used the terminal transferase technique to detect apoptosis, bromodeoxyuridine incorporation to reveal mitosis, antibodies to identify myelin and oligodendrocytes, and Lucifer yellow injections to reveal cell morphology. Along with the reappearance of the myelin molecules 36K protein, galactocerebroside, and myelin basic protein, myelinating oligodendrocytes (identified by Lucifer yellow injections) reappear 21 days postlesion. Prior to this time, the dye-filled cells had few processes oriented along the regenerating axons. They resembled oligodendrocytes seen both in vitro and in vivo which express the L1-related E587 antigen and synthesize the 36K myelin protein in coculture with axons. No signs of oligodendrocyte apoptosis were detected after lesion and only few of the oligodendrocytes present had recently arisen. 36K/E587 double-labeled oligodendrocytes which were most likely dedifferentiating oligodendrocytes were identified in 8-day postlesion nerves among E587-positive elongate cells whose numbers increased until 14 days postlesion. These findings suggest that oligodendrocytes dedifferentiate-like Schwann cells-from cells which express myelin molecules to elongate cells which express the L1/E587 antigen. They redifferentiate to myelinate axons from roughly 3 weeks onward. These findings suggest an adaptive plasticity of goldfish oligodendrocytes beneficial to the repair of the visual pathway.

Animals↗
PubMed1999

Distributed representation of objects in the human ventral visual pathway.

Brain imaging and electrophysiological recording studies in humans have reported discrete cortical regions in posterior ventral temporal cortex that respond preferentially to faces, buildings, and letters. These findings suggest a category-specific anatomically segregated modular organization of the object vision pathway. Here we present data from a functional MRI study in which we found three distinct regions of ventral temporal cortex that responded preferentially to faces and two categories of other objects, namely houses and chairs, and had a highly consistent topological arrangement. Although the data could be interpreted as evidence for separate modules, we found that each category also evoked significant responses in the regions that responded maximally to other stimuli. Moreover, each category was associated with its own differential pattern of response across ventral temporal cortex. These results indicate that the representation of an object is not restricted to a region that responds maximally to that object, but rather is distributed across a broader expanse of cortex. We propose that the functional architecture of the ventral visual pathway is not a mosaic of category-specific modules but instead is a continuous representation of information about object form that has a highly consistent and orderly topological arrangement.

Adult↗
PubMed1993

Unilateral atrophy of the optic nerve associated with retrograde and anterograde degenerations in the visual pathways in Slc: Wistar rats.

Unilateral degenerative atrophy of the optic nerve (ON) occurred in 6 of 80 male and 4 of 80 female Slc: Wistar rats. Two of these cases completely lost the intracranial portion of the unilateral ON and the remainder had the small ON. The optic disc and ON were located histologically in the posterior pole of the eyeball of 2 rats with no intracranial ON. ON lesions in all cases were characterized by a reduced number of axons with a small number of myelinated axons and marked astrogliosis. There were also swelling, fragmentation and spheroid formation of axons, as well as thickening of the connective tissue sheaths and vessel walls in the ON. One side of the optic chiasma and optic tract contralateral to the affected ON reduced in volume, became degenerated and were accompanied by gliosis. Focal or diffuse degeneration of the retina was observed in the eyeballs with affected ON. Retinal ganglion cells decreased in the number showing chromatolysis. These retinae became thin and developed degeneration of both inner and outer portions with sclerotic changes in the retinal vessels. The ophthalmic and ciliary arteries in the eyeballs with affected ON often developed proliferative or occlusive endoarteritis, suggesting that retinal lesions may have resulted not only from axonal degeneration in the ON but also from ischemia. Histologic lesions suggestive of transneuronal degeneration were found in the contralateral lateral geniculate body and rostral colliculus. Based on the data presented, it was presumed that a primary lesion may have been induced in the ON by a circulatory disturbance and followed by retrograde and anterograde degenerations in the visual pathways.

Animals↗
PubMedDate not supplied

Retinotopic order appears before ocular separation in developing visual pathways.

