Visual Stress is said to affect 20% of the population – 13 million people in UK. It is not the same as dyslexia but it affects about 40% of dyslexics.
Visual Stress is a visual processing disorder due to sensitivity to light and a believed hyper- excitability of visual brain.
- Print blurs or goes out of focus
- Letters move, shimmer or shake
- Patterns like ‘rivers’ or ‘worms’ appearing when reading black on white text
- Glare from page or VDU
- Coloured halos around words
- Poor tracking, -losing place when reading.
- Sore , watery eyes and headaches when reading
As humans we are adapted to view natural images. Imagine a picture of a lake and mountains, beach, garden – is that comfortable to look at? Now imagine a stripy black and white shirt or a zebra – is that comfortable?
Our brain is only 2% of body mass but requires 20% of ALL blood oxygen to fire 5-10% of neurones at any one time. Uncomfortable images cause a higher amount of neurons being engaged in the visual brain and this creates a stressful situation for our visual cortex. An increased blood oxygen is being diverted to the visual brain to enable it to cope with the additional energy needed for the neurones which are firing to process what the visual system is seeing. This is a very inefficient energy use and when the body and brain is unable to sustain this high demand it causes a response like ‘pain’ which makes the person to look away thus removing the stimuli and this calms the brain activity. Some people are genetically more sensitive and more susceptible to hyper excitability of the visual brain.
How does this link to reading text?
English text is made of striped patterns which are mainly written in black on white paper, to our brain look like stripes – not natural!
Filters reduce discomfort by reducing contrast and filtering out a particular wavelength of light that causes the neurons to fire unnecessarily. But it has to be correct colour, saturation and brightness. A person may be sensitive to a particular wavelength of light and this can explain why a tint can stabilize the visual brain.
Binocular vision and reading
Lot of symptoms of visual stress are the same as if the eyes have binocular vision insufficiency so do not work together properly. This could be due to eye muscles weakness so it’s VERY important to have full eye test and detailed binocular vision assessment. Unstable binocular vision can cause fixation to swap between eyes. This can be fixed with prescription lenses that stabilize the vision at near. Then we can proceed to Colorimetry assessment which goes through 6000 colour combinations to find the correct tint (as shown in the picture above)
What is involved in a Full Assessment?
- Full eye examination to establish prescription – (may be covered by NHS if applies)
- Eye dominance – to establish fixating eye the ‘locks’ onto the word when reading.
- Saccadic eye movement – ability to jump accurately from letter to letter or word to word.
- Binocular stability – to ensure that the eyes work together aligned at the near point of reading. This includes assessment of accommodation – focusing ability and convergence – ability to pull eyes together to make test single.
- Light sensitivity/Visual Stress – Colorimetry assessment with Intuitive colorimeter to establish a specific tint that can stabilize visual brain activity (hypersensitivity of neurones). Some younger patients or those with poor comprehension are assessed using Eye Bright Test which is more basic but very effective method used in Schoolvision method.
- Clinical eye tracker – to assess eye movements during reading and statistical analysis to monitor reading performance and treatment progress.