Disorders of saccades

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.

The frequency and characteristics of saccadic dysmetria in isolated cerebellar infarction

OBJECTIVES

To investigate the frequency and pattern of horizontal saccadic dysmetria in unilateral cerebellar infarction and identify the responsible region for horizontal saccadic dysmetria.

METHODS

From the acute stroke registry of Keimyung University Dongsan Medical Center between July 2016 and October 2020, 43 patients with acute unilateral cerebellar infarction were enrolled. Eye movements were recorded during the acute period and the lesion was mapped using MRIcron software for subtraction analysis. Saccadic dysmetria was marked as hypometric when the gain is < 0.85 and hypermetric when > 1.0.

RESULTS

Among the 43 participants, 30 patients (69.8%) demonstrated saccadic dysmetria. The age was significantly higher in patients with dysmetria (66.87 ± 12.82 vs. 53.54 ± 14.09, p = 0.004). Type of dysmetria showed a significant difference according to the vascular territory of the lesion. The posterior inferior cerebellar artery (PICA) infarction group presented ipsiversive saccadic dysmetria, while the superior cerebellar artery (SCA) group showed contraversive dysmetria (p < 0.001). In the SCA group, the culmen, fastigium, and dentate were the most frequently damaged regions, while the tonsil and inferior semilunar lobule were in the PICA group.

CONCLUSION

Saccadic dysmetria was observed in a large proportion of cerebellar stroke patients, and the types of saccades were distinctive according to the vascular territory of the lesion.

Vestibular function in children with generalized epilepsy and treated with valproate

BACKGROUND

Studies that evaluated vestibular function with epilepsy are fewer than auditory studies. We assessed vestibular function in children with epilepsy in inter-ictal period.

RESEARCH DESIGN AND METHODS

This cross-sectional study included 35 children with generalized epilepsy (boys=15; girls=20; mean age=11.20±1.21yrs; epilepsy duration=3.54±1.80yrs) and treated with valproate (VPA) and 24 healthy children as controls (mean age=12.42±2.80yrs). Vestibular evaluation was conducted using videonystagmography (VNG) and cervical vestibular evoked myogenic potentials (cVEMPs).

RESULTS

Dizziness was the vestibular symptom in 22.86% of cases. Vestibular dysfunctions (VDs) were found in 65.71%. Manifestations of peripheral VD (65.71%) included unilateral caloric weakness and reduced cVEMPs amplitudes. Manifestations of central VD (28.57%) included oculomotor abnormalities, positional nystagmus with normal calorics, and prolonged cVEMPs latencies. Significant correlations were found between VDs and duration of epilepsy and its treatment [r=-0.368, P=0.01] and VPA dose [r=-0.286, P=0.02] and level [r=-0.355, P=0.01]. Logistic regression analysis showed that duration of epilepsy and its treatment [OR=3.55 (95% CI=2.54-6.50), P=0.001] were independently associated with VDs.

CONCLUSIONS

VDs are common in children with epilepsy. Dizziness was a common symptom. Bilateral peripheral VD was more common than central VD, suggesting an adverse effect of VPA. However, epilepsy cannot be excluded as a cause of central VD.

[The use of the visuo-motor reaction training device for the improvement of the coordination in the eye-hand system of the children and adolescents following the completion of the antineoplastic treatment of brain tumours]

The survivors among the children and adolescents with a brain tumour are likely to show evidence of the impairment of the most important cognitive functions, such as attention, visual-motor integration, and working memory, following the completion of the antineoplastic treatment. The basic characteristics of these functions compromised in the patients presenting with the most serious cognitive deficiency are the information processing rate and the time needed for carrying out any cognitive activity in the patients experiencing deficit of white matter in the brain.

AIM

The objective of the present study was to demonstrate the possibility and the effectiveness of the application of the new method for the stimulation of the information processing activity of the brain, the enhancement of its effectiveness, and the improvement of the quality of the visual-motor coordination in the children and adolescents following the completion of the antineoplastic treatment of brain tumours. This paper reports the first experience of the application of the Dynavision d2 visuo-motor reaction training device which has been used for the visual-motor integration and the increase of the information processing speed.

MATERIAL AND METHODS

The sample included in the study was comprised of a total of 46 children at the mean age of 10.6±3.34 years that had undergone the treatment of the brain neoplasm. Each patient participated in 5 to 8 sessions of exercises with the use of the the Dynavision d2 visuo-motor reaction training device during 21 days.

RESULTS

All the treated patients exhibited the stable reduction of the mean time of the reaction from the first session to the last one. The comparison of the outcomes of the treatment between the children of different sexes has demonstrated better results (in absolute terms and in dynamics) in the girls in comparison with the boys. The exercises with the use of the Dynavision d2 visuo-motor reaction training device were not accompanied by any negative subjective sensations in the treated patients, nor did they induce the adverse somatic side effects.

CONCLUSION

The results of the present study give evidence of both the applicability and the effectiveness of the application of the Dynavision d2 visuo-motor reaction training device for the diagnostics of the disturbances in the motor and visual coordination and the associated cognitive functions and for their correction in the children following the treatment of the neoplasm of the posterior cranial fossa.