In mammals, the major subcortical visual structures receive projections from both eyes, with the uncrossed projection being smaller than the crossed. Each projection is arranged as a separate orderly map of one hemiretina. Although these hemiretinal maps are separate in the nuclei, they are aligned so that the representations of points in the visual field are in register, thus there is a continuity of visual field representation between them. During the early development of the binocular pathways, terminals from the two eyes overlap almost entirely. As development proceeds, terminals arising from each eye segregate to form the adult pattern. In the present study, local retinal lesions were made in ferrets at various stages in development before the separation of the projections from the two eyes. A neuronal tracer was then injected into the damaged eye, defining the pattern of projection from that eye. As reported here, the lesion resulted in a limited interruption in the pattern of terminal label on both sides of the brain, demonstrating that terminals from each eye are arranged in an orderly retinotopic manner at this stage. hence, during later development, as one projection is reduced relative to the other, the two maps must slide in relation to each other.

Albinism↗
PubMed1998

Protection of visual pathway in gamma knife radiosurgery for craniopharyngiomas.

Craniopharyngiomas present a major challenge to Gamma Knife radiosurgery (GKRS) due to their proximity to the optic apparatus. Based on observations of the evolving tumoral change on MRI and clinical results, an optimization of the treatment strategy and dose selection is possible. From March 1993 to September 1996, 21 patients with craniopharyngiomas were treated by GKRS. Every patient received stereotactic MRI exclusively for targeting and dose planning. The tumor and adjacent structures, including optic nerves, chiasm, and tracts were carefully identified and delineated on sagittal, coronal and axial films. The tumor volume ranged from 0.3 to 28 ml (average 9 ml). We purposefully apply multiple isocenters (average 9.1 shots) to create an isodose curve that covered the tumor optimally while sparing the optic pathway. The marginal dose prescribed was 9.5 to 16 Gy (50%). The maximal dose was 19 to 32 Gy. The maximal dose to the optic apparatus was 3.2 to 12.5 Gy. After GKRS, all patients were followed up clinically every month. MR studies were conducted every six months with the same techniques on the same scanner to investigate evolution of tumor volume and any adverse radiation effect. The follow-up period ranged from 6 to 40 months (mean: 18.4, median: 19). All patients were followed more than 6 months. Nineteen out of 21 cases (90.5%) achieved tumor control; that is, 18 tumor shrinkage (volume reduction: 15-95%) and 1 stabilized tumor growth. Among these 21 patients, 7 had improved visual acuity or visual field after GKRS, and the rest remained stable. Two patients developed mild T2 change on MRI without any endocrinological disturbance or visual impairment. Protection of the visual pathway can be secured by a sophisticated delineation on 3-dimensional stereotactic images with multiple-shot dose planning. Craniopharyngiomas with tumor volume up to 25 ml were treated safely and effectively, because the dose to the optic apparatus was kept as low as possiby this strategy. Further follow-up is needed to determine the highest tolerable dose to surrounding critical structures and the long-term outcome of tumor control.

Adolescent↗
PubMed1999

Spatial characteristics of the second-order visual pathway revealed by positional adaptation.

The visual system is thought to process luminance (first-order) and contrast (second-order) information by dedicated cortical streams. To explore the spatial characteristics of the second-order pathway, we examined the effect of adaptation on spatial localization in human subjects. We show that, unlike first-order adaptation, second-order positional adaptation via cortical mechanisms transfers across orientations but not across spatial frequencies. These results support physiological evidence that these two processing streams are distinct and suggest that the cortical mechanism mediating second-order positional adaptation maintains spatial frequency information but sums signals across orientations.

Adaptation, Ocular↗
PubMed1994

The timing of processing along the visual pathway in the cat.

We obtained visual response latencies and response durations following visual stimulation of neurones recorded in the lateral geniculate nucleus (LGN), areas 17, 18, 19, the posteromedial lateral suprasylvian sulcus (PMLS), and area 7 of the cat. We found an increasing lengthening of the mean response latencies, consistent with the view of a progressive advance of processing from stage to stage. However, we also observed a substantial and increasing scatter in these latencies. Moreover, response durations vastly supersede this gradual increase in latencies. Taken together, these results suggest that most of the neurones within different stages of a hierarchically organized sensory pathway are simultaneously active when stimulated. Implications of a time-based processing scheme for models of information processing in highly interconnected, multi-layered systems are discussed.

Animals↗