Optic Nerve Magnetic Resonance Imaging Research Articles

Classification of optic neuritis in neuromyelitis optica spectrum disorders (NMOSD) on MRI using CNN with transfer learning and manipulation of pre-processing on augmentation

Neuromyelitis optica spectrum disorder (NMOSD), also known as Devic disease, is an autoimmune central nervous system disorder in humans that commonly causes inflammatory demyelination in the optic nerves and spinal cord. Inflammation in the optic nerves is termed optic neuritis (ON). ON is a common clinical presentation; however, it is not necessarily present in all NMOSD patients. ON in NMOSD can be relapsing and result in severe vision loss. To the best of our knowledge, no study utilises deep learning to classify ON changes on MRI among patients with NMOSD. Therefore, this study aims to deploy eight state-of-the-art CNN models (Inception-v3, Inception-ResNet-v2, ResNet-101, Xception, ShuffleNet, DenseNet-201, MobileNet-v2, and EfficientNet-B0) with transfer learning to classify NMOSD patients with and without chronic ON using optic nerve magnetic resonance imaging. This study also investigated the effects of data augmentation before and after dataset splitting on cropped and whole images. Both quantitative and qualitative assessments (with Grad-Cam) were used to evaluate the performances of the CNN models. The Inception-v3 was identified as the best CNN model for classifying ON among NMOSD patients, with accuracy of 99.5%, sensitivity of 98.9%, specificity of 93.0%, precision of 100%, NPV of 99.0%, and F1-score of 99.4%. This study also demonstrated that the application of augmentation after dataset splitting could avoid information leaking into the testing datasets, hence producing more realistic and reliable results.

Optic nerve topography in multiple sclerosis diagnostic criteria: Existing knowledge and future directions.

Current diagnostic criteria for multiple sclerosis (MS) do not consider the optic nerve as a typical topography for establishing the diagnosis. Recent studies have proved the utility of optic nerve magnetic resonance imaging, optical coherence tomography and visual evoked potentials in detecting optic nerve lesions during the early stages of MS. In addition, emerging evidence supports the inclusion of optic nerve topography as a fifth region to fulfil the dissemination in space criteria. Anticipating a modification in the McDonald criteria, it is crucial for neurologists to familiarize with the diagnostic properties of each test in detecting optic nerve lesions and understand how to incorporate them into the MS diagnostic process. Therefore, the objective of this article is to review the existing evidence supporting the use of these tests in the diagnostic process of MS and provide a practical algorithm that can serve as a valuable guide for clinical practice.

Clinical and radiological features, treatment responses and prognosis in pediatric patients with co-existing anti-N-methyl-D-aspartate receptor and myelin oligodendrocyte glycoprotein antibody-associated encephalitis: A single center study

To characterize the clinical and radiological features, treatment responses and outcomes of children with co-existing anti-N-methyl-D-aspartate receptor(NMDAR) and myelin oligodendrocyte glycoprotein(MOG) antibody-associated encephalitis. Clinical manifestations, imaging features, effectiveness of treatment and outcomes of patients who were cerebral spinal fluid(CSF)-positive for NMDAR-antibody(NMDAR-ab) and seropositive for MOG-antibody(MOG-ab) were analyzed. Twelve patients including 8 females and 4 males were enrolled. The median onset age was 9 years, ranging from 2.2 to 12.8 years. Behavioral changes and/or psychiatric symptoms (n=8/12), seizures (n=8/12), encephalopathy (n=7/12) were 3 of the most common symptoms. Brain magnetic resonance imaging(MRI) of all the patients showed T2/fluid attenuation inversion recovery(FLAIR) abnormal signal in the cerebral white matter at least once in the courses of disease, 2 of whom developed new brain lesions which were asymptomatic. All of the patients had supratentorial lesions. Spinal cord MRI was performed in 7 patients. Only 1 patient showed related abnormalities with increased T2 signal in the spinal cord C1-5. Nine patients underwent optic nerve MRI; 5 patients demonstrated abnormal results, among whom 4 exhibited T2 abnormal signal (2 were symptom-free) and 1 showed a little effusion in bilateral optic nerve sheats. Intravenous immunoglobulin (IVIG) and intravenous methylprednisolone (IVMP) were the most common used therapies in those patients. Nine patients were treated with second-line therapy to prevent relapses. For total 29 clinical attacks, the median modified Rankin Scale (mRS) before treatment and after therapy of acute stage was 1 and 0, respectively. Seven of 12 patients(58.3%) experienced clinical relapses. In terms of outcome, all of the patients' mRS of last follow-up (≥6 months) was ≤2. Behavioral changes and/or psychiatric symptoms, seizures and encephalopathy were common in children with co-existing anti-NMDAR and MOG antibody-associated encephalitis. A minority of subjects may develop asymptomatic lesions on brain and optic nerve MRI. The relapse rate of this disease is relatively high. The majority of patients responded well to the immunotherapies and had a good outcome(mRS of last follow-up≤2).

