Extra-visual functional and structural connection abnormalities in Leber's hereditary optic neuropathy

Altered small-world and disrupted topological properties of functional connectivity networks in patients with nonarteritic anterior ischemic optic neuropathy

BACKGROUND

Nonarteritic anterior ischemic optic neuropathy (NAION) is a disease of the optic nerve, but its effect on brain network topology is still unclear.This study aimed to investigate brain network alterations in NAION patients and to explore their relationship with functional impairment.

METHODS

Resting-state functional MRI data were collected from 23 NAION patients and 23 matched healthy control subjects.We used graph theory analysis to investigate the global and nodal network topological properties,and network-based statistical (NBS) methods were used to explore intergroup differences in functional connectivity (FC) strength.

RESULTS

Compared to the control group, NAION patients had lower global efficiency, normalized clustering coefficient and small-world values and higher characteristic path length (P < 0.05). In the hub distributions of functional networks, the NAION group had one hub region disappearing and four hub regions appearing in nodal degree centrality (Dc), and two hubs disappearing and one hub region appearing in nodal betweenness centrality (Bc). The NAION group also had enhanced brain FC primarily associated with the frontal, prefrontal, parietal lobes and cerebellum. Furthermore, the right temporal pole, superior temporal gyrus (r = -0.424), the right inferior temporal gyrus (r = -0.414), the right cerebellar lobule Ⅵ (r = 0.450), and the left cerebellar lobule crus Ⅰ (r = 0.584) were significantly correlated with clinical severity.

CONCLUSION

NAION patients show disruption and redistribution of FC in specific regions of the brain network, which may be associated with visual impairment.

Abnormal cerebral blood flow in patients with Leber's hereditary optic neuropathy

PURPOSE

The study aimed to unravel abnormal cerebral blood flow (CBF) in patients with Leber's hereditary optic neuropathy (LHON) using arterial spin labeling (ASL) and to investigate the associations among disrupted CBF, disease duration, and neuro-ophthalmological impairment.

METHODS

ASL perfusion imaging data was collected from 20 patients with acute LHON, 29 patients with chronic LHON, and 37 healthy controls. We used a one-way analysis of covariance to test the intergroup differences in CBF. Linear and nonlinear curve fit models were applied to explore the associations among CBF, disease duration, and neuro-ophthalmological metrics.

RESULTS

Brain regions differed in LHON patients, including the left sensorimotor and bilateral visual areas (p < 0.05, cluster-wise family-wise error correction). Acute and chronic LHON patients demonstrated lower CBF in bilateral calcarine than the healthy controls. Chronic LHON had lower CBF in the left middle frontal gyrus and sensorimotor cortex, and temporal-partial junction than the healthy controls and acute LHON. A significant logarithmic negative correlation was shown between CBF of left middle frontal gyrus and disease duration. A significant linear positive correlation was found between retinal nerve fiber layer thickness and CBF in left middle frontal gyrus, and negative correlations between loss of variance and CBF in left middle frontal gyrus and sensorimotor cortex (p < 0.05, Bonferroni correction).

CONCLUSION

LHON patients exhibited reduced CBF in the visual pathway, sensorimotor and higher-tier cognitive areas. Disease duration and neuro-ophthalmological impairments can influence the metabolism of non-visual areas.

Aberrant neurovascular coupling in Leber's hereditary optic neuropathy: Evidence from a multi-model MRI analysis

