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PubMed2005

[Conventional techniques of visual field examination Part 2: confrontation visual field testing -- kinetic perimetry].

Evaluation of visual field findings is an essential ophthalmological task. Applying psychophysical principles enables noninvasive (topo-)diagnosis in cases of unexplained visual loss or suspected lesions of the visual pathway. Furthermore, any kind of expert opinion or ability test critically depends on adequate visual field findings. Repeated examinations allow functional follow-up of a disease and assessment of therapeutic efficiency. This paper explicitly focuses on conventional strategies since these are widespread, easily accessible, standardized, and well established in everyday practice over years. Standardized white-on-white perimetry with moving targets (kinetic perimetry) is the major topic of this paper (part 2) in addition to "rough"/preliminary confrontation visual field testing. This review series is aimed at imparting basic concepts in perimetry and psychophysics to ophthalmologists and also addresses interested physicians from other disciplines.

Eye Movements↗
PubMed1991

Lithium reduces ocular dominance plasticity in kitten visual cortex.

Activity-dependent processes within the visual pathway play a crucial role in the expression of ocular dominance plasticity in immature visual cortex. The necessity of non-retinal, modulatory afferents to the regulation of ocular dominance plasticity has been recognized. Among a few chemically defined signaling systems, the noradrenaline-activated beta-adrenoreceptors seem to have a prime role in this matter. The involvement of acetylcholine afferents was also proven. We looked for plausible molecular mechanisms which integrate the contribution of the two neuromodulator systems to ocular dominance plasticity. At the first step, based on the rich literature on psychotropic action of lithium and the recent advancement in understanding of its molecular mechanisms, we physiologically studied visual cortex of kittens which had been repeatedly injected with the lithium solution intraperitoneally or the cortex directly infused with it. We found (1) that ocular dominance plasticity was significantly reduced in lithium-injected kittens, (2) that the decrease was directly correlated with plasma concentrations of lithium (i.e. the higher the lithium concentration, the lower the plasticity), and (3) that the comparable decrease in the plasticity was obtained from kitten visual cortex which had been directly infused with the lithium solution. The present results suggest that lithium-sensitive processes, through most likely reduced production of second messengers, underlie the regulation of ocular dominance plasticity.

Animals↗
PubMed2005

The implications of foveal splitting for saccade planning in reading.

The human fovea and visual pathways are precisely split: information in one hemifield is initially projected to the contralateral visual cortex. This fundamental anatomical constraint on word recognition in reading has been largely ignored in eye movement research. We explore the consequences of this constraint through analyses of a large corpus of eye movement data, and demonstrate that aspects of saccade planning (target selection, initial landing position) are sensitive to both hemispheres, estimated uncertainty about the identity of the currently fixated word. We interpret these findings in terms of a hemispheric division of labour. We suggest that anatomical, visual and lexical factors all contribute to the decision of where to send the eyes next in reading.

Fixation, Ocular↗
PubMed1995

Recovery of vision following transsphenoidal surgery for pituitary adenomas.

The degree of recovery of vision is reported in 67 patients who underwent transsphenoidal surgery for pituitary adenomas compressing the visual pathways. There were no deaths, but 14 patients experienced postoperative complications. Overall, 88% showed visual improvement, 7% were unchanged and 4% were worse after surgery.

Adenoma↗
PubMed1993

Scrapie pathogenesis.

There is no specific marker for scrapie infectivity, and therefore no means other than prolonged bioassay for estimating levels of infection in tissues. Our knowledge of replication dynamics depends on precise rodent models which have enabled us to determine how the disease spreads and in which cells it replicates. We know, firstly, that infection replicates in the lymphoreticular system, and can identify a candidate cell; secondly, the factors which control the length of the disease process, and how difficult it is to influence this; thirdly, that clinical disease depends on access to the nervous system, and that once neuroinvasion has occurred, the spread of infectivity in both PNS and CNS is along neuroanatomical pathways at a similar rate to slow axonal transport in uninfected mice. Infecting the visual pathways of the CNS through the retina has shown that spongiform pathology occurs as a consequence of replication, and that the Sinc gene, which has a major effect on incubation period length in mice, acts by controlling the initiation, but not the rate, of replication. The localisation of PrP, a host protein of unknown function which accumulates in an abnormal form in diseased animals provides an important pointer to pathogenetic mechanisms.

Animals↗
PubMed2006

Cortical visual impairment in children.

