November is National Epilepsy Awareness Month in the United States. According to the World Health Organization, epilepsy is the most common serious brain disorder worldwide with no age, racial, social class, national, or geographic boundaries. One in 10 people will have a seizure at some point in their life and 1 in 26 will be diagnosed with epilepsy. Currently, there are approximately 65 million people around the world who have epilepsy.
Epilepsy and Photosensitive Seizures
Epilepsy is the most commonly known type of photosensitive seizure disorder. Photosensitive seizures can be caused by flashing lights, images, and repetitive patterns. Video content on the web and in computer games can include unsafe flickering, colors, or high-contrast patterns, all of which can initiate these seizures.
Web Accessibility for Seizure Disorders
The World Wide Web Consortium (W3C) has included guidance related to seizures in its Web Content Accessibility Guidelines (WCAG). The W3C has provided success criterion that is intended to allow users to access all web content without seizures being induced due to photosensitivity. They recommend a “three flashes or below threshold” and suggest that developers incorporate the following techniques to ensure criterion is met.
- Ensure that no component of any content flashes more than three times in any 1-second time period
- Keep any flashing areas small, generally to an area approximately 341 by 256 pixels or less
- Use a tool to ensure that content doesn’t violate the flash thresholds
- Reduce contrast for any flashing content
- Avoid using fully-saturated reds for any flashing content
- Reduce the number of flashes, even if they don’t violate the flash thresholds
- Provide a mechanism to suppress any flashing content before it begins
- Slow down live material in order to avoid rapid flashes
- Freeze the image momentarily if three flashes are detected within one second
- Drop the contrast ratio if three flashes are detected within one second
- Allow users to set a custom flash rate limit
Most web content is harmless to those with epilepsy and/or photosensitive seizure disorders. However, because of the potentially serious nature of seizures, developers need to be aware of the possible dangers of using flashing or flickering graphics and animations. They should also keep in mind that even those who do not suffer from seizures can experience nausea or dizziness caused by animations and moving objects.
Want to learn more about accessibility? WeCo has a variety of free public and paid single-seat trainings available. Some examples of the training we offer:
- Getting Started in Accessibility
- Improving UX for Users Living with Disabilities
- Web Content Accessibility Guidelines (WCAG) 2.1 Jump Start
For a complete list of WeCo’s training events, visit our Eventbrite page.
Further reading from WeCo’s Accessibility Blog about epilepsy and web accessibility: