Recovery of vision and pupil responses in optic neuritis and multiple sclerosis

Dynamic Pupillary Response in Multiple Sclerosis Patients with and without Optic Neuritis

Multiple sclerosis (MS) is a neurodegenerative disease that affects the central nervous system which produces abnormalities in visual function, as disturbed pupillary responses, even after an episode of optic neuritis (ON). The aim was to assess different parameters of the pupillary response in MS subjects with and without ON. Therefore, 24 eyes of healthy age-matched subjects were included, 22 eyes of subjects with MS (MS group), and 13 subjects with MS with previous ON (MSON group). Pupillary parameters (ratio pupil max/min; latency; velocity and duration; contraction and dilation; and amplitude of contraction) were recorded with the MYAH topographer. Statistical analysis was performed by IBM SPSS Statistics, and parametrical or non-parametrical tests were used according to the normality of the data. MS patients did not significantly differ from healthy patients in any of the parameters analyzed (p > 0.05). Only patients with previous ON were different from healthy patients in the amplitude (40.71 ± 6.73% vs. 45.22 ± 3.29%, respectively) and latency of contraction (0.35 ± 0.13 s vs. 0.26 ± 0.05 s, respectively). The time to recover 75% of the initial diameter was abnormal in 9% of the MS subjects and 12% of MSON subjects. Based on the results of this study, the contraction process, especially latency and amplitude, was found to be affected in subjects with MS and previous ON. The degree of disability and the relation of the decrease in pupil response with other indicators of MS disease should be further investigated considering other comorbidities such as ON in the affection.

Comparison of Two Printed Pseudoisochromatic Tests for Color Vision Assessment

SIGNIFICANCE

The Waggoner PIP24 is a pseudoisochromatic test with a pattern similar to the Ishihara test. This study determined that the W-PIP24 can be used clinically to yield screening results (or sensitivity and specificity) comparable with the Ishihara.

PURPOSE

This study aimed to determine whether the W-PIP24 is equivalent to the Ishihara 38 edition pseudoisochromatic test in detecting red-green color vision defects. Also, the performance of each plate of the W-PIP24 in detecting the color vision defects relative to the Ishihara test was determined.

METHODS

Sixty-three individuals with congenital red-green color vision defects and 57 with normal trichromacy were recruited. Participants were tested with both the Ishihara and W-PIP24. The first-order agreement coefficients were calculated for the Ishihara and W-PIP24. The results were also analyzed using specificity, sensitivity, efficiency, and predictive pass and fail values.

RESULTS

The agreement between the W-PIP24 and Ishihara test using the recommended criterion of using all plates was perfect. The sensitivity, specificity, predictive pass, and predictive fail were 1.00 (95% confidence interval, 0.94 to 1.00).

CONCLUSIONS

This study showed that the W-PIP24 using a failure criterion of three or more errors on screening plates 1 to 15 is equivalent to the Ishihara test while screening for red-green color vision deficiency using a failure criterion of three or more errors on screening plates 1 to 17 of the Ishihara 38 edition.

Static and dynamic pupillary characteristics in multiple sclerosis

PURPOSE

To examine the static and dynamic pupillary functions with automated pupillography in multiple sclerosis (MS) patients with preserved visual acuity.

METHODS

Forty-seven MS patients with preserved visual acuity were included in the study group and 43 healthy volunteers in the control group. The visual evoked potential of the patients was obtained. After routine ophthalmologic examination contrast sensitivity and the retinal nerve fiber layer (RNFL) thickness were measured. Finally scotopic, mesopic, and photopic pupillographies followed by dynamic pupillography were undertaken, and the pupillary dilatation speed was calculated.

RESULTS

The contrast sensitivity and RNFL thickness of the MS group were significantly lower than those of the control group (p < 0.05; for both). In the MS and control groups, the scotopic pupil diameters were 5.48 ± 1.03 and 5.28 ± 0.78 mm, mesopic pupil diameters were 4.82 ± 0.83 and 4.48 ± 0.70 mm, and photopic pupil diameters were 3.84 ± 0.79 and 3.42 ± 0.49 mm, respectively (p = 0.315, p = 0.044, and p = 0.004, respectively). In dynamic pupillography, the pupil in the MS group was more dilated than control group at all time sections examined except the sixth second (p < 0.05; for all). Although the mean pupillary dilation speed in the first second was higher in the MS group (p = 0.044), there was no significant difference between the groups for the other time intervals examined (p > 0.05; for all). There was no correlation between pupillary parameters and P100-wave latency, RNFL thickness, or contrast sensitivity (p > 0.05; for all).

