Sign language aphasia due to left occipital lesion in a deaf signer

Localization of sign language production and comprehension in deaf people has been described as similar to that of spoken language aphasia. However, sign language employs a visuospatial modality through visual information. We present the first report of a deaf signer who showed substantial sign language aphasia with severe impairment in word production due to a left occipital lesion. This case may indicate the possibility of other localizations of plasticity.

Relation of vision to global and regional brain MRI in multiple sclerosis

OBJECTIVE

To examine the relation between low-contrast letter acuity, an emerging visual outcome for multiple sclerosis (MS) clinical trials, and brain MRI abnormalities in an MS cohort.

METHODS

T2 lesion volume and brain parenchymal fraction were determined for whole brain and within visual pathway regions of interest. Magnetization transfer ratio histograms were examined. Vision testing was performed binocularly using low-contrast letter acuity (2.5%, 1.25% contrast) and high-contrast visual acuity (VA). Linear regression, accounting for age and disease duration, was used to assess the relation between vision and MRI measures.

RESULTS

Patients (n = 45) were aged 44 +/- 11 years, with disease duration of 5 years (range <1 to 21), Expanded Disability Status Scale score of 2.0 (0 to 6.0), and binocular Snellen acuity of 20/16 (20/12.5 to 20/25). The average T2 lesion volume was 18.5 mm(3). Patients with lower (worse) low-contrast letter acuity and high-contrast VA scores had greater T2 lesion volumes in whole brain (2.5% contrast: p = 0.004; 1.25%: p = 0.002; VA: p = 0.04), Area 17 white matter (2.5%: p < 0.001; 1.25%: p = 0.02; VA: p = 0.01), and optic radiations (2.5%: p = 0.001; 1.25%: p = 0.02; VA: p = 0.007). Within whole brain, a 3-mm(3) increase in lesion volume corresponded, on average, to a 1-line worsening of low-contrast acuity, whereas 1-line worsening of high-contrast acuity corresponded to a 5.5-mm(3) increase.

CONCLUSIONS

Low-contrast letter acuity scores correlate well with brain MRI lesion burden in multiple sclerosis (MS), supporting validity for this vision test as a candidate for clinical trials. Disease in the postgeniculate white matter is a likely contributor to visual dysfunction in MS that may be independent of acute optic neuritis history.

Vision loss: overview

Visual loss is a common complaint to the neurologist. The visual pathways represent one third of the supratentorial brain mass and are frequently affected by structural lesions and a wide range of neurological disorders. By performing a basic ocular examination and asking the right questions, the neurologist should be able to evaluate a patient with visual loss. However, a detailed ocular examination is always necessary before obtaining further neurological workup.

Aggressive behavior and posterior cerebral artery stroke

OBJECTIVE

To describe the mechanisms leading to aggressive behavior among patients with acute posterior cerebral artery stroke.

DESIGN, SETTING, AND PATIENTS

We prospectively included all of the patients with posterior cerebral artery stroke and aggressive behavior admitted to our department from January 1, 2003, to December 31, 2004. Patients with history of stroke, cognitive impairment, or prior history of psychiatric disease were excluded.

RESULTS

Aggressive behavior was found in 3 patients (7.3%) among 41 patients with posterior cerebral artery stroke. One patient had right occipitotemporal and ventrolateral thalamic stroke. The second patient had left occipitotemporal and lateral thalamic stroke. The third patient had right isolated occipital stroke. In addition to a contralateral homonymous hemianopsia, the patients, who were physically and emotionally balanced before the stroke, suddenly manifested an acute, unusual, aggressive behavior. The patients became agitated and aggressive when they were stimulated by the environment, and they responded to solicitation by their relatives or medical personnel by shouting obscenities and hitting and biting others. In all of the 3 cases, temporary physical restraint was required and neuroleptics were administered. This unusual behavioral pattern resolved within 2 weeks after stroke.

CONCLUSIONS

Aggressive behavior is a rare presentation of acute posterior cerebral artery stroke, which may be difficult to diagnose in patients presenting with hemianopsia as the only concomitant neurological sign. The postulated mechanisms include dysfunction of the limbic or serotoninergic system.

Cerebral atrophy in Parkinson's disease patients with visual hallucinations

Although visual hallucinations (VH) are relatively frequent in Parkinson's disease (PD) patients, their neural substrates are only known from neuropathological and functional magnetic resonance studies. The aim of this study was to investigate possible structural brain changes on MRI in non-demented PD patients with VH using voxel-based morphometry. Eighteen PD patients with VH were compared to 20 patients with PD without VH and 21 healthy controls. Compared with both controls and the non-hallucinating PD group, PD patients with VH had grey matter volume reductions in the lingual gyrus and superior parietal lobe. Structural changes in these areas involved in higher visual processing may be important in understanding the VH and visual deficits in PD patients.

Of Roman chariots and goats in overcoats: The syndrome of Charles Bonnet

Charles Bonnet syndrome (CBS) is a widely under-recognised disorder typically characterised by complex visual hallucinations in the visually impaired. The lack of consensus over a uniform definition for CBS has much to do with the unresolved pathophysiology of the disorder. A leading hypothesis proposes that complex hallucinations arise from visual association cortical areas following their de-afferentation from the central visual pathway. While treatment aimed at improving the visual deficit can limit the symptoms of CBS, at present there is no reliably effective pharmacotherapy for the disorder. Once correctly recognised, a key management principle is to reassure the patient that CBS is a well-documented clinical entity that is not a harbinger of psychiatric illness.

fMRI Demonstrates Diaschisis in the Extrastriate Visual Cortex

Background and Purpose— Diaschisis may play a critical role in motor recovery, but in other cortical networks its role is unclear. Some visual system regions, such as the fusiform gyri, depend on intact striate regulation for their function. We evaluated visual cortical diaschisis by serial functional magnetic resonance imaging.

Methods— Using a high-level visual activation task, we studied patients with visual system stroke by functional magnetic resonance imaging within 10 days and at 6 months. Their activation data were compared with those of age-appropriate healthy control subjects.

Results— Three patients were studied. In the short term, patients displayed absent or significantly reduced activation in ventral extrastriate sites. All displayed a restitution of activation to these sites at 6 months.

Conclusions— Functional magnetic resonance imaging revealed evidence of ipsilesional cortical diaschisis within ventral extrastriate sites. Diaschisis may play an underrecognized role in visual recovery after stroke.

