What is Visual Stress

Visual Stress refers to discomfort and print distortion brought about by pattern glare: certain repeating shapes, high contrasts and brightness. It occurs in patterns that are unnatural, meaning our eyes and brain have to work harder than normal to interpret the image/text. The most common form of this pattern glare is found when an individual is reading black text on a white background. People who suffer with this can get headaches and migraines in the most severe cases with the ability to comprehend what is written and the speed at which an individual reads being severely hampered.

One reason that this occurs is over-excitement in the Visual Cortex ("cortical hyperexcitability") caused by sensitivity to a specific wavelength of light. This over-activity can cause visual symptoms (e.g. the blurring of letters and skipping of lines), and physical symptoms (e.g. headaches and eye tiredness) which will decrease an individual's reading speed and comprehension. For many people this can be after 10-15 minutes, however for some individuals it can be immediate. Visual difficulties are often associated with dyslexia, but can exist independently. Difficulties that are perceptual in nature and stem from the visual cortex rather than the eye itself are often termed "visual dyslexia," but they are not dyslexia and should not be confused with it. Visual stress is a scientific term for this set of difficulties. 

Not everyone will experience visual symptoms; for a lot of people the main signs are physical, such as:

Getting tired whilst reading.
Having to re-read text over before you remember it.
Reading slowly.
Experiencing difficulty looking at a computer screen
Being unusually sensitive to bright lights, especially fluorescent lighting.
Having difficulty judging heights or distances, which sometimes causes problems with stairs and/or escalators.
Finding driving at night particularly stressful, sometimes experiencing a fragmentation of reflected light.
Developing headaches and migraines when reading.
Fatiguing quickly when working with text
Experiencing problems copying from the board
Skipping words or lines when reading
Seeming to experience increased difficulty after an initial period of about 10 minutes
Frequently moving the head or body position, or moving closer to or further away from the page
Reading slowly and haltingly and have difficulty absorbing information
Tracking with the finger

Using a Coloured Overlay or Reading Ruler of the correct tint has been shown to increase reading speed by an average of 22% (page overlays) and 20% (reading rulers). Screening with the Visual Stress Colour Assessment Pack helps schools to identify which tints may be helpful on an individual basis for children with visual difficulties. Sensitivity and response to coloured filters can change over time, meaning a new colour may help more, or the filter may no longer be needed.