CONCLUSIONS

Static and dynamic pupillary functions may be affected in MS patients with preserved visual acuity. Although scotopic pupillary functions are preserved, mesopic, and photopic pupil functions are weakened.

Visual function deficits in eyes with resolved endophthalmitis

To evaluate the changes in functional vision in patients with resolved endophthalmitis. This was a cross-sectional study. The study included 20 patients with resolved endophthalmitis and best-corrected visual acuity of 20/100 or better. Visual acuity (VA), contrast threshold (CT), red/green (RG) and yellow/blue (YB) colour vision and 15 Hz flicker modulation threshold (FMT) were assessed using standard psychophysical techniques. The median age was 54 years. The median visual acuity was 0.27 (~ 20/40-Snellen Equivalent) ((interquartile range [IQR]), 0.30) logMAR). The median log contrast threshold (CT) was - 1.13 (IQR, 0.36) log units (normative value for age-matched CT: - 1.61 log units). The median red/green (RG) and yellow/blue (YB) thresholds were 11.52 (IQR, 26.19) and 9.45 (IQR, 16.20) CAD units respectively, which were at least 5 times higher than age-matched normative RG and YB thresholds. The median central cone- mediated FMT was 17.64% (IQR, 23.40%), which was much higher compared to age-matched FMT (5.48% [IQR, 3.47]). Linear regression revealed significant relationship between contrast thresholds and foveal thickness (y = 0.001x-1.47, R2 = 0.20, p = 0.048). Though endophthalmitis may resolve with a good visual acuity, deficits in visual functions like chromatic discrimination, cone-mediated flicker and contrast sensitivity persist.

Binocular, Accommodative and Oculomotor Alterations In Multiple Sclerosis: A Review

Multiple sclerosis (MS) is an acquired demyelinating and inflammatory neurodegenerative disease affecting the central nervous system (CNS). Clinical and subclinical ocular disturbances occur in almost all patients with MS. The objective of this narrative review was to collect and summarize the available scientific information on oculomotor, accommodative and binocular alterations that have been reported in MS. A systematic search strategy with the following descriptors was carried out: multiple sclerosis, ocular motility disorders, internuclear ophthalmoplegia, nystagmus, vergences, fixation, pupil reflex, accommodation and stereopsis. According to the search, some oculomotor alterations were found to be commonly reported in MS, such as alterations in saccades and nystagmus. In contrast, accommodative, vergence and stereopsis alterations have not been comprehensively studied despite their relevance, with only minimal evidence showing a potential negative impact of the disease on these aspects. In conclusion, oculomotor impairment is a common component of disability in MS patients and should be considered when managing this type of patients. More research is still needed to know the real impact of this disease on binocular vision and accommodation.

A novel method of inducing endogenous pupil oscillations to detect patients with unilateral optic neuritis

Purpose

To use and test a new method of inducing endogenously generated pupillary oscillations (POs) in patients with unilateral optic neuritis (ON), to describe a signal analysis approach quantifying pupil activity and to evaluate the extent to which POs permit to discriminate patients from control participants.

Method

Pupil size was recorded with an eye-tracker and converted in real time to modulate the luminance of a stimulus (a 20° disk) presented in front of participants. With this biofeedback setting, an increasing pupil size transforms into a high luminance, entraining a pupil constriction that in turn decreases the stimulus luminance, and so on, resulting in endogenously generated POs. POs were recorded for 30 seconds in the affected eye, in the fellow eye and in binocular conditions with 22 patients having a history of unilateral ON within a period of 5 years, and with 22 control participants. Different signal analysis methods were used to quantify the power and frequency of POs.