Morphologie des Chiasma opticum bei Albinismus

Albinism is associated with a misrouting of fibers at the optic chiasm where the majority of fibers cross to the contralateral side. The cause of this abnormal decussation pattern reflects a disturbance of cell cycle regulation in the development of the retina which is in part controlled by melanin. Growing axons from retinal ganglion cells therefore arrive later than usual at the optic chiasm and are misrouted contralaterally. This atypical decussation leads to morphological changes of the optic chiasm including a reduced chiasm width with larger angles between optic nerves and tracts which can be shown by magnetic resonance imaging.

Selective vulnerability of cerebral white matter in a murine model of multiple sclerosis detected using diffusion tensor imaging

In this study, axial (lambda(parallel)) and radial (lambda(perpendicular)) diffusivities derived from diffusion tensor imaging (DTI) were used to evaluate white matter injury in brains of mice affected by experimental autoimmune encephalomyelitis (EAE). Sixteen female C57BL/6 mice were immunized with amino acids 35-55 of myelin oligodendrocyte glycoprotein (MOG(35-55)). Three months after immunization, optic nerve and tract were severely affected with 19% and 18% decrease in lambda(parallel) respectively, suggesting the presence of axonal injury. In addition, a 156% and 86% increase in lambda( perpendicular) was observed in optic nerve and tract respectively, suggestive of myelin injury. After in vivo DTI, mice were perfusion fixed and immunohistochemistry for the identification of myelin basic protein (MBP) and phosphorylated neurofilament (pNF) was performed to verify the presence of axonal and myelin injury. The present study demonstrated that the visual pathway is selectively affected in MOG(35-55) induced murine EAE and these injuries are non-invasively detectable using lambda(parallel) and lambda( perpendicular).

Morphological substrate of face matching in healthy ageing and mild cognitive impairment: a combined MRI-fMRI study

Functional MRI during face matching shows activation of the ventral visual stream, including the ventral temporal lobes and fusiform gyrus. In contrast, a location-matching task activates the dorsal visual stream, compromising parietal lobe areas. The morphological basis of the functional coupling between brain regions may be related to the distribution of neuron numbers and neuropil density, but has not yet been demonstrated in the living human brain. Regional neuron density can indirectly be assessed in vivo using structural MRI. The progression of Alzheimer's disease pathology along specific functional systems provides an in vivo lesion model to determine the interaction between reduced neuron numbers and reduced neuronal activation. In this study, we determined correlations between activation of the fusiform gyrus in fMRI during face matching and cortical grey matter density derived from structural MRI in 17 healthy elderly subjects (mean age = 67.5 years, SD = 4.5 years, 10 women) and 16 patients with amnestic mild cognitive impairment (MCI) (mean age = 69.9 years, SD = 8.0 years, 8 women), a predementia stage of Alzheimer's disease. Independently of diagnosis, stronger activation of the fusiform gyrus was correlated with larger grey matter density in the fusiform gyrus, inferior and middle temporal gyrus, parahippocampal gyrus and dorsolateral prefrontal cortex. In contrast, smaller activation of the fusiform gyrus was associated with larger grey matter density in the inferior parietal lobule, post-central gyrus and dorsolateral prefrontal cortex. Compared to controls, MCI patients had more pronounced positive correlations in the ventral temporal lobes and more pronounced negative correlations in the parietal lobes. Our data suggest that fusiform activation is positively correlated with cortical grey matter density of brain areas belonging to the ventral visual stream and negatively correlated with grey matter density of brain areas belonging to the dorsal visual stream and that, these effects are more pronounced in MCI patients than in controls. These findings support the notion that the functional segregation within the visual system is based on the distribution of cortical grey matter volumes, possibly reflecting the spatial distribution of neuron density.

Optic pathway gliomas in neurofibromatosis-1: controversies and recommendations

Optic pathway glioma (OPG), seen in 15% to 20% of individuals with neurofibromatosis type 1 (NF1), account for significant morbidity in young children with NF1. Overwhelmingly a tumor of children younger than 7 years, OPG may present in individuals with NF1 at any age. Although many OPG may remain indolent and never cause signs or symptoms, others lead to vision loss, proptosis, or precocious puberty. Because the natural history and treatment of NF1-associated OPG is different from that of sporadic OPG in individuals without NF1, a task force composed of basic scientists and clinical researchers was assembled in 1997 to propose a set of guidelines for the diagnosis and management of NF1-associated OPG. This new review highlights advances in our understanding of the pathophysiology and clinical behavior of these tumors made over the last 10 years. Controversies in both the diagnosis and management of these tumors are examined. Finally, specific evidence-based recommendations are proposed for clinicians caring for children with NF1.

Diffusion tensor fiber tractography for arteriovenous malformations: quantitative analyses to evaluate the corticospinal tract and optic radiation

BACKGROUND AND PURPOSE

We hypothesized that diffusion tensor fiber tractography would be affected by intracranial arteriovenous malformation (AVM). The purpose of the present study was to evaluate the influence of intracranial AVM on corticospinal tract and optic radiation tractography.

MATERIALS AND METHODS

The subject group comprised 34 patients with untreated intracranial AVM. Hemorrhage was present in 13 patients and absent in 21 patients. Perinidal fractional anisotropy (FA) and number of voxels along the reconstructed corticospinal and optic radiation tracts were measured, and left-to-right asymmetry indices (AIs) for those values were quantified. Patients were assigned to 1 of 3 groups: tracts distant from nidus, tracts close to nidus without neurologic symptoms, and tracts close to nidus associated with neurologic symptoms. One-way analysis of variance was used to compare differences in AI between groups. Hemorrhagic and nonhemorrhagic groups were assessed separately.

RESULTS

In patients without hemorrhage, AI of optic radiation volume (P<.0001), AI of perinidal FA along corticospinal tract (P=.006), and optic radiation (P=.01) differed significantly between groups. In patients associated with hemorrhage, AI of corticospinal tract volume (P=.01), AI of perinidal FA along corticospinal tract (P=.04), and optic radiation (P=.004) differed significantly between groups.

CONCLUSIONS

Corticospinal tract and optic radiation tractography were visualized in patients with AVM. In patients with both hemorrhagic and nonhemorrhagic AVM, the 2 fiber tracts close to the nidus were less visualized in the affected hemisphere than those distant from the nidus. Tracts were less visualized in patients with neurologic symptoms than in asymptomatic patients.

Screening and Diagnosis of Optic Pathway Gliomas in Children with Neurofibromatosis Type 1 by Using Sweep Visual Evoked Potentials

PURPOSE

Neurofibromatosis type 1 (NF-1) is an autosomal dominant phakomatosis with a prevalence of 1 in 2000 to 1 in 5000. Up to 24% of these patients have optic pathway gliomas (OPGs). In the present study, the use of sweep visual evoked potentials (SVEPs) was investigated as a screening tool for identifying patients with NF-1 who had OPGs by comparing them to those patients with no OPGs and to normally developing children.

