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PubMed1995

[Novel GABAc receptors].

Considerable evidence has shown that there is a kind of special pharmacological GABA receptors in central nervous system, especially prominent along visual pathways. These receptors are neither antagonized by bicuculline nor activated by baclofen, but are activated selectively by the GABA analogue cis-4-aminocrotonic acid (CACA), its response did not show desensitization. These receptors have been termed GABAc receptors. It may play an important role in the visual information transmission and modulation of retinal rod pathway.

Animals↗

PubMed1997

Brain activity in visual cortex predicts individual differences in reading performance.

The relationship between brain activity and reading performance was examined to test the hypothesis that dyslexia involves a deficit in a specific visual pathway known as the magnocellular (M) pathway. Functional magnetic resonance imaging was used to measure brain activity in dyslexic and control subjects in conditions designed to preferentially stimulate the M pathway. Dyslexics showed reduced activity compared with controls both in the primary visual cortex and in a secondary cortical visual area (MT+) that is believed to receive a strong M pathway input. Most importantly, significant correlations were found between individual differences in reading rate and brain activity. These results support the hypothesis for an M pathway abnormality in dyslexia and imply a strong relationship between the integrity of the M pathway and reading ability.

Dyslexia↗

PubMed2005

A new preparation for visualizing lymphatic flow pathway in isolated rat lymph nodes.

BACKGROUND: There is no reported study in which the lymphatic flow pathway in lymph nodes has been visualized and investigated in in vitro studies. The purpose of the present study is first to develop an isolated rat lymph node preparation circulated through the afferent and efferent lymph vessels in order to visualize lymphatic flow pathway within the node by using a video microscope system, and then to evaluate lymphatic flow dynamics by using fluorescence-labeled substances. METHODS AND RESULTS: In the present study, rat iliac lymph node was isolated. The afferent and efferent lymph vessels of the lymph node were cannulated with glass micropipettes in an organ chamber, while the small-sized arteries and veins connected to the lymph node were secured with sutures. Krebs-bicarbonate solution with or without fluorescent probes [FITCdextran, mol. weight; 77,000 and/or fluoresbrite carboxylate-microspheres (FC-microspheres) mean diameter of 1 microm] was circulated through the lymph vessels of the node. The time-dependent lymphatic pathway of fluorescent probes was investigated with a video microscope system. FTIC-dextran first spread through the cortex and subsequently reached the medulla of the lymph node. A follicle-like structure became evident in the cortex. FITC-dextran appeared in the efferent lymph vessel at 109 +/- 21 sec after its circulation began, while FC-microspheres distributed in the lymph node did not emerge from the node within 20 min after their introduction. CONCLUSIONS: In vitro preparations constructed in the present study will enable us to visualize the lymphatic flow pathway of fluorescent substances within the isolated iliac lymph nodes of rats in the absence of blood circulation.

Animals↗

PubMed1982

Visual afferents to norepinephrine-containing neurons in cat locus coeruleus.