Results

On average, pupil size oscillated at around 1 Hz. The amplitude of POs appears not to be a reliable marker of ON. In contrast, the frequency of POs was significantly lower, and was more variable over time, in the patients’ affected eye, as compared to their fellow eye and to the binocular condition. No such differences were found in control participants. Receiver operating characteristic analyses based on the frequency and the variability of POs to classify patients and control participants gave an area under the curve of 0.82, a sensitivity of 82% (95%CI: 60%-95%) and a specificity of 77% (95%CI: 55%-92%).

Conclusions

The new method used to induce POs allowed characterizing the visual afferent pathway defect in ON patients with encouraging accuracy. The method was fast, easy to use, only requiring that participants look ahead, and allows testing many stimulus parameters (e.g. color, stimulus location, size, etc).

Predictors of response to opicinumab in acute optic neuritis

Objective

The objective of this study was to evaluate prespecified and post hoc analyses in RENEW subgroups to identify participants more likely to benefit from opicinumab.

Methods

RENEW assessed the efficacy/safety of opicinumab versus placebo in participants with a first unilateral acute optic neuritis (AON) episode. Difference in visual evoked potential (VEP) latency of the affected eye at 24 weeks versus the fellow eye at baseline was the primary endpoint. Interactions between the primary endpoint and prespecified baseline variables (including age, timing of treatment initiation, and visual impairment) using the median as cut-off were evaluated in the per protocol population using analysis of covariance (ANCOVA); subgroups based on preexisting brain T2 lesion volume were also analyzed. Interactions between the primary endpoint and retinal ganglion cell layer/inner plexiform layer (RGCL/IPL) and retinal nerve fiber layer (RNFL) thickness were assessed post hoc as was weight gain by treatment.

Results

Treatment benefit of opicinumab (n = 33) over placebo (n = 36) on the primary endpoint was greatest in participants older than the median age at baseline (≥33 years); the difference versus placebo for baseline age ≥33 years was -14.17 msec [P = 0.01] versus -0.89 msec for baseline age <33 years, [P = 0.87]). Post hoc analysis showed that VEP latency recovery was significantly associated with less RGCL/IPL thinning (P = 0.0164), occurring early on.

Interpretation

Age was the strongest prespecified baseline characteristic associated with a treatment effect of opicinumab. A strong association between VEP latency recovery at week 24 and early RGCL/IPL preservation was observed.

Colour vision requirements in visually demanding occupations

Normal trichromatic colour vision (CV) is often required as a condition for employment in visually demanding occupations. If this requirement could be enforced using current, colour assessment tests, a significant percentage of subjects with anomalous, congenital trichromacy who can perform the suprathreshold, colour-related tasks encountered in many occupations with the same accuracy as normal trichromats would fail. These applicants would therefore be discriminated against unfairly. One solution to this problem is to produce minimum, justifiable CV requirements that are specific to each occupation. This has been done successfully for commercial aviation (i.e. the flight crew) and for Transport for London train drivers. An alternative approach is to make use of new findings and the statistical outcomes of past practices to produce graded, justifiable CV categories that can be enforced. To achieve this aim, we analysed colour assessment outcomes and quantified severity of CV loss in 1363 subjects. The severity of CV loss was measured in each subject and statistical, pass/fail outcomes established for each of the most commonly used, conventional colour assessment tests and protocols. This evidence and new findings that relate severity of loss to the effective use of colour signals in a number of tasks provide the basis for a new colour grading system based on six categories. A single colour assessment test is needed to establish the applicant's CV category which can range from 'supernormal', for the most stringent, colour-demanding tasks, to 'severe colour deficiency', when red/green CV is either absent or extremely weak.

Safety and efficacy of opicinumab in acute optic neuritis (RENEW): a randomised, placebo-controlled, phase 2 trial

BACKGROUND

The human monoclonal antibody opicinumab (BIIB033, anti-LINGO-1) has shown remyelinating activity in preclinical studies. We therefore assessed the safety and tolerability, and efficacy of opicinumab given soon after a first acute optic neuritis episode.

