Badham SP, Hutchinson CV
College of Medicine, Biological Sciences and Psychology, University of Leicester, Leicester, UK
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.
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.
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).
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.
This research was funded by ME Research UK and the Irish ME Trust. We are extremely grateful to all our participants, especially those suffering from ME/CFS, for taking part in the study. We thank Professor Leonard Jason, DePaul University, Chicago for kindly providing us with the DePaul Symptom Questionnaire (DSQ).
Comment by ME Research UK
Problems with eyes and vision are common in people with ME/CFS – yet there is very little formal evidence in the scientific literature that visual symptoms actually exist. This group published the first scientific paper on its findings several months ago, and this second report has now appeared, specifically on eye movements. The experiments measured cognitive speed, and eye movement tracking during ‘smooth pursuit’ of a slowly moving object and during reflexive (prosaccade) and inhibitory (antisaccade) movements to visual targets on screen.
Although the ME/CFS patients and matched controls (20 in each group) were similar in many respects, patients generally performed worse than controls in tasks that required quick and accurate eye movements. In particular, the ability to perform eye movements opposite a target (antisaccades) was more impaired in ME/CFS patients than controls, particularly for positional errors. In addition, patients were deficient in their ability to track closely a moving target during ‘smooth pursuit’, and their performance deteriorated as the testing session went on, something not seen in the healthy people. As the authors point out, it may be that patients are susceptible to fatigue even at these very short timescales – the ‘smooth pursuit’ requires sustained musculature activity for 30 seconds, and the 3 test-runs take only 5–10 minutes.
Intriguingly, the visual deficits seemed to be related to age in the ME/CFS patients but not in the healthy people, suggesting that older adults with the illness are less able than young adults to compensate for ME/CFS-related vision deficits. In fact, the overall disease impact may be proportionately greater in older ME/CFS patients, as a recent ME Research UK-funded report has also suggested.