A total of 208 single neurons were extracellularly recorded in the locus coeruleus (LC) of 11 cats. In later histofluorescence studies, greenish fluorescent LC neurons, from which we believed to have recorded well-isolated action potentials, were always found in or close to the center of red fluorescent halo due to an injected dye which marked the recording site. One hundred twelve of these 208 neurons were further subjected to electrical stimulation of the dorsal bundle of ascending axons originating from the norepinephrine (NE)-containing LC neurons and thus activated antidromically with a mean latency of 8.9 ms (the remaining neurons were lost before this examination). The mean conduction velocity was 1.2 m/s. Furthermore, it is suggested that 22% of thus antidromically identified NE neurons in the cat LC had an ascending axon of the conduction velocity faster than 2.4 m/s. This finding may be related with an electron-microscopic observation which indicated the presence of myelinated catecholamine (CA) axons, though not many in number, in the cat visual cortex. Responses by the NE-containing LC neurons to various natural visual stimuli, such as flashlight, moving and stationary light-slit, multiple spots, and gratings were examined. It turned out, however, that flash alone was effective to activate LC neurons. The latency of flash evoked activity was between 48 and 96 ms (N = 12; mean: 60 ms). Furthermore, the following areas in the central visual pathway were electrically stimulated to activate LC neurons orthodromically: the optic chiasm (OX), the dorsal lateral geniculate nucleus (LGN), the superior colliculus (SC), and the visual cortex (VC). The range and the mean of the latency for orthodromic responses were as follows: OX (N = 36, 8.4-42 ms; mean: 21 ms); LGN (N = 17, 6.0-17 ms; mean: 8.1 ms); SC (N = 12, 3.6-12 ms; mean: 5.6 ms); VC (N = 10, 7.8-40 ms; mean: 16.4 ms). The long latency of these orthodromic responses and its wide distribution suggest that afferents to the LC from the above-mentioned visual structures are most likely polysynaptic in nature. The extensive input convergence, including acoustic and nociceptive afferents, and the polysynaptic connection in each afferent pathway indicated a strong similarity between the afferent connectivity of NE-containing LC neurons revealed in the present study and that known for reticular formation neurons. Then, we would like to suggest that visual signals from the eyes impinge upon the NE-containing LC neurons via the reticular formation and that the afferents from the LGN, the SC, and the VC also join this common path through the reticular formation to reach the LC.

Animals↗

PubMed1987

Importance of the visual and vestibular cortex for self-motion perception in man (circularvection).

Circularvection (CV), the optokinetically induced perception of self-motion, is based neurophysiologically upon visual-vestibular convergence. It is yet not known which visual pathways--subcortical accessory optic tract and/or cortical striate projection--convey optokinetic information to the central vestibular system in order to make possible the convergence that has been found: the vestibular nuclei, the thalamus and the vestibular cortex. The functional significance of the visual cortex was demonstrated in 12 patients with homonymous hemianopia who neither perceived CV nor exhibited a postural destabilization when exposed to optokinetic pattern motion (yaw or roll) restricted to the scotoma. The functional significance of the vestibular cortex as well as ipsilateral visual-vestibular interaction was demonstrated in 4 (out of 20) patients with tumour lesions involving the vestibular cortex areas. They either failed to perceive CV or showed a significant increase of CV-latencies when monocular optokinetic stimulation was restricted to the ipsilateral visual cortex. Arguments for and against the following hypothesis are discussed: circularvection is induced by visual motion stimulation of the primary visual cortex which then activates vestibular nuclei neurons by descending pathways and which also informs the vestibular cortex that self-motion with a perceptual direction is involved. Determination of the velocity of CV is mediated by direct visual-vestibular cortex interaction, which most probably is also involved in the perceptual interpretation of motion perception: Self-motion versus object-motion.

Adult↗

PubMed1997

Prolonged Uhthoff phenomenon in sarcoidosis.

PURPOSE: To report a patient with sarcoidosis of the anterior visual pathways in whom one of the primary symptoms was visual loss lasting 24 hours after exposure to heat. METHODS: Case report and review of the literature. RESULTS: The transient visual loss was exquisitely sensitive to intravenous corticosteroids and lasted longer than the typical Uhthoff phenomenon. Serum angiotensin-converting enzyme level was increased, chest x-ray showed hilar adenopathy, gallium scan disclosed bilateral intense tracer uptake in the hila, and transbronchial lung biopsy showed noncaseating granulomas with negative stains for fungi and mycobacteria, consistent with sarcoidosis. CONCLUSIONS: Uhthoff phenomenon, typically associated with demyelinating optic neuritis, may occur in an atypical form in patients with sarcoidosis of the optic nerve.

Adult↗

PubMed2003

Cognitive vision, its disorders and differential diagnosis in adults and children: knowing where and what things are.