METHODS

This randomised, double-blind, placebo-controlled, phase 2 study (RENEW) was done at 33 sites in Australia, Canada, and Europe in participants (aged 18-55 years) with a first unilateral acute optic neuritis episode within 28 days from study baseline. After treatment with high-dose methylprednisolone (1 g/day, intravenously, for 3-5 days), participants were assigned with a computer-generated sequence with permuted block randomisation (1:1) using a centralised interactive voice and web response system to receive 100 mg/kg opicinumab intravenously or placebo once every 4 weeks (six doses) and followed up to week 32. All study participants and all study staff, including the central readers, were masked to treatment assignment apart from the pharmacist responsible for preparing the study treatments and the pharmacy monitor at each site. The primary endpoint was remyelination at 24 weeks, measured as recovery of affected optic nerve conduction latency using full-field visual evoked potential (FF-VEP) versus the unaffected fellow eye at baseline. Analysis was by intention-to-treat (ITT); prespecified per-protocol (PP) analyses were also done. This study is registered with ClinicalTrials.gov, number NCT01721161.

FINDINGS

The study was done between Dec 21, 2012, and Oct 21, 2014. 82 participants were enrolled, and 41 in each group comprised the ITT population; 33 participants received opicinumab and 36 received placebo in the PP population. Adjusted mean treatment difference of opicinumab versus placebo was -3·5 ms (17·3 vs 20·8 [95% CI -10·6 to 3·7]; 17%; p=0·33) in the ITT population, and -7·6 ms in the PP population (14·7 vs 22·2 [-15·1 to 0·0]; 34%; p=0·050) at week 24 and -6·1 ms (15·1 vs 21·2 [-12·7 to 0·5]; 29%; p=0·071) in the ITT population and -9·1 ms (13·2 vs 22·4 [-16·1 to -2·1]; 41%; p=0·011) in the PP population at week 32. The overall incidence (34 [83%] of 41 in each group) and severity of adverse events (two [5%] of 41 severe adverse events with placebo vs three [7%] of 41 with opicinumab) were similar between groups and no significant effects on brain MRI measures were noted in either group (mean T2 lesion volume change, 0·05 mL [SD 0·21] for placebo vs 0·20 mL [0·52] with opicinumab; 27 [77%] of 35 participants with no change in gadolinium-enhancing [Gd+] lesion number with opicinumab vs 27 [79%] of 34 with placebo; mean 0·4 [SD 0·79 for the placebo group and 0·85 for the opicinumab group] new Gd+ lesions per participant in both groups). Treatment-related serious adverse events were reported in three (7%) of 41 participants in the opicinumab group (hypersensitivity [n=2], asymptomatic increase in transaminase concentrations [n=1]) and none of the participants in the placebo group.

INTERPRETATION

Remyelination did not differ significantly between the opicinumab and placebo groups in the ITT population at week 24. However, results from the prespecified PP population suggest that enhancing remyelination in the human CNS with opicinumab might be possible and warrant further clinical investigation.

FUNDING

Biogen.

Colorimetric evaluation of iPhone apps for colour vision tests based on the Ishihara test

Given the versatility of smart phone displays, it was inevitable that applications (apps) providing colour vision testing would appear as an option. In this study, the colorimetric characteristics of five available iPhone apps for colour vision testing are assessed as a prequel to possible clinical evaluation. The colours of the displays produced by the apps are assessed with reference to the colours of a printed Ishihara test. The visual task is assessed on the basis of the colour differences and the alignment to the dichromatic confusion lines. The apps vary in quality and while some are colorimetrically acceptable, there are also some problems with their construction in making them a clinically useful app rather than curiosity driven self-testing. There is no reason why, in principle, a suitable test cannot be designed for smart phones.

