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PubMedDate not supplied

Can my child see? The evaluation of visual function in children.

Careful evaluation of all parameters of ocular function are required to delineate the cause of lack of visual responses in children. Any visual fixation, no matter how fleeting, is a sign of intact visual pathways. If no sign of ocular pathology can be found on the routine exam of the visually inattentive child, electrophysiologic testing may be necessary to confirm the presence of abnormality of the visual pathways. In the child with a generalized CNS disorder, the lack of visual response may be due to his inability to respond to visual information (perceptual blindness) rather than to organic pathology in the occipital cortex (cortical blindness).

Age Factors↗
PubMed1997

[Local electroretinogram and pattern visual evoked potential in maculopathies].

OBJECTIVES: To observe the changes of local electroretinogram (LERG) and pattern visual evoked potential (PVEP) in maculopathies and to evaluate the value of both LERG and PVEP in clinical application. METHODS: LERGs at 5 degrees, 10 degrees and 15 degrees macular region were recorded from 27 normal subjects (54 eyes). The LERG and PVEP were recorded from 25 patients (35 eyes) with maculopathies. RESULTS: In the patients with maculopathies, the amplitudes of LERG a wave and b wave at 5 degrees, 10 degrees and 15 degrees macular region were significantly lowered (P < 0.01), the mean value of P1 latency was prolonged and that of N1-P1 amplitude of VEP was lowered at 36.5', 73' and 146' in the comparison with the control group. In approximately the same stimulated area (15 degrees LERG and 14.8 degrees x 19.0 degrees PVEP), the abnormal rate of LERG was 62.2%, and the abnormal rates of PVEPs were 48.5% (146'), 54.5% (73') and 48.5% (36.5') respectively, no significant difference in the abnormal rate between LERG and each value of PVEP (P > 0.05) being found. CONCLUSION: The abnormal rates of LERG and PVEP in maculopathies are close. Because LERG is not influenced by visual pathway diseases and visual acuity, LERG is more effective than PVEP and is a direct way in measuring macular function.

Adult↗
PubMed1999

Aneurysms and subarachnoid hemorrhage.

Most unruptured intracranial aneurysms that produce neuro-ophthalmologic signs arise from the junction of the internal carotid and posterior communicating arteries. These aneurysms typically compress the third nerve in the subarachnoid space. Compression of cranial nerves within the cavernous sinus is less common, resulting in single or multiple and often painful ocular motor nerve pareses. Unruptured aneurysms of the proximal and distal segments of the intracranial portion of the internal carotid artery can compress the anterior visual pathways and cause visual loss. Ocular symptoms and signs may be the presenting manifestations of intracranial aneurysms. Prompt recognition of an aneurysm prior to rupture can prevent devastating intracerebral or subarachnoid hemorrhage. Moreover, visual complications are a not infrequent source of morbidity in those patients surviving acute intracranial bleeding. Recent advances in noninvasive neuroimaging and endovascular therapies facilitate early diagnosis and treatment and therefore may limit such complications.

Adult↗
PubMed1987

[Immunohistochemical characterization of serotoninergic afferent pathways in the visual system of the rat].

Using the immunohistochemical PAP-method occurrence, distribution and terminal aborization of serotoninergic axons were investigated in the visual system of the albino rat. The present study reveals that the innervation varies in quantitative and qualitative manner in the different parts of the visual system. A sparsly serotoninergic innervation was observed in the dorsal lateral geniculate body (d lgb) and in the nucleus lateralis posterior. An intensive serotoninergic innervation was found in the lateral part of the ventral lateral geniculate body (v lgb) and in the area praetectalis. Serotoninergic axons show a lamina specific orientation in the colliculus superior and in the visual cortex. Our findings indicate that serotoninergic axons have an intensive terminal aborization in subcortical visual nuclei, which are more or less connected with oculomotoric functions.

Animals↗
PubMedDate not supplied

[Study of the ancient tecto-thalamo-cortical pathway of the visual system in rats].

Recording the evoked potentials and neuronal activity, electrophysiological studies have been made on tecto-thalamo-cortical tract in rats. The existence of a system of efferent projections in the superficial, visual layers of the superior colliculi was shown which are diffusely present in the nucleus lateralis posterior (n. LP), indicating low level of morpho-functional organization of this region of the dorsal thalamus in rats. In response to electrical stimulation of the n. LP, in laterocaudal parts of the visual system (fields 17 and 18a of the cortex) the evoked potentials of primary-negative polarity were observed which are associated mainly with the superficial (I--IV) cortical layers. Predominant representation of tecto-thalamo-cortical system in the laterocaudal visual area of the cortex indicates the tendency to separate representation (with respect to cortical areas and cortical layers) of retino-geniculate and retino-tecal visual systems in rats.

