The Causes of Visual Stress
Visual stress refers to discomfort and print distortion brought about by pattern glare: certain repeating shapes, high contrasts and brightness. The most common form of this pattern glare is found when an individual is reading black text on a white background.
Pattern glare occurs in patterns that are unnatural, meaning our eyes and brain have to work harder than normal to interpret the image. One reason this occurs is due to over-excitement in the visual cortex (where the picture from the eyes are processed by the brain and given meaning). This over-activity can cause the visual symptoms of visual stress (e.g. the blurring of letters), and after a period of exposure to these symptoms is when physical symptoms can occur (e.g. headaches and eye tiredness); for some people this can be after 10-15 minutes, however for some it can be immediately.
Visual Stress is the most common term used in the UK, however it can also be known as Meares-Irlen Syndrome (named after the two researchers who first discovered the connection between white page "glare" and reading difficulties in the early 1980s), Visual Dyslexia, and Scotopic Sensitivity. However the latter is now considered by scientists to be a misnomer.
The reason visual stress occurs is not yet fully known, however there are some contributing factors that have been proven to cause an increase in symptoms of visual stress: