Causes Of Photosensitive Epileptic Seizures

Photosensitive epilepsy is a type of reflex epilepsy¹ that occurs when seizures are triggered by sensory stimuli. In photosensitive epilepsy, this stimulus is the exposure to flashing or flickering lights, which includes many light sources. 

Who’s more likely to have photosensitive seizures?

Photosensitive seizures occur in up to 30% of all people with epilepsy, so it’s not too common. About 1 in 4,000² people in the general population will experience a photosensitive seizure. 

Photosensitive seizures are more common in children and adolescents. It becomes less common with age, and by age 25, around a quarter of people³ who have experienced photosensitive seizures lose their photosensitivity. 

In addition, women are twice as likely as men to experience photosensitive seizures. 

What causes photosensitive seizures?

Photosensitive seizures are caused by visual stimuli — usually flashing or flickering lights in a natural or artificial environment. 

Not all lights cause seizures equally. Factors that affect what lights trigger seizures include:

• The rate of flashing (frequency). Lights that flash or flicker between 16 and 25Hz⁴ are more likely to cause seizures, especially if they flash brighter than 20 candelas/m^2. (For comparison, an old iPhone 4 had a max brightness of 550cd/m2 while an iPhone 13 has a max brightness of 1200cd/m2.) However, this can vary based on the individual, and lights that flicker between 3–60 times⁵ per second may cause seizures.

• Duration of flashing

• Red color flashes

• Oscillating strips

• How much area the light stimulus occupies in the visual field

• Distance between the light source and eyes 

• The contrast between light and dark

A seizure usually happens during exposure to the stimuli or very shortly afterward. 

Photosensitive seizures can be triggered by many sources of light, and an individual may have more than one trigger. 

Video games and TV are the most common triggers of photosensitive epileptic seizures. Interestingly, movies in theaters usually do not provoke seizures due to low light intensity compared to TV or computer screens.

There are various other triggers.

Artificial lights

Several types of artificial lights may contribute to photosensitive seizures, such as:

• Strobe lights, which are common at nightclubs and dances

• Cameras with multiple flashes or multiple cameras flashing at the same time

• Multiple strings of Christmas lights that flash together

• Flashing bicycle lights

• Flashing lights of emergency vehicles

• Fireworks on a dark night, in rare cases 

Natural light sources

Sunlight may trigger photosensitive seizures. For example, light that:

• Shimmers off water or snow 

• Flickers through trees or moving leaves 

• Shines through the slats of window blinds 

Some visual patterns

Some visual patterns can contribute to photosensitive seizures. For example:

• Stripes of contrasting colors

• Patterns that change direction or flash

• Looking down at a moving escalator 

TV or computer screens 

TV screens may cause photosensitive seizures if:

• The screen flickers, particularly with old cathode ray monitors

• The screen is close to a person’s eyes

• The image has high intensity or is overly bright

• The room is dark — this can increase the contrast between the dark room and the bright screen 

It’s unknown whether 3D screens put people at a greater risk of having a photosensitive seizure. 

Video games

Up to 70% of the seizures induced by video games are thought to be due to photosensitivity. They’re more common in boys — however, this could be because more boys play video games than girls. 

Due to their wavelengths, the color red (wavelength greater than 700nm) is more likely to provoke photosensitive seizures compared to blue and white colors. Video games are believed to be significant causes of photosensitive seizures because they often contain deep red colors.

In one example, a rocket launch sequence in Pokemon was elucidated as the trigger due to red and blue alternating flashing lights. 

Games played on TV were also more likely to trigger a seizure than those on a handheld device, possibly due to increased brightness and subtle flickering. Finally, the increased frequency of TVs was less implicated than the lower frequency.

Genetics

Certain genes are believed to be associated with an increased risk of developing photosensitive epilepsy. Monozygotic twins demonstrate almost 100% concordance, and siblings of affected individuals have five times the risk of photosensitivity.

Studies⁶ suggest photosensitivity is inherited in an autosomal dominant fashion and age-dependent penetrance. It’s thought that people with certain variations in the CHD2 gene are more likely to get photosensitive seizures. Other genes associated have been GABAa receptors, SYNGAP1, or RORβ.

What happens in the brain to cause a photosensitive seizure?

How exactly photosensitivity leads to seizures is unclear.

The abnormal electrical activity in the brain likely occurs in the occipital lobe (the region of the brain responsible for vision). This abnormal electrical activity can spread to other areas in the brain to cause larger generalized seizures. 

The visual system has evolved through millions of years to provide natural images with as little input as possible.

Patterns such as flickers or images with large color/brightness differences that are not normally encountered in nature most likely overstimulate certain parts of the brain in those that are susceptible, and they cause the nerve cells to create aberrant electrical impulses, subsequently leading to a seizure. 

Can photosensitive seizures be prevented?

It’s not always possible to prevent photosensitive epileptic seizures from occurring. You can easily get caught off guard when suddenly exposed to flashing or flickering lights. 

You can try to prevent photosensitive seizures from occurring by following these tips:

• Watch TV at least two meters (6.5 feet) from the screen.

• Use a remote control rather than the buttons on the TV screen.

• Make sure the TV is high frequency (at least 100 Hz). 

• Avoid watching TV for long periods. 

• Avoid watching TV or playing video games when feeling tired.

• Use non-glare polarized blue glasses on a sunny day or when exposed to other types of flickering light or screens. 

• Close one eye and turn your head away when exposed to flashing lights. Alternate the eye that’s shut at regular intervals, and don’t close both eyes simultaneously. 

• Avoid exposure to flashing lights as much as possible, such as those in nightclubs.

• Reduce the brightness of the TV or computer screen. 

• Watch TV in a well-lit room rather than a dark one. This helps to reduce the contrast with the screen. 

• Use a monitor glare guard on a computer screen.

• Use a flicker-free computer monitor. 

• Call ahead before attending a movie or event to check whether strobe lights or any other flashing lights will be used. 

• Watch TV on small screens (12 inches or smaller).

• Disable the “autoplay” function on social media and other online videos and GIFs to prevent being surprised by flashing images or videos. 

• Avoid stress, extreme fatigue, and sleep deprivation.

• Avoid prolonged video game playing.

• Avoid playing video games alone.

• Use a lamp beside the TV.

Anti-epileptic drugs, such as sodium valproate, can also help control photosensitive epileptic seizures. 

However, it’s generally recommended to focus on avoiding the stimuli rather than using the medication as a first-line treatment for photosensitive seizures. 

The lowdown

Flashing or flickering lights can cause seizures in some people with epilepsy. 

With the increased use of technology in our world, understanding the causes of photosensitive seizures is vital so that people can do their best to avoid potential triggers as much as possible. 

Frequently asked questions 

What type of epilepsy is linked to photosensitivity?

Photosensitivity is linked to numerous kinds of seizures. It’s most common in generalized genetic epilepsies, which can include:

• Juvenile myoclonic epilepsy

• Childhood absence epilepsy

• Juvenile absence epilepsy

• Generalized tonic-clonic seizures on awakening

• Benign myoclonic epilepsy in infancy

Less commonly, photosensitivity can also cause focal epileptic seizures. 

Can you develop photosensitive epilepsy later in life?

It’s possible to develop photosensitive epilepsy at any age, including later in life. However, it’s much more common for a child or adolescent under 20 years old to develop photosensitive epilepsy. 

Can bright sunlight cause a seizure?

Bright sunlight can cause a photosensitive seizure. This is more likely to occur if the light is shining through objects like the slats of window blinds or trees or if it’s reflecting through the water.