METHODS

Contrast sensitivity and grating acuity were measured with the SVEP. Sixteen children with OPGs (OPG group), 14 children with NF-1 without OPGs (nOPG), and 16 aged-matched control subjects were recruited. All participants had best-corrected visual acuity of 6/9 or better. All were tested monocularly.

RESULTS

Comparisons between groups by using the Tukey B test showed a significant reduction of mean log contrast sensitivity in the OPG group (1.55) compared with the nOPG (1.9, P = 0.006) and control (2.10, P < 0.001) group. There was no significant difference between the nOPG and control groups (P = 0.195). Grating acuity was comparable between groups, and no statistically significant differences were found. Log contrast sensitivity was moderately sensitive in identifying patients with OPG and was highly specific in screening out patients with no OPG.

CONCLUSIONS

Children with OPGs have reduced contrast sensitivity when assessed using the SVEP. Children with no OPGs display no differences in visual functioning compared with control subjects. The findings suggest that the SVEP can be a useful and noninvasive screening tool for early detection of visual pathway gliomas in children with NF-1 and normal visual acuity.

Large ophthalmic segment aneurysms with anterior optic pathway compression: assessment of anatomical and visual outcomes after endosaccular coil therapy

Object

The optimal therapy for ophthalmic segment aneurysms with anterior optic pathway compression (AOPC) is undecided. Surgical results have been described, but the results of endovascular coil therapy have not been well documented.

Methods

The authors retrospectively reviewed data obtained in all patients who harbored unruptured ophthalmic segment aneurysms with AOPC who underwent endovascular coil therapy at their institution. They analyzed baseline and outcome visual function, aneurysm features, extent of aneurysm closure, internal carotid artery (ICA) occlusion, additional interventions, and neurological outcome.

In 17 patients (16 women), age 38 to 83 years, there were 28 affected eyes. All aneurysms were greater than 10 mm in diameter. In the initial procedures 16 of 17 patients received endosaccular coils and the ICA was preserved; in one patient the aneurysm was trapped and the ICA occluded. Patients then underwent follow up for a mean of 2.90 years (range 1 month–11.2 years) after the last procedure. One patient died of subarachnoid hemorrhage (SAH) 1 month postoperatively and thus no follow-up data were available for this case. Vision worsened in six patients, stabilized in four, and improved in six. Twelve patients underwent 13 subsequent procedures, including endovascular ICA occlusion in seven, repeated coil therapy in five, and optic nerve decompression in one; vision improved in 83% of these cases after ICA occlusion. A second patient died of SAH 5 months after repeated coil treatment. At the final follow up, vision had improved in eight patients (50%), stabilized in four (25%), and worsened in four (25%). In 16 patients with follow-up studies, aneurysm closure was complete in eight (50%) and incomplete in eight (50%).

Conclusions

The authors found that in patients with ophthalmic segment aneurysms causing chronic AOPC, endosaccular platinum coil therapy, with ICA preservation, may not benefit vision and that additional procedures may be needed. Evaluation of their results suggests that endovascular trapping of the aneurysm and sacrifice of the ICA appear to result in good visual, clinical, and anatomical outcomes.

Palinopsia From Posterior Visual Pathway Lesions Without Visual Field Defects

Palinopsia, or perseveration of a previously viewed image, may be caused by drug use or by posterior visual pathway lesions. Most cases of palinopsia due to visual pathway lesions have an associated homonymous hemianopic visual field defect. We report two patients with palinopsia caused by structural lesions of the posterior visual pathway in the absence of visual field defects. Patients with palinopsia should undergo neuroimaging even in the presence of normal visual fields.

Progressive atrophy in the optic pathway and visual cortex of early blind Chinese adults: A voxel-based morphometry magnetic resonance imaging study

Many previous neuroimaging studies have shown that the early visual cortex of the early blind (EB) exhibits significant functional plasticity. However, only few previous studies have addressed the question whether or not such functional plasticity is accompanied by, and even related to, structural plasticity. In this study, we acquired high-resolution whole-brain anatomical magnetic resonance images form 14 Chinese EB adults, who lost sight before 6 years of age, and 16 age/gender-matched normal-sighted controls (SC), and compared pixel-by-pixel the gray matter (GM) and white matter (WM) volumes between the two groups with voxel-based morphometry. The results showed that, relative to the SC, the EB exhibits significantly reduced WM volumes in the optic tract and optic radiation and significant GM losses in the early visual cortex. The reduction of WM volume in the optic radiation of the EB was found be modulated by both the age at blindness onset and the duration of blindness. The reduction of GM volume in the early visual cortex of the EB appeared to be unaffected by the age at blindness onset. However, it was found in localized regions of the atrophic early visual cortex of the EB that the GM loss was progressive with aging and increasing duration of blindness. These results suggest that early visual deprivation induces significant structural plasticity in the optic pathway and early visual cortex of the EB, which likely occurs during both the critical period of early neurodevelopment and the course of persisted blindness later in life through activity-dependent mechanisms.

Complete resection of a cavernous haemangioma of the optic nerve, the chiasm, and the optic tract

The involvement of the optic nerve, the chiasma, and the optic tract by a cavernoma has been reported in only three patients. In all of them, a biopsy of the vascular lesion was obtained. We report a further example of a 38-year-old male patient who suffered from acute onset of severe headache and progressive loss of vision. The vascular malformation of the optic pathways was completely removed via a pterional approach. This is the first reported instance of complete resection of a cavernoma involving the optic nerve, the chiasm, and the optic tract.

Congruency in homonymous hemianopia

PURPOSE

To evaluate the value of congruency in the localization of brain lesions in patients with homonymous hemianopia (HH).

DESIGN

Retrospective observational study.

METHODS

Charts of all patients with HH seen over 15 years were reviewed. Only patients with incomplete HH documented on formal visual field testing and neuroimaging were included. HH was said to be congruent when the fields of both eyes were identical in shape, depth, and size. Patients were divided into two groups based on congruency of HH; demographic, clinical, and radiological characteristics were compared.

RESULTS

Five hundred and thirty patients with 548 incomplete HH were included (373 congruent HH and 175 incongruent HH). Demographic variables were similar in both groups. Stroke caused 75% of congruent HH and 55.8% of incongruent HH; trauma and tumors caused 20.5% of congruent HH and 34.5% of incongruent HH (P < .001). The lesion locations in congruent HH vs incongruent HH included occipital lobe in 47.9% vs 21.3%, occipital lobe and optic radiations in 8.3% vs 5.6%, optic radiations in 32.4% vs 50.6%, optic tract in 7.2% vs 16.3%, and other locations in 4.2% vs 6.3% (P < .0001). Although there was a trend toward more congruent HH for lesions of the posterior visual pathways (P < .001), 50% of optic tract lesions and 59% of optic radiation lesions produced congruent HH.