The study aimed to investigate the neurovascular coupling abnormalities in Leber's hereditary optic neuropathy (LHON) and their associations with clinical manifestations. Twenty qualified acute Leber's hereditary optic neuropathy (A-LHON, disease duration ≤ 1 year), 29 chronic Leber's hereditary optic neuropathy (C-LHON, disease duration > 1 year), as well as 37 healthy controls (HCs) were recruited. The neurovascular coupling strength was quantified as the ratio between regional homogeneity (ReHo), which represents intrinsic neuronal activity and relative cerebral blood flow (CBF), representing microcirculatory blood supply. A one-way analysis of variance was used to compare intergroup differences in ReHo/CBF ratio with gender and age as co-variables. Pearson's Correlation was used to clarify the association between ReHo, CBF, and neurovascular coupling strength. Furthermore, we applied linear and exponential non-linear regression models to explore the associations among ReHo/CBF, disease duration, and neuro-ophthalmological metrics. Compared with HCs, A_LHON, and C_LHON patients demonstrated a higher ReHo/CBF ratio than the HCs in the bilateral primary visual cortex (B_CAL), which was accompanied by reduced CBF while preserved ReHo. Besides, only C_LHON had a higher ReHo/CBF ratio and reduced CBF in the left middle temporal gyrus (L_MTG) and left sensorimotor cortex (L_SMC) than the HCs, which was accompanied by increased ReHo in L_MTG (p < 1.85e^-3, Bonferroni correction). A-LHON and C-LHON showed a negative Pearson correlation between ReHo/CBF ratio and CBF in B_CAL, L_SMC, and L_MTG. Only C_LHON showed a weak positive correlation between ReHo/CBF ratio and ReHo in L_SMC and L_MTG (p < 0.05, uncorrected). Finally, disease duration was positively correlated with ReHo/CBF ratio of L_SMC (Exponential: Radj² = 0.23, p = 8.66e^-4, Bonferroni correction). No statistical correlation was found between ReHo/CBF ratio and neuro-ophthalmological metrics (p > 0.05, Bonferroni correction). Brain neurovascular "dyscoupling" within and outside the visual system might be an important neurological mechanism of LHON.

Brain Gray Matter Atrophy and Functional Connectivity Remodeling in Patients With Chronic LHON

Purpose

The aim of this study was to investigate the brain gray matter volume (GMV) and spontaneous functional connectivity (FC) changes in patients with chronic Leber's hereditary optic neuropathy (LHON), and their relations with clinical measures.

Methods

A total of 32 patients with chronic LHON and matched sighted healthy controls (HC) underwent neuro-ophthalmologic examinations and multimodel magnetic resonance imaging (MRI) scans. Voxel-based morphometry (VBM) was used to detect the GMV differences between the LHON and HC. Furthermore, resting-state FC analysis using the VBM-identified clusters as seeds was carried out to detect potential functional reorganization in the LHON. Finally, the associations between the neuroimaging and clinical measures were performed.

Results

The average peripapillary retinal nerve fiber layer (RNFL) thickness of the chronic LHON was significantly thinner (T = −16.421, p < 0.001), and the mean defect of the visual field was significantly higher (T = 11.28, p < 0.001) than the HC. VBM analysis demonstrated a significantly lower GMV of bilateral calcarine gyri (CGs) in the LHON than in the HC (p < 0.05). Moreover, in comparison with the HC, the LHON had significantly lower FC between the centroid of the identified left CG and ipsilateral superior occipital gyrus (SOG) and higher FC between this cluster and the ipsilateral posterior cingulate gyrus (p < 0.05, corrected). Finally, the GMV of the left CG was negatively correlated with the LHON duration (r = −0.535, p = 0.002), and the FC between the left CG and the ipsilateral posterior cingulate gyrus of the LHON was negatively correlated with the average peripapillary RNFL thickness (r = −0.522, p = 0.003).

Conclusion

The atrophied primary visual cortex of the chronic LHON may be caused by transneuronal degeneration following the retinal damage. Moreover, our findings suggest that the functional organization of the atrophied primary visual cortex has been reshaped in the chronic LHON.

Neuroimaging in Leber Hereditary Optic Neuropathy: State-of-the-art and future prospects

Leber Hereditary Optic Neuropathy (LHON) is an inherited mitochondrial retinal disease that causes the degeneration of retinal ganglion cells and leads to drastic loss of visual function. In the last decades, there has been a growing interest in using Magnetic Resonance Imaging (MRI) to better understand mechanisms of LHON beyond the retina. This is partially due to the emergence of gene-therapies for retinal diseases, and the accompanying expanded need for reliably quantifying and monitoring visual processing and treatment efficiency in patient populations. This paper aims to draw a current picture of key findings in this field so far, the challenges of using neuroimaging methods in patients with LHON, and important open questions that MRI can help address about LHON disease mechanisms and prognoses, including how downstream visual brain regions are affected by the disease and treatment and why, and how scope for neural plasticity in these pathways may limit or facilitate recovery.

Occult primary white matter impairment in Leber hereditary optic neuropathy

BACKGROUND AND PURPOSE

Leber hereditary optic neuropathy (LHON) is a disease maternally inherited from mitochondria that predominantly impairs the retinal ganglion cells and their axons. To identify whether occult brain white matter (WM) impairment is involved, a voxel-based analysis (VBA) of diffusion metrics was carried out in LHON patients with normal-appearing brain parenchyma.

