Effects of edrophonium on saccadic velocity in normal subjects and myasthenic and nonmyasthenic ocular palsies

Quantification of saccadic fatigability and diagnostic efficacy for myasthenia gravis

BACKGROUND AND OBJECTIVES

The diagnostic challenge of myasthenia gravis (MG) is exacerbated by the variable efficacy of current testing methodologies, necessitating innovative approaches to accurately identify the condition. This study aimed to assess ocular muscle fatigue in patients with MG using video-oculography (VOG) by examining repetitive saccadic eye movements and comparing these metrics to those of healthy control participants.

METHODS

This prospective, cross-sectional study was conducted at a tertiary care center and involved 62 patients diagnosed with MG (48 with ocular MG and 14 with generalized MG) and a control group of 31 healthy individuals, matched for age and sex. The assessment involved recording saccadic eye movements within a ± 15° range, both horizontally and vertically, at a rate of 15 saccades per minute over a 5-min period, resulting in 75 cycles. Participants were afforded a 3-min rest interval between each set to mitigate cumulative fatigue. The primary outcome was the detection of oculomotor fatigue, assessed through changes in saccadic waveforms, range, peak velocity, latency, and the duration from onset to target, with a focus on comparing the second saccade against the average of the last five saccades.

RESULTS

In the evaluation of repetitive saccadic movements, patients with MG exhibited a reduced saccadic range and a prolonged duration to reach the target, compared to healthy subjects. Furthermore, a significant elevation in the frequency of multistep saccades was observed among MG patients, with a marked rise observed over consecutive trials. Receiver operating characteristic (ROC) analysis revealed the discriminative performance of multistep saccade frequency, in conjunction with variations in saccadic range and duration from onset to target achievement between the second saccade and the mean of the final five saccades, as effective in distinguishing MG patients from healthy subjects. Although alterations in peak saccadic velocity and latency were less pronounced, they were nevertheless detectable.

DISCUSSION

The utilization of VOG for repetitive saccadic testing in the diagnosis of MG has demonstrated considerable diagnostic precision. This methodology affords significant accuracy in evaluating ocular muscle fatigue in MG patients, providing class III evidence supportive of its clinical application.

Tracking Eye Movements for Diagnosis in Myasthenia Gravis: A Comprehensive Review

BACKGROUND

Around 60%--75% of myasthenia gravis (MG) patients initially present with nonspecific ocular symptoms. Failed recognition of these symptoms may delay the diagnosis of MG up to 5 years or more, leading to a reduced likelihood of remission and increased morbidity. Current diagnostic tests are either poorly sensitive for patients presenting with ocular symptoms alone or are time consuming, invasive, require a high level of technical expertise, and generally are universally difficult to obtain. This review will explore quantitative eye and pupil tracking as a potential noninvasive, time-effective, and less technically demanding alternative to current diagnostic tests of MG.

EVIDENCE ACQUISITION

Comprehensive literature review.

RESULTS

Thirty-two publications using oculography for the diagnosis of MG and 6 studies using pupillometry were evaluated. In MG patients, extra ocular muscle fatigue was evident in reports of intersaccadic, intrasaccadic and postsaccadic abnormalities, changes in optokinetic nystagmus, slow eye movements, disconjugate saccades, and pupillary constrictor muscle weakness.

CONCLUSIONS

Our review identified several potentially useful variables that derive from oculography and pupillometry studies that could assist with a timely diagnosis of MG. Limitations of this review include heterogeneity in design, sample size, and quality of the studies evaluated. There is a need for larger, well-designed studies evaluating eye-tracking measures in the diagnosis of MG, especially for patients presenting with purely ocular symptoms.

Preserved eye movements in adults with spinal muscular atrophy

INTRODUCTION

Spinal muscular atrophy (SMA) most prominently affects proximal limb and bulbar muscles. Despite older case descriptions, ocular motor neuron palsies or other oculomotor abnormalities are not considered part of the phenotype.

METHODS

We investigated oculomotor function by testing saccadic eye movements of 15 patients with SMA. Their performance was compared with that of age-matched healthy controls. Horizontal rightward and leftward saccades were recorded by means of video-oculography, whereas subjects looked at light-emitting diode targets placed at ±5°, ±10°, and ±15° eccentricities.

RESULTS

No differences in saccade amplitude gains, peak velocities, peak velocity-to-amplitude ratios, or durations were observed between controls and patients. More specifically, for 5° target eccentricities, patients had a mean saccadic peak velocity of 153°/s, whereas for 10° and 15° these values were 268°/s and 298°/s, respectively. The corresponding mean peak velocities of the control group were 151°/s, 264°/s, and 291°/s.

DISCUSSION

Our results indicate that patients with SMA perform fast and accurate horizontal saccades without evidence of extraocular muscle weakness. These quantitative oculomotor data corroborate clinical experience that neuro-ophthalmic symptoms in SMA are not common and, if present, should prompt suspicion for an alternative neuromuscular disorder.

