Visual Stress is the term used to describe any form of visual discomfort and perceptual distortion that is not explained by a refractive errror.

Also sometimes called Meares-Irlen syndrome, scotopic sensitivity syndrome or just ‘Irlens’ the condition is linked to hyper-excitability in the brains visual cortex.

Potential Problems

It is not a particularly unusual condition and it affects more than 20% of the population in various ways. Sometimes it can manifest as a visual problem linked to various other conditions such as Migraine, photophobia, recovery from a stroke or Charles Bonnet Syndrome but it is most common in school age patients where it commonly causes discomfort and distortion or movement of text that makes reading extremely difficult. It can exist both alongside and independently of Dyslexia and whilst the use of colour has been found to significantly reduce symptoms in all of the conditions mentioned above it cannot be said to cure them.  It helps alleviate the symptoms and can hugely impact on quality of life. There is not just one colour that works for everyone, indeed some people report that a particular colour makes their symptoms much worse so it is important to do a proper assessment to establish the right colour for an individual.


The first step of the Assessment would be to do a full eye examination is the first step in the Colorimetry assessment journey.  This is free when under 16 & when up to and including 18 whilst in full time education. Adults may be covered through the NHS or may have to pay privately. We always start with an eye examination to rule out any refractive error that might explain the symptoms. Visual Stress cannot be corrected by prescription lenses and it can occur in people with 20/20 vision so if we found a refractive error we would want to be sure that this was not what was causing problems before moving on to assessing for colour.  We follow this with a visual stress assessment which is free to everyone.

The Results

If we identify visual stress we would suggest an appointment for an Overlay assessment to establish is colour is effective in reducing symptoms. If reading is the main problem we can run a Rate of Reading test which will give us a measure of improvement in reading accuracy and speed which is useful with younger sufferers. Colour can also improve comprehension and retention, people often report that without their colour they have to read and re read a passage to make sense of it. If a simple colour is useful we can offer overlays, clipons and screen tinters for computer work.


If we feel that we can improve further by using a bespoke or precision tint then we would use our Colorimeter to run an assessment to establish the exact colour and saturation of colour that helps best. The colour prescribed in this way would be dispensed as tinted lenses in a pair of glasses, either with or without prescription. The NHS will only fund the basic cost of a frame and lenses if there is also a refractive error. Otherwise unfortunately there is no NHS funding towards spectacles or overlays with both the cost of assessments and overlays/ lenses being paid for privately (although Higher education students can access help with funding through a DSA from student finance).

If you feel you or a relative would benefit from these assessments then please speak to our Dispensing Optician partner Cathy Rogers who will advise you individually on the best way forward.