Neuroprotective effect of melatonin in experimental optic neuritis in rats

Optic neuritis (ON) is an inflammatory, demyelinating, and neurodegenerative condition of the optic nerve, which might induce permanent vision loss. Currently, there are no effective therapies for this disorder. We have developed an experimental model of primary ON in rats through a single microinjection of 4.5 μg of bacterial lipopolysaccharide (LPS) into the optic nerve. Since melatonin acts as a pleiotropic therapeutic agent in various neurodegenerative diseases, we analyzed the effect of melatonin on LPS-induced ON. For this purpose, LPS or vehicle were injected into the optic nerve from adult male Wistar rats. One group of animals received a subcutaneous pellet of 20 mg melatonin at 24 hr before vehicle or LPS injection, and another group was submitted to a sham procedure. Melatonin completely prevented the decrease in visual evoked potentials (VEPs), and pupil light reflex (PLR), and preserved anterograde transport of cholera toxin β-subunit from the retina to the superior colliculus. Moreover, melatonin prevented microglial reactivity (ED1-immunoreactivity, P < 0.01), astrocytosis (glial fibrillary acid protein-immunostaining, P < 0.05), demyelination (luxol fast blue staining, P < 0.01), and axon (toluidine blue staining, P < 0.01) and retinal ganglion cell (Brn3a-immunoreactivity, P < 0.01) loss, induced by LPS. Melatonin completely prevented the increase in nitric oxide synthase 2, cyclooxygenase-2 levels (Western blot) and TNFα levels, and partly prevented lipid peroxidation induced by experimental ON. When the pellet of melatonin was implanted at 4 days postinjection of LPS, it completely reversed the decrease in VEPs and PLR. These data suggest that melatonin could be a promising candidate for ON treatment.

Autonomic Dysregulation in Multiple Sclerosis

Multiple sclerosis (MS) is a chronic, progressive central neurological disease characterized by inflammation and demyelination. In patients with MS, dysregulation of the autonomic nervous system may present with various clinical symptoms including sweating abnormalities, urinary dysfunction, orthostatic dysregulation, gastrointestinal symptoms, and sexual dysfunction. These autonomic disturbances reduce the quality of life of affected patients and constitute a clinical challenge to the physician due to variability of clinical presentation and inconsistent data on diagnosis and treatment. Early diagnosis and initiation of individualized interdisciplinary and multimodal strategies is beneficial in the management of autonomic dysfunction in MS. This review summarizes the current literature on the most prevalent aspects of autonomic dysfunction in MS and provides reference to underlying pathophysiological mechanisms as well as means of diagnosis and treatment.

Experimental optic neuritis induced by the microinjection of lipopolysaccharide into the optic nerve

Optic neuritis (ON) is a condition involving primary inflammation, demyelination, and axonal injury in the optic nerve which leads to retinal ganglion cell (RGC) loss, and visual dysfunction. We investigated the ability of a single microinjection of bacterial lipopolysaccharide (LPS) directly into the optic nerve to induce functional and structural alterations compatible with ON. For this purpose, optic nerves from male Wistar rats remained intact or were injected with vehicle or LPS. The effect of LPS was evaluated at several time points post-injection in terms of: i) visual pathway and retinal function (visual evoked potentials (VEPs) and electroretinograms, (ERGs), respectively), ii) anterograde transport from the retina to its projection areas, iii) consensual pupil light reflex (PLR), iv) optic nerve histology, v) microglia/macrophage reactivity (by Iba-1- and ED1-immunostaining), vi) astrocyte reactivity (by glial fibrillary acid protein-immunostaining), vii) axon number (by toluidine blue staining), vii) demyelination (by myelin basic protein immunoreactivity and luxol fast blue staining), viii) optic nerve ultrastructure, and ix) RGC number (by Brn3a immunoreactivity). LPS induced a significant and persistent decrease in VEP amplitude and PLR, without changes in the ERG. In addition, LPS induced a deficit in anterograde transport, and an early inflammatory response consisting in an increased cellularity, and Iba-1 and ED1-immunoreactivity in the optic nerve, which were followed by changes in axonal density, astrocytosis, demyelination, and axon and RGC loss. These results suggest that the microinjection of LPS into the optic nerve may serve as a new experimental model of primary ON.