Animals↗
PubMed1986

Effects of hyperventilation on pattern-reversal visual evoked potentials in patients with demyelination.

The effects of hyperventilation on the pattern-reversal visual evoked potential (VEP) were studied in seven normal subjects and 13 multiple sclerosis patients with visual pathway involvement. Significantly greater reductions in P100 latency occurred in the multiple sclerosis patients than in controls and normalisation of the half-field response topography occurred in one patient after hyperventilation. The VEP changes are attributed to improved impulse transmission in demyelinated fibres in the visual pathway as a result of the alkalosis and changes in ionised calcium levels induced by hyperventilation.

Adult↗
PubMed1998

Color reversal-learning deficits after tectofugal pathway lesions in the pigeon telencephalon.

Pigeons were post-operatively trained to discriminate two colors presented simultaneously. After reaching criterion on this task, they were required to perform a series of reversals of the color discrimination in which the positive and negative consequences of the stimuli were interchanged. Lesions of ectostriatum (the telencephalic target of the avian tectofugal visual pathway) impaired the ability of pigeons to learn a color-reversal task. An examination of the pattern of sparing and loss of performance on this task after lesions of various components of the ascending visual pathways suggests that deficits in color-reversal learning observed after lesions of the visual Wulst are not due to the Wulst's connections with the thalamofugal pathway. Instead, the data suggest that the visual Wulst maintains a role in color-reversal learning through its connections with the tectofugal pathway.

Animals↗
PubMed2006

Melanopsin regulates visual processing in the mouse retina.

The discovery of melanopsin-dependent inner retinal photoreceptors in mammals has precipitated a fundamental reassessment of such non-image forming (NIF) light responses as circadian photoentrainment and the pupil light reflex. By contrast, it remains unclear whether these new photoreceptors also play a role in classical image-forming vision. The retinal ganglion cells that subserve inner retinal photoreception (ipRGCs) project overwhelmingly to brain areas involved in NIF responses, indicating that, in terms of central signaling, their predominant function is non-image forming. However, ipRGCs also exhibit intraretinal communication via gap junction coupling, which could allow them to modulate classical visual pathways within this tissue. Here, we explore this second possibility by using melanopsin knockout (Opn4-/-) mice to examine the role of inner retinal photoreceptors in diurnal regulation of retinal function. By using electroretinography in wild-type mice, we describe diurnal rhythms in both the amplitude and speed of the retinal cone pathway that are a function of both prior light exposure and circadian phase. Unexpectedly, loss of the melanopsin gene abolishes circadian control of these parameters, causing significant attenuation of the diurnal variation in cone vision. Our results demonstrate for the first time a melanopsin-dependent regulation of visual processing within the retina, revealing an important function for inner retinal photoreceptors in optimizing classical visual pathways according to time of day.

Animals↗
PubMed1985

Aspartate and glutamate as synaptic transmitters of parallel visual cortical pathways.

Push-pull cannulae were inserted into both medial and lateral banks of the suprasylvian sulcus and used for local perfusion with artificial extracellular fluid (aECF). Electrical stimulations of regions of cortex projecting to the lateral suprasylvian area (LSA) were accompanied by enhanced levels of release of excitatory amino acids. Electrical stimulation of the area 17/18 border evoked a greater release of aspartate relative to glutamate in the medial bank of the LSA (posteromedial lateral suprasylvian: PMLS), of glutamate over aspartate in the lateral bank (posterolateral lateral suprasylvian: PLLS) while in the fundus, both were released equally or glutamate levels were slightly elevated over those of aspartate. These data support and extend the earlier proposition (Hicks and Guedes 1983) that an excitatory amino acid mediates synaptic transmission within visual cortico-cortical pathways.

Animals↗
PubMed1979

Retinofugal pathways in fetal and adult spiny dogfish, Squalus acanthias.

Retinofugal pathways in fetal and adult spiny dogfish were determined by intraocular injection of [3H]proline for autoradiography. Distribution and termination of the primary retinal efferents were identical in pups and adults. The retinal fibers decussate completely, except for a sparse ipsilateral projection to the caudal preoptic area. The decussating optic fibers terminate ventrally in the preoptic area and in two rostral thalamic areas, a lateral neuropil area of the dorsal thalamus and more ventrally in the lateral half of the ventral thalamus. At this same rostral thalamic level, a second optic pathway, the medial optic tract, splits from the lateral marginal optic tract and courses dorsomedially to terminate in the rostral tectum and the central and periventricular pretectal nuclei. The marginal optic tract continues caudally to terminate in a superficial pretectal nucleus and also innervates the superficial zone of the optic tectum. A basal optic tract arises from the ventral edge of the marginal optic tract and courses medially into the central pretectal nucleus, as well as continuing more caudally to terminate in a dorsal neuropil adjacent to nucleus interstitialis and in in a more ventrally and medially located basal optic nucleus. Comparison of the retinofugal projections of Squalus with those of other sharks reveals two grades of neural organization with respect to primary visual projections. Squalomorph sharks possess a rostral dorsal thalamic nucleus whose visual input is primarily, if not soley, axodendritic, and an optic tectum in which the majority of the cell bodies are located deep to the visual terminal zone. In contrast, galeomorph sharks are characterized by an enlarged and migrated rostrodorsal thalamic visual nucleus, and an optic tectum in which the majority of the cell bodies are located within the visual terminal zone. These data suggest that evolution of primary visual pathways in sharks occurs by migration and an increase in neuronal number, rather than by the occurrence of new visual pathways.