METHODS

Fifty-four symptomatic LHON patients (including 22 acute LHON with vision loss for ≤12 months, and 32 chronic LHON) without any visible brain lesions and 36 healthy controls (HCs) were enrolled in this study. VBA was applied to quantify the WM microstructural changes of LHON patients. Finally, the associations of the severity of WM impairment with disease duration and ophthalmologic deficits were assessed.

RESULTS

Compared with the HCs, the average retinal nerve fiber layer (RNFL) thickness was significantly reduced in patients with chronic LHON, whereas it was increased in patients with acute LHON (p < 0.05, corrected). VBA identified significantly decreased fractional anisotropy widely in WM in both the acute and chronic LHON patients, including the left anterior thalamic radiation and superior longitudinal fasciculus, and bilateral corticospinal tract, dentate nuclei, inferior longitudinal fasciculus, forceps major, and optic radiation (OR; p < 0.05, corrected). The integrity of most WM structures (except for the OR) was correlated with neither disease duration nor RNFL thickness (p > 0.05, corrected).

CONCLUSIONS

Occult primary impairment of widespread brain WM is present in LHON patients. The coexisting primary and secondary WM impairment may jointly contribute to the pathological process of LHON.

Abnormal large-scale structural rich club organization in Leber's hereditary optic neuropathy

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LHON patients suffered large-scale structural network disruption.

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Non-rich club connections may be more vulnerable in the LHON.

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Both primary and secondary connectivity damage may coexist in the LHON.

Objective

The purpose of this study was to investigate whether the large-scale structural rich club organization was abnormal in patients with Leber's hereditary optic neuropathy (LHON) using diffusion tensor imaging (DTI), and the associations among disrupted brain structural connectivity, disease duration, and neuro-ophthalmological impairment.

Methods

Nineteen acute, 34 chronic LHON patients, and 36 healthy controls (HC) underwent DTI and neuro-ophthalmological measurements. The brain structural network and rich club organization were constructed based on deterministic fiber tracking at the individual level. Then intergroup differences among the acute, chronic LHON patients and healthy controls (HC) in three types of structural connections, including rich club, feeder, and local ones, were compared. Network-based Statistics (NBS) was also used to test the intergroup connectivity differences for each fiber. Several linear and nonlinear curve fit models were applied to explore the associations among large-scale brain structural connectivity, disease duration, and neuro-ophthalmological metrics.

Results

Compared to the HC, both the acute and chronic LHON patients had consistently significantly lower fractional anisotropy (FA) and higher radial diffusion (RD) for feeder connections (p < 0.05, FDR correction). Acute LHON patients had significantly lower FA and higher RD for local connections (p < 0.05, FDR correction). There was no significant difference in large-scale brain structural connectivity between acute and chronic LHON (p > 0.05, FDR correction). NBS also identified reduced FA of three feeder connections and five local ones linking visual, auditory, and basal ganglia areas in LHON patients (p < 0.05, FDR correction). No structural connections showed linear or nonlinear association with either disease duration or neuro-ophthalmological indicators (p > 0.05, FDR correction). A significant negative correlation was shown between the retinal nerve fiber layer (RNFL) thickness and disease duration (p < 0.05, FDR correction).

Conclusions

Abnormal rich club organization of the structural network was identified in both the acute and chronic LHON. Furthermore, our findings suggest the coexistence of both primary and secondary connectivity damage in the LHON.

Aberrant Structural Network Architecture in Leber's Hereditary Optic Neuropathy. Minimum Spanning Tree Graph Analysis Application into Diffusion 7T MRI

Examining individuals with Leber's hereditary optic neuropathy (LHON) provides a rare opportunity to understand how changes in mitochondrial DNA and loss of vision can be related to changes in organization of the whole-brain structural network architecture. In comparison with the previous neuroimaging studies with LHON participants, which were focused mainly on analyzing changes which occur in different areas of the patient's brain, network analysis not only makes it possible to observe single white matter fibers' aberrations but also the whole-brain nature of these changes. The purpose of our study was to better understand whole-brain neural network changes in LHON participants and see the correlation between the clinical data and the changes. To achieve this, we examined fifteen LHON patients and seventeen age-matched healthy subjects with the usage of ultra-high filed 7T magnetic resonance imaging (MRI). Basing on the analysis on MRI diffusion tensor imaging (DTI) data, whole-brain structural neural networks were reconstructed with the use of the minimum spanning tree algorithm (MST) for every participant. Our results revealed that the structural network in LHON participants was altered at both the local and the global level. The global network structures of LHON subjects were less centralized with path-like organization and there was an imbalance in the main hub centrality. Moreover, the inspection of nodes and hubs in terms of their anatomical placement revealed that in the LHON participants the prominent hubs were located within the basal ganglia (i.e. bilateral caudate, left pallidum), which differed them from healthy controls. An analysis of the relationships between the global MST metrics and LHON participants' clinical characteristics revealed significant correlations between the global network metrics and the duration of illness. Furthermore, the nodal parameters of the optic chiasm were significantly correlated with the duration of illness and the averaged thickness of the right retinal nerve fiber layer (RNFL). These findings clearly showed that the progression of the disease is accompanied by alterations within the brain network structure and its efficiency.