P-61 Characterization of subclinical optic nerve magnetic resonance imaging lesions in the N-Momentum trial

P-61 Characterization of subclinical optic nerve magnetic resonance imaging lesions in the N-Momentum trial

Prediction of Retinal Loss Based on Lesion of the Optic Nerve in Acute Stage of Optic-Neuritis

Aim: To assess the predictive features of optic neuritis in retinal loss through optic nerve lesion identification. Study design: Prospectively longitudinal study Place and duration of study: Ghulam Muhammad Mahar Medical College Sukkur and Shaheed Mohtarma Benazir Bhutto Medical University Larkana from 1st January 2021 to 30th June 2022. Methodology: One hundred and ten patients suffering from acute optic neuritis ≤8 weeks were enrolled. Retinal optical-coherence tomography was performed in all patients. Fifty five patients in the whole cohort while clinically isolated syndrome (CIS) 25 patients and relapsing remitting multiple sclerosis (RRMS) as well as neuromyelitis-optica spectrum disorders (NMOSD) and isolated optic neuritis as 20, 3 and 7 respectively. Brain optic nerve magnetic resonance imaging which included three-dimensional double inversion recovery sequence was also conducted at acute phase (M0) and then post 12 months (M12). Results: The mean age of the cases was 30.85±8.9 years. There was a higher frequency of males then females. The duration of the disease was found highest in RRMS cases with 50.31±77.45 months. The variance in estimated and standard error of the ganglion cell-inner plexiform layer volume change was significantly different in whole acute optic neuritis cases as well as the one with CIS and multiple sclerosisat cohort. Conclusion: Optic nerve-lesion length in prediction of retinal-neuroaxonal loss in cases of optic neuritis. The optic-nerve lesion length can also be considered as a biomarker for the process of retinal remodeling as well as visual impairment. Key words: Optic nerve lesion, Acute phase, Optic neuritis (ON), Retinal neuronal loss

Early predictors of visual and axonal outcomes after acute optic neuritis.

BackgroundPredicting long-term visual outcomes and axonal loss following acute optic neuritis (ON) is critical for choosing treatment. Predictive models including all clinical and paraclinical measures of optic nerve dysfunction following ON are lacking.ObjectivesUsing a prospective study method, to identify 1 and 3 months predictors of 6 and 12 months visual outcome (low contrast letter acuity 2.5%) and axonal loss [retinal nerve fiber layer thickness and multifocal evoked potential (mfVEP) amplitude] following acute ON.MethodsIn total, 37 patients of acute ON onset were evaluated within 14 days using between-eye asymmetry of visual acuity, color vision (Ishihara plates), optical coherence tomography, mfVEP, and optic nerve magnetic resonance imaging [magnetic transfer ratio (MTR) and diffusion tensor imaging (DTI)].ResultsVisual outcome at 6 and 12 months was best predicted by Ishihara asymmetry at 1 and 3 months following ON onset. Axonal loss at 6 and 12 months was reliably predicted by Ishihara asymmetry at 1 month. Optic nerve MTR and DTI at 3 months post-acute ON could predict axonal loss at 6 and 12 months.ConclusionsSimple Ishihara asymmetry testing 1 month after acute ON onset can best predict visual outcome and axonal loss at 6 and 12 months in a clinical or research setting.

