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Current Thumbnail: Benjamin Zifkin And Frederick Andermann update their chapter on visual sensitive epilepsy with recent references and explain the basics of photosensitive epilepsy, pattern-sensitive epilepsy, and seizures triggered by television screens and video games. A simple method for pattern stimulation is also described. Visual sensitive seizures are the commonest reflex seizures and most neurologists can expect to encounter them, especially in children and young adults.

Historical Note and Nomenclature
Seizures triggered by visual stimuli were known in classical antiquity (Temkin 1971). Before clinical EEG, seizures were reported with environmental flicker or with sudden changes in light intensity. Gastaut and colleagues reported an early series of patients investigated with stroboscopic intermittent photic stimulation during EEG recording (Gastaut et al 1948). Historically, photosensitivity has meant an abnormal response to light, and since the development of the stroboscope, an abnormal response to flicker stimulation during EEG recording is generally called photosensitivity. Flicker sensitivity is common to different types of seizures induced by visual stimuli, but subtypes in which patients are reproducibly sensitive to more complex visual stimuli can be distinguished among patients, who are almost always sensitive to intermittent photic stimulation at some time. Pure photosensitive epilepsy, in which seizures occur only with environmental light stimulation, is the most common reflex epilepsy. The induction of occipital lobe seizures by the same types of visual stimuli is more common than previously thought. Television and sunlight are the most common environmental triggers of visual sensitive seizures; triggering by television broadcasts and video games has become notorious in recent years. Visual sensitive epilepsy is included as a reflex epilepsy syndrome in the most recent proposed classification of epilepsy syndromes (Engel 2001). In this proposal, reflex epilepsy syndromes are those “in which all epileptic seizures are precipitated by sensory stimuli. Reflex seizures that occur in focal and generalized epilepsy syndromes that are also associated with spontaneous seizures, are listed as seizure types.” There are many reviews on photosensitive epilepsy and seizures of different types (Wilkins et al 1980; Harding and Jeavons 1994; Binnie and Wilkins 1998; Kasteleijn-Nolst Trenite 1998; Zifkin and Kasteleijn-Nolst Trenite 2000; Kasteleijn-Nolst Trenite et al 2004).

Clinical Manifestations
Pure photosensitive epilepsy is characterized by seizures exclusively provoked by flicker. Partial seizures may be triggered and can generalize. These are considered in the clinical summary on idiopathic photosensitive occipital lobe epilepsy. Earlier reports often did not consider these specifically, and the seizures are reported to be typically generalized tonic-clonic from their onset. In one study, 84% of patients had seizures reoprted as generalized tonic-clonic, whereas absences occurred in only 6%, partial motor seizures (possibly asymmetric myoclonus in some cases) in 2.5%, and myoclonic seizures in 1.5% of patients (Jeavons and Harding 1975). However, even these proportions are subject to bias; patients will come to medical attention after a convulsion in front of the television but may have already had many subtle unobserved reflex seizures with brief myoclonic or absence-like events. The developmental and neurologic examinations are normal.

Pattern sensitive epilepsy consists of seizures triggered by viewing patterns, typically stripes. Almost all such patients are sensitive to intermittent photic stimulation, and about one third of photosensitive patients may have epileptiform EEG abnormalities on viewing stationary striped patterns. Pattern sensitivity is not an independent epilepsy syndrome. Some subjects sensitive to pattern are not sensitive to flicker (Harding and Jeavons 1994). Pattern sensitivity is enhanced if the pattern vibrates. Clinical pattern sensitivity is much less common, found in about 2% of photosensitive subjects in one study (Jeavons and Harding 1975), and in 6% in another study (Kasteleijn-Nolst Trenite 1989). Pattern sensitive epilepsy is characterized by generalized convulsions, absences, or brief myoclonic attacks provoked by viewing patterns such as escalator steps, striped wallpaper, or patterned clothing (Binnie and Wilkins 1998).

Some photosensitive patients are sensitive to eye closure alone. Reflex absences or brief myoclonic attacks can occur in patients not sensitive to intermittent photic stimulation and are thought to be precipitated by the abolition of central vision and fixation (Panayiotopoulos 1998; 2002).

Patients with all types of visually induced seizures may induce attacks with maneuvers producing visual stimulation and may be compulsively drawn to sources of flicker or pattern stimulation such as television screens. Patients sensitive to eye closure may use a compulsively repeated eye rolling and eyelid flicker movement to self-stimulate. Monitoring has shown that the stimulatory behaviors indeed trigger the seizures rather than being manifestations of the seizures. Intensely pleasurable sensations have been reported with these types of seizures, and some patients induce seizures to relieve stress or to gain attention (Tassinari et al 1998).

Reflex seizures triggered by television, computer screens, and video games have become notorious. The Japanese cartoon episode that triggered a nationwide outbreak of photosensitive seizures is a well known example (Harding 1998; Ishida et al 1998). Many of these events represent pure photosensitive epilepsy with or without pattern sensitivity. Some have occurred in subjects not previously known to have epilepsy, and others have occurred in known photosensitive patients. Some were likely focal occipital visual reflex seizures with autonomic manifestations. Seizures associated with video screens may also have occurred by chance or in relation to other reflex seizure triggers, such as thinking with or without manipulation of objects during computer use or game play. Broadcasting of potentially dangerous screen content has led to outbreaks of photosensitive seizures, and guidelines in Japan and the United Kingdom now prohibit such program material.

Clinical Vignette
No information was provided by the author.

Etiology
The etiology of visual sensitive epilepsies is unknown. An important genetic component is identified, but no single gene for photosensitivity has been identified.

Pathogenesis and Pathophysiology
Photosensitive epilepsy has been extensively studied in the genetically photosensitive baboon Papio papio (Menini and Silva-Barrat 1998). The corpus callosum is critical for interhemispheric synchronization and generalization of the EEG paroxysms in Papio papio, and probably in humans, as shown in a photosensitive subject with agenesis of the corpus callosum (Brinciotti et al 1990). In both, the occipital primary visual cortex appears necessary to trigger systems for propagation and generalization of electrical activity with associated clinical manifestations. The occipital cortex in the photosensitive baboon is not, however, the site of hyperexcitability as it is in humans. However, studies in ferret visual cortex support a cortical etiology of pattern sensitivity (Schwartz 2003). The physiology of human photosensitivity has been recently reviewed (Wilkins et al 2004). Studies in pattern-sensitive subjects suggest that generalized seizures can occur if normal excitation of visual cortex involves a "critical mass" of cortical area with synchronization and subsequent spreading of excitation from the occipital lobe trigger (Binnie et al 1985). The magnocellular system of the primary visual cortex seems to be particularly involved in pattern sensitivity. Functional MRI (Hill et al 1999) and magnetoencephalography (Ricci et al 1990; Parra et al 2003) also suggest regional occipital cortical hyperexcitability, regional activations, and abnormal neuronal synchronization in photosensitive subjects. Magnetoencephalography studies also support a predominant role for the parvocellular system in the genesis of the abnormal response to flicker, as described by Harding and Fylan (Harding and Fylan 1999) in contrast to the importance of the magnocellular system in pattern sensitivity described above.

The model of human pattern-sensitive epilepsy is of special interest because it is an example of apparently generalized or bilateral clinical events and EEG abnormalities activated by a specific functional stimulation with a known localization. This model may apply to other types of reflex seizures and reflex epilepsy syndromes and may operate in seizures induced by thinking and praxis and in many subjects with primary reading epilepsy.

Television-induced seizures and similar attacks in patients with pure photosensitive epilepsy can be understood in relation to the properties of video screens and to the images on the screen. Visual reflex seizures and the characteristics of the effective triggers have been recently reviewed (Zifkin and Inoue 2004). Flicker rate, pattern, luminous intensity, size, location, and duration of the stimulus need to be considered. A television screen produces flicker at the mains frequency, effectively generating intermittent photic stimulation at 60 Hz in North America and 50 Hz in Europe. Photosensitivity is more common at the lower frequency, with nearly 50% of patients sensitive to 50 Hz intermittent photic stimulation (Jeavons and Harding 1975), and television sensitivity has indeed been a greater problem in Europe than in North America. Television-induced seizures, however, are not only related to alternating current frequency flicker. Wilkins and colleagues studied patients who were not sensitive to the alternating current frequency flicker but who responded to the vibrating pattern of interleaved lines at half the alternating current frequency (25 Hz in Europe and 30 Hz in North America) to which about 75% of photosensitive subjects are sensitive and which can be discerned only close to the screen (Wilkins et al 1979). Special 100 Hz television screens, marketed in Europe, reduce the risk of television-induced seizures (Ricci et al 1998). Color is important even without luminance changes; photoparoxysmal EEG responses can be elicited in sensitive subjects by noncolor-opponent stimuli even if they are isoluminant (Harding and Fylan 1999). Sensitivity is greater with red stimulation at wavelengths greater than 700 nm, and red stimulation was important in the Japanese cartoon incident (Harding 1998). Red-cyan flicker, even when isoluminant, is reportedly even more provocative of epileptic discharge (Shirakawa et al 2001). It is, thus, not surprising that seizures can be triggered even at greater distances and by noninterlaced screens without intrinsic flicker, and flashing or patterned screen content has been implicated in these. Although the 50 Hz television screen is an important determinant of screen sensitivity and 100 Hz screens reduce the ability of the screen to trigger seizures, it is important to note that all systems are equally dangerous if certain patterns or other dangerous screen content is broadcast (see Management section).