As ophthalmologists we need a basic model of how the higher visual system works and its common disorders. This presentation aims to provide an outline of such a model. Our ability to survey a visual scene, locate and recognise an object of interest, move towards it and pick it up, recruits a number of complex cognitive higher visual pathways, all of which are susceptible to damage. The visual map in the mind needs to be co-located with reality and is primarily plotted by the posterior parietal lobes, which interact with the frontal lobes to choose the object of interest. Neck and extraocular muscle proprioceptors are probably responsible for maintaining this co-location when the head and eyes move with respect to the body, and synchronous input from both eyes is needed for correct localisation of moving targets. Recognition of what is being looked at is brought about by comparing the visual input with the "image libraries" in the temporal lobes. Once an object is recognised, its choice is mediated by parietal and frontal lobe tissue. The parietal lobes determine the visual coordinates and plan the visually guided movement of the limbs to pick it up, and the frontal lobes participate in making the choice. The connection between the occipital lobes and the parietal lobes is known as the dorsal stream, and the connection between the occipital lobes and the temporal lobes, comprises the ventral stream. Both disorders of neck and extraocular muscle proprioception, and disorders leading to asynchronous input along the two optic nerves are "peripheral" causes of impaired visually guided movement, while bilateral damage to the parietal lobes can result in central impairment of visually guided movement, or optic ataxia. Damage to the temporal lobes can result in impaired recognition, problems with route finding and poor visual memory. Spontaneous activity in the temporal lobes can result in formed visual hallucinations, in patients with impaired central visual function, particularly the elderly. Deficits in cognitive visual function can occur in different combinations in both children and adults depending on the nature and distribution of the underlying brain damage. In young children the potential for recovery can lead to significant improvement in parietal lobe function with time. Patients with these disorders need an understanding of their deficits and a structured positive approach to their rehabilitation.

Adult↗

PubMed1993

Activation of human primary visual cortex during visual recall: a magnetic resonance imaging study.

The degree to which the process involved in visual perception and visual imagery share a common neuroanatomical substrate is unclear. Physiological evidence for localization of visual imagery early in the visual pathways would have important bearing on current theories of visual processing. A magnetic resonance imaging technique sensitive to regional changes in blood oxygenation was used to obtain functional activation maps in the human visual cortex. During recall of a visual stimulus, focal increases in signal related to changes in blood flow were detected in V1 and V2 cortex in five of seven subjects. These experiments show that the same areas of the early visual cortex that are excited by visual stimulation are also activated during mental representation of the same stimulus. Some of the processes used in topographically mapped cortical areas during visual perception may also be utilized during visual recall.

Adult↗

PubMed1979

The contribution of the 'second' visual system to directed visual attention in man.

The visual functions of a patient suffering from a brain lesion incorporating the left n. pulvinar was examined in order to assess the contribution of this structure to human vision. With the exception of the following abnormalities visual functions were normal. First, there was a decrease in the critical flicker frequency in the periphery (but not in the parafoveal region) of the right visual hemifield, that is, that contralateral to the pulvinar lesion. However, the second and most striking characteristic was--as shown by presenting visual stimuli bilaterally and simultaneously-a 'neglect' for the periphery of this contralateral visual half-field. This 'neglect' was a function of (a) position in the visual field (eccentricity), (b) stimulus properties (size and luminance), (c) temporal properties (length of presentation and interstimulus interval). In addition to this reduced capacity to detect stimuli appearing in the periphery of the right visual hemifield, there was also prolonged latency of visually evoked saccadic eye movements and a paucity of spontaneous eye movements directed towards the right visual hemifield. These results are interpreted in terms of a contribution of the n. pulvinar to the detection of light stimuli presented in the periphery of the visual field, and support the view that the tectopulvinar extrastriate visual pathway plays an important role in the control of visual attention.

Attention↗

PubMed1978

Psychogenic visual disorders in an abused child: a case report.