Relation between retina, cognition and brain volumes in MS: a consequence of asymptomatic optic nerve lesions.

Asymptomatic optic nerve lesions are frequent in multiple sclerosis (MS) and their impact on cognition and/or brain volume has never been taken into account. We used the data from the cross-sectional Visual Ways in MS (VWIMS) study including relapsing remitting MS. All patients underwent brain and optic nerve Magnetic Resonance Imaging (MRI) including Double Inversion Recuperation (DIR) sequence, retinal OCT, and cognitive evaluation with the Brief International Cognitive Assessment in MS (BICAMS). We measured the association between OCT findings (thickness/volume of retinal layers) and extra-visual parameters (cerebral volumes and BICAMS scores) in optic nerves with and/or without the presence of DIR asymptomatic optic nerve hypersignal. Between March and December 2017, we included 98 patients. Two patients were excluded. Over the 192 eyes, 73 had at least one clinical history of optic neuritis (ON-eyes) whereas 119 were asymptomatic (NON-eyes). Among the 119 NON-eyes, 58 had 3D-DIR optic nerve hypersignal (48.7%). We confirmed significant associations between some retinal OCT measures and some extra-visual parameters (cerebral volumes, cognitive scores) in NON-eyes. Unexpectedly, these associations were found when an asymptomatic optic nerve DIR-hypersignal was present on MRI, but not when it was absent. Our study showed a relation between OCT measures and extra-visual parameters in NON-eyes MS patients. As a confusion factor, asymptomatic optic nerve lesions may be the explanation of the relation between OCT measures and extra-visual parameters. Retinal OCT seems to be far more a "window over the optic nerve" than a "window over the brain".

Clinical features and prognosis analysis of myelin oligodendrocyte glycoprotein antibody-positive optic neuritis

Objective: To investigate the clinical characteristics and prognosis of myelin oligodendrocyte glycoprotein (MOG) antibody-positive optic neuritis (ON). Methods: The data of 39 patients with MOG antibody-positive ON in the Department of Neurology of Beijing Tongren Hospital, Capital Medical University from January 1, 2017 to October 31, 2019 were retrospectively collected. There were 25 males and 14 females, aged from 15 to 80 (40±16) years. According to the recurrence, the patients were divided into two groups: the recurrence group (n=12) and the non-recurrence group (n=27). The clinical manifestations, relapse-related factors, magnetic resonance imaging (MRI) manifestations, treatment and prognosis of the two groups were analyzed. Results: A total of 63 eyes were involved, including 30 cases of optic perineuritis (OPN), accounting for 47.6% (30/63). The number of attacks ranged from 1 to 9, among which 12 patients had more than 2 attacks. There were 37 eyes [58.7% (37/63)] with severe visual loss (SVL) at the time of onset, and 7 eyes [11.1% (7/63)] with SVL at the final follow-up. Forty-eight eyes [76.2% (48/63)] had optic disc edema. Forty seven eyes [74.6% (47/63)] showed long-segment disease on optic nerve MRI. One case was complicated with aseptic meningitis and encephalitis. The recurrence group was younger than the non-recurrence group [(28.5±9.8) years vs (43.3±16.4) years, P=0.001]. There were no statistically significant differences between the two groups in gender, bilateral onset, initial visual acuity, final visual acuity, optic disc edema, head and spinal cord lesions, and immunosuppressant (all P>0.05). All patients were treated with methylprednisolone (MP) pulse therapy during the acute attack, and 16 of them were additively treated with immunosuppressive agents; the pain was alleviated or relieved significantly after the application of glucocorticoids. Conclusions: MOG antibody-positive ON often occurred in both eyes at the same time, often manifesting as OPN, often accompanied by optic disc edema, and SVL at the beginning of the disease, but most of the visual recovery was good, might be associated with meningitis and encephalitis. MRI of the optic nerve showed that the lesions often manifested as long-segment lesions. Glucocorticoids could alleviate pain and promote the recovery of visual function.

Clinical analysis of severe visual loss caused by inhalational methanol poisoning in a chronic process with acute onset:a retrospective clinical analysis

BackgroundTo analyze the clinical features and prognosis of the visual loss resulted from inhalational methanol poisoning in 8 Chinese patients.MethodsEight consecutive patients seen at the Beijing Tongren Hospital of Capital Medical University, Beijing, China between January 2003 to August 2017, with complains of vision loss in both eyes, identified as inhalational methanol poisoning. Detailed medical history was extracted. All patients underwent optic nerve and brain magnetic resonance imaging (MRI) scan, laboratory tests, and visual function analysis. Treatment protocols were large dosage of methylprednisolone and B vitamins over 3 months. Patients were seen at 3-month intervals until a year.ResultsEight patients with optic neuropathy caused by inhalation toxicity of methanol were under observation, whose methanol-contact time spans were form 4 days to 5 years for occupational exposure. All the patients had acute onset, transient systemic symptoms on early stage, both eyes involved with severe visual impairment (visual acuity 0.1 or even worse). Retrobulbar optic nerves (ONs) were the major sites involved. Optic nerve MRI scan showed increased signal of bilateral ONs in the orbit and the canal parts, with enhancement. After treatment, the visual function of these patients got improved in different degree in a year follow-up, but not satisfactorily.ConclusionsInhalational methanol toxicity may lead to serious damage to ON in a process of chronic intoxication with acute attack, and with poor prognosis.

Incidence and Mimickers of Acute Idiopathic Optic Neuritis: Analysis of 291 Consecutive Patients from Southern Finland

ABSTRACTPurpose: To estimate the population-based incidence of acute idiopathic optic neuritis (ON) and analyse its differential diagnosis in patients referred with symptoms suggestive of ON.Methods: Patients with suspected ON referred to the Helsinki University Hospital, serving a population of 1.5 million in Southern Finland, were reviewed between 1st May 2008 and 14th April 2012. Brain and optic nerve magnetic resonance imaging (MRI) was performed within 24 hours in 83% of patients.Results: Of 291 referred patients, 184 (63%; 95% confidence interval [CI], 57–69%) were diagnosed with ON whereas 107 (37%) had another condition. The estimated crude incidence of ON in Southern Finland was 3.0 (95% CI 2.8–3.3) per 100,000 (females, 4.6 and males, 1.4). Mean age was 34 years (range 15–61), 76% were female. Two (1%) were diagnosed with neuromyelitis optica. ON as the first demyelinative episode was diagnosed in 108 (59%) patients, and MRI showed demyelinating lesions (MRI+) in 82% (95% CI, 75–89) of them. MRI+ predicted the development of multiple sclerosis (MS): 54% of MRI+ vs. 5% MRI− patients were diagnosed as MS during a mean follow-up of 7.7 years. The most common differential diagnosis was non-arteritic anterior ischemic optic neuropathy (12%). Six (2%) intracranial compressive lesions were found upon MRI scan.Conclusions: More than a third of patients with symptoms suggestive of ON had another condition. Demyelinative lesions on MRI indicated higher risk of developing MS. We recommend the use of MRI to improve the differential diagnostic accuracy of ON and to identify patients with high risk of MS.

Quantifying Synovial Enhancement of the Pediatric Temporomandibular Joint

The purposes of this study were to assess a novel method for quantifying temporomandibular joint (TMJ) synovial enhancement on gadolinium-enhanced magnetic resonance imaging (MRI) and to establish normative values to allow early detection of synovitis. This is a retrospective cohort study of pediatric patients (aged 0 to 16years) without jaw pathology who underwent MRI scans with contrast that included the TMJs. From a coronal T1-weighted image, the signal intensity within the superior and inferior joint spaces was divided by the signal intensity of the longus capitis muscle to establish a ratio by age. Intrarater reliability and inter-rater reliability were assessed. A mixed-model regression analysis was used to determine the 95% specificity threshold for normal ratios. Temporal and optic nerve MRI scans of 158 patients were included. Normative synovial enhancement ratios (95% specificity) thresholds were established: 1.52, 1.68, and 1.55 for superior joint space, inferior joint space, and average of both joint spaces, respectively. Intrarater and inter-rater agreement was excellent. A ratio of signal intensity of the TMJ synovium to the longus capitis is a reliable method to quantify enhancement controlling for time after contrast infusion and may be useful for diagnosis of TMJ synovitis.

