Problems with vision are relatively common among people with ME/CFS, the majority of whom report symptoms such as hypersensitivity to light, difficulties focusing, and dry eyes.

But despite their significant impact on quality of life, there is still a lack of scientific research into these symptoms, and they are not included in any clinical and diagnostic guidelines for ME/CFS.

Fortunately, scientists such as Dr Claire Hutchinson of the University of Leicester have recognised that this is an area worthy of study. Supported in part by grants from ME Research UK, Dr Hutchinson and her group have looked at a number of vision-related problems in ME/CFS.

Applying sophisticated eye-tracking techniques, they showed that patients have difficulties focusing on an object while ignoring irrelevant information, are slower than normal in shifting attention between objects, are slower and less accurate in their eye movements, and are vulnerable to pattern-related visual stress.

Furthermore, the group found that around 90% of ME/CFS patients reported a degree of eye pain and sensitivity to bright lights at least some of the time.

Also helping to fill this gap in our knowledge is a group from Antwerp in Belgium, which has recently published an interesting study on binocular vision in the American Orthoptic Journal.

The investigators carried out full orthoptic examinations on 41 patients fulfilling the CDC criteria for CFS and 41 healthy individuals matched for age and gender.

A series of tests looked at how the eye adjusts to keep focus on an object as it moves closer or further away, an adjustment that requires both vergence and accommodation.

Vergence is the simultaneous movement of the pupils of both eyes, either inwards (convergence) or outwards (divergence), while accommodation is the ability of the eye to change its focal length to maintain a clear image.

Compared with the control group, the patients in this study showed reductions in convergence, divergence and accommodation amplitude; i.e. all three factors necessary for smooth focusing.

This ties in neatly with Dr Hutchinson’s findings of difficulties in focusing, and also means, say the authors, that these factors should be routinely assessed in patients with CFS, who may also benefit from reading glasses at an earlier stage.

(Interestingly, an article in the Washington Post from 2010 suggests that convergence problems may affect one’s ability to watch 3D movies, because the special glasses require healthy convergence.)

Exercises to improve convergence may help some people, but they can be very tiring, and the investigators emphasise that there is not yet any evidence of how effective they might be in ME/CFS.