Vision in ME/CFS
While the defining symptoms of ME/CFS are fatigue, pain, post-exertional malaise and unrefreshing sleep, sufferers also experience many other lesser-publicised symptoms such as problems with vision. These can have an impact on many aspects of daily life.
People living with ME/CFS often speak of an aversion to bright lights or even normal daylight. Such symptoms may fall under the umbrella term of ‘sensory overload’, and explain why many sufferers do not go outside when the sun is high, or avoid areas with high visual stimulus such as town centres, and shops with bright lights or loud noises.
In an ME Research UK-funded project, Dr Claire Hutchinson and colleagues at the University of Leicester found objective evidence of vision-related reading difficulty in a cohort of ME/CFS patients. The patients had a slower reading speed than healthy control subjects, and were less able to focus on a target while ignoring other information (see the diagram below).
The work led to a publication in Frontiers in Psychology in 2018 that has been viewed more than 10,000 times.
The findings also built on the group’s other research reporting eye pain and sensitivity to bright lights, and their studies showing that ME/CFS patients struggle to focus on one object while ignoring irrelevant information, are slow in shifting attention between objects, are slower than normal and less accurate in their eye movements, and are vulnerable to pattern-related visual stress.
The researchers could not say what was the primary cause of the differences between ME/CFS patients and healthy controls, but sensitivity to bright lights and slowed attention and eye movements suggest potential inflammatory processes affecting the neural network.
Vision in COVID-19
More recently, a Brazilian study found detectable vision deficits in around a quarter of people following mild COVID-19 infection. These symptoms were possibly associated with changes in the results of molecular and structural brain imaging.
In addition, eleven immune biomarkers were upregulated in patients with vision complaints, showing the extent of the immune response post-COVID. The authors say that their study provides evidence of a neuroinflammatory burden causing cognitive deficits.
Understanding why some patients overcome COVID relatively unharmed, while others experience neurobiological changes, will be key future research in this area.
What does this mean for ME/CFS?
We know that viruses such as Epstein-Barr virus are implicated as a potential trigger for ME/CFS. Viruses can invade the central nervous system and induce an inflammatory response as the immune system attempts to fight off the virus or keep it under control.
It is likely that the aversion to bright lights, visual complaints and brain fog experienced by people living with ME/CFS result from low-grade inflammation of the brain, which may alter the biochemistry of the brain and disrupt normal neural processing.
The identification of this phenomenon in COVID patients may well help explain some of the symptoms reported by ME/CFS patients.
The emergence of vision and cognitive deficits following COVID-19 infection suggests a common pathway that might be triggered by viral infections, and the central feature of this is neurological inflammation, which therefore requires more attention.
COVID-19 has received substantial funding from the UK Government and is high up the research agenda worldwide. As researchers begin to unpick the biological mechanisms that reflect post-COVID symptoms, this is also likely to benefit people living with ME/CFS.
Not only will doctors gain a better understanding of the types of symptoms ME/CFS patients experience, there is a greater chance for the development of potential treatments that could be used in the treatment of both COVID-19 and ME/CFS.