Longitudinal evidence for anterograde trans-synaptic degeneration after optic neuritis.

In multiple sclerosis, microstructural damage of normal-appearing brain tissue is an important feature of its pathology. Understanding these mechanisms is vital to help develop neuroprotective strategies. The visual pathway is a key model to study mechanisms of damage and recovery in demyelination. Anterograde trans-synaptic degeneration across the lateral geniculate nuclei has been suggested as a mechanism of tissue damage to explain optic radiation abnormalities seen in association with demyelinating disease and optic neuritis, although evidence for this has relied solely on cross-sectional studies. We therefore aimed to assess: (i) longitudinal changes in the diffusion properties of optic radiations after optic neuritis suggesting trans-synaptic degeneration; (ii) the predictive value of early optic nerve magnetic resonance imaging measures for late optic radiations changes; and (iii) the impact on visual outcome of both optic nerve and brain post-optic neuritis changes. Twenty-eight consecutive patients with acute optic neuritis and eight healthy controls were assessed visually (logMAR, colour vision, and Sloan 1.25%, 5%, 25%) and by magnetic resonance imaging, at baseline, 3, 6, and 12 months. Magnetic resonance imaging sequences performed (and metrics obtained) were: (i) optic nerve fluid-attenuated inversion-recovery (optic nerve cross-sectional area); (ii) optic nerve proton density fast spin-echo (optic nerve proton density-lesion length); (iii) optic nerve post-gadolinium T1-weighted (Gd-enhanced lesion length); and (iv) brain diffusion-weighted imaging (to derive optic radiation fractional anisotropy, radial diffusivity, and axial diffusivity). Mixed-effects and multivariate regression models were performed, adjusting for age, gender, and optic radiation lesion load. These identified changes over time and associations between early optic nerve measures and 1-year global optic radiation/clinical measures. The fractional anisotropy in patients' optic radiations decreased (P = 0.018) and radial diffusivity increased (P = 0.002) over 1 year following optic neuritis, whereas optic radiation measures were unchanged in controls. Also, smaller cross-sectional areas of affected optic nerves at 3 months post-optic neuritis predicted lower fractional anisotropy and higher radial diffusivity at 1 year (P = 0.007) in the optic radiations, whereas none of the inflammatory measures of the optic nerve predicted changes in optic radiations. Finally, greater Gd-enhanced lesion length at baseline and greater optic nerve proton density-lesion length at 1 year were associated with worse visual function at 1 year (P = 0.034 for both). Neither the cross-sectional area of the affected optic nerve after optic neuritis nor the damage in optic radiations was associated with 1-year visual outcome. Our longitudinal study shows that, after optic neuritis, there is progressive damage to the optic radiations, greater in patients with early residual optic nerve atrophy, even after adjusting for optic radiation lesions. These findings provide evidence for trans-synaptic degeneration.

Baseline magnetic resonance imaging of the optic nerve provides limited predictive information on short-term recovery after acute optic neuritis.