Photosensitivity is genetically determined. Familial sensitivity to intermittent photic stimulation was first described in 1949 (Fairweather et al 1949). There is no difference in rates of photosensitivity between relatives of nonphotosensitive epileptic subjects and relatives of controls, but photosensitivity is significantly more common in relatives of photosensitive patients. Results of such studies (van Hedenstrom 1969; Waltz et al 1992; Waltz and Stephani 2000), and of other studies of the response to intermittent photic stimulation, are complicated by the age and sex dependence of the phenomenon, which is most frequent in adolescents and females, by different patient selection criteria, and by differences in how intermittent photic stimulation is performed. Waltz and Stephani report that photosensitivity is significantly more common in 5- to 10-year-old siblings of proband offspring of a photosensitive parent (50%) than in siblings of photosensitive children without parental photosensitivity (14%). The highest risk of seizure (33%) was in photosensitive siblings of a proband with parental photosensitivity, and the lowest (4%) in nonphotosensitive siblings of probands without parental photosensitivity (Waltz and Stephani 2000).

Photosensitivity occurring in some patients with identifiable epileptic syndromes, eg, juvenile myoclonic epilepsy, is inherited separately from the other epileptic disorder. A single gene for photosensitivity has not yet been identified.

Epidemiology
Paroxysmal responses to intermittent photic stimulation, distinct from any form of epilepsy, are well documented in about 7% to 8% of apparently normal subjects, especially children and adolescent girls. The prevalence of this sensitivity is highly dependent on the age and sex of the population studied, and on the criteria for normality and on the definition of an abnormal response (Zifkin and Kasteleijn-Nolst Trenite 2000). Kasteleijn-Nolst Trenite and colleagues have shown that over half of known photosensitive epilepsy patients questioned immediately after stimulation denied having had brief but clear-cut seizures induced by intermittent photic stimulation and documented by video-EEG monitoring (Kasteleijn-Nolst Trenite et al 1987). This must raise the question of whether asymptomatic photosensitive subjects have unnoticed reflex seizures triggered by stimuli encountered in daily life.

Studies in epileptic patients show that an epileptiform response to intermittent photic stimulation is found in about 10% to 20% of children and 5% to 10% of adults, and that this response is more common in females at any age. The flash frequencies most likely to elicit a photoparoxysmal response range typically from 9 to 18 flashes per second. Only about 3% of the photosensitive population is sensitive to intermittent photic stimulation at 1 to 3 flashes per second. It is important to note that about 48% are sensitive at 50 flashes per second and that about 15% are sensitive at 60 flashes per second; these are the frequencies of alternating current in Europe and North America respectively. The authors estimate that about 40% of photosensitive patients have pure photosensitive epilepsy (Jeavons and Harding 1975).

Prevention
Not applicable.

Differential Diagnosis
Pure photosensitive epilepsies cannot be diagnosed on the basis of an epileptiform response to flicker alone. This EEG finding occurs in asymptomatic subjects (especially children) in several forms of epilepsy, and with different seizure types, which are usually easily distinguished from pure photosensitive epilepsies on clinical and EEG grounds. Moreover, some patients with pattern sensitive epilepsy may not be sensitive to flash intermittent photic stimulation. Photosensitivity with generalized seizures may accompany idiopathic generalized epilepsies with spontaneous seizures, especially juvenile myoclonic epilepsy, and is typical in eyelid myoclonia with absences. It also may occur with symptomatic generalized epilepsies such as severe myoclonic epilepsy of infancy (Dravet syndrome) or with degenerative gray matter encephalopathies such as Lafora disease, Unverricht-Lundborg disease, Kufs disease, the neuronal ceroid lipofuscinoses, and others collectively known as the progressive myoclonus epilepsies in which photosensitivity at low flash frequencies is typical. These syndromes are associated with photic cortical reflex myoclonus, and the patients also have clear-cut action myoclonus. Photosensitivity is not typical of idiopathic occipital lobe epilepsies either of the Panayiotopoulos or Gastaut type and is not typically associated with fixation-off sensitivity; sensitivity to flicker is unusual in these conditions despite the florid occipital EEG epileptiform activity (Panayiotopoulos 1998).