CONCLUSION

Although lesions involving the occipital lobe characteristically produce congruent HH, at least 50% of lesions in other locations also produce congruent HH, especially if these lesions are stroke-related. The rule of congruency should be used cautiously and may not apply to optic tract lesions.

Effect of binocular retinal lesions on CRMP2 and CRMP4 but not Dyn I and Syt I expression in adult cat area 17

Removal of retinal input from a restricted region of adult cat visual cortex leads to a substantial reorganization of the retinotopy within the sensory-deprived cortical lesion projection zone (LPZ). Still little is known about the molecular mechanisms underlying this cortical map reorganization. We chose two members of the collapsin response mediator protein (CRMP) family, CRMP2 and CRMP4, because of their involvement in neurite growth, and compared gene and protein expression levels between normal control and reorganizing visual cortex upon induction of central retinal lesions. Parallel analysis of Dynamin I (Dyn I) and Synaptotagmin I (Syt I), two molecules implicated in the exocytosis-endocytosis cycle, was performed because changes in neurotransmitter release have been implicated in cortical plasticity. Western blotting and real-time polymerase chain reaction revealed a clear time-dependent effect of retinal lesioning on CRMP2 and CRMP4 expression, with maximal impact 2 weeks post-lesion. Altered CRMP levels were not a direct consequence of decreased visual activity in the LPZ as complete surgical removal of retinal input to one hemisphere had no effect on CRMP2 or CRMP4 expression. Thus, CRMP expression is correlated to cortical reorganization following partial deafferentation of adult visual cortex. In contrast, Dyn I and Syt I were not influenced and thereby do not promote exocytosis-endocytosis cycle modifications in adult cat cortical plasticity.

The fidelity of the cortical retinotopic map in human amblyopia

To delineate the fidelity of the functional cortical organization in humans with amblyopia, we undertook an investigation into how spatial information is mapped across the visual cortex in amblyopic observers. We assessed whether the boundaries of the visual areas controlled by the amblyopic and fellow fixing eye are in the same position, the fidelity of the retinotopic map within different cortical areas and the average receptive field size in different visual areas. The functional organization of the visual cortex was reconstructed using a fMRI phase-encoded retinotopic mapping analysis. This method sequentially stimulates each point in the visual field along the axes of a polar-coordinate system, thereby reconstructing the representation of the visual field on the cortex. We found that the cortical areas were very similar in normals and amblyopes, with only small differences in boundary positions of different visual areas between fixing and fellow amblyopic eye activation. Within these corresponding visual areas, we did find anomalies in retinotopy in some but not all amblyopes that were not simply a consequence of the poorer functional responses and affected central and peripheral field regions. Only a small increase in the average (or collective) receptive field size was found for full-field representation in amblyopes and none at all for central field representation. The former may simply be a consequence of the poorer functional responses.

l-3-n-Butylphthalide Improves Cognitive Impairment Induced by Chronic Cerebral Hypoperfusion in Rats

3-n-Butylphthalide (NBP) may be beneficial for the treatment of ischemic stroke with multiple actions on different pathophysiological processes. In the present study, we investigated the effect of NBP isomers on learning and memory impairment induced by chronic cerebral hypoperfusion in rats. Male Wistar rats were orally administered 10 and 30 mg/kg l-, d-, or dl-NBP daily for 23 days after bilateral permanent occlusion of the common carotid arteries. Rats receiving 10 mg/kg l-NBP performed significantly better in tests for spatial learning and memory, and they had attenuated cerebral pathology, including neuronal damage, white matter rarefaction, and glial activation compared with controls. Furthermore, 10 mg/kg l-NBP-treated rats had significantly higher choline acetyltransferase activity, decreased cortical lipid peroxide, and reduced hippocampal superoxide dismutase activity, compared with vehicle controls. However, d- and dl-NBP did not show significant beneficial effects. The present findings demonstrate that the beneficial effects of l-NBP on hypoperfusion-induced cognitive deficits may be due to preventing neuropathological alterations, inhibiting oxidative damage and increasing acetylcholine synthesis. Our results strongly suggest that l-NBP has therapeutic potential for the treatment of dementia caused by decreased cerebral blood flow.

Interhemisphere connections of the visual cortex in cats with bilateral strabismus

The distribution of retrograde labeled callosal cells after microiontophoretic application of horseradish peroxidase into individual cortical columns in fields 17 and 18 was studied in cats reared with bilateral strabismus (with an angle of eye deviation of 10-35 degrees ). The area containing labeled cells was located asymmetrically in relation to the position of the injected column in the opposite hemisphere. Some of the cells were located in those parts of the transitional zone between fields 17 and 18 whose retinotopic coordinates corresponded to the column coordinates (as in intact cats). Other labeled cells were located in fields 17 and 18 and were grouped into clusters located at distances of about 1000 microm from the marginal clusters of the transitional zone. The locations of labeled cells in the lateral geniculate body showed that most columns receive inputs from the ipsilateral eye. Evidence for eye specificity of these monosynaptic interhemisphere connections is presented. The functional significance of changes in these connections in bilateral strabismus is discussed.

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.

Correlation in Lewy pathology between the claustrum and visual areas in brains of dementia with Lewy bodies

We investigated Lewy pathologies in the claustrum and the related cerebral cortices and subcortical nuclei of dementia with Lewy bodies (DLB) brains using alpha-synuclein-immunohistochemistry to clarify the relationship between Lewy pathology in the claustrum and visual misidentification of DLB patients. The claustrum is known to have strong reciprocal connections with the visual areas. Consequently, the claustrum demonstrated many Lewy bodies (LB) and LB-related neurites. The insular and inferior temporal cortices, amygdala, BA 18, 19, transentohrinal and cingulate cortices showed stronger or similar Lewy pathology as compared with the claustrum, while BA 17, precentral, postcentral and transverse temporal cortices showed weaker Lewy pathology. Comparing the correlation coefficient of Lewy pathology between the clausturm and other regions, BA 18 and 19 as well as the insular and transentorhinal cortices demonstrated a higher correlation coefficient. These findings suggest that Lewy pathology in the claustrum is more closely associated with that in visual areas than in auditory, somatosensory or motor areas, and that dysfunction of the visuo-claustral pathway participates in visual misidentification in addition to the visuo-amygdaloid pathway. The paralimbic cortices including the insular and transentorhinal cortices may connect visual areas with limbic areas by relay of the visuo-claustral or visuo-amygdaloid pathway.