BackgroundIn acute optic neuritis, magnetic resonance imaging (MRI) may help to confirm the diagnosis as well as to exclude alternative diagnoses. Yet, little is known on the value of optic nerve imaging for predicting clinical symptoms or therapeutic outcome.PurposeTo evaluate the benefit of optic nerve MRI for predicting response to appropriate therapy and recovery of visual acuity.MethodsClinical data as well as visual evoked potentials (VEP) and MRI results of 104 patients, who were treated at the Department of Neurology with clinically definite optic neuritis between December 2010 and September 2012 were retrospectively reviewed including a follow up within 14 days.ResultsBoth length of the Gd enhancing lesion (r = -0.38; p = 0.001) and the T2 lesion (r = -0.25; p = 0.03) of the optic nerve in acute optic neuritis showed a medium correlation with visual acuity after treatment. Although visual acuity pre-treatment was little but nonsignificantly lower if Gd enhancement of the optic nerve was detected via orbital MRI, improvement of visual acuity after adequate therapy was significantly better (0.40 vs. 0.24; p = 0.04). Intraorbitally located Gd enhancing lesions were associated with worse visual improvement compared to canalicular, intracranial and chiasmal lesions (0.35 vs. 0.54; p = 0.02).ConclusionOrbital MRI is a broadly available, valuable tool for predicting the improvement of visual function. While the accurate individual prediction of long-term outcomes after appropriate therapy still remains difficult, lesion length of Gd enhancement and T2 lesion contribute to its prediction and a better short-term visual outcome may be associated with detection and localization of Gd enhancement along the optic nerve.

Correlation of magnetic resonance imaging optic nerve parameters to optical coherence tomography and the visual field in glaucoma

To determine the viability of using magnetic resonance imaging measurement of optic nerve morphology as an objective analysis of glaucomatous damage. Retrospective study conducted at Tohoku University Hospital. Thirty-eight eyes of 19 patients with open-angle glaucoma. Patients were scanned with T2-weighted and 3-T diffusion tensor magnetic resonance imaging, and parameters of the optic nerve, including fractional anisotropy, apparent diffusion coefficient and cross-sectional area, were determined. Conventional parameters of glaucomatous damage, including circumpapillary and macular retinal nerve fibre layer thickness, and mean deviation and average total deviation of the central 16 test points from the Humphrey Field Analyzer, were then compared with the magnetic resonance imaging-derived parameters. Spearman's coefficient of correlation was calculated to determine the significance of the correlation. Correlation coefficient between the magnetic resonance imaging parameters and the parameters of glaucomatous damage. Mean deviation was significantly correlated with all magnetic resonance imaging parameters (fractional anisotropy: r = 0.53, apparent diffusion coefficient: r = -0.44, cross-sectional area: r = 0.70). Circumpapillary retinal nerve fibre layer thickness was significantly correlated with fractional anisotropy (r = 0.60) and cross-sectional area (r = 0.47), but not apparent diffusion coefficient (r = -0.29). Central macular function and macular retinal nerve fibre layer thickness were also significantly correlated with magnetic resonance imaging parameters. Optic nerve magnetic resonance imaging parameters were significantly correlated to glaucomatous damage. Magnetic resonance imaging analysis of the optic nerve may, thus, have value as an objective instrument to assess glaucomatous degeneration, including the function of the macula.

Early factors associated with axonal loss after optic neuritis

Acute optic neuritis due to an inflammatory demyelinating lesion of the optic nerve is often seen in association with multiple sclerosis. Although functional recovery usually follows the acute episode of visual loss, persistent visual deficits are common and are probably due to axonal loss. The mechanisms of axonal loss and early features that predict it are not well defined. We investigated clinical, electrophysiological, and imaging measures at presentation and after 3 months as potential markers of axonal loss following optic neuritis. We followed 21 patients after their first attack of acute unilateral optic neuritis for up to 18 months. Axonal loss was inferred from optical coherence tomography measures of retinal nerve fiber layer (RNFL) thickness at least 6 months following the episode. Visual function, visual evoked potential, and optic nerve magnetic resonance imaging measures obtained during the acute episode and 3 months later were investigated for their association with later axonal loss. After multivariate analysis, prolonged visual evoked potential latency and impaired color vision, at baseline and after 3 months, were significantly and independently associated with RNFL thinning. Low-contrast acuity measures exhibited significant univariate associations with RNFL thinning. The association of RNFL loss with a prolonged visual evoked potential (VEP) latency suggests that acute and persistent demyelination is associated with increased vulnerability of axons. VEP latency and visual function tests that capture optic nerve function, such as color and contrast, may help identify subjects with a higher risk for axonal loss who are thus more suitable for experimental neuroprotection trials.