Pupillary behavior in relation to wavelength and age

Pupil light reflex can be used as a non-invasive ocular predictor of cephalic autonomic nervous system integrity. Spectral sensitivity of the pupil's response to light has, for some time, been an interesting issue. It has generally, however, only been investigated with the use of white light and studies with monochromatic wavelengths are scarce. This study investigates the effects of wavelength and age within three parameters of the pupil light reflex (amplitude of response, latency, and velocity of constriction) in a large sample of younger and older adults (N = 97), in mesopic conditions. Subjects were exposed to a single light stimulus at four different wavelengths: white (5600°K), blue (450 nm), green (510 nm), and red (600 nm). Data was analyzed appropriately, and, when applicable, using the General Linear Model (GLM), Randomized Complete Block Design (RCBD), Student's t-test and/or ANCOVA. Across all subjects, pupillary response to light had the greatest amplitude and shortest latency in white and green light conditions. In regards to age, older subjects (46–78 years) showed an increased latency in white light and decreased velocity of constriction in green light compared to younger subjects (18–45 years old). This study provides data patterns on parameters of wavelength-dependent pupil reflexes to light in adults and it contributes to the large body of pupillometric research. It is hoped that this study will add to the overall evaluation of cephalic autonomic nervous system integrity.

Assessment of novel binocular colour, motion and contrast tests in glaucoma

The effects of glaucoma on binocular visual sensitivity for the detection of various stimulus attributes are investigated at the fovea and in four paracentral retinal regions. The study employed a number of visual stimuli designed to isolate the processing of various stimulus attributes. We measured absolute contrast detection thresholds and functional contrast sensitivity by using Landolt ring stimuli. This psychophysical Landolt C-based contrast test of detection and gap discrimination allowed us to test parafoveally at 6 ° from fixation and foveally by employing interleaved testing locations. First-order motion perception was examined by using moving stimuli embedded in static luminance contrast noise. Red/green (RG) and yellow/blue (YB) colour thresholds were measured with the Colour Assessment and Diagnosis (CAD) test, which utilises random dynamic luminance contrast noise (± 45 %) to ensure that only colour and not luminance signals are available for target detection. Subjects were normal controls (n = 65) and glaucoma patients with binocular visual field defects (n = 15) classified based on their Humphrey Field Analyzer mean deviation (MD) scores. The impairment of visual function varied depending on the stimulus attribute and location tested. Progression of loss was noted for all tests as the degree of glaucoma increased. For subjects with mild glaucoma (MD -0.01 dB to -6.00 dB) significantly more data points fell outside the normal age-representative range for RG colour thresholds than for any other visual test, followed by motion thresholds. This was particularly the case for the parafoveal data compared with the foveal data. Thus, a multifaceted measure of binocular visual performance, incorporating RG colour and motion test at multiple locations, might provide a better index for comparison with quality of life measures in glaucoma.

Evidence for Non-Opponent Coding of Colour Information in Human Visual Cortex: Selective Loss of "Green" Sensitivity in a Subject with Damaged Ventral Occipito-Temporal Cortex

Damage to ventral occipito-temporal extrastriate visual cortex leads to the syndrome of prosopagnosia often with coexisting cerebral achromatopsia. A patient with this syndrome resulting in a left upper homonymous quadrantanopia, prosopagnosia, and incomplete achromatopsia is described. Chromatic sensitivity was assessed at a number of locations in the intact visual field using a dynamic luminance contrast masking technique that isolates the use of colour signals. In normal subjects chromatic detection thresholds form an elliptical contour when plotted in the Commission Internationale d'Eclairage, (x-y), chromaticity diagram. Because the extraction of colour signals in early visual processing involves opponent mechanisms, subjects with Daltonism (congenital red/green loss of sensitivity) show symmetric increase in thresholds towards the long wavelength ("red") and middle wavelength ("green") regions of the spectrum locus. This is also the case with acquired loss of chromatic sensitivity as a result of retinal or optic nerve disease. Our patient's results were an exception to this rule. Whilst his chromatic sensitivity in the central region of the visual field was reduced symmetrically for both "red/green" and "yellow/blue" directions in colour space, the subject's lower left quadrant showed a marked asymmetry in "red/green" thresholds with the greatest loss of sensitivity towards the "green" region of the spectrum locus. This spatially localized asymmetric loss of "green" but not "red" sensitivity has not been reported previously in human vision. Such loss is consistent with selective damage of neural substrates in the visual cortex that process colour information, but are spectrally non-opponent.

