I don’t think I’ve ever experienced anything as terrifying as my first seizure. It’s something I wouldn’t wish on my worst enemy.
Cathy Vice, IndieGamerChick.com
In 1997, a Pokemon cartoon containing a red flickering sequence was aired in Japan, resulting in more than 600 children being admitted to hospital after suffering epileptic seizures. Three-quarters of those had never suffered from symptoms of epilepsy before. Although video games do not create epilepsy in people who do not have it, there are at least 27 cases of people having their first seizure while gaming, and physical injury from seizures is common.
People with photosensitive epilepsy can have seizures as a result of choice of visual treatments. Seizure risk cannot be completely avoided, but there are certain triggers that can easily be avoided:
Any sequence of flashing* images that lasts for more than 5 seconds
More than three flashes* in a single second, covering 25%+ of the screen
Moving repeated patterns** or uniform text***, covering 25%+ of the screen
Static repeated patterns** or uniform text***, covering 40%+ of the screen
* an instantaneous high change in brightness/contrast (including fast cuts), or to/from the colour red
** more than five evenly spaced high contrast repeated stripes – rows or columns such as grids and checkerboards, that may be composed of smaller regular elements such as polkadots
**** more than five lines of text formatted as capital letters only, with not much spacing between letters, and line spacing the same height as the lines themselves, effectively turning it into high contrast evenly alternating rows
There are specific formulas for calculating what a difference in contrast has an effect and for what portion of a person’s field of view is affected, but these are complex to work out, so it is better to stay on the side of caution, and simply avoid flickering and regular patterns completely wherever possible. Particularly in VR, as the 25%/40% above is based on a typical screen display, not a display that takes up 100% of your field of view.
If it is not possible to avoid them without harming the game, ensure that adequate and obvious warning is given, and investigate providing an option to disable them.
An epilepsy test service is available, originally developed for testing TV footage but also suitable for testing videos of gameplay. It is recommended by industry bodies, and used by both publishers and studios (most notably Ubisoft, who made a public commitment to epilepsy testing following a seizure incident). Again, it does not guarantee a game is epilepsy-safe, but it does greatly reduce common triggers.
There is always a chance of seizure from any game, even a game that avoids all common triggers. So the term ‘epilepsy safe’ must never be used. If you include a setting called ‘epilepsy safe mode’, you risk harming players and risk legal action being brought against yourself. Instead, describe what the setting relates to – ‘screen flash effects’, ‘effects intensity’, etc.
Best practice example: Towerfall
Epilepsy test (paid service): Harding test
More information: OFCOM guidance on flicker and pattern usage
More information: ‘The Epilepsy Thing’ article on indiegamerchick.com