Saccade metrics in multiple sclerosis: versional velocity disconjugacy as the best clue?

Visual outcome measures in clinical trials of remyelinating drugs

One of the most promising approaches to delay, prevent or reverse disability progression in multiple sclerosis (MS) is to enhance endogenous remyelination and limit axonal degeneration. In clinical trials of remyelinating drugs, there is a need for reliable, sensitive and clinically relevant outcome measures. The visual pathway, which is frequently affected by MS, provides a unique model system to evaluate remyelination of acute and chronic MS lesions in vivo and non-invasively. In this review, we discuss the different measures that have been used and scrutinise visual outcome measure selection in current and future remyelination trials.

Accuracy of clinical versus oculographic detection of pathological saccadic slowing

Saccadic slowing as a component of supranuclear saccadic gaze palsy is an important diagnostic sign in multiple neurologic conditions, including degenerative, inflammatory, genetic, or ischemic lesions affecting brainstem structures responsible for saccadic generation. Little attention has been given to the accuracy with which clinicians correctly identify saccadic slowing. We compared clinician (n = 19) judgements of horizontal and vertical saccade speed on video recordings of saccades (from 9 patients with slow saccades, 3 healthy controls) to objective saccade peak velocity measurements from infrared oculographic recordings. Clinician groups included neurology residents, general neurologists, and fellowship-trained neuro-ophthalmologists. Saccades with normal peak velocities on infrared recordings were correctly identified as normal in 57% (91/171; 171 = 9 videos × 19 clinicians) of clinician decisions; saccades determined to be slow on infrared recordings were correctly identified as slow in 84% (224/266; 266 = 14 videos × 19 clinicians) of clinician decisions. Vertical saccades were correctly identified as slow more often than horizontal saccades (94% versus 74% of decisions). No significant differences were identified between clinician training levels. Reliable differentiation between normal and slow saccades is clinically challenging; clinical performance is most accurate for detection of vertical saccade slowing. Quantitative analysis of saccade peak velocities enhances accurate detection and is likely to be especially useful for detection of mild saccadic slowing.

A model for interrogating the clinico-radiological paradox in multiple sclerosis: Internuclear ophthalmoplegia

Background and purpose

The clinico‐radiological paradox in multiple sclerosis (MS) is well recognized, relevant and yet poorly understood. The suitability of an in vivo model for the clinico‐radiological paradox was tested, using internuclear ophthalmoplegia (INO) and the medial longitudinal fasciculus (MLF).

Methods

In this cross‐sectional study lesions of the MLF were rated by an experienced MS neuroradiologist blinded to all other information. The presence of an INO was objectively determined by a validated infrared oculography protocol (DEMoNS). Clinical information, including the National Eye Institute Visual Function Questionnaire, was obtained.

Results

This study included 202 patients with MS. The clinico‐radiological paradox occurred in 50 patients (25%). This consisted of 45 patients having an INO without an MLF lesion and five patients with an MLF lesion but without an INO. The visual function overall score was related to the presence of an INO (p = 0.016), but not to MLF lesions seen on magnetic resonance imaging (MRI) (p = 0.207). A consensus list of potential causes for the clinico‐radiological paradox was compiled and the MRI images were deposited in a repository.

Conclusion

This study provides an objective and quantitative model to investigate the clinico‐radiological paradox. Our data suggest that pathology of the MLF is more frequently detected and more clinically relevant by infrared oculography than by MLF lesion rating on MRI.

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.

Diagnosing and quantifying a common deficit in multiple sclerosis: Internuclear ophthalmoplegia

OBJECTIVE

We present an objective and quantitative approach for diagnosing internuclear ophthalmoplegia (INO) in multiple sclerosis (MS).

METHODS

A validated standardized infrared oculography protocol (DEMoNS [Demonstrate Eye Movement Networks with Saccades]) was used for quantifying prosaccades in patients with MS and healthy controls (HCs). The versional dysconjugacy index (VDI) was calculated, which describes the ratio between the abducting and adducting eye. The VDI was determined for peak velocity, peak acceleration, peak velocity divided by amplitude, and area under the curve (AUC) of the saccadic trajectory. We calculated the diagnostic accuracy for the several VDI parameters by a receiver operating characteristic analysis comparing HCs and patients with MS. The National Eye Institute Visual Function Questionnaire-25 was used to investigate vision-related quality of life of MS patients with INO.

