What is Irlen? The long answer
What is Irlen Syndrome?
Here's a great answer by Rhonda Stone, Irlen advocate and author of The Light Barrier:
Irlen Syndrome, Meares-Irlen Syndrome, or Scotopic Sensitivity Syndrome is a very specific problem associated with the photoreceptors of the eye and how wavelengths are absorbed and processed by multiple systems of the brain. There are different manifestations of this complex problem. An individual may experience just a couple or all of the symptoms: eye-strain, fatigue, headaches (including migraine), nausea, motion sickness, confusion or lack of clarity in thinking, the perception that text is moving (rising, falling, shaking, swirling, disappearing, etc.) and even problems with depth perception. Individuals with this problem may love to read but struggle to read for long periods of time; resist reading altogether because the physical issues make it a struggle; or simply appear disinterested in reading because they “don’t like it” (but they don’t know why –most adults with Irlen Syndrome live all their lives with it and, therefore, don’t know that issues they experience aren’t normal). One of the most serious manifestations is epileptic seizure (now widely understood to be caused by strobing, but less understood to be caused by what researcher Arnold Wilkins, Ph.D. University of Essex, calls “visual stress” and “pattern glare.” Reading involves patterns of text and is a visually stressful task.)
Dyslexia is commonly thought of as a learning issue. The neurobiological issues associated with it are little understood. Irlen Syndrome is a neurobiological issue that affects a variety of brain systems (beginning with the photoreceptors) and a handful of researchers are doing excellent work to define and document it. It is a neurobiological problem that can affect both health and learning, just health, or just learning.
Think of the human visual system as beginning with a “solar power plant.” The “photoreceptors” capture the energy (literally, the individual wavelengths), a biochemical reaction occurs, signals are sent as a result of this biochemical reaction through the visual pathways to the deeper structures of the brain. What the photoreceptors have captured is pure ENERGY. The human skin also has photoreceptive qualities. Do you know people who burn easily? Tan easily? Some react better to ultraviolet (UV) radiation than others, right?
Well, Irlen Syndrome exists because some people have photoreceptive “solar power plants” that react inappropriately to UV radiation and a myriad of other aspects of light(short wavelengths, medium wavelengths, long wavelengths, volume of lights as expressed through dark and bright, and pattern and contrast modulation). The resulting effect is physical stress on the eyes and/or brain AND/OR unstable visual perception. For many of these people, fluorescent lighting and computer screens are particularly problematic because both are in a constant state of flicker (except LCD screens), which adds to the visual stress.
Irlen Syndrome is a very specific condition that manifests in different ways. Tinted lenses reduce the symptoms by modifying the wavelengths (or ENERGY) absorbed by the photoreceptors. The modification improves how the physical system receives and processes the light. This is totally logical to physicists and a few people studying both photosensitivity and the neurobiology of the brain. Sadly many ophthalmologists and optometrists have never studied the physics of light, let alone photosensitivity and neurobiology.
I was pleased to see that the first International Symposium on Visually-Induced Motion Sickness, Fatigue, and Epileptic Seizure (VIMS) was held in Hong Kong in December 2007. Because thousands of children were stricken by epileptic seizures during and immediately after a popular Pokemon movie in theaters following a short strobing segment a number of years ago, the scientific community finally became interested in this important new area of brain science.