Animals↗
PubMed1985

Pattern-reversal visual evoked potentials in patients with hydrocephalus.

Pattern-reversal visual evoked potentials (VEP's) in response to whole- and half-field stimulation were studied in 10 patients with hydrocephalus. Abnormalities consistent with optic nerve dysfunction were recorded in four patients. Two patients had response asymmetry to half-field stimulation, which suggested dysfunction of the visual pathway in the right hemisphere. The remaining four patients had normal responses. Measurement of VEP's was repeated after the surgical treatment of hydrocephalus in four patients, and showed marked improvement in two of the three patients with preoperative abnormalities. This study suggests that, in patients with hydrocephalus, VEP's are more sensitive than clinical methods in detecting visual pathway dysfunction and that they can be useful in the follow-up monitoring of surgically treated hydrocephalic patients.

Adult↗
PubMed1998

Complex visual hallucinations. Clinical and neurobiological insights.

Complex visual hallucinations may affect some normal individuals on going to sleep and are also seen in pathological states, often in association with a sleep disturbance. The content of these hallucinations is striking and relatively stereotyped, often involving animals and human figures in bright colours and dramatic settings. Conditions causing these hallucinations include narcolepsy-cataplexy syndrome, peduncular hallucinosis, treated idiopathic Parkinson's disease, Lewy body dementia without treatment, migraine coma, Charles Bonnet syndrome (visual hallucinations of the blind), schizophrenia, hallucinogen-induced states and epilepsy. We describe cases of hallucinosis due to several of these causes and expand on previous hypotheses to suggest three mechanisms underlying complex visual hallucinations. (i) Epileptic hallucinations are probably due to a direct irritative process acting on cortical centres integrating complex visual information. (ii) Visual pathway lesions cause defective visual input and may result in hallucinations from defective visual processing or an abnormal cortical release phenomenon. (iii) Brainstem lesions appear to affect ascending cholinergic and serotonergic pathways, and may also be implicated in Parkinson's disease. These brainstem abnormalities are often associated with disturbances of sleep. We discuss how these lesions, outside the primary visual system, may cause defective modulation of thalamocortical relationships leading to a release phenomenon. We suggest that perturbation of a distributed matrix may explain the production of similar, complex mental phenomena by relatively blunt insults at disparate sites.

Brain Diseases↗
PubMed1981

Do blue-eyed white cats have normal or abnormal retinofugal pathways?

Three white cats that had blue eyes and no tapetum were studied by behavioral, electrophysiological, and anatomical methods in order to determine whether they showed evidence of abnormal retinofugal pathways comparable to those found in Siamese cats and in other mammalian forms having melanin deficits. The three cats were normal in every respect. However, several other white cats, obtained subsequently, do show an abnormality of the retinogeniculate pathway identical to the abnormality of Siamese cats. Cats of the second type are thought to be homozygous for the Siamese gene and also the express the White gene. Because the characteristics Siamese pigmented "points" fail to develop in the presence of the white gene, cats of the second type are not distinguishable from other white cats on the basis of eye color or coat color. In terms of their central visual pathways and of their patterns, however, they are recognizably Siamese. It is not known how common "crypto-Siamese" cats are in the white cat population, but the possibility of their occurrence suggests that, in general, white cats should not be used for studied of the central visual pathways.

Animals↗
PubMed1994

Optic gliomas in neurofibromatosis type 1: role of visual evoked potentials.

Optic gliomas occur in 15% of patients with neurofibromatosis type 1 (NF 1) and are a significant cause of morbidity. Of these tumors, 20-30% become symptomatic, usually before age 10 years. Previous studies have suggested that visual evoked potentials (VEPs) are a sensitive method for the detection of asymptomatic optic gliomas. Because routine neuroimaging of children with NF 1 is currently not recommended, the role of pattern-shift VEPs (PS VEPs) as a screening test for optic gliomas was evaluated. PS VEPs were performed on 10 children with NF 1 and optic gliomas and 20 children with NF 1 and normal visual pathways (as defined on MRI). PS VEPs had 90% sensitivity for detecting optic gliomas, with an increase in sensitivity to 100% when hemifield stimulation was used. The specificity of the test was 60%. Four of 20 children without optic gliomas had thickened optic nerves on computed tomography which represented dural ectasia with normal visual pathways on MRI; PS VEPs were normal in these patients. The efficacy of PS VEPs as a routine screen for optic gliomas is limited by the age at which children will cooperate with the test procedure and the high incidence of false-positive results; however, VEPs do provide a useful adjunct to routine clinical ophthalmologic assessment in the detection of optic gliomas in children with NF 1. Abnormal test results provide a stronger indication for neuroimaging. The early detection of optic gliomas allows for close monitoring of tumor progression and earlier intervention prior to significant visual loss.