Widespread Reductions of Spontaneous Neurophysiological Activity in Leber’s Disease—An Application of EEG Source Current Density Reconstruction

Leber’s hereditary optic neuropathy (LHON) is a rare, maternally inherited genetic disease caused by a mutation of mitochondrial DNA. Classical descriptions have highlighted structural abnormalities in various parts of patients’ optic tracts; however, current studies have proved that changes also affect many cortical and subcortical structures, not only these belonging to the visual system. This study aimed at improving our understanding of neurophysiological impairments in LHON. First of all, we wanted to know if there were any differences between the health control and LHON subjects in the whole-brain source electroencephalography (EEG) analysis. Second, we wanted to investigate the associations between the observed results and some selected aspects of Leber’s disease’s clinical picture. To meet these goals, 20 LHON patients and 20 age-matched healthy control (HC) subjects were examined. To investigate the electrophysiological differences between the HC and LHON groups, a quantitative analysis of the whole-brain current source density was performed. The signal analysis method was based on scalp EEG data and an inverse solution method called low-resolution brain electromagnetic tomography (eLORETA). In comparison with the healthy subjects, LHON participants showed significantly decreased neuronal activity in the alpha and gamma bands; more specifically, in the alpha band, the decrease was mainly found in the occipital lobes and secondary visual cortex, whereas, in the gamma band, the reduced activity occurred in multiple cortical areas. Additionally, a correlation was found between the alpha band activity of the right secondary visual cortex and the averaged thickness of the right retinal nerve fiber layer in the LHON participants. Our study suggests that LHON is associated with widespread cortical de-activation, rather than simply abnormalities of structures constituting the visual system.

Neuroanatomical Changes in Leber's Hereditary Optic Neuropathy: Clinical Application of 7T MRI Submillimeter Morphometry

Leber’s hereditary optic neuropathy (LHON) is one of the mitochondrial diseases that causes loss of central vision, progressive impairment and subsequent degeneration of retinal ganglion cells (RGCs). In recent years, diffusion tensor imaging (DTI) studies have revealed structural abnormalities in visual white matter tracts, such as the optic tract, and optic radiation. However, it is still unclear if the disease alters only some parts of the white matter architecture or whether the changes also affect other subcortical areas of the brain. This study aimed to improve our understanding of morphometric changes in subcortical brain areas and their associations with the clinical picture in LHON by the application of a submillimeter surface-based analysis approach to the ultra-high-field 7T magnetic resonance imaging data. To meet these goals, fifteen LHON patients and fifteen age-matched healthy subjects were examined. For all individuals, quantitative analysis of the morphometric results was performed. Furthermore, morphometric characteristics which differentiated the groups were correlated with variables covering selected aspects of the LHON clinical picture. Compared to healthy controls (HC), LHON carriers showed significantly lower volume of both palladiums (left p = 0.023; right p = 0.018), the right accumbens area (p = 0.007) and the optic chiasm (p = 0.014). Additionally, LHON patients have significantly higher volume of both lateral ventricles (left p = 0.034; right p = 0.02), both temporal horns of the lateral ventricles (left p = 0.016; right p = 0.034), 3rd ventricle (p = 0.012) and 4th ventricle (p = 0.002). Correlation between volumetric results and clinical data showed that volume of both right and left lateral ventricles significantly and positively correlated with the duration of the illness (left R = 0.841, p = 0.002; right R = 0.755, p = 0.001) and the age of the LHON participants (left R = 0.656, p = 0.007; right R = 0.691, p = 0.004). The abnormalities in volume of the LHON patients’ subcortical structures indicate that the disease can cause changes not only in the white matter areas constituting visual tracts, but also in the other subcortical brain structures. Furthermore, the correlation between those results and the illness duration suggests that the disease might have a neurodegenerative nature; however, to fully confirm this observation, longitudinal studies should be conducted.

