Photosensitive epilepsy: flashing light triggers, testing and staying safe

Epilepsy Society explains that photosensitive epilepsy is when seizures are triggered by flashing lights or contrasting light and dark patterns. The seizure happens straightaway when the trigger is seen. It is not common, and it may be diagnosed when you have an EEG test.

Most people with photosensitive epilepsy also have epileptic seizures at other times, but some have seizures only when triggered by flashing, flickering or patterned effects. Seizures are most commonly tonic-clonic but can be of any type. Epilepsy Society also stresses that flashing or patterned effects can make people with or without epilepsy feel disorientated, uncomfortable or unwell, which does not necessarily mean they have photosensitive epilepsy.

Epilepsy Society says most people who develop photosensitive epilepsy are between 7 and 19 years old, women are more likely to have it than men, and you are more likely to have it if someone in your family has it. If someone in your family has juvenile myoclonic epilepsy you are at higher risk. It is most common in certain syndromes: childhood absence epilepsy, Dravet syndrome, juvenile absence epilepsy, juvenile myoclonic epilepsy, Lennox-Gastaut syndrome and West syndrome.

Epilepsy Action says most cases develop in people under 20 years old. Published figures vary by source and by definition: Epilepsy Action gives 3 to 5 in every 100 people with epilepsy and about 1 in 4,000 people overall, while Epilepsy Society gives around 3% of people with epilepsy.

Epilepsy Society says flashing or flickering lights or images between 3 and 60 hertz may trigger seizures, and that lights flashing between 16 and 25 times a second are the most likely to do so. Triggers are individual. Sensitivity under 3 hertz is not common.

• Flashing or flickering lights, strobe lighting at clubs and concerts, rapid camera flashes and some Christmas lights and fireworks.

• High-contrast geometric patterns such as black and white stripes or checks, particularly if moving quickly or changing direction.

• Sunlight flickering through trees, blinds, railings, or reflected on water or snow.

• Faulty or flickering light bulbs, or the wrong bulb with a dimmer switch.

• Flashing images in games, videos, GIFs and some online content.

• Virtual reality, because the large field of view stimulates more of the brain.

Epilepsy Society lists tiredness, stress or excitement, such as playing a video game for a long time without breaks; the effect taking up all of your field of vision, for example sitting very close to a screen; a light and dark pattern moving quickly or changing direction; and seeing the effect against a dark background, such as watching a screen in a darkened room.

Epilepsy Action advises viewing screens from further away, at least 2 metres or 3 times the width of the screen, and increasing the brightness of the environment, and suggests dark or coloured glasses and wide-brimmed hats outdoors. It also says research suggests patterns on a screen are more likely to trigger a seizure if they have at least 5 to 8 pairs of repeating stripes, are very bright and cover a larger part of the field of vision, appear for longer than half a second, or vibrate, reverse colours or flicker.

Epilepsy Society says UK television programme content is regulated by Ofcom, restricting the flash rate to three per second or less and limiting the area of the screen allowed for flashing lights or alternating patterns. Modern computer or TV screens, phones and tablets do not flicker and are unlikely to be triggers themselves, and flatscreen LCD monitors are even less likely to trigger seizures. Cinema and hand-held screens rarely trigger seizures, and a 3D film carries about the same risk as a normal cinema film.

Content is the main risk: flashing imagery or animated patterns in games, GIFs, videos or animated backgrounds in video conferencing. Many platforms allow autoplay to be turned off. Epilepsy Action notes that older cathode ray TV sets tend to refresh at a slower speed, and that high-definition or curved screens that take up more visual space might increase the risk for some people.

An electroencephalogram (EEG) can help with diagnosis and may include testing for photosensitive epilepsy. Epilepsy Society says this usually involves looking at a light that flashes at different speeds, and that if there are changes in brain activity the physiologist will stop the flashing light before a seizure develops. Epilepsy Action says the EEG may include structured patterns such as bars as well as flashing lights.

Epilepsy Action notes that if you have a diagnosis of epilepsy you may already have had an EEG, and you can ask your doctor to check your records for photosensitivity testing. A neurologist or epilepsy specialist interprets the results and advises on treatment and safety.

Epilepsy Society says the most common way to treat photosensitive epilepsy is with anti-seizure medication to lower the risk of a seizure, and that avoiding triggers can also reduce the risk, which can work well for those who only have photosensitive seizures. Epilepsy Action says that if your epilepsy is well controlled by medicines you are less likely to have photosensitive seizures.

What to do if suddenly exposed: Epilepsy Society advises covering one eye completely with your hand, turning away from the trigger, and not closing your eyes because that might cause a flicker effect. Epilepsy Action gives the same advice to cover one eye with your hand and turn away.

The NHS says to call 999 if someone has a seizure and it is the first time it has happened, it lasts longer than is usual for them or longer than 5 minutes if you do not know how long their seizures usually last, they do not recover as usual or have another seizure without recovering, or they have had 3 or more seizures in 24 hours.

Most people with photosensitive epilepsy lead full lives, studying, working, using screens and going out, with attention to risk factors. Schools and employers can make reasonable adjustments, such as screen position and lighting.

The NHS suggests keeping a diary to identify triggers, carrying medical ID and making sure family and friends know what to do if you have a seizure. Driving rules apply to all people with epilepsy and the DVLA decides eligibility, so discuss them with your specialist.

On the NHS the route is from the GP or emergency department to a paediatrician, neurologist or epilepsy specialist, with EEG testing in a neurophysiology department. Epilepsy specialist nurses can provide advice and support.

Private neurology assessments and EEGs can provide quicker access. The EEG protocol for photic stimulation is the same, so the most important thing is that the findings are shared with your NHS team and your treatment plan is coordinated.