What is Photosensitive Epilepsy?
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Photosensitive epilepsy (PSE) is a kind of epilepsy that is characterized by seizures which are triggered by some kind of visual stimuli, such as a flickering or flashing lights, regular, bold patterns or patterns that are regular and moving. Patterns like checks or stripes can trigger seizures in some people having this condition.
Both artificial and natural light might be responsible for triggering such seizures.
Photosensitive Epilepsy Epidemiology
Almost 3 in every 100 individuals with epilepsy have got photosensitive epilepsy. It generally begins before 20 years of age, mostly when a person is in between 7 and 19. The condition is more prevalent in girls than in boys.
Photosensitive Epilepsy Causes
Seizure triggers may vary from one person to another. However, there are some common seizure triggers which include:
- Flashing light
- Certain colors like red and blue
- Flashing white light that is followed by darkness
- Bright, contrasting patterns like white bars against black background
- Stimulating images taking up the entire field of vision, like when sitting very close to the television screen
Photosensitivity is a complex and intricate health problem. Medical experts and scientists have been successful in identifying many of the triggering stimuli. However, the exact mechanism by which stimulation of the retina in a specific way leads to hyper-excitation of the brain has not been properly understood. The essential features of an excitable stimulus, as stated by Epilepsy Foundation are listed below:
- The flickering of a light source as well as the frequency in which a light changes is an important factor. Simply put, the number of times a light flashes in a second. Flashing lights that range between 5 to 30 flashes per sec (Hertz) are the ones that are most likely to cause seizures.
- The intensity or brightness of the source of light and also the contrast between the light and dark parts during the flicker is also another important factor. If the contrast ratio is greater than 20 candelas/square meter, it poses as a risk to the epileptic patients.
- The area of the visual field covered by the light stimulus is an essential factor as it determines how much of one’s brain is getting stimulated by the light.
- Finally, epileptic seizures can be triggered by the pattern of the image as well. Moving or static patterns of clearly discernable light ‘n’ dark stripes can induce the same influence as the flashing lights due to the alteration of the dark and bright portions. The danger depends on the number of the stripes as well as the contrast between the two.
There are other factors that can influence photosensitive epilepsy as well. These include distance between the light source and an individual as well as the color of the light source. Certain colors, such as red and blue, have been found to have a greater effect on photosensitive patients than others.
Some specific instances of events or situations, that can trigger seizures in PSE individuals, include:
- Computer monitors and TV screens
- Bold, striped wallpapers and fabrics
- Strobe lights, nightclubs and theater lights
- Light observed through a quick-moving ceiling fan
- Visual effects in TV shows, movies and video games
- Sunlight viewed through stair railings or slanted blinds
- Malfunctioning moving escalators and fluorescent lights
- Sunlight reflecting off water or shining through the tree leaves
- Cameras using multiple flashes or several cameras flashing altogether
- Flashing lights on safety alarms, fire trucks, police cars and ambulances
People having photosensitive epilepsy might be at an increased risk for developing seizures if they are ill, tired, sleep deprived, intoxicated or have been playing video games for too long without any break.
Photosensitive Epilepsy Symptoms
Individuals having PSE can experience epileptiform seizures when they are exposed to certain specific visual stimuli. The causative factors for seizures may vary from one patient to another along with the nature and intensity of the resulting seizure episodes, which may range from being short absence seizures to tonic-clonic seizures. Several PSE patients report of feeling an aura or certain kind of odd sensations prior to the seizure, which can act as a warning for a sufferer to get away from the triggering stimulus.
A convulsive seizure or tonic-clonic seizure lasts for less than 5 minutes. Common symptoms include:
- Loss of consciousness
- Contraction of muscles
- Loss of bladder control
- The patient may cry out
- Stiffening of the entire body
- Changes in the breathing patterns
- Patient may bite the tongue and insides of the cheeks
- Jerking or twitching of limbs as the muscles alternately tighten and relax
Once the seizure is over, the muscles relax after which the person regains consciousness slowly. Following the seizure, the individual may feel:
- Loss of memory for a short period of time
Photosensitive Epilepsy Diagnosis
The diagnosis of PSE is carried out by understanding the correlation between the seizure activity and exposure to certain specific visual stimuli. More specific investigations can be conducted by EEG with an Intermittent Photic Stimulation or IPS device. The IPS device creates specific forms of stimuli which can be adjusted and managed precisely. A diagnostician adjusts the device and then looks for the characteristic anomalies present in the EEG, like photoparoxysmal response (PPR), which goes hand in hand with photosensitive epilepsy and/or may indicate the onset of seizures. The testing is stopped before the seizure actually takes place.
Sometimes, diagnostic indications consistent with photosensitive epilepsy may be found by provocative testing with the IPS device, even though no such seizure episodes may occur in real life. Many patients might show abnormalities that resemble photosensitive epilepsy in his or her brain activity when bombarded with adequately aggressive stimulation. However, they may never experience seizure episodes and are not believed to have photosensitive epilepsy.
Photosensitive Epilepsy Treatment
Although there are no cures available for this condition, the sensitivity to light may be diminished over time in case of some patients. Sensitivity to light may be reduced by medical treatment, where medications such as sodium valproate are used for the purpose. PSE patients also need to avoid situations which may expose them to a seizure-triggering stimuli or at least cover one eye using a hand, as this reduces the risk of having a seizure. Performing these actions alone can reduce the potentiality of having seizures to nearly zero for many sufferers having photosensitive epilepsy.
Some patients of PSE may have trigger stimuli that they are very unlikely to encounter in day to day real life. PSE, in such cases, might be discovered only by an accident in some unusual situation or while conducting diagnostic examinations for other complaints.
Photosensitive Epilepsy Prognosis
With time, the sensitivity to bright lights may diminish in case of some patients. People having photosensitive epilepsy should consult their doctor to ask for safety measures and avoid any circumstances that might trigger their epileptic seizures. A controlled life may bring down the instances of epilepsy to almost zero. People having this condition are known to lead an otherwise normal life by following certain adjustments.
Photosensitive epilepsy is still being studied by experts as there is a dearth of information as to what anatomical defects within the brain might be responsible for causing this condition.