A 17-yr-old female, classified as retarded educable, was found to have uncorrected visual acuity of 20/800 in both eyes, unimproved by a pinhole disc. A low myopic correction determined objectively did not improve her visual acuity. Tangent-screen studies uncovered neurasthenic spiral fields superimposed on hysterical tubular contractions of both eyes. Investigation uncovered a history of child abuse since infancy. To rule out organic lesions of the oculocalcarine visual pathways, the patient was referred for electrodiagnostic evaluation. Her visual evoked responses were found to be normal. With the use of strong suggestion, her visual fields were brought out to normal limits and her visual acuity with correction was improved to 20/20 in each eye. With the cooperation of her school counselor, the patient was referred for psychiatric evaluation and therapy.

Adolescent↗

PubMed2003

Lens-sparing vitreous surgery for infantile amblyogenic vitreous hemorrhage.

PURPOSE: To report on a series of infants with amblyogenic vitreous and/or subinternal limiting membrane hemorrhage managed by lens-sparing vitrectomy. DESIGN: Retrospective case series studying retinal attachment status and visual acuity. RESULTS: Eleven eyes sustained vitreous hemorrhage as a consequence of shaken baby syndrome, 1 due to hyaloidal canal hemorrhage extending into the vitreous, 1 due to Terson syndrome, 1 due to birth trauma, and 2 due to a presumed coagulation disorder. Age of the patients at the time of surgery ranged from 2 to 23 months (age adjusted for prematurity). Follow-up ranged from 7 to 81 months (mean, 28 months). Ten eyes had visual improvement. Two infants with shaken baby syndrome had bilateral nonrecordable flash visual evoked potential before surgery; one eye of one infant had a better than expected visual outcome after surgery. One eye sustained a retinal tear without detachment. One eye in an infant with severe shaken baby syndrome and traumatic retinopathy developed a total rhegmatogenous retinal detachment with proliferative vitreoretinopathy. CONCLUSIONS: Infantile amblyogenic vitreous hemorrhage may be effectively managed by lens-sparing vitreous surgery. Visual outcome of shaken baby syndrome may be limited as a consequence of structural damage to the retina, optic nerve, or posterior visual pathways.

Amblyopia↗

PubMed2005

Frequency doubling technology perimetry and standard automated perimetry in migraine.

The literature suggests that visual field defects may be more common in people who experience migraine. The Humphrey frequency doubling (FDT) visual field instrument selectively examines the magnocellular visual pathway, but has not previously been used to investigate visual function in migraine. In a masked controlled study we compared Humphrey FDT and Humphrey Swedish Interactive Threshold Algorithm fields of 25 migraine sufferers with 25 age- and gender-matched controls. Although both mean deviation and pattern standard deviation were a little worse in the migraine group, these differences did not reach statistical significance. There were no inter-eye visual field differences in the migraine group compared with controls. Comparing the mean of all the contrast thresholds in each hemisphere, there were no more inter-hemifield visual field differences in the migraine group compared with controls. There was no significant difference between the migraine and control groups in intra-ocular pressures. The visual field parameters were not correlated with the interval since the last migraine headache, the severity of migraine headache, the duration of migraine headache or the number of migraine headaches per annum. In our data, there was no evidence of visual field deficits, a magnocellular deficit, or indications of glaucomatous pathology.

Adolescent↗

PubMed2004

Contrast sensitivity threshold measured by sweep-visual evoked potential in term and preterm infants at 3 and 10 months of age.

Although healthy preterm infants frequently seem to be more attentive to visual stimuli and to fix on them longer than full-term infants, no difference in visual acuity has been reported compared to term infants. We evaluated the contrast sensitivity (CS) function of term (N = 5) and healthy preterm (N = 11) infants at 3 and 10 months of life using sweep-visual evoked potentials. Two spatial frequencies were studied: low (0.2 cycles per degrees, cpd) and medium (4.0 cpd). The mean contrast sensitivity (expressed in percentage of contrast) of the preterm infants at 3 months was 55.4 for the low spatial frequency (0.2 cpd) and 43.4 for the medium spatial frequency (4.0 cpd). At 10 months the low spatial CS was 52.7 and the medium spatial CS was 9.9. The results for the term infants at 3 months were 55.1 for the low spatial frequency and 34.5 for the medium spatial frequency. At 10 months the equivalent values were 54.3 and 14.4, respectively. No difference was found using the Mann-Whitney rank sum T-test between term and preterm infants for the low frequency at 3 or 10 months or for the medium spatial frequency at 3 or 10 months. The development of CS for the medium spatial frequency was equally fast for term and preterm infants. As also observed for visual acuity, CS was equivalent among term and preterm infants, suggesting that visual experience does not modify the development of the primary visual pathway. An earlier development of synapses in higher cortical visual areas of preterm infants could explain the better use of visual information observed behaviorally in these infants.