Progression in multiple sclerosis: further evidence of an age dependent process

The relapsing-remitting phase and the progressive phase of multiple sclerosis (MS) seem to be the result of distinct pathophysiological processes. Previous research on the natural history of MS was largely focussed on relapses and disability scores. In this study we evaluated 438 patients with secondary or primary progressive MS. The influence of gender, initial disease course, onset manifestation and age at disease onset on age at progression and time to progression were evaluated with Kaplan-Meier survival analysis and Cox multivariate regression models. The analysis of these data showed that the initial disease course (SPMS or PPMS) had no influence on the age at progression. Gender had no influence on age at progression in PPMS and SPMS patients nor on time to progression in SPMS patients. PPMS patients with visual or brainstem/cerebellar onset had a significantly younger age at progression. SPMS patients with motor onset had a significantly higher age at progression and longer time to progression. Time to progression was significantly shorter in SPMS patients with higher age at disease onset. Our data give further support to the notion that progression in MS is an age dependent process independent of relapses.

Neurofibromatosis type 1 and optic pathway glioma. A long-term follow-up

AIM

Optic pathway gliomas (OPG) are the predominant intracranial tumours associated with neurofibromatosis type 1 (NF1). The aim of this study was to evaluate the prevalence and the outcome of OPG in 200 NF1 patients (122 males and 78 females, aged 1-25 years) followed up to 16 years (mean of 6 years).

METHODS

All children were evaluated by a detailed physical, neurological and ophthalmological examination. Fifteen out of 200 (7.5%) of these patients (7 males, 8 females) were identified with evidence of optic pathway tumours.

RESULTS

Nine children had symptoms such as endocranial hypertension, seizures, headache; 4 patients only showed anomalies at ophthalmological examination; 2 patients had no symptoms or signs. All children had evidence of optic pathway tumour on magnetic resonance imaging. Three had a prechiasmal tumour, 2 had a chiasmal tumour, 1 had prechiasmal/chiasmal tumour, 2 had a prechiasmal/chiasmal and postchiasmal tumour, 2 had a chiasmal and postchiasmal tumour, 4 had a massive involvement of the optic system, 1 child exhibited a bilateral involvement of the optic nerves with additional impairment of the chiasm. Four patients had partial and/or subtotal spontaneous regression.

CONCLUSIONS

Because optic pathway tumours arise in children younger than 6 years of age, all NF1 children should undergo yearly ophtalmologic examination and growth assessment to monitor signs of precocious puberty.

Optic neuritis and the neuro-ophthalmology of multiple sclerosis

Multiple sclerosis (MS) is the most common cause of neurological disability in young adults. Since approximately 40% of the brain is devoted to vision, demyelination commonly affects visual function, resulting in a myriad of neuro-ophthalmic symptoms. In this chapter, we examine the seminal afferent and efferent neuro-ophthalmological manifestations of MS, highlighting those history and examination findings critical for the diagnosis and treatment of various visual and ocular motor disorders. Among the topics, a special emphasis will be placed on optic neuritis, the most common clinically isolated demyelinating syndrome. This chapter focuses on the evaluation and treatment of visual sensory and oculomotor disorders in MS. The objective is to provide the reader with a working model for enhancing their care of patients with demyelinating disease.

Neuro-ophthalmology for neuroradiologists

Combining an understanding of neuro-ophthalmologic anatomy with proper imaging techniques provides a powerful method to detect lesions involving the afferent and efferent visual pathways. Precise documentation of the extent of injury within the nervous system is becoming increasingly important to assess and monitor the effect of neurologic therapies. This review will focus on those common neuro-ophthalmologic problems that have exquisite localizing value on neuro-imaging.

Implantable visual prostheses

Visual impairment and blindness is primarily caused by optic neuropathies like injuries and glaucomas, as well as retinopathies like agerelated macular degeneration (MD), systemic diseases like diabetes, hypertonia and hereditary retinitis pigmentosa (RP). These pathological conditions may affect retinal photoreceptors, or retinal pigment epithelium, or particular subsets of retinal neurons, and in particular retinal ganglion cells (RGCs). The RGCs which connect the retina with the brain are unique cells with extremely long axons bridging the distance from the retina to visual relays within the thalamus and midbrain, being therefore vulnerable to heterogeneous pathological conditions along this pathway. When becoming mature, RGCs loose the ability to divide and to regenerate their accidentally or experimentally injured axons. Consequently, any loss of RGCs is irreversible and results to loss of visual function. The advent of micro- and nanotechnology, and the construction of artificial implants prompted to create visual prostheses which aimed at compensating for the loss of visual function in particular cases. The purpose of the present contribution is to review the considerable engineering expertise that is essential to fabricate current visual prostheses in connection with their functional features and applicability to the animal and human eye. In this chapter, 1) Retinal and cortical implants are introduced, with particular emphasis given to the requirements they have to fulfil in order to replace very complex functions like vision. 2) Advanced work on material research is presented both from the technological and from the biocompatibility aspect as prerequisites of any perspectives for implantation. 3) Ultimately, experimental studies are presented showing the shaping of implants, the procedures of testing their biocompatibility and essential modifications to improve the interfaces between technical devices and the biological environment. The review ends by pointing to future perspectives in the rapidly accelerating process of visual prosthetics and in the increasing hope that restoration of the visual system becomes reality.

Regenerating optic axons restore topography after incomplete optic nerve injury

Following complete optic nerve injury in a lizard, Ctenophorus ornatus, retinal ganglion cell (RGC) axons regenerate but fail to restore retinotectal topography unless animals are trained on a visual task (Beazley et al. [ 1997] J Comp Neurol 370:105-120, [2003] J Neurotrauma 20:1263-1270). Here we show that incomplete injury, which leaves some RGC axons intact, restores normal topography. Strict RGC axon topography allowed us to preserve RGC axons on one side of the nerve (projecting to medial tectum) while lesioning those on the other side (projecting to lateral tectum). Topography and response properties for both RGC axon populations were assessed electrophysiologically. The majority of intact RGC axons retained appropriate topography in medial tectum and had normal, consistently brisk, reliable responses. Regenerate RGC axons fell into two classes: those that projected topographically to lateral tectum with responses that tended to habituate and those that lacked topography, responded weakly, and habituated rapidly. Axon tracing by localized retinal application of carbocyanine dyes supported the electrophysiological data. RGC soma counts were normal in both intact and axotomized RGC populations, contrasting with the 30% RGC loss after complete injury. Unlike incomplete optic nerve injury in mammals, where RGC axon regeneration fails and secondary cell death removes many intact RGC somata, lizards experience a "win-win" situation: intact RGC axons favorably influence the functional outcome for regenerating ones and RGCs do not succumb to either primary or secondary cell death.