Sudomotor dysfunction in patients with optic neuritis

OBJECTIVES

Optic neuritis (ON) is a frequent initial manifestation of multiple sclerosis (MS). Autonomic failure affecting the pupillary function is known to exist in ON patients, and patients with MS are known to have more widespread autonomic dysfunction. For example, sudomotor dysfunction is well known in MS. We carried out a study investigating sudomotor abnormalities in ON patients, and later followed these patients at risk of developing MS.

METHODS

Firstly, sudomotor function was measured by sympathetic skin responses (SSRs) in 13 ON patients and in 22 healthy controls. Secondly, thermoregulatory sweating was measured by an evaporimeter after a heating stimulus in 13 ON patients and in 14 healthy control subjects.

RESULTS

The SSR latencies to electrical stimuli in the ON patients were significantly prolonged in the upper and lower extremities (p = 0.013-0.002), indicating sudomotor dysfunction. No statistically significant thermoregulatory sweating dysfunction could be found in the ON patients compared to the controls. All ON patients underwent a follow-up (mean duration 12.5 years) during which eight ON patients (62%) converted to clinically definite MS. It seemed that SSRs had no value for identifying patients who later developed MS.

INTERPRETATION

Our results enlarge the knowledge of autonomic disorders in ON patients, showing that sudomotor function may also be involved.

Assessing structure and function of the afferent visual pathway in multiple sclerosis and associated optic neuritis

The afferent visual pathway is commonly affected in MS. Assessment of the afferent visual pathway using clinical, imaging and electrophysiological methods not only provides insights into the pathophysiology of MS, but also provides a method of investigating potential therapeutic measures in MS. This review summarises the various assessment methods, in particular imaging techniques of the visual pathway. Retinal nerve fibre layer (RNFL) thickness is usually reduced following an episode of optic neuritis. Techniques such as optical coherence tomography, scanning laser polarimetry, and confocal scanning laser ophthalmoscopy are used to quantify RNFL thickness. MRI of the optic nerve is not routinely used in the diagnosis of MS or optic neuritis, but is valuable in atypical cases and in research. T2- weighted images of the optic nerve usually show the hyperintense lesion in optic neuritis and gadolinium enhancement is seen in the acute attack. Quantifying atrophy of the optic nerve using MRI gives an indication of the degree of axonal loss. Magnetization transfer ratio (MTR) of the optic nerve provides an indication of myelination. Diffusion tensor imaging (DTI) of the optic nerve and optic radiation provide information about the integrity of the visual white matter tracts. Functional MRI following visual stimulation is used to assess the contribution of cortical reorganisation to functional recovery following optic neuritis. Investigations including logMAR visual acuity, Sloan contrast acuity, Farnsworth- Munsell 100-hue colour vision tests and Humphrey perimetry provide detailed quantitative information on different aspects of visual function. Visual evoked potentials identify conduction block or delay reflecting demyelination. These collective investigative methods have advanced knowledge of pathophysiological mechanisms in MS and optic neuritis. Relevant ongoing studies and future directions are discussed.

Chromatic discrimination losses in multiple sclerosis patients with and without optic neuritis using the Cambridge Colour Test

We assessed chromatic discrimination in multiple sclerosis (MS) patients both with (ON) and without (no ON) a history of optic neuritis using the Cambridge color test (CCT). Our goal was to determine the magnitude and chromatic axes of any color vision losses in both patient groups, and to evaluate age-related changes in chromatic discrimination in both patient groups compared to normals. Using the CCT, we measured chromatic discrimination along the protan, deutan and tritan axes in 35 patients with MS (17 ON eyes) and 74 age matched controls. Color thresholds for both patient groups were significantly higher than controls' along the protan and tritan axes (p < 0.001). In addition, the ON and no-ON groups differed significantly along all three-color axes (p < 0.001). MS patients presented a progressive color discrimination impairment with age (along the deutan and tritan axes) that was almost two times faster than controls, even in the absence of ON. These findings suggest that demyelinating diseases reduce sensitivity to color vision in both red-green and blue-yellow axes, implying impairment in both parvocellular and koniocellular visual pathways. The CCT is a useful tool to help characterize vision losses in MS, and the relationship between these losses and degree of optic nerve involvement.