An objective measure of fatigue - saccades?

[Marco]

No need to repeat that 'fatigue' can be hard to describe and even harder to demonstrate objectively.

A new blog on health rising suggests that deterioration in rapid eye movements (aka saccades where both eyes move rapidly to scan or fixate on a target) may objectively demonstrate increasing fatigue in healthy controls and a range of conditions (including breast cancer survivors) :

https://www.healthrising.org/blog/2018/02/20/objective-fatigue-measure-chronic-fatigue-fibromyalgia/

Interestingly a ME/CFS specific study found some impairment in saccades but marked impairment in tracking a smoothly moving target (smooth pursuit) :

http://irep.ntu.ac.uk/id/eprint/25859/1/221920_3205preprint.pdf

It would be good if we could piggyback on fatigue research in other areas.

 

[Trish]

This is one of the papers linked in Cort Johnson's article.

https://www.ncbi.nlm.nih.gov/pubmed/28619425

Using endogenous saccades to characterize fatigue in multiple sclerosis. Ferreira et al. May 2017.
Abstract
PURPOSE:
Multiple Sclerosis (MS) is likely to cause dysfunction of neural circuits between brain regions increasing brain working load or a subjective overestimation of such working load leading to fatigue symptoms. The aim of this study was to investigate if saccades can reveal the effect of fatigue in patients with MS.

METHODS:
Patients diagnosed with MS (EDSS<=3) and age matched controls were recruited. Eye movements were monitored using an infrared eyetracker. Each participant performed 40 trials in an endogenous generated saccade paradigm (valid and invalid trials). The fatigue severity scale (FSS) was used to assess the severity of fatigue. FSS scores were used to define two subgroups, the MS fatigue group (score above normal range) and the MS non-fatigue. Differences between groups were tested using linear mixed models.

RESULTS:
Thirty-one MS patients and equal number of controls participated in this study. FSS scores were above the normal range in 11 patients. Differences in saccade latency were found according to group (p<0.001) and trial validity (p=0.023). Differences were 16.9ms, between MS fatigue and MS non-fatigue, 15.5ms between MS fatigue and control. The mean difference between valid and invalid trials was 7.5ms. Differences in saccade peak velocity were found according to group (p<0.001), the difference between MS fatigue and control was 22.3°/s and between MS fatigue and non-fatigue was 12.3°/s. Group was a statistically significant predictor for amplitude (p<0.001). FSS scores were correlated with peak velocity (p=0.028) and amplitude (p=0.019).

CONCLUSION:
Consistent with the initial hypothesis, our study revealed altered saccade latency, peak velocity and amplitude in patients with fatigue symptoms. Eye movement testing can complement the standard inventories when investigating fatigue because they do not share similar limitations. Our findings contribute to the understanding of functional changes induced by MS and might be useful for clinical trials and treatment decisions.

 

[Trish]

And this is another one on healthy people:
https://www.ncbi.nlm.nih.gov/pubmed/24466334

Eye movements discriminate fatigue due to chronotypical factors and time spent on task--a double dissociation.
by Cazzoli, 2014

Abstract
Systematic differences in circadian rhythmicity are thought to be a substantial factor determining inter-individual differences in fatigue and cognitive performance. The synchronicity effect (when time of testing coincides with the respective circadian peak period) seems to play an important role.

Eye movements have been shown to be a reliable indicator of fatigue due to sleep deprivation or time spent on cognitive tasks. However, eye movements have not been used so far to investigate the circadian synchronicity effect and the resulting differences in fatigue.

The aim of the present study was to assess how different oculomotor parameters in a free visual exploration task are influenced by:
a) fatigue due to chronotypical factors (being a 'morning type' or an 'evening type');
b) fatigue due to the time spent on task.

Eighteen healthy participants performed a free visual exploration task of naturalistic pictures while their eye movements were recorded. The task was performed twice, once at their optimal and once at their non-optimal time of the day. Moreover, participants rated their subjective fatigue.

The non-optimal time of the day triggered a significant and stable increase in the mean visual fixation duration during the free visual exploration task for both chronotypes. The increase in the mean visual fixation duration correlated with the difference in subjectively perceived fatigue at optimal and non-optimal times of the day.

Conversely, the mean saccadic speed significantly and progressively decreased throughout the duration of the task, but was not influenced by the optimal or non-optimal time of the day for both chronotypes.

The results suggest that different oculomotor parameters are discriminative for fatigue due to different sources. A decrease in saccadic speed seems to reflect fatigue due to time spent on task, whereas an increase in mean fixation duration a lack of synchronicity between chronotype and time of the day.

 

[Trish]

And here's the one @Marco linked on ME/CFS patients:

http://irep.ntu.ac.uk/id/eprint/25859/1/221920_3205preprint.pdf

Characterising eye movement dysfunction in Myalgic Encephalomyelitis/Chronic Fatigue Syndrome by Stephen P. Badham and Claire V. Hutchinson, University of Leicester, UK.

Abstract

Background

People who suffer from Myalgic Encephalomyelitis/Chronic Fatigue Syndrome (ME/CFS) often report that their eye movements are sluggish and that they have difficulties tracking moving objects. However, descriptions of these visual problems are based solely on patients’ self-reports of their subjective visual experiences and there is a distinct lack of empirical evidence to objectively verify their claims.

This paper presents the first experimental research to objectively examine eye movements in those suffering from ME/CFS.

Methods
Patients were assessed for ME/CFS symptoms and were compared to age, gender and education matched controls for their ability to generate saccades and smooth pursuit eye movements.

Results
Patients and controls exhibited similar error rates and saccade latencies (response times) on prosaccade and antisaccade tasks. Patients showed relatively intact ability to accurately fixate the target (prosaccades) but were impaired when required to focus accurately in a specific position opposite the target (antisaccades). Patients were most markedly impaired when required to direct their gaze as closely as possible to a smoothly moving target (smooth pursuit).

Conclusions
It is hypothesised that the effects of ME/CFS can be overcome briefly for completion of saccades, but that continuous pursuit activity (accurately tracking a moving object) even for a short time period highlights dysfunctional eye movement behaviour in ME/CFS patients. Future smooth pursuit research may elucidate and improve diagnosis of ME/CFS.

 

[Amw66]

Dr Bansal checks for this : i think it is mentioned on his liME Stockholm video.