Functional MRI study in a case of Charles Bonnet syndrome related to LHON

INTRODUCTION

Charles Bonnet syndrome is characterized by simple or complex visual hallucinations (VH) due to damage along the visual pathways. We report a functional MRI study of brain correlates of VH in the context of a severe optic atrophy in a patient with Leber's Hereditary Optic Neuropathy (LHON).

CASE REPORT

A 62-year-old man was diagnosed with LHON (11778/ND4 mtDNA mutation) after subacute visual loss in left eye (right eye was amblyopic). One month later, he experienced VH of a few seconds consisting in "moving red and blue miniature cartoons". One year later VH content changed in colored mosaic (10-15 s duration), usually stress-related, and blue and white flashes (2-5 s), triggered by unexpected auditory stimuli. Audiometry revealed mild sensorineural hearing loss. Three block design functional MRI paradigms were administrated: 1) random "clap", 2) "checkerboard" and 3) non-random "beep". After random "claps" simple flashes were evoked with bilateral activation of primary and secondary visual cortex, cuneus, precuneus and insula. Neither hallucinations nor cortex activation were registered after "checkerboard" stimulation, due to the severe visual impairment. Primary and secondary auditory cortices were "beep"-activated, without eliciting VH by non-random "beep".

CONCLUSIONS

The peculiarity of our case is that VH were triggered by random auditory stimuli, possibly due to a cross-modal plasticity between visual and auditory networks, likely influenced by the sensorineural deafness. Functional alterations of both networks in resting conditions have been demonstrated in LHON patients, even without an auditory deficit. Finally, the absence of VH triggered by expected stimuli is consistent with the "expectation suppression theory", based on increased neural activations after unexpected but not by predicted events.

Association of Visual Impairment in Neuromyelitis Optica Spectrum Disorder With Visual Network Reorganization

Importance

Severe visual impairment is one of the major symptoms in neuromyelitis optica spectrum disorder (NMOSD), but functional network reorganization induced by the diminished sensory input has not been investigated thus far.

Objective

To examine adaptive visual network connectivity changes in NMOSD.

Design, Setting, and Participants

In this cross-sectional study, data were collected from May 1, 2013, through February 31, 2016, from 31 patients with aquaporin-4 antibody-positive NMOSD and 31 age- and sex-matched healthy control individuals at the Department of Neurology and NeuroCure Clinical Research Center at Charité-Universitätsmedizin Berlin, Berlin, Germany.

Main Outcomes and Measures

Visual function (high-contrast visual acuity and contrast sensitivity), optical coherence tomography (peripapillary retinal nerve fiber layer and ganglion cell layer thickness), and resting-state functional magnetic resonance imaging (functional connectivity of large-scale brain networks).

Results

Thirty-one patients with NMOSD (mean [SD] age, 48.2 [13.9] years; 28 women and 3 men) and 31 healthy controls (mean [SD] age, 47.2 [15.3] years; 28 women and 3 men) participated in the study. Patients had a selective and pronounced increase of functional connectivity in the primary and secondary visual networks. Increased primary visual network connectivity correlated with reduced high-contrast visual acuity (r = -0.39, P = .006), reduced low-contrast sensitivity (r = -0.33, P = .03), and more severe retinal damage measured by optical coherence tomography (r = -0.4, P = .01). Furthermore, visual functional connectivity was significantly higher in patients with a history of optic neuritis compared with patients without optic neuritis (mean [SD] regression coefficients, 50.0 [4.3] vs 34.6 [5.6]; P = .04).

Conclusions and Relevance

Impaired visual function and retinal damage are associated with selective reorganization of the visual network in NMOSD. These findings advance the understanding of visual system dysfunction in NMOSD and, more generally, provide insight into pathophysiologic responses of the visual system to impaired visual input.