PURPOSE OF REVIEW: Cortical visual impairment is rapidly becoming a leading cause of visual loss in children in developed countries predominately because of the improved survival rates of premature infants over the past decade. RECENT FINDINGS: Most cases of cortical visual impairment arise from hypoxic ischemic injury to watershed areas of the brain. In the preterm infant the watershed areas are in the subcortex around the ventricles, while in the term infant the watershed areas are between the major arteries with injury to the subcortex and cortex. Therefore, preterm and term injury will manifest different ocular and visual system abnormalities as a result of this damage. Cognitive visual dysfunction, a type of cortical visual impairment, may occur in cases of damage to the peristriate cortex (association areas of the brain). The anterior visual pathways may also be damaged in a retrograde, transsynaptic fashion in cases of cortical visual impairment. SUMMARY: Cortical visual impairment is a prevalent cause of visual loss in children. It encompasses a wide range of visual disabilities from no light reception to normal visual acuity with cognitive visual dysfunction.

Blindness, Cortical↗
PubMed1989

Retinocortical time exhibits spatial selectivity.

We recorded simultaneous electroretinograms and visual evoked potentials to pattern-reversal stimulus in ten normal subjects employing check sizes subtending 7.5, 15, 30, 60, 120, 240 and 480 min of visual arc. The mean peak latency of the pattern electroretinogram (PERG) b wave decreased logarithmically with increasing check size. The mean peak latency of the pattern visual evoked potential (PVEP) P100 component was shortest for 30 min check size and was longer at both smaller and larger check sizes, a phenomenon termed spatial selectivity. Retinocortical time (RCT) was calculated as the latency difference between the PVEP P100 peak and the PERG b wave. The RCT also exhibited spatial selectivity similar to that of the PVEP P100 component; mean RCT was shortest for 30 min check size and was longer at both smaller and larger check sizes. Implications are discussed in light of our current knowledge of the origins of the PERG and PVEP and visual processing of pattern-reversal stimuli. Simultaneous recording of PERGs and PVEPs in patients with disease of the afferent visual pathways employing a large range of check sizes may increase the diagnostic sensitivity of visual electrophysiologic testing.

Adult↗
PubMed1994

Orbital and optic pathway sarcoidosis: MR findings.

PURPOSE: To identify and characterize the MR findings of sarcoidosis when it involves the orbit and visual pathways. METHODS: The MR scans of 15 patients, 3 with presumed and 12 with proved orbital or optic pathway sarcoidosis were retrospectively reviewed. RESULTS: Eight patients had MR evidence of optic nerve involvement by sarcoid granuloma. Perineural enhancement was seen in four cases, optic atrophy in one. Three who had had unenhanced scans showed optic nerve enlargement. Nine patients had optic chiasmal involvement. One patient had increased T2 signal in the optic radiations. Three patients had orbital masses that had MR signal characteristics similar to pseudotumor. Five patients had periventricular white matter abnormalities closely resembling multiple sclerosis. CONCLUSIONS: Sarcoidosis should be considered in the differential diagnosis of optic nerve or nerve sheath enhancement on MR. Orbital sarcoidosis has MR characteristics very similar to pseudotumor.

Adolescent↗
PubMed1993

Visual field loss secondary to radiation-induced cerebral necrosis.

Radiation-induced cerebral necrosis has been well documented in the literature. Because radiation induced cerebral necrosis can occur to any part of the central nervous system that falls within the irradiated area, the visual pathway is highly susceptible to damage as it passes from the eye to the visual cortex. With proper visual field testing and interpretation, optometrists may serve as primary diagnosticians in radiation-induced cerebral necrosis and actively participate in the long-term management of these patients. This case presents a patient with visual field loss secondary to a temporal lobe lesion whose etiology was thought to be radiation-induced. The incidence, pathophysiology, and clinical features of radiation-induced cerebral necrosis as well as other differential diagnoses are discussed.

Aged↗
PubMed2004

Short-term depression of synaptic transmission from rat lateral geniculate nucleus to primary visual cortex in vivo.

Two forms of short-term synaptic plasticity, paired-pulse depression (PPD) and frequency depression, were prominent in the adult rat geniculo-cortical visual pathway in vivo. Iontophoresis of GABAa receptor antagonist (bicuculline methiodide) or GABAb receptor antagonist (2-hydroxy-saclofen) in the primary visual cortex significantly reduced the short-term synaptic depression. When NMDA or AMPA/kainate receptors were blocked, no obvious change of synaptic depression was observed. Application of high [Ca(2+)] enhanced the short-term synaptic depression. Our results suggest that the presynaptic Ca(2+)-dependent neurotransmitter depletion and postsynaptic GABAergic inhibition may be crucial for short-term synaptic depression in the geniculo-cortical pathway.