Ocular dominance columns in strabismus

During development, the projection from the lateral geniculate nucleus to striate cortex becomes segregated into monocular regions called ocular dominance columns. Prior studies in cats have suggested that experimental strabismus or alternating monocular occlusion increases the width and segregation of columns. In the squirrel monkey, strabismus has been reported to induce the formation of ocular dominance columns. However, these studies are difficult to interpret because no animal can serve as its own control and the degree of inter-individual variability among normal subjects is considerable. We have re-examined the effect of strabismus on ocular dominance columns in a large group of strabismic and normal squirrel monkeys. Five animals rendered strabismic at age one week had well-developed, widely spaced columns. Among 16 control animals, a wide spectrum of column morphology was encountered. Some control animals lacked ocular dominance columns, whereas others had columns similar to those observed in strabismic animals. Natural variation in column expression in normal squirrel monkeys, and potential uncontrolled genetic influences, made it impossible to determine if strabismus affects ocular dominance columns. It was evident however, that strabismus does not affect the binocular projection from the lateral geniculate nucleus to each CO patch in the upper layers. In strabismic monkeys, just as in normal animals, each patch received input from geniculate afferents serving both the left eye and the right eye. In addition, in strabismic monkeys, as in normal animals, patches were not aligned with ocular dominance columns.

Non-arteritic anterior ischaemic optic neuropathy: evaluation of the brain and optic pathway by conventional MRI and magnetisation transfer imaging

The purpose of the study was to examine the brain and the visual pathway of patients with non-arteritic anterior ischaemic optic neuropathy (NAION) by using conventional MRI (cMRI) and volumetric magnetisation transfer imaging (MTI). Thirty NAION patients, aged 67.5 +/- 8.14 years, and 28 age- and gender-matched controls were studied. MTI was used to measure the magnetisation transfer ratio (MTR) of the chiasm and for MTR histograms of the brain. The presence of areas of white matter hyperintensity (WMH) was evaluated on fluid-attenuated inversion recovery (FLAIR) images. Area of the optic nerves (ONs) and volume of the chiasm were assessed, as were coronal short-tau inversion recovery (STIR) and MTI images, respectively. More areas of WMH were observed in patients (total 419; mean 14.4; SD 19) than in controls (total 127; mean 4.7; SD 5.7), P < 0.001. Area (in square millimetres) of the affected ONs, volume(in cubic millimetres) and MTR (in percent) of the chiasm (10.7 +/- 4.6), (75.8 +/- 20.2), (56.4 +/- 6.5), respectively, were lower in patients than in controls (13.6 +/- 4.3), (158.2 +/- 75.3) (62.1 +/- 6.2), respectively, P < 0.05. Mean MTR of brain histograms was lower in patients (53.0 +/- 8.0) than in controls (58.0 +/- 5.6), P < 0.05. NAION is characterised by decreased ON and chiasmatic size. The low MTR of the chiasm and brain associated with increased areas of WMH may be suggestive of demyelination and axonal damage due to generalised cerebral vascular disease.

Interpretation of visual field defects respecting the vertical meridian and not related to distinct chiasmal or postchiasmal lesions

Hemianopia respecting the vertical meridian generally results from a disturbance in the optic chiasm or the postchiasmal visual pathway. We present five unusual patients with visual field defects respecting the vertical meridian that were not related to distinct chiasmal or postchiasmal lesions, as determined by magnetic resonance imaging (MRI). Optic neuritis, plus the influence of the testing algorithm for perimetry, was a possible cause in two cases. The symptoms of one patient with homonymous hemianopia were a functional deficit. In the two other cases, the visual field defects may have been caused by optic disc abnormalities. Although visual field defects respecting the vertical meridian, and without any evidence of distinct disease, are uncommon, neurologists and neuro-ophthalmologists should consider the differential diagnosis if MRI is negative for distinct lesions in the optic chiasm or the postchiasmal visual pathway.

Visual white matter integrity in schizophrenia

OBJECTIVE

Patients with schizophrenia have visual-processing deficits. This study examines visual white matter integrity as a potential mechanism for these deficits.

METHOD

Diffusion tensor imaging was used to examine white matter integrity at four levels of the visual system in 17 patients with schizophrenia and 21 comparison subjects. The levels examined were the optic radiations, the striate cortex, the inferior parietal lobule, and the fusiform gyrus.

RESULTS

Schizophrenia patients showed a significant decrease in fractional anisotropy in the optic radiations but not in any other region.

CONCLUSIONS

This finding indicates that white matter integrity is more impaired at initial input, rather than at higher levels of the visual system, and supports the hypothesis that visual-processing deficits occur at the early stages of processing.

[A follow-up of patients with anterior optic tract glioma concurrent with type 1 neurofibromatosis]

Fifty-nine patients with anterior optic tract (AOT) lesion concurrent with type neurofibromatosis (NF-1) were followed up for 1 to 36 years (median 5 years). Based on the study, the authors identified several grades of the disease: - stabilization without intervention; - stabilization after treatment; - insignificant negative changes as a slight tumor growth and a further stabilization of the process; - occasionally negative changes irrespective of treatment. The behavior of a tumor is unpredictable. The onset of progression in infancy is a poor predictor. Ophthalmological symptoms are not the criterion that can be used to make a prognosis. The prognosis is largely determined by neurovisualization techniques and primarily magnetic resonance imaging. A uniform slight thickening of AOT structures irrespective of the extent of the process along the AOT should be referred to as a good prognosis. There was no spontaneous tumor regression in any case. By taking into account the beneficial effect of radiotherapy, the authors consider it expedient to use it as monotherapy and in combination with surgery. Bypass surgery on the spinal fluid system frequently fails to entirely solve the problem intracranial hypertension.

Absence of S-cone input in human blindsight following hemispherectomy

Destruction of the occipital cortex presumably leads to permanent blindness in the contralateral visual field. Residual abilities to respond to visual stimuli in the blind field without consciously experiencing them have, however, been described in cortically blind patients and are termed 'blindsight'. Although the neuronal basis of blindsight remains unknown, possible neuronal correlates have been proposed based on the nature of the residual vision observed. The most prominent but still controversial hypothesis postulates the involvement of the superior colliculi in blindsight. Here we demonstrate, using a computer-based reaction time test in a group of hemispherectomized subjects, that human 'attention-blindsight' can be measured for achromatic stimuli but disappears for stimuli that solely activate S-cones. Given that primate data have shown that the superior colliculi lacks input from S-cones, our results lend strong support to the hypothesis that 'attention-blindsight' is mediated through a collicular pathway. The contribution of a direct geniculo-extrastriate-koniocellular projection was ruled out by testing hemispherectomized subjects in whom a whole hemisphere has been removed or disconnected for the treatment of epilepsy. A direct retino-pulvinar-cortical connection is also unlikely as the pulvinar nucleus is known to receive input from S-cones as well as from L/M-cone-driven colour-opponent ganglion cells.

