There are about 65 million people worldwide who have Epilepsy. Between 4 and 10 out of 1,000 people are living with active Epilepsy at one time.

Epilepsy is more than twice as common in the U.S. as cerebral palsy, muscular dystrophy, multiple sclerosis, and cystic fibrosis combined. Epilepsy can happen by itself, or with other conditions that affect the brain, such as cerebral palsy, intellectual disability, autism spectrum disorders, Alzheimer’s, and traumatic brain injury.

Epilepsy is a neurological condition effecting the nervous system and is known as a seizure disorder. It is normally diagnosed after a person has had at least two seizures that were not caused by some known medical condition.

Seizures seen in persons with Epilepsy are caused by disturbances in the electrical activity of the brain. Seizures may be related to a brain injury or a family tendency, but often times the cause is unknown. Some seizures are so mild that you hardly notice them, while others are very severe.

Photosensitive Epilepsy is a type of Epilepsy, in which all, or almost all, seizures are triggered by flashing or flickering light. Both natural and artificial light may trigger seizures. Some patterns, like stripes or checks, can also trigger seizures for some people with Photosensitive Epilepsy.

Around 3 in every 100 people with Epilepsy have Photosensitive Epilepsy. It usually begins before the age of 20, most commonly between the ages of seven and 19. Most people with Photosensitive epilepsy are sensitive to 16-25 Hz. Some people may be sensitive to rates as low as 3 Hz and as high as 60 Hz.

Epilepsy and Web Accessibility

Most web content is completely harmless to individuals with photoepileptic tendencies. Even most animations, videos, moving text, and Flash objects do not present any danger. However, some developers insist on dramatic effects of flashing or flickering lights and strobe-like effects. Science-fiction style Flash objects, horror movie previews, and cheap-looking banner ads are among the worst offenders. Maybe the creators of these effects think they’re “cool,” but they are also potentially dangerous. Developers should make every effort to ensure that their content does not have strobing, flickering, or flashing effects.

Even if the object does not cause a seizure, it may cause nausea or dizziness in some people. Neither of these is as serious of a health risk as a full-blown seizure, but having users mentally associate your web site with feelings of nausea is probably not the best design decision, at least in terms of user satisfaction and repeat visits. In some instances, an image does not even need to move to cause these effects. High contrast graphics with tight parallel lines can have similar effects, due to the optical illusion that parts of the image are in motion. Additionally, animating content may be distracting to some users, particularly users with high levels of distractibility.

Because of the potentially serious nature of seizures, developers should be extra careful to avoid any graphics, animations, movies, or other objects which have strobing, flickering, or flashing effects. Developers should also avoid graphics which may induce nausea or dizziness, or that may be distracting.