Oculomotor Function in Individuals With Rett Syndrome

BACKGROUND

Individuals with Rett syndrome (RTT) are notoriously reliant on the use of eye gaze as a primary means of communication. Underlying an ability to communicate successfully via eye gaze is a complex matrix of requirements, with an intact oculomotor system being just one element. To date, the underlying neural and motor pathways associated with eye gaze are relatively under-researched in RTT.

PURPOSE

This study was undertaken to plug this gap in knowledge and to further the understanding of RTT in one specific area of development and function, namely oculomotor function.

MATERIAL AND METHODS

The eye movements of 18 girls and young women with RTT were assessed by electronystagmography (ENG). This tested their horizontal saccadic and smooth pursuit eye movements as well as optokinetic nystagmus and vestibulo-ocular reflex. Their results were compared with normative data collected from 16 typically developing children and teenagers.

RESULTS

Overall, the individuals with RTT demonstrated a range of eye movements on a par with their typically developing peers. However, there were a number of difficulties in executing the ENG testing with the RTT cohort which made quantitative analysis tricky, such as reduced motivation and attention to test materials and low-quality electrode signals.

CONCLUSIONS

This study suggests that individuals with RTT have an intact oculomotor system. However, modifications should be made to the ENG assessment procedure to combat problems in testing and add strength to the results. Further investigation into these testing difficulties is warranted in order to inform such modifications.

The Area under the Main Sequence as an Alternative Method to Measure Saccadic Dynamics

SIGNIFICANCE

This study shows that the area under the main sequence (MSAREA) is a valid alternative to the standard peak-velocity main sequence in measuring saccadic dynamics. A one-parameter area model, MSAREA = GPW = 1.55 × SACSIZE, with SACSIZE as the size of the saccade, 1.55 as a power factor, and GPW = 1.55 as a gain parameter, is presented.

PURPOSE

SACPEAK = Vmax × (1 - e) is the traditional model used to describe the saccadic main sequence, the relationship between the size of the movement and its peak velocity (SACPEAK). In the previous article, we have shown that there is a strong linear correlation between the two parameters Vmax and SAT, which severely affects the model's clinical applicability. The purpose of this study is to see if, by using the MSAREA as an alternative approach, we can overcome the limitations of the traditional model.

METHODS

Participants and main sequence data are the same as the previous study. A trapezoidal integration was used to estimate the MSAREAs as a function of SACSIZE.

RESULTS

A two-parameter area model was computed to determine the range of variability of its parameters and R values. These were then used as reference values in the search for one-parameter alternatives. The one-parameter model MSAREA = GPW = 1.55 × SACSIZE performed well for all data sets. We tested its validity by performing a comparison with other one-parameter area models.

CONCLUSIONS

Area models are superior to peak-velocity models in terms of R and stability and can be reduced to robust one-parameter expressions with only limited degradation in R. This not only greatly simplifies the determination if a set is inside or outside a reference population but also allows for direct comparisons between sets, with the saccadic dynamics expressed by a simple linear gain factor (GPW = 1.55).

The Relationship between Saccades and Locomotion

Human locomotion involves a complex interplay among multiple brain regions and depends on constant feedback from the visual system. We summarize here the current understanding of the relationship among fixations, saccades, and gait as observed in studies sampling eye movements during locomotion, through a review of the literature and a synthesis of the relevant knowledge on the topic. A significant overlap in locomotor and saccadic neural circuitry exists that may support this relationship. Several animal studies have identified potential integration nodes between these overlapping circuitries. Behavioral studies that explored the relationship of saccadic and gait-related impairments in normal conditions and in various disease states are also discussed. Eye movements and locomotion share many underlying neural circuits, and further studies can leverage this interplay for diagnostic and therapeutic purposes.

Vestibular Function in Adults With Epilepsy of Unknown Etiology

OBJECTIVE

This study aimed to evaluate vestibular function in adults with chronic epilepsy of unknown etiology in the inter-ictal period.

BACKGROUND

Epilepsy is a chronic medical disorder. Life-long therapy may be required in one-third of patients. Epilepsy is associated with comorbid somatic conditions which impairs patients' quality of life.

METHODS

This cross-sectional study included 28 with generalized tonic clonic (GTC) convulsions and 14 and 3 with temporal (TLE) and frontal lobe (FLE) epilepsies with secondary generalization (all were on regular carbamazepine therapy) and 40 healthy control subjects. The patients' mean age was 34.97 ± 7.35 years and the duration of illness was 18.75 ± 7.99 years. All underwent videonystagmography (VNG).

RESULTS

Compared with controls, patients had frequent vestibular symptoms including dizziness (62.22%) (p = 0.0001) and sense of imbalance (44.44%) (p = 0.0001). Eleven patients (24.44%) had central vestibular dysfunction (p = 0.0001); 9 (20%) had mixed vestibular dysfunction and one (2.22%) had peripheral vestibular dysfunction (p = 0.0001). Abnormalities were observed in saccadic (44.4%) and pursuit (42.2%) eye movements, optokinetic nystagmus (42.2%) and positioning/positional (11.11%) and caloric (13.33%) testing. TLE and FLE were associated with more VNG abnormalities than GTC. No significant differences were observed in the demographic and clinical characteristics between patients with and without VNG abnormalities.