[Specific features of manifestation of anterior optic tract gliomas in patients with type 1 neurofibromatosis: ophthalmological and neurovisualizational aspects]

Gliomas of the anterior optic tract (AOT) (optic nerves, chiasms, and visual tracts) are benign slowly growing tumors usually detectable in childhood. These are a rather heterogenic group of tumors. The pattern and course of the disease are frequently affected by the presence of type 1 neurofibromatosis (NF-1) in the patient. The ophthalmological symptoms of AOT lesion in the presence of NF-1 were analyzed in 80 patients aged 1 to 24 years (median 5 years). According to the ophthalmological symptoms and the pattern and extent of lesions to AOT structures, the authors identified 4 groups by the data of neurovisualization techniques (magnetic resonance imaging, computed tomography) and revealed that the ophthalmological pattern reflected the site and degree of lesion to AOT structures. At the same time it is shown that there is a group of silent tumors attending without visual disorders. These tumors have the similar neurovisualization pattern, such as a moderate thickening of AOT structures and they occur in 13.8% of cases, as shown by the authors.

Photophobia associated with a demyelinating lesion of the retrochiasmal visual pathway

PURPOSE

To present two patients in whom photophobia was a predominant presenting symptom of retrochiasmal demyelination.

DESIGN

Observational case report.

METHODS

Two women who experienced an acute onset of photophobia underwent neuroophthalmic examination and investigations at a single institution.

RESULTS

Examination revealed a homonymous visual field defect in both patients. Magnetic resonance imaging (MRI) demonstrated a hyperintense lesion in the area of the right posterior thalamus in one patient and enhancing lesions in the deep white matter of the temporal lobes bilaterally with contrast enhancement of the right optic tract in the second patient. Additional investigations, including lesion biopsy in the first patient, revealed demyelination as the most likely etiology. Improvement of photophobia, visual field defect, and radiographic abnormalities was documented over the next three to four months without accompanying treatment in both patients.

CONCLUSIONS

Central pathology, including demyelination of the retrochiasmal visual pathway, should be considered in patients who experience acute photophobia.

Assessment of axonal degeneration along the human visual pathway using diffusion trace analysis

PURPOSE

The effectiveness of diffusion trace value analysis for non-invasive assessment of retinal ganglion cell (RGC) axonal degeneration at multiple anatomic levels along the human visual pathway under clinical setting was evaluated.

DESIGN

Imaging study.

METHODS

Ten patients with unilateral chronic optic neuropathy of varying cause and 16 age-matched normal subjects were studied. Trace, a tensor invariant that is considered to be a sensitive index for pathologic changes in axons, was analyzed at nine anatomic sites in each subject, namely, bilaterally at the level of the optic nerves, uncrossed chiasmal fibers, optic tracts and optic radiations, and crossed chiasmal fibers, using a 3.0 Tesla magnetic resonance imaging system.

RESULTS

Trace values of the optic nerve and uncrossed chiasmal fibers ipsilateral to the affected eye, the crossed chiasmal fibers, and optic tracts bilaterally were significantly higher than those of the corresponding anatomic sites in normal subjects. The optic nerve and uncrossed chiasmal fibers ipsilateral to the unaffected side and optic radiations, bilaterally, had trace values which were not significantly different from the values of the corresponding anatomic levels in normal subjects. The increase in trace value in the optic nerve and uncrossed chiasmal fibers ipsilateral to the affected side was greater than those of the crossed chiasmal fibers and optic tracts.

CONCLUSIONS

Findings are highly consistent with a degenerative process of RGC axons and trace values are quantitatively well correlated to predicted pathology at the given anatomical sites. Trace value measurement at multiple sites along fiber pathways appears to be a powerful addition to clinical assessment of the functionality of components of the visual pathways during various stages of a pathologic process.

Optic gliomas of the anterior visual pathway

PURPOSE OF REVIEW

To review advances in the diagnosis and management of optic-pathway gliomas made within the past 5 years.

RECENT FINDINGS

Important papers regarding optic-pathway gliomas have been published recently in the following areas: neuroimaging, natural history and how the presence of neurofibromatosis type 1 affects it, unusual presentations, visual prognosis, and treatment with fractionated stereotactic radiotherapy.

SUMMARY

The diagnosis and treatment of optic-pathway gliomas has been aided greatly by a greater understanding of the natural history of these tumors and their prognosis related to the presence of neurofibromatosis type 1. Advances in magnetic resonance imaging are helping to delineate tumor extent. Newer radiation techniques that spare surrounding tissues are being used to treat optic-pathway gliomas, but chemotherapy has become the first-line treatment modality.

Early blindness results in abnormal corticocortical and thalamocortical connections

Studies in congenitally blind and bilaterally enucleated individuals show that an early loss of sensory driven activity can lead to massive functional reorganization. However, the anatomical substrate for this functional reorganization is unknown. In the present study, we examined patterns of corticocortical and thalamocortical connections in adult opossums that had been bilaterally enucleated neonatally, prior to the formation of retinogeniculate and geniculocortical connections. We show that in addition to normal thalamocortical projection patterns from visual nuclei, enucleated animals also receive input from nuclei associated with the somatosensory (ventral posterior nucleus, VP), auditory (medial geniculate nucleus, MGN), motor (ventrolateral nucleus, VL), and limbic/hippocampal systems (anterior dorsal nucleus, AD; and anterior ventral nucleus, AV). Likewise, in addition to normal corticocortical projections to area 17, bilaterally enucleated opossums also receive input from auditory, somatosensory, and multimodal cortex. These aberrant patterns of thalamocortical and corticocortical connections can account for alterations in functional organization observed in the visual cortex of bilateral enucleated animals, and indicate that factors extrinsic to the cortex play a large role in cortical field development and evolution. On the other hand, the maintenance of normal patterns of connections in the absence of visual input suggests that there are formidable constraints imposed on the developing cortex that highly restrict the types of evolutionary change possible.

Neuropsychiatry of complex visual hallucinations

OBJECTIVE

To describe the phenomenology and pathophysiology of complex visual hallucinations (CVH) in various organic states, in particular Charles Bonnet syndrome and peduncular hallucinosis.

METHOD

Three cases of CVH in the setting of pontine infarction, thalamic infarction and temporoparietal epileptiform activity are presented and the available psychiatric, neurological and biological literature on the structures of the central nervous system involved in producing hallucinatory states is reviewed.

