Photosensitive epilepsy

Last updated 22 Mar 2010, review date due 22 Mar 2012

What is photosensitive epilepsy?

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.

Various types of seizure can be triggered by flashing or flickering light. However, the most common is a tonic-clonic seizure.

In these web pages, we look at various things that can trigger seizures in people with photosensitive epilepsy. We also look at ways to minimise the risks.

More information about seizures

How many people have photosensitive epilepsy?

Many people think that everybody with epilepsy has photosensitive epilepsy. In fact only five in a hundred people with epilepsy have this type of epilepsy.

When does photosensitive epilepsy begin?

Photosensitive epilepsy usually begins before the age of 20. It is most common between the ages of seven and 19. More girls than boys have photosensitive epilepsy.

Diagnosing photosensitive epilepsy

When doctors are diagnosing epilepsy, one of the tools they use is an electroencephalogram (EEG). The EEG records brainwave patterns from the tiny electrical signals that are constantly coming from the brain. During one part of the EEG, you are asked to look at flashing lights, to see if this triggers epileptic activity in your brain. If it does, then this may indicate that you have photosensitive epilepsy.

An explanation of hertz (Hz)

The word hertz (Hz) refers to how often something happens in a second. In these web pages, Hz refers to two different things. It refers to the number of flashes or flickers a second. It also refers to the rate the scanning lines on televisions and computer monitors ‘refresh’ themselves.

Most people with photosensitive epilepsy are sensitive to 16-25 Hz, although some people may be sensitive to rates as low as 3 Hz and as high as 60 Hz.

Acknowledgements

Epilepsy Action would like to thank Professor G F A Harding, Emeritus Professor of Clinical Neurophysiology at Aston University, UK, and also Professor Stefano Seri, Professor of Clinical Neurophysiology at Aston University and Consultant at the Birmingham Children’s Hospital NHS Foundation Trust, UK, for reviewing this information.