CONCLUSION

Vestibular manifestations are frequent in patients with epilepsy. This may be a result of the permanent damaging effect of chronic epilepsy on the vestibular cortical areas and/or a toxic effect from prolonged carbamazepine therapy on the peripheral and central vestibular systems.

SacLab: A toolbox for saccade analysis to increase usability of eye tracking systems in clinical ophthalmology practice

PURPOSE

Many open source software packages have been recently developed to expand the usability of eye tracking systems to study oculomotor behavior, but none of these is specifically designed to encompass all the main functions required for creating eye tracking tests and for providing the automatic analysis of saccadic eye movements. The aim of this study is to introduce SacLab, an intuitive, freely-available MATLAB toolbox based on Graphical User Interfaces (GUIs) that we have developed to increase the usability of the ViewPoint EyeTracker (Arrington Research, Scottsdale, AZ, USA) in clinical ophthalmology practice.

METHODS

SacLab consists of four processing modules that enable the user to easily create visual stimuli tests (Test Designer), record saccadic eye movements (Data Recorder), analyze the recorded data to automatically extract saccadic parameters of clinical interest (Data Analyzer) and provide an aggregate analysis from multiple eye movements recordings (Saccade Analyzer), without requiring any programming effort by the user.

RESULTS

A demo application of SacLab to carry out eye tracking tests for the analysis of horizontal saccades was reported. We tested the usability of SacLab toolbox with three ophthalmologists who had no programming experience; the ophthalmologists were briefly trained in the use of SacLab GUIs and were asked to perform the demo application. The toolbox gained an enthusiastic feedback from all the clinicians in terms of intuitiveness, ease of use and flexibility. Test creation and data processing were accomplished in 52±21s and 46±19s, respectively, using the SacLab GUIs.

CONCLUSIONS

SacLab may represent a useful tool to ease the application of the ViewPoint EyeTracker system in clinical routine in ophthalmology.

Diffusion tensor imaging correlates of saccadic reaction time in children with fetal alcohol spectrum disorder

BACKGROUND

Eye movement tasks provide a simple method for inferring structural or functional brain deficits in neurodevelopmental disorders. Oculomotor control is impaired in children with fetal alcohol spectrum disorder (FASD), yet the neuroanatomical substrates underlying this are not known. Regions of white matter have been shown by diffusion tensor imaging (DTI) to be different in FASD and thus may play a role in the delayed saccadic eye movements. The objective of this study was to correlate oculomotor performance with regional measures of DTI-derived white matter anisotropy in children with FASD.

METHODS

Fourteen children (8 to 13 years) with FASD were recruited for oculomotor assessment and DTI. Eye movement control was evaluated using the pro- and antisaccade tasks, in which subjects look at (prosaccade) or away from (antisaccade) a peripheral target. Saccadic reaction time (SRT; time for subjects to move their eyes after the target appears) and direction errors (saccades made in the incorrect direction relative to the instruction) were measured and correlated to fractional anisotropy (FA) on a voxel-by-voxel basis across the whole brain white matter.

RESULTS

A significant positive correlation was observed between antisaccade SRT and FA in a large cluster containing anterior and posterior sections of the corpus callosum just to the right of the midline; prosaccade SRT and FA correlated positively in the genu of the corpus callosum and the right inferior longitudinal fasciculus (ILF), and correlated negatively in the left cerebellum.

CONCLUSIONS

The negative correlation for prosaccade SRT and cerebellum demonstrated that individuals with slower reaction times had lower FA values relative to their faster responding counterparts, a finding that implicates cerebellar dysfunction as a significant contributor to deficits in oculomotor control. The higher FA in the corpus callosum and ILF corresponding to longer reaction times for both pro- and antisaccade was opposite to what was expected, but nonetheless implies that altered brain structure in these regions underlies deficits in oculomotor control.

Saccadic eye movement applications for psychiatric disorders

OBJECTIVE

The study presented here analyzed the patterns of relationship between oculomotor performance and psychopathology, focusing on depression, bipolar disorder, schizophrenia, attention-deficit hyperactivity disorder, and anxiety disorder.

METHODS

Scientific articles published from 1967 to 2013 in the PubMed/Medline, ISI Web of Knowledge, Cochrane, and SciELO databases were reviewed.

RESULTS

Saccadic eye movement appears to be heavily involved in psychiatric diseases covered in this review via a direct mechanism. The changes seen in the execution of eye movement tasks in patients with psychopathologies of various studies confirm that eye movement is associated with the cognitive and motor system.

CONCLUSION

Saccadic eye movement changes appear to be heavily involved in the psychiatric disorders covered in this review and may be considered a possible marker of some disorders. The few existing studies that approach the topic demonstrate a need to improve the experimental paradigms, as well as the methods of analysis. Most of them report behavioral variables (latency/reaction time), though electrophysiological measures are absent.