Contrast Sensitivity↗

PubMed2004

[New chapter in the study of visual evoked potentials--clinical application of the multifocal VEP method].

The multifocal visual evoked potentials are the evoked responses over the visual cortex in response to the stimulation of circumscribed small areas in the central 30 degree region of the retina. The recording of multifocal visual evoked potentials was made possible by the computer algorhythm elaborated by Sutter in 1991. Multifocal electroretinography, developed upon the same theoretical principles, is already an routine clinical examination method for the topographic analysis of functional damages in the central part of the retina and for the differential diagnostics in neuro-ophthalmology. The multifocal visual evoked potential, however, has not been introduced into the clinical practice, although it displays the function of ganglion cells in a given region of the retina in a more detailed way than the sensitivity threshold in the perimetry. This examination makes the objective verification of defects possible in the visual pathway, too. In our department the recording of multifocal visual evoked potentials was started in 2002. In this paper we present the basics of this method and also deal with the problems concerning its application and its status in the history of visual evoked potentials.

Electroretinography↗

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↗

PubMed1995

Activity-dependent remodeling of connections in the mammalian visual system.

The development of precise connections in the mammalian central nervous system requires neural activity. Synchronous patterns of afferent activity, and coincident afferent and target activity are required for specifying the neuronal connectivity that characterizes the adult visual pathway in mammals. During development, postsynaptic target neurons communicate with presynaptic afferents. Recent evidence suggests that the mechanisms that underlie activity-dependent development of connections in the visual system may share significant similarities with the mechanisms responsible for synaptic plasticity in the adult brain.

Afferent Pathways↗

PubMed1990

Magnetic resonance imaging of radiation optic neuropathy.

Three patients with delayed radiation optic neuropathy after radiation therapy for parasellar neoplasms underwent magnetic resonance imaging. The affected optic nerves and chiasms showed enlargement and focal gadopentetate dimeglumine enhancement. The magnetic resonance imaging technique effectively detected and defined anterior visual pathway changes of radionecrosis and excluded the clinical possibility of visual loss because of tumor recurrence.

Adenoma↗

PubMedDate not supplied

Retinal prosthesis for the blind.

Most of current concepts for a visual prosthesis are based on neuronal electrical stimulation at different locations along the visual pathways within the central nervous system. The different designs of visual prostheses are named according to their locations (i.e., cortical, optic nerve, subretinal, and epiretinal). Visual loss caused by outer retinal degeneration in diseases such as retinitis pigmentosa or age-related macular degeneration can be reversed by electrical stimulation of the retina or the optic nerve (retinal or optic nerve prostheses, respectively). On the other hand, visual loss caused by inner or whole thickness retinal diseases, eye loss, optic nerve diseases (tumors, ischemia, inflammatory processes etc.), or diseases of the central nervous system (not including diseases of the primary and secondary visual cortices) can be reversed by a cortical visual prosthesis. The intent of this article is to provide an overview of current and future concepts of retinal and optic nerve prostheses. This article will begin with general considerations that are related to all or most of visual prostheses and then concentrate on the retinal and optic nerve designs. The authors believe that the field has grown beyond the scope of a single article so cortical prostheses will be described only because of their direct effect on the concept and technical development of the other prostheses, and this will be done in a more general and historic perspective.

Blindness↗