The use of coloured filters and coloured paper to ease eye strain while reading has been noted in the literature for decades. In the 1980s, Maeres and Irlen each described a cluster of symptoms that affected reading, including print distortion, eye strain, and headaches. Since then, investigators and researchers have attempted to define this cluster of symptoms. This has been labeled Irlen Syndrome, Meares-Irlen Syndrome, Perceptual Dyslexia, Visual Dyslexia, Scotopic Sensitivity (which is now realized to be a misnomer but can still be found in literature), Pattern Related Visual Stress, and Visual Stress.
Visual stress is a broad term and refers to a condition that occurs in a wide range of neurological disorders. Thought to affect approximately 20% of the population, visual stress is a scientifically-confirmed neurological condition characterized by hyperactivity of the brain’s visual cortex, whereby this area of the brain is not processing visual information properly.
Visual stress can also be triggered by patterns of light, such as flickering light or strobe effects. The results include visual and perceptual distortions which can affect what a person sees when they look at a repeating pattern, such as stripes or lines of text. Illusions of colour around letters or around the page, doubling of print, and washed out areas of print may also be seen. The distortions can also affect how a person feels.
The initial approach for treating visual stress, developed by Irlen, was based on the use of coloured filters. However, Irlen’s method has been questioned due to lack of scientific evidence surrounding the diagnostic process. Newer systems using the Intuitive Colorimeter have been well-described in the scientific literature, and are gaining acceptance in the optometric community, but also require additional research. There are confounding factors when reviewing the published literature on this condition and treatment, including participant selection, definition of visual stress or similar condition, corrections for other visual factors (e.g. binocular instability), inability to mask the filter to the subjects, and others.
Despite the limitations of the research, the balance of evidence suggests that coloured filters can alleviate symptoms or improve performance in people who suffer from visual stress. Other ophthalmic conditions such as refractive error and binocular function should be addressed before coloured filters are considered as an option for anyone experiencing visual stress. A consistent and accepted definition and method of diagnosing visual stress would lead to a more consistent body of evidence surrounding this condition. Larger and more rigorously controlled trials of interventions for visual stress are required.