Animals↗
PubMed1989

Optic pathway gliomas in neurofibromatosis.

Two patients, a 5-year-old girl and a 3-year-old boy, with documented neurofibromatosis (NF-1) and visual pathway gliomas are reported. In the first patient, the tumor was a typical pilocytic astrocytoma confined to the proximal half of the right optic nerve just near the globe. The tumor was excised; after a follow-up of 7 years recurrence has not occurred. The second patient had a glioma of the left optic nerve, with involvement of the chiasm, optic tracts, probably lateral geniculate body, optic radiations and basal ganglia. Biventricular hydrocephalus, possibly due to the occlusion of Monro's foramina, was also noted. In this case, magnetic resonance imaging (MRI) was superior to computed tomography for visualizing the posterior extension of the lesions. The patient received X-ray therapy and after a follow-up of 3 years the clinical symptomatology remains stationary. It is suggested that the optic pathway involvement detected by MRI may represent a dysplastic element NF-1 rather than a truly neoplastic change.

Child, Preschool↗
PubMed1983

Chiasmal syndrome in sarcoidosis.

Four patients had involvement of the anterior visual pathway by sarcoidosis. In two cases recognition of the systemic disease was delayed because only visual symptoms were present. Three cases had evidence of hypothalamic-pituitary axis dysfunction, with histologically proved granulomatous infiltration of this region. The chiasmal syndrome in sarcoidosis is characterized by a pattern of blindness in one eye, atrophy of the optic discs, and temporal visual field loss in the contralateral eye with variable degrees of pituitary dysfunction. The condition is medically treatable and simulates the clinical and even the roentgenographic appearance of a pituitary tumor.

Adult↗
PubMed1987

Pattern electroretinogram plus visual evoked potential: a decisive test in patients suspected of malingering.

Along the processing chain in the visual pathway the pattern electroretinogram (PERG) is a better indicator of the peripheral function than the visual evoked potential (VEP). Therefore the PERG and the VEP will be impaired equally by disturbances before the ganglion cell layer (e.g., blurred image or retinal disease) and differently by further centrally located diseases (e.g., tumor compression of the optic nerve). Thus in patients complaining of reduced visual acuity who show disturbed VEP but a normal PERG, malingering can be definitely ruled out. Representative combinations of PERG and VEP findings are described.

Adult↗
PubMed1988

Neurotransmitter systems in the outer plexiform layer of mammalian retina.

Melatonin represents a second type of chemical signal released from photoreceptors in response to increased darkness, one with characteristics which are significantly different from those of glutamate. Concise spatial and temporal aspects of the photoreceptor signal are conserved through discrete glutamatergic synapses. Different classes of post-synaptic neurons each have appropriate subclasses of glutamate receptors which transmit sign conserving or sign inverting images of the visual mosaic. In contrast, melatonin, because of its highly lipophilic nature is not released by stimulus-coupled secretion mechanisms, but rather by simple diffusion. Thus control of melatonin "release" may be less concise than glutamate. In addition, melatonin may diffuse beyond the confines of the synaptic area to target cells throughout the retina. Effects of melatonin in retina are not well understood; however, current hypotheses suggest that, perhaps via its control of dopamine systems in the inner retina, melatonin plays an important role in dark adaptation and in various retinal processes which exhibit a circadian rhythm. Melatonin and glutamate may represent "co-transmitters" which provide the visual pathway with two types of signals, with melatonin providing widespread modulatory influences on the discrete visual information conveyed via glutamatergic circuits.

Animals↗
PubMed2004

A sequential study of visual evoked potential in patients with vitamin B12 deficiency neurological syndrome.

OBJECTIVE: Visual pathways are vulnerable to vitamin B(12) deficiency but there is paucity of studies evaluating visual evoked potential (VEP) changes following vitamin B(12) supplementation. Our aim was to evaluate the visual evoked potential changes in patients with vitamin B(12) deficiency neurological syndrome and their changes after vitamin B(12) therapy. METHODS: Seventeen patients with vitamin B(12) deficiency neurological syndromes diagnosed on the basis of megaloblastic bone marrow or low serum vitamin B(12) level or both were subjected to testing of visual acuity, field of vision, colour vision and neurological examination. Cranial magnetic resonance imaging was done in 9 patients and pattern reversal VEP was carried out on admission. P(100) latency and amplitude were measured. Visual function and VEP studies were repeated at 3 and 6 months after vitamin B(12) therapy. RESULTS: The patients' age ranged between 17 and 69 years; 7 were females and 16 were lactovegetarians. The duration of symptoms ranged between 10 days and 10 years. Visual acuity, colour vision, field of vision and fundus oculi were normal. VEP revealed prolongation of P(100) latency in 10 patients (17 eyes) which was mild in 2, moderate in 10 and marked in 5 eyes. Six months after treatment, P(100) latency improved to normal in all except 4 eyes. VEP abnormality was related to duration of illness and antiparietal cell antibodies. CONCLUSIONS: VEP is frequently prolonged in patients with vitamin B(12) deficiency neurological syndrome although asymptomatic. It usually returns to normal after treatment.