RESULTS

Two hundred ten patients with MS and 58 HCs were included. The highest diagnostic accuracy was achieved by the VDI AUC of 15° horizontal prosaccades. Based on a combined VDI AUC and peak velocity divided by amplitude detection, the prevalence of an INO in MS calculated to 34%. In the INO group, 35.2% of the patients with MS reported any complaints of double vision, compared to 18.4% in the non-INO group (p = 0.010). MS patients with an INO had a lower overall vision-related quality of life (median 89.9, interquartile range 12.8) compared to patients without an INO (median 91.8, interquartile range 9.3, p = 0.011).

CONCLUSIONS

This study provides an accurate quantitative and clinically relevant definition of an INO in MS. This infrared oculography-based INO standard will require prospective validation. The high prevalence of INO in MS provides an anatomically well described and accurately quantifiable model for treatment trials in MS.

Treatment of internuclear ophthalmoparesis in multiple sclerosis with fampridine: A randomized double-blind, placebo-controlled cross-over trial

Aim

To examine whether the velocity of saccadic eye movements in internuclear ophthalmoparesis (INO) improves with fampridine treatment in patients with multiple sclerosis (MS).

Methods

Randomized, double‐blind, placebo‐controlled, cross‐over trial with fampridine in patients with MS and INO. Horizontal saccades were recorded at baseline and at multiple time points post‐dose. Main outcome measures were the change of peak velocity versional dysconjugacy index (PV‐VDI) and first‐pass amplitude VDI (FPA‐VDI). Both parameters were compared between fampridine and placebo using a mixed model analysis of variance taking patients as their own control. Pharmacokinetics was determined by serial blood sampling.

Results

Thirteen patients had a bilateral and 10 had a unilateral INO. One patient had an INO of abduction (posterior INO of Lutz) and was excluded. Fampridine significantly reduced both PV‐VDI (−17.4%, 95% CI: −22.4%, −12.1%; P < 0.0001) and FPA‐VDI (−12.5%, 95% CI: −18.9%, −5.5%; P < 0.01). Pharmacokinetics demonstrated that testing coincided with the average t_max at 2.08 hours (SD 45 minutes). The main adverse event reported after administration of fampridine was dizziness (61%).

Conclusion

Fampridine improves saccadic eye movements due to INO in MS. Treatment response to fampridine may gauge patient selection for inclusion to remyelination strategies in MS using saccadic eye movements as primary outcome measure.

A standardized protocol for quantification of saccadic eye movements: DEMoNS

OBJECTIVE

Quantitative saccadic testing is a non-invasive method of evaluating the neural networks involved in the control of eye movements. The aim of this study is to provide a standardized and reproducible protocol for infrared oculography measurements of eye movements and analysis, which can be applied for various diseases in a multicenter setting.

METHODS

Development of a protocol to Demonstrate Eye Movement Networks with Saccades (DEMoNS) using infrared oculography. Automated analysis methods were used to calculate parameters describing the characteristics of the saccadic eye movements. The two measurements of the subjects were compared with descriptive and reproducibility statistics.

RESULTS

Infrared oculography measurements of all subjects were performed using the DEMoNS protocol and various saccadic parameters were calculated automatically from 28 subjects. Saccadic parameters such as: peak velocity, latency and saccade pair ratios showed excellent reproducibility (intra-class correlation coefficients > 0.9). Parameters describing performance of more complex tasks showed moderate to good reproducibility (intra-class correlation coefficients 0.63-0.78).

CONCLUSIONS

This study provides a standardized and transparent protocol for measuring and analyzing saccadic eye movements in a multicenter setting. The DEMoNS protocol details outcome measures for treatment trial which are of excellent reproducibility. The DEMoNS protocol can be applied to the study of saccadic eye movements in various neurodegenerative and motor diseases.

Diagnostic Efficacy of Conventional MRI Pulse Sequences in the Detection of Lesions Causing Internuclear Ophthalmoplegia in Multiple Sclerosis Patients

PURPOSE

The purpose of this study was to investigate the diagnostic efficacy of a range of conventional magnetic resonance imaging (MRI) pulse sequences in the identification of internuclear ophthalmoplegia (INO) caused by medial longitudinal fasciculus (MLF) lesions in multiple sclerosis patients using a receiver-operating characteristic (ROC) methodology.

METHODS

A total of 15 clinically confirmed INO and 15 control subjects underwent conventional MRI at 1.5 T consisting of T2-weighted, proton density (PD)-weighted, and fluid-attenuated inversion recovery (FLAIR) sequences, following full institutional approval. A free-response, multiple-reader multiple-case design ROC study was used to evaluate the diagnostic efficacy of each sequence. All imaging sequences were evaluated by 10 board-certified neuroradiologists. Area under the curve (AUC), sensitivity, and specificity were analysed statistically for all three pulse sequences using repeated-measures analyses of variance and post-test analysis using Bonferroni's multiple comparison test of differences.