Glaucoma and the brain: Trans-synaptic degeneration, structural change, and implications for neuroprotection

A recent hypothesis to enter the literature suggests that glaucoma is a neurodegenerative disease. The basis for this has been the finding of central nervous system changes in glaucoma patients on histology and neuroimaging. It is known that retinal ganglion cell pathology of any cause leads to anterograde and retrograde retinal ganglion cell degeneration, as well as trans-synaptic (transneuronal) anterograde degeneration. Trans-synaptic degeneration has been demonstrated in a range of optic neuropathies including optic nerve transection, optic neuritis, and hereditary optic neuropathies. More recently, similar changes have been confirmed in glaucoma patients using the neuroimaging techniques of voxel-based morphometry and diffusion tensor imaging. Some studies have reported brain changes in glaucoma outside the retino-geniculo-cortical pathway; however, these are preliminary and exploratory in nature. Further research is required to identify whether the degenerative brain changes in glaucoma are entirely secondary to the optic neuropathy or whether there is additional primary central nervous system pathology. This has critical implications for neuroprotective and regenerative treatment strategies and our basic understanding of glaucoma.

The Contribution of Resting State Networks to the Study of Cortical Reorganization in MS

Resting State fMRI (RS-fMRI) represents an emerging and powerful tool to explore brain functional connectivity (FC) changes associated with neurologic disorders. Compared to activation/task-related fMRI, RS-fMRI has the advantages that (i) BOLD fMRI signals are self-generated and independent of subject's performance during the task and (ii) a single dataset is sufficient to extract a set of RS networks (RSNs) that allows to explore whole brain FC. According to these features RS-fMRI appears particularly suitable for the study of FC changes related to multiple sclerosis (MS). In the present review we will first give a brief description of RS-fMRI methodology and then an overview of most relevant studies conducted so far in MS by using this approach. The most interesting results, in particular, regard the default-mode network (DMN), whose FC changes have been correlated with cognitive status of MS patients, and the visual RSN (V-RSN) whose FC changes have been correlated with visual recovery after optic neuritis. The executive control network (ECN), the lateralized frontoparietal network (FPN), and the sensory motor network (SMN) have also been investigated in MS, showing significant FC rearrangements. All together, RS-fMRI studies conducted so far in MS suggest that prominent RS-FC changes can be detected in many RSNs and correlate with clinical and/or structural MRI measures. Future RS-fMRI studies will further clarify the dynamics and clinical impact of RSNs changes in MS.

Brain connectivity abnormalities extend beyond the sensorimotor network in peripheral neuropathy

OBJECTIVES

To investigate, using resting state (RS) functional connectivity (FC), the selectivity of involvement of the sensorimotor network in patients with acquired (A) and with hereditary (H) peripheral neuropathies (PN) and the correlations of RS FC abnormalities with clinical impairment and structural brain damage. Temporal associations among RS networks were also explored.

EXPERIMENTAL DESIGN

RS fMRI scans were acquired from 13 APN, 12 HPN, and 18 age- and sex-matched healthy controls. Independent component analysis and functional network connectivity were used to investigate RS FC within and among RS networks with potential functional relevance.

PRINCIPAL OBSERVATIONS

Compared to controls, patients had a decreased FC of the right precentral gyrus and an increased RS FC of the precuneus within the sensorimotor network. Both decreased and increased RS FC also involved the visual and auditory networks, which additionally had an increased coherence of function with the sensorimotor network (more pronounced in HPN). RS FC modifications in patients extended to several cognitive networks and were correlated with disease duration. In APN, they were also correlated with the severity of clinical impairment and corpus callosum atrophy.

CONCLUSIONS

In PN, RS FC modifications extend beyond the sensorimotor network and involve other sensory and cognitive networks. The correlations between RS FC patterns and disease duration in patients as well as with clinical impairment in patients with APN suggest that modifications of FC might reflect an adaptive mechanism, which takes time to occur and helps to limit the clinical consequences of peripheral damage.

Radiology update in neuro-ophthalmology

PURPOSE OF REVIEW

Radiologic imaging is indispensible for the diagnosis and management of many neuro-ophthalmologic conditions. Advances in the radioimaging of neuro-ophthalmologic disorders may evolve from the clinical or the radiological side, meaning there is a constant stream of new information for the clinician.

RECENT FINDINGS

Functional MRI, diffusion tensor MRI, magnetization transfer imaging, and magnetic resonance spectroscopy are examples of nonstandard radiographic techniques, which have expanded the knowledge of neuro-ophthalmologic conditions. Studies using conventional MRI have also led to advances in understanding optic neuropathies, the ocular motor system, pseudotumor cerebri, posterior reversible encephalopathy syndrome and migraine.

SUMMARY

This article discusses recent radiologic advances relevant to neuro-ophthalmology.