Adolescent↗
PubMed2005

Multifocal visual evoked potentials--a method study of responses from small sectors of the visual field.

OBJECTIVE: A method study of the mfVEP technique to establish a standardised way to identify stable response components from small areas in all parts of the visual field and a test-retest reliability study. METHODS: MfVEP was recorded from 26 healthy volunteers. RESULTS: Two response components could be clearly identified. The latencies corresponded to those of the traditional VEP response (N75 and P100). The visual field was divided into 12 sectors. A characteristic pattern was obtained. Component I was mainly negative in the upper sectors and positive in the lower sectors. Component II was positive in the upper sectors and negative in the lower ones. Most of the sectors with missing responses were the ones adjacent to the horizontal meridian, corresponding to the phase reversals. In a test-retest reliability study, the amplitude and latency measurements of the second test were plotted against those of the first test. Correlation coefficients between 0.84 and 0.93 were obtained. CONCLUSIONS: The mfVEP allows a reliable quantification of two response components from small parts of the visual field. SIGNIFICANCE: This paper suggests that mfVEP could be a valuable supplement to the traditional VEP for exploring restricted parts of the visual pathways.

Adult↗
PubMed2006

Retinotopic organization of primary visual cortex in glaucoma: Comparing fMRI measurements of cortical function with visual field loss.

Primary open angle glaucoma (POAG) is a progressive optic neuropathy characterized by retinal ganglion cell loss. Experimental primate glaucoma indicates neuronal degeneration of the lateral geniculate nucleus (LGN) and activity changes in the visual cortex (V1). Neuronal degeneration has also been shown in a post-mortem human study of the optic nerve, LGN and visual cortex. Functional magnetic resonance imaging (fMRI), a non-invasive means of inferring function-specific neuronal activity, provides an opportunity to evaluate glaucomatous changes in neuronal activity throughout the visual pathway in vivo. The purpose of this study is to demonstrate that the relationship between visual field loss in human POAG and the functional organization of V1 can be measured using novel fMRI analysis methods. Visual field defects were measured using standard automated perimetry (SAP). A retinotopic map of visual space was obtained for V1, and the retinotopy data was fit with a template. The template was used to project regions within the visual field onto a flattened representation of V1. Viewing through the glaucomatous vs. fellow eye was compared by alternately presenting each eye with a scotoma-mapping stimulus. The resulting blood oxygen level dependent (BOLD) fMRI response was compared to interocular differences in thresholds for corresponding regions of the visual field. The spatial pattern of activity observed in the flattened representation agreed with the pattern of visual field loss. Furthermore, the amplitude of the BOLD response was correlated on a pointwise basis with the difference in sensitivity thresholds between the glaucomatous and fellow eyes (r = 0.53, p < 0.0001). The BOLD signal in human V1 is altered for POAG patients in a manner consistent with the loss of visual function. FMRI of visual brain areas is a potential means for quantifying glaucomatous changes in neuronal activity. This should enhance our understanding of glaucoma, and could lead to new diagnostic techniques and therapies.

Animals↗
PubMed2000

Environmental light and the preterm infant.

The lighting environment of the preterm baby is quite unlike that experienced at any other time of life. Physical and physiological factors control how much light reaches the retina of the preterm baby. With respect to the former, although many neonatal intensive care units are brightly and continuously lit, there is a trend to employ lower levels of illumination and to introduce cycling regimens. Physiological determinants of the retinal light dose include: eyelid opening and transmission, pupil diameter and the transmission characteristics of the ocular media. Early exposure to light does not significantly hasten or retard normal visual development, and it is not a factor in the development of retinopathy of prematurity. However, ambient neonatal intensive care unit illumination may be implicated in some of the more subtle visual pathway sequelae that cannot be attributed to other major complications of preterm birth including altered visual functions and arrested eye growth.

Animals↗