RESULTS

No significant AUC differences were found between the three sequences (p = 0.0697), with T2 recording the highest AUC (0.8346). Sensitivity differences between PD (0.7927) and FLAIR (0.6329) were significant (p < 0.05). Non-significant differences were also evident between T2 and FLAIR (p = 0.0511). The specificity analysis revealed an overall difference (p = 0.0005), with specific inter-sequence differences shown between T2 and PD (p < 0.05) and PD and FLAIR (p < 0.001) with the PD values being lower than those provided with the other two sequences.

CONCLUSION

T2-weighted axial imaging through the MLF region resulted in the greatest overall diagnostic efficacy when viewing a combination of mean AUC, sensitivity, and specificity, in terms of the identification of INO-causing lesions.

Diagnosing disconjugate eye movements: phase-plane analysis of horizontal saccades

BACKGROUND

Saccades are fast eye movements that conjugately shift the point of fixation between distant features of interest in the visual environment. Several disorders, affecting sites from brainstem to extraocular muscle, may cause horizontal saccades to become disconjugate. Prior techniques for detection of saccadic disconjugacy, especially in internuclear ophthalmoparesis (INO), have compared only one point in abducting vs adducting saccades, such as peak velocity.

METHODS

We applied a phase-plane technique that compared each eye's velocity as a function of change in position (normalized displacement) in 22 patients with disease variously affecting the brainstem reticular formation, the abducens nucleus, the medial longitudinal fasciculus, the oculomotor nerve, the abducens nerve, the neuromuscular junction, or the extraocular muscles; 10 age-matched subjects served as controls.

RESULTS

We found three different patterns of disconjugacy throughout the course of horizontal saccades: early abnormal velocity disconjugacy during the first 10% of the displacement in patients with INO, oculomotor or abducens nerve palsy, and advanced extraocular muscle disease; late disconjugacy in patients with disease affecting the neuromuscular junction; and variable middle-course disconjugacy in patients with pontine lesions. When normal subjects made disconjugate saccades between two targets aligned on one eye, the initial part of the movement remained conjugate.

CONCLUSIONS

Along with conventional measures of saccades, such as peak velocity, phase planes provide a useful tool to determine the site, extent, and pathogenesis of disconjugacy. We hypothesize that the pale global extraocular muscle fibers, which drive the high-acceleration component of saccades, receive a neural command that ensures initial ocular conjugacy.

A new measure of dysconjugacy in INO: the first-pass amplitude

BACKGROUND

The ratios of abducting to adducting eye movements (versional dysconjugacy index, VDI) for saccadic velocity and acceleration have been useful measures by which to objectively characterize internuclear ophthalmoparesis (INO). Amplitude measures of dysconjugacy have been less useful, given that many patients maintain the ability to ultimately reach a centrifugal fixation target and that traditional amplitude measures of VDI have focused on this 'final amplitude' (FA) position.

METHODS

We utilized infrared oculography to define a new amplitude measure of dysconjugacy in 42 multiple sclerosis (MS) patients with INO. The first-pass amplitude (FPA)-VDI is the ratio of abduction/adduction eye movement amplitudes computed at the time when the abducting eye initially achieves the centrifugal horizontal fixation target.

RESULTS

FPA-VDI values were significantly more sensitive and specific than FA-VDI values in demonstrating dysconjugacy in INO, and there was a 14-fold increase in dysconjugacy as measured by FPA-VDI Z-scores when compared to FA-VDI Z-scores.

CONCLUSION

Consideration of velocity (pulse) and amplitude (step) components of dysconjugacy in patients with INO can provide a greater understanding of the dynamic aspects of this syndrome. We propose to characterize the relationship between the pathophysiology of INO and neuroradiologic measures of tissue injury in MS.

Quantitative oculographic characterisation of internuclear ophthalmoparesis in multiple sclerosis: the versional dysconjugacy index Z score

BACKGROUND

There is a poor correlation between multiple sclerosis disease activity, as measured by magnetic resonance imaging, and clinical disability.

OBJECTIVE

To establish oculographic criteria for the diagnosis and severity of internuclear ophthalmoparesis (INO), so that future studies can link the severity of ocular dysconjugacy with neuroradiological abnormalities within the dorsomedial brain stem tegmentum.