Adolescent↗
PubMed2006

Representation of object images by combinations of visual features in the macaque inferior temporal cortex.

The ventral visual pathway is essential for object recognition where features necessary for recognition are extracted from object images. This pathway is not directly related to action; nevertheless extraction of features from object images through this pathway is closely related to actions since we determine our behaviour based on sensory information, such as object images in the scene. To link perception and action, we have investigated neural representation of object images in area TE. Area TE, the anterior part of the inferior temporal (IT) cortex, is the final purely visual area in the ventral visual pathway. Since individual neurons in this area respond to features less complex than object images, an object image is supposed to be represented by multiple features. Here, to investigate sets of features necessary for representation of object images, we conducted a combination study of an optical imaging technique and single cellular recordings from anesthetized macaque monkeys.

Animals↗
PubMed1986

Effects of systemic methyl mercury-adulterated water consumption on fast axonal transport in the rat visual system.

The present study was designed in an effort to determine whether changes in fast axonal transport in the mature rat visual system can be directly correlated with the onset of neurological dysfunction. Methyl mercury was administered in the drinking water at a concentration of 54 micrograms Hg/ml. Fast axonal transport of proteins in the optic nerve and tract was quantified by scintillation spectrometry of protein-bound radioactivity along the visual pathway after an intraocular injection of 3H-proline. At 8 hours after injection the labeled protein had reached the lateral geniculate body both in controls and treated animals. However, two-way analysis of variance revealed a significant decrease in the volume of transported protein-bound radioactivity along the visual pathway. Thus, while the rate of fast axonal transport does not seem to be correlated with the onset of motor dysfunction, the onset of neurological symptoms may be associated with abnormal transport capacity. Treatment lowered body weight to the same extent in males and females. Hind limb cross-over occurred after 25.6 +/- 0.8 days and was followed quickly by hind limb paralysis (32 +/- 0.6 days). The cerebellum revealed pyknotic nuclei throughout the internal granular layer. Purkinje cells appeared normal. No pathological changes were noted in the kidneys.

Animals↗
PubMed1977

Tectal efferents in the branded water snake, Natrix sipedon.

Visual information reaches the dorsal thalamus by two distrinct routes in most reptiles. Retinal efferents terminate directly in the dorsal lateral geniculate nucleus (DLGN). Retinal information is also channeled indirectly through the tectum to nucleus rotundus. Retinal projections to DLGN and tectum are also well established in snakes, but the status of the tecto-rotundal link of the indirect visual pathway is uncertain. Thus, tectal efferents were studied with Fink-Heimer methods in banded water snakes (Natrix sipedon). The tectum gives rise to crossed and uncorssed projections to the brainstem reticular formation. Commissural connections are effected with the contralateral tectum via the tectal and posterior commissures. Tectum projects densely to the ipsilateral basal optic nucleus. Bilateral ascending projections reach the pretectal area, nucleus lentiformis mescencephali, lateral habenular nuclei, and posterodorsal nuclei. Ascending projections reach the ventral lateral geniculate and suprapeduncular nuclei. There is a diffuse projection to the central part of the caudal thalamus and a dense, bilateral projection to the DLGN. These results indicate that the relation of the tectum to the dorsal thalamus is different in snakes than in other reptiles. Nucleus rotundus is either absent or poorly differentiated and there is a strong convergence of the direct and indirect visual pathways at DLGN.

Animals↗
PubMed2005

Neural correlates of fine depth discrimination in monkey inferior temporal cortex.

Binocular disparity is an important visual cue that gives rise to the perception of depth. Disparity signals are widely spread across the visual cortex, but their relative role is poorly understood. Here, we addressed the correlation between the responses of disparity-selective neurons in the occipitotemporal (ventral) visual pathway and the behavioral discrimination of stereoscopic depth. We recorded activity of disparity-selective neurons in the inferior temporal cortex (IT) while monkeys were engaged in a fine stereoscopic depth discrimination (stereoacuity) task. We found that trial-to-trial fluctuations in neuronal responses correlated with the monkey's perceptual choice. We suggest that disparity signals in the IT, located in the ventral visual pathway, are functionally linked to the discrimination of fine-grain depth.

Animals↗