Scotoptic Sensitivity Syndrome /
Irlen Syndrome (also referred to at times as Meares-Irlen Syndrome, Scotopic Sensitivity Syndrome, and Visual Stress) is a perceptual processing disorder. It is not an optical problem. It is a problem with the brain’s ability to process visual information. Children with this problem are either sensitive to light or when they look at the words on the page (especially a white page) they may move or change size. Providing them with color overlays can be very helpful. Any child who complains of light sensitivity or is having a hard time reading when it seems like they shouldn't, should be tested for SSS. Also, SSS has been linked to the unintegration of the moro reflex and being sympathetic dominant, and these children should be doing exercises and activities to help integrate this reflex and to stimulate the parasympathetic nervous system.
This video is found on the Irlen website and describes what this syndrome is and how children and adults perceive printed words when they have it. The website also has some great books. I, however, prefer to by my overlays, and testing kits from the NRSI website.