METHODS

The study involved 58 patients with multiple sclerosis and chronic INO and 40 normal subjects. Two dimensional infrared oculography was used to derive the versional dysconjugacy index (VDI)-the ratio of abducting to adducting eye movements for peak velocity and acceleration. Diagnostic criteria for the diagnosis and severity of INO were derived using a Z score and histogram analysis, which allowed comparisons of the VDI from multiple sclerosis patients and from a control population.

RESULTS

For a given saccade, the VDI was typically higher for acceleration v velocity, whereas the Z scores for velocity measures were always higher than values derived from comparable acceleration VDI measures; this was related to the greater variability of acceleration measures. Thus velocity was a more reliable measure from which to determine Z scores and thereby the criteria for INO and its level of severity. The mean (SD) value of the VDI velocity derived from 40 control subjects was 0.922 (0.072). The highest VDI for velocity from a normal control subject was 1.09, which was 2.33 SD above the normal control mean VDI. We therefore chose 2 SD beyond this value (that is, a Z score of 4.33) as the minimum criterion for the oculographic confirmation of INO. Of patients thought to have unilateral INO on clinical grounds, 70% (16/23) were found to have bilateral INO on oculographic assessment.

CONCLUSIONS

INO can be confirmed and characterised by level of severity using Z score analysis of quantitative oculography. Such assessments may be useful for linking the level of severity of a specific clinical disability with neuroradiological measures of brain tissue pathology in multiple sclerosis.

Multiple sclerosis: a cause of sudden hearing loss

Sudden hearing loss is a clinical entity which has numerous aetiologies. In cases where the aetiology is not determined, evaluation and treatment of sudden hearing loss are very difficult. A case of probable multiple sclerosis with sudden hearing loss as the initial symptom is reported. The pure-tone audiometry showed a quasi-total sensorineural hearing loss in the left ear; the left side displayed only wave I in the auditory brainstem response (ABR). Electronystagmographic examination revealed hypometric dysmetria and saccadic pursuit abnormalities. Magnetic resonance imaging (MRI) showed high-intensity lesions with multiple foci. After steroid therapy, the patient's hearing loss, vertigo and visual problems improved, but the ABR findings remained unchanged. We have decided to present this case because of the interesting ABR finding revealing the presence of wave I and the absence of all other waves after the normalization of the hearing.

Binocular saccadic eye movements in multiple sclerosis

We attempted to increase the sensitivity for detection of abnormal binocular saccadic eye movements, particularly of the internuclear ophthalmoplegia (INO) type associated with multiple sclerosis (MS). Saccades of 10 and 20 degrees were binocularly recorded with scleral sensor coils in 10 normal control subjects and 26 patients with definite or probable MS, seven of whom had a clinically manifest INO in one or both directions. In the cases in which this was accompanied by a dissociated nystagmus of the abducting eye, our recordings showed that such secondary saccades were also expressed, in a strongly reduced form, by the adducting eye. The patients with manifest INO showed lower average peak velocities and peak accelerations, especially for adduction of the eye on the affected side, but the distribution of these parameters overlapped with the normal distribution. A much sharper distinction between normals and patients with INOs was found by considering the ratios between peak accelerations and velocities of saccade pairs (abducting eye/adducting eye). These ratios, which eliminate much intra- and inter-individual variability, had a narrow range in normals, and all values for INOs were outside this range. On this basis, the 19 patients without clinically manifest INO were easily separated into subgroups of 14 patients with completely normal interocular ratios and five patients with elevated peak velocity and acceleration ratios, identified as sub-clinical (uni- or bilateral) INOs. Measurements of vertical saccades and of interocular timing differences provided no useful criteria for disturbances of binocular coordination in MS. We conclude that in particular, the acceleration of the adducting eye is strongly reduced in patients with an INO, and that this reduction is best identified by interocular comparison between binocular pairs of saccades.

Saccades in internuclear ophthalmoplegia: are abduction disorders related to interocular disconjugacy?

We studied horizontal saccades by direct-current electro-oculography in 18 patients with internuclear ophthalmoplegia (INO), and in 16 healthy, age-matched subjects. The occurrence of abducting signs, i.e. overshoot and dissociated nystagmus, was related to an increase of interocular dissociation (measured by the ratio of abduction and adduction peak velocities). The amplitude of abduction hypermetria was strongly correlated with the intensity of adduction slowing. These findings support the idea of an adaptive mechanism underlying the overshoot and nystagmus of abduction saccades in INO.