Sharing the vision epilepsy: life’s turning point Gavin Dimitri

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THE EPILEPSY REPORT OCTOBER 2008

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                          THE EPILEPSY REPORT OCTOBER 2008

epilepsy and light

combination of flicker and pattern 

would be sunlight through the trees as 

seen from a moving car.  Escalators and 

occasionally fly-screens can also be an 

issue for some people. Brighter lights 

and patterns with greater contrast are 

more likely to induce photosensitive 

seizures than those that are dim or faint. 

In addition, the more of the field of 

vision taken up by a pattern or flickering 

light, the more likely it is that a seizure 

will be triggered.

The earliest descriptions of 

photosensitivity focused on seizures 

triggered by sunlight, usually shining 

off the water or filtered into a pattern 

by trees. Sunlight is quite difficult to 

avoid but sunglasses, particularly those 

with polarised lenses, can be of help. 

Thankfully, sunlight is a problem for 

only a few people, even among those 

who suffer photosensitive epilepsy. 

Television and video games

In the last decades the focus has 

switched to television and video games.

 This was brought to public attention 

in 1997 when an episode of the cartoon 

“Pokemon” was aired in Japan. This 

episode contained a brief sequence 

where the whole screen flashed at 12Hz 

for a period of four seconds. Over 700 

people nation-wide, mostly children, 

suffered a seizure provoked by this 

cartoon. There was a similar but less 

wide-spread problem caused by an 

advertisement in the United Kingdom. 

There are now careful guidelines in 

place to make sure that programs shown 

do not have the kinds of flicker or 

patterns that can produce seizures. 

Despite the sensible design of 

programs, television is still the 

commonest cause for photosensitive 

seizures due to how the picture is 

produced. 

Televisions are divided into hundreds 

of vertical lines, known as the raster. 

Although in standard definition 

broadcasts the screen is said to refresh 

at 50Hz (50 times a second), in fact, 

only every second line is changed each 

time. This produces a 25Hz flicker 

when viewed from up close. This is 

within the range of frequencies that is 

commonly a problem and, when viewed 

from a short distance, a television is 

usually both bright and filling the field 

of vision. Console games, usually played 

via a television screen, have the same 

problems. 

Computer screens do not have a 

raster and usually refresh at 60Hz or 

more, therefore not flickering at the 

critical frequency. Although computers, 

particularly when playing games, are not 

completely without risk, the absence of 

the hardware-related flicker makes them 

less of a trouble then television. 

The risk from television can usually be 

T

he tendency to suffer seizures 

triggered by seeing flicker or 

patterns is known as photosensitivity. 

Although flicker is a widely known 

cause of seizures the proportion 

of people with epilepsy who are 

photosensitive is reasonably small 

(5%). This is mainly among those with 

idiopathic generalised epilepsy.

 Photosensitivity can be relatively 

easily seen on an electroencephalogram 

(EEG) as bursts of epileptic activity 

triggered by patterns or strobe light. The 

ability to test what is and is not likely to 

cause seizures in the laboratory means 

much is known about the things that 

are a risk to people with photosensitive 

epilepsy. This is important as although 

medication can help a great deal, for 

some people avoidance of flicker is still 

required.

Flicker and patterns

Flicker frequency, usually measured 

in flashes per second or Hertz (Hz), has 

the strongest effect on whether a sight is 

likely to cause a seizure. The frequencies 

most associated with seizures are 10Hz 

to 25Hz. Faster and slower frequencies 

are a problem in occasional people. 

Patterns can also precipitate 

photosensitive seizures.  The main issue 

is fine patterns, particularly stripes 

and checkers, or the combination of 

pattern and flicker. The most common 

What is photosensitivity? What does flicker-rate mean?  Can television and computers 

trigger  seizures?  In  this  article  Dr  Saul  Mullen,  from Austin  Health  in  Melbourne 

explains the relationship between epilepsy and light and suggests some strategies 

that can help reduce the risk of triggering seizures.

reduced by sitting further back, making 

the raster invisible and eliminating the 

flicker. If approaching the screen, to 

insert a DVD for instance, covering one 

eye with a hand will usually reduce the 

risk. Unfortunately, closing both eyes 

can make things worse as the act of eye 

closure while looking at flicker can itself 

trigger photosensitive seizures. More 

modern televisions, particularly LCD 

or plasma screens, with high definition 

pictures and fast (100Hz) refresh rates 

are less likely to cause photosensitive 

seizures. 

Electric lighting

Electric light, particularly fluorescent 

light, is a cause of much concern. 

Incandescent bulbs, those that heat a 

filament to produce light, are being 

phased out and replaced by small, 

energy-saving fluorescent bulbs. Older 

fluorescent tubes do have a subtle flicker. 

This is at 50Hz or 100Hz and is due to 

the alternating current used in mains 

electricity. This is just perceptible by 

the human eye but outside the critical 

frequency range for photosensitive 

seizures. Modern, energy-saver bulbs 

are designed to eliminate this flicker. 

Even with the older tubes, although 

many people find them unpleasant, the 

light does not produce EEG changes 

as are seen with the types of flicker 

described above.  

Strobe lighting

Other sources of flicker are 

comparatively uncommon. The strobe 

lights used in night clubs occasionally 

precipitate seizures but they are usually 

relatively slow (<5Hz). It is also often 

difficult to separate the risks posed by 

alcohol and sleep deprivation from that 

of the strobe light. 

Emergency services also use relatively 

slow strobe lights but, when multiple 

vehicles are parked together, these can 

combine together to produce frequencies 

in the critical range. 

Managing photosensitivity 

Photosensitivity is uncommon but 

for those who suffer it can be very 

troublesome. For many, medication is 

sufficient but for those who need to avoid 

lights and patterns the main offender is 

television. Keeping at least two metres 

from the set as well as considering 

a modern screen can be helpful. 

When presented with flicker that is 

uncomfortable looking away or covering 

one eye is most useful. Closing both eyes 

can worsen the situation, particularly 

with very bright lights.  

For those who have suffered 

photosensitive seizures it is best to 

discuss these issues with your treating 

specialist. There is great variability 

between people with this condition and 

individual advice is very important. 

Saul Mullen 

Austin Health, Melbourne Victoria

Practical ways 

to reduce risk



Sit at least 2  

metres from TV 

screen 



Cover one eye 

when approaching 

the TV screen eg 

to insert a DVD, or 

when unexpectedly 

confronted with 

flicker that is 

uncomfortable



Wear sunglasses 

with polarised 

lenses 

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