Extraocular muscle function in adult-onset Pompe disease tested by saccadic eye movements

Glycogen storage disease type II (Pompe disease) affects mainly proximal skeletal muscles. Despite older histological evidence of extraocular muscle involvement, ocular motor palsies or other eye movement abnormalities are not considered part of the clinical picture. We investigated the dynamics of saccadic eye movements of five patients suffering from late-onset Pompe disease and compared their performance to that of age matched healthy controls. Horizontal rightward and leftward saccades were recorded binocularly, while subjects looked at LED targets placed at ±5°, 10° and 15° eccentricities. No differences in saccade amplitudes, peak velocities or durations were observed between controls and patients. More specifically, for 5° saccades, patients had a mean peak velocity of 146°/s with duration of 76ms. For 10° and 15° saccades these values were 258°/s, 86ms and 324°/s, 101ms respectively, thereby lying well within one standard deviation of the mean of normal data. Moreover, saccadic amplitude accuracy was also unimpaired. These results indicate that patients with late onset Pompe disease perform fast and accurate horizontal saccades without evidence of muscle paresis or other ocular motor abnormalities. Reported histological abnormalities of extraocular muscles do not appear to have a phenotypic impact.

The man who could not see what he could not eat

A 55-year-old Hispanic man born in New Mexico presented with progressively worsening bilateral upper eyelid ptosis and dysphagia. External levator advancement 5 years before did not improve his ptosis. A thorough systemic workup for myasthenia gravis was negative, but electromyography suggested a myopathic process. Molecular genetic testing was positive for oculopharyngeal muscular dystrophy.

My, what asthenia you have

A 59-year-old woman noted intermittent ptosis, diplopia, dysphagia, and proximal muscle weakness for several years. She had a strong family history of myasthenia gravis. Chest computed tomography and sternotomy revealed a micronodular spindle cell thymoma. Electromyography and antibody testing was negative for myasthenia gravis. Genetic testing confirmed a diagnosis of oculopharyngeal muscular dystrophy.

Recovery of Peripheral Versus Central Nerves Identified by Saccadic Velocity After Abducens Neuropathy

The abducens is the motor nerve with the most substantial course, both within and outside the brain and it innervates only one muscle. Sixth nerve palsy affords an opportunity to compare recovery after central versus peripheral nerve damage by assessing the dynamics of abduction. Horizontal saccade peak velocities and durations in 14 patients with unilateral peripheral sixth nerve palsies (5 acute, 9 chronic) are compared with those in 5 patients with central sixth nerve palsies (2 acute, 3 chronic) and with those in 10 normal subjects. Acutely, abducting saccades in the paretic eye were slow in both central and peripheral palsies, as anticipated from weakness of the lateral rectus muscle. In chronic central palsies, abducting saccadic velocities remained reduced, but in chronic peripheral palsies, they increased to normal within the limited range of excursion. The chronically damaged peripheral nerve behaves like a high-pass filter in transmitting phasic velocity commands, whereas tonic position commands remain defective, accounting for limited abduction but normal velocities within the range of duction. In chronic central (fascicular) palsies, saccade velocities remain reduced. Impaired conduction from damage to central myelin or axons is more persistent in central palsies, consistent with limited regeneration within the brain. Recording of saccade velocities may aid the distinction of fascicular from peripheral palsies. Saccade speed is repaired in peripheral palsies, probably by remyelination, and perhaps also by central monocular adaptation of innervation selectively to the paretic eye in order to drive both eyes rapidly and simultaneously to a target in the paretic field of motion.

Open-loop and closed-loop optokinetic nystagmus (OKN) in myasthenia gravis and nonmyasthenic subjects

Optokinetic nystagmus (OKN) eye movements of myasthenia gravis (MG) and nonmyasthenic ocular palsies, and normal subjects were examined under closed-loop and open-loop conditions. The open-loop OKN condition was achieved by adding the signal of eye-movement velocity of OKN to the computer-generated signal controlling the stimulus grating moving. The OKN was recorded by means of electromagnetic search scleral coil technique. In MG patients, the open-loop gains of OKN increased significantly after the intramuscular injection of an acetylcholinesterase inhibitor, neostigmine, while the closed-loop OKN gains were not significantly changed. Both the closed-loop and open-loop OKN gains of normal subjects and nonmyasthenic patients were not increased for the administration of neostigmine. The experimental results indicated that the open-loop OKN gain could be sensitive to reflect the changes of the function of neuromuscular junction in MG patients.

Quantitative ocular tests for myasthenia gravis: a comparative review with detection theory analysis

Many reports in the literature describe a variety of ocular signs in myasthenia gravis. To determine the utility of laboratory recordings of ocular signs in the evaluation for myasthenia, we reviewed all previous studies of quantitative measures of eye movements or intra-ocular pressures. We selected those studies with data presented for both myasthenic and non-myasthenic ocular palsies. Signal detection theory was used to evaluate the discriminative power of each variable. The characteristics of saccades and quick phases of optokinetic nystagmus at the start of recording were poor at distinguishing between myasthenic and non-myasthenic palsies, except when the comparison was solely between myasthenia and chronic progressive external ophthalmoplegia. The effects of fatigue on saccadic parameters were also not discriminative, though there was insufficient data to evaluate this adequately. Changes induced by edrophonium in the amplitude or peak velocity of saccades or optokinetic quick phases were good diagnostic tests, retaining high sensitivities when criteria were set to yield a specificity of 95%. Most of these parameters were less efficient as screening tests, with modest specificities when criteria were set to yield a sensitivity of 95%. The change in optokinetic quick phase amplitude recorded by infrared oculography was the best test, with ideal characteristics of 97% specificity and sensitivity at a criterion of zero change. This analysis suggests that eye movement recordings of saccades or optokinetic nystagmus have potential as useful and inexpensive tests for myasthenia, and warrant further study.