RESULTS

Complex visual hallucinations can arise from a variety of processes involving the retinogeniculocalcarine tract, or ascending brainstem modulatory structures. The cortical activity responsible for hallucinations results from altered or reduced input into these regions, or a loss of ascending inhibition of their afferent pathways.

CONCLUSIONS

A significant degree of overlaps exists between the concepts of Charles Bonnet syndrome and peduncular hallucinosis. The fluidity of these eponymous syndromes reduces their validity and meaning, and may result in an inappropriate attribution of the underlying pathology. An understanding of how differing pathologies may produce CVH allows for the appropriate tailoring of treatment, depending on the site and nature of the lesion and content of perceptual disturbance.

Pathological findings in retina and visual pathways associated to natural Scrapie in sheep

This work represents a comprehensive pathological description of the retina and visual pathways in naturally affected Scrapie sheep. Twenty naturally affected Scrapie sheep and 6 matched controls were used. Eyes, optic nerves and brain from each animal were fixed and histologically processed using hematoxylin-eosin, followed by immunohistochemical staining for prion protein (PrPsc) and glial fibrillar acidic protein (GFAP). Retinal histopathological changes were observed in only 7 clinically affected animals and mainly consisted of loss of outer limitant layer definition, outer plexiform layer atrophy, disorganization and loss of nuclei in both nuclear layers, and Müller glia hypertrophy. PrPsc was detected in the retina of 19 of the 20 sheep and characterized by a disseminated granular deposit across layers and intraneuronally in ganglion cells. The inner plexiform and the ganglion cell layers were the structures most severely affected by PrPsc deposits. PrPsc exhibited a tendency to spread from these two layers to the others. A marked increase in the number and intensity of GFAP-expressing Müller cells was observed in the clinical stage, especially at the terminal stage of the disease. Spongiosis and PrPsc were detected within the visual pathways at the preclinical stage, their values increasing during the course of the disease but varying between the areas examined. PrPsc was detected in only 3 optic nerves. The results suggest that the presence of PrPsc in the retina correlates with disease progression during the preclinical and clinical stages, perhaps using the inner plexiform layer as a first entry site and diffusing from the brain using a centrifugal model.

Congenital absence of optic chiasm: demonstration of an uncrossed visual pathway using monocular flash visual evoked potentials

A 35 month old child was referred for electrophysiology testing with pendular nystagmus, corresponding head oscillations and reduced vision. Flash visual evoked potential (VEP) revealed large responses at the right occiput (but not the left occiput) from the right eye and similar large responses at only the left occiput from the left eye, indicating absent/deficient crossover at the chiasm. A magnetic resonance imaging (MRI) scan subsequently confirmed absence of the optic chiasm. There was no other evidence of midline brain defects. Her subsequent development to age 11 has been followed. The nystagmus has remained mainly horizontal but a torsional component was noted from age 5 years and described as see-saw at age 6 years. A small right esotropia was noted at 6 years and spectacles prescribed for low hypermetropic refractive error. Bilateral superior rectus recessions at age 7 years produced an improved head posture. Her visual acuity has remained stable at around 6/24 from age 4 years. No binocularity nor stereopsis has been demonstrated over subsequent visits.

Can screening for optic nerve gliomas in patients with neurofibromatosis type I be performed with visual-evoked potential testing?

BACKGROUND

Screening for optic nerve gliomas (ONGs) in children with neurofibromatosis type 1 (NF1) is problematic. Visual acuity (VA) can be unreliable in children. Magnetic resonance imaging is the most sensitive test for ONG, but it is expensive. This study was designed to determine whether visual-evoked potential testing (VEP) is a sensitive and cost-effective screening test for ONG in NF1 in children.

METHODS

We undertook a retrospective review of patients with NF1 at a tertiary care eye center that were born between 1983 and 2003. VA was considered abnormal if 20/40 or worse or more than 2 lines difference between eyes. VEP was abnormal if the P100 was >108 ms (ms) or the interocular difference was greater than 5.0 ms.

RESULTS

Of 297 patients found with NF1, 144 were children and 30 had VEP and MRI. Of those, 14 had ONG and 16 did not. The average P100 of the VEP was 110.5 ms in patients with ONG compared with 103.1 ms (p = 0.004) in those without ONG. VEP was 86% sensitive and 75% specific in detecting ONG. VA was 50% sensitive and 50% specific. Six patients with ONG had normal vision and abnormal VEP. Two subjects had initial abnormal VEP but normal MRI and showed ONG on follow-up imaging. One subject with ONG had a normal VEP initially but subsequent VEP was abnormal.

CONCLUSION

Using serial VEPs, the sensitivity is 93%. Cost of VEP and MRI is $150 and $1750, respectively. VEP is a sensitive and cost-effective screening test for ONG in NF1. VEP may assist in earlier diagnoses of ONG, especially in children with equivocal or difficult ophthalmic examinations.

Comparison of pattern visual-evoked potentials to perimetry in the detection of visual loss in children with optic pathway gliomas

PURPOSE

We sought to compare visual evoked potentials (VEPs) with standard visual field testing in children with visual pathway gliomas.

METHODS

Fifteen of 40 children with visual pathway gliomas verified on magnetic resonance imaging scan who cooperated with Goldmann visual field (GVF) and 3-channel VEPs were studied. GVFs were obtained in 25 eyes with adequate vision. VEP amplitudes, latencies, and signal-to-noise ratios (SNRs) were compared with control subjects. Four of the patients (5 eyes) also had Humphrey visual field testing.

RESULTS

Twenty-two of 25 eyes had a field defect, 15 eyes showed a relative or absolute hemianopia, 7 eyes showed a central or generalized depression, and 3 eyes were normal. In hemianopic eyes, 87% showed a depression (GVF) or reduced sensitivity (Humphrey field) in the opposite hemifield. VEP amplitudes and SNRs, normally largest at the midline electrode, were significantly reduced in all eyes with visual field loss. By comparison, lateral electrodes showed significantly lower amplitudes and SNRs in patients and controls. Interhemispheric VEP asymmetry (>2:1 ratio) was seen in 67% of patients with hemianopia and 53% of controls.

CONCLUSIONS

Reduction of amplitude and SNR at the midline VEP electrode was a sensitive indicator of visual field loss. Interhemispheric VEP asymmetry was not reliable in detection of a hemianopic field defect. VEPs can be a reliable and objective alternative for the detection of visual loss due to optic pathway glioma in children who are intolerant to visual field testing. We recommend the test protocol include pattern-onset and check reversal stimuli of at least one high and one low spatial frequency.

[From the eye to the visual cortex: imaging of the visual pathways]

This paper aims to give an overview of the various methods used for imaging of the visual pathways from the globe to the visual cortex and some examples of the most commonly encountered lesions.