Optic nerve diffusion changes and atrophy jointly predict visual dysfunction after optic neuritis

Recently, there has been strong interest in the development of imaging techniques to quantify axonal and myelin pathology in patients with multiple sclerosis (MS). Optic neuritis, a condition characterised by inflammatory demyelination of the optic nerve, is one of the commonest sites of MS relapse, and exhibits similar pathological alterations to MS lesions elsewhere in the central nervous system (CNS). Unlike other regions of the CNS, however, the function of the optic nerve can be accurately assessed using clinical measures, as well as electrophysiological techniques such as visual evoked potential recordings. Therefore, optic neuritis is useful for investigating the relationship between abnormalities in optic nerve structure, assessed using magnetic resonance imaging (MRI), and visual dysfunction, assessed clinically and electrophysiologically. The aims of the present study were to assess optic nerve structural abnormalities in patients with a history of unilateral optic neuritis using MRI, and then to identify correlations between abnormalities in optic nerve MRI and visual dysfunction. Ten controls and sixteen patients underwent high resolution optic nerve diffusion tensor imaging (DTI), T2- and T1-weighted MRI. In addition, Snellen visual acuity and the latency and amplitude of multifocal visual evoked potentials (mfVEP) were tested in all patients. Diffusion and volumetric MRI indices were correlated to mfVEP functional indices. Significant abnormalities were detected in MRI and mfVEP measures in patients' affected nerves compared to unaffected optic nerves or optic nerves from healthy controls. Reduced mfVEP amplitude in the affected side significantly correlated with both affected optic nerve atrophy (R=0.58, p=0.02) and reduced fractional anisotropy (FA) (R=0.52, p=0.04). However, atrophy and reduced FA did not correlate with each other. To further investigate this disassociation, we used linear regression analysis with optic nerve atrophy and optic nerve FA as independent variables and mfVEP amplitude as the dependent variable. The resulting linear regression model was highly significant (R=0.819, p=0.001). These results show that, 4 years after unilateral optic neuritis, MRI-based measures of optic nerve structural abnormalities (decreased anisotropy and volume) independently predict visual dysfunction.

Magnetic resonance imaging in the differential diagnosis and monitoring of the treatment of multiple sclerosis.

Treatments with potentially beneficial effects on the course of multiple sclerosis are now emerging and magnetic resonance imaging techniques are needed which have a high specificity for diagnosing multiple sclerosis, and which can characterize the heterogeneous nature of multiple sclerosis lesions and define disease evolution over time. Differential diagnosis may be improved by the use of gadolinium-enhanced magnetic resonance imaging, high-resolution spinal cord and optic nerve magnetic resonance imaging and non-conventional magnetic resonance imaging techniques. In the monitoring of treatment, a number of different approaches have been used to increase magnetic resonance imaging accuracy in describing and predicting disease activity and evolution. These include optimization of the acquisition and post-processing of data obtained with conventional magnetic resonance imaging techniques (T2-weighted and postcontrast T1-weighted sequences) and the use of newer nonconventional magnetic resonance imaging techniques.

THE PATHOPHYSIOLOGY OF ACUTE OPTIC NEURITIS

Eighteen patients with acute optic neuritis underwent optic nerve magnetic resonance imaging (MRI) before and after injection of gadolinium-diethylene triamine pentacetic acid (Gd-DTPA). Ten were re-examined 4 weeks later. Leakage of Gd-DTPA across the blood-optic nerve barrier was a consistent finding in the acute lesion, and its presence was associated with abnormal visual acuity and colour vision, retro-ocular pain on eye movement, and afferent pupillary defect, and a reduced amplitude of the P100 component of the visual evoked potential. Gd-DTPA leakage had ceased in 9/11 nerves when restudied 4 wks later, and this evolution was associated with improved visual acuity and an increased P100 amplitude. Leakage is likely to reflect inflammation, and we conclude that the latter plays an important part in the production of conduction block and clinical deficit, and that its resolution is an important step in clinical remission from acute episodes of demyelination.