Generalized seizures and EEG abnormalities induced by visual stimulation are conventionally differentiated from idiopathic photosensitive partial seizures with typical secondary generalization, but detailed clinical and EEG studies may be needed to make this distinction, and it should be recalled that the initial stimulus activates occipital lobe structures in both types. Idiopathic photosensitive partial seizures may be confused with nonepileptic events especially migraine, discussed in the clinical summary on idiopathic photosensitive occipital lobe epilepsy.

Nonepileptic paroxysmal eyelid movements may occur in children and adults with generalized photosensitive epilepsy and may be mistaken for absence seizures. There is often a family history of eyelid movements, and EEG monitoring readily distinguishes the 2 (Camfield et al 2004).

Diagnostic Workup
Patients with pure photosensitive epilepsy or pattern sensitive epilepsy have no evident brain lesions with CT or MR imaging. EEG demonstration of sensitivity to flicker is performed with stroboscopic stimulation. Because of the important role of the television screen itself in triggering seizures independent of program content, routine intermittent photic stimulation should include stimulation at frequencies of 50 or 60 flashes per second, depending on the local alternating current frequency, and the corresponding 25 or 30 flashes per second rate. Some degenerative disorders are associated with abnormal responses to low flash rates, and stimulation protocols should include rates of 1, 2, and 3 flashes per second.

Responses to intermittent photic stimulation depend on certain characteristics of the photostimulator. The flashes must be sufficiently bright, and the stimulator must deliver consistently bright flashes throughout the required frequency range of 1 to 60 flashes per second. A stimulation protocol has been devised that permits rapid screening of subjects and determination of the photosensitivity range and takes into account the possible differences in response with eyes open, closed, or with eye closure (Kasteleijn-Nolst Trenite et al 1999). In untreated subjects, only generalized paroxysmal epileptiform discharges in response to intermittent photic stimulation (spikes, polyspikes, and spike-and-wave complexes) are clearly linked to epilepsy. These responses are most common with stimulation from 10 to 30 flashes per second. Responses to intermittent photic stimulation must be evaluated carefully including the photosensitivity range: some are striking but not predictive of epilepsy (Kasteleijn-Nolst Trenite 1998). Responses can be greatly attenuated or abolished by some antiepileptic drugs, especially valproate, and this must be considered in interpreting the EEG. With treatment, the triggered EEG activity can be confined to posterior head regions; this is more readily shown with pattern stimulation than with intermittent photic stimulation (Darby et al 1986).

Testing for pattern sensitivity requires a pattern of sharply contoured black and white stripes of equal width and spatial frequency of 2 to 4 cycles per degree of visual arc, viewed with both eyes under adequately bright conditions. If patterns are presented on a screen, the background should have the same mean luminance to avoid flash effects, and screen flicker must be avoided. Similarly, patterns presented on cards should be illuminated by sources that avoid flicker. Darby and colleagues described a practical method for pattern stimulation (Darby et al 1980):

• The pattern is circular, diameter 48 cm, with a central fixation point, viewed at a distance of 57 cm.
• The pattern consists of parallel black and white stripes, each 2.5 cm wide.
• The pattern should be well-illuminated, eg, in the beam of a slide projector, so the average luminance is at least 200 cd/m2.
• The patient stares at the fixation point in the center of the pattern.
• The pattern is held steady for 30 seconds and then oscillated orthogonal to the line orientation if no EEG abnormality has been evoked. The optimal frequency of oscillation is about 20 Hz, attainable only with special devices; a hand held pattern cannot be oscillated at more than 10 Hz.

Prognosis and Complications
Photosensitive epilepsies are usually diagnosed in childhood or adolescence. The prognosis for control of the seizures induced by visual stimulation is generally good, especially in pure photosensitive epilepsy. However, only about 25% of patients with these conditions reportedly will lose their photosensitivity, and this only in their third decade (Harding et al 1997). Most such patients will relapse if medication is discontinued and especially if this is done too early in their teens. Patients with juvenile myoclonic epilepsy who are also photosensitive will in any case likely need long-term or lifelong antiepileptic drugs. Current studies are not adequate to determine if drug treatment affects the natural history of photosensitivity. Serial EEG evaluation using a standardized protocol with determination of the photosensitivity range can, thus, be helpful to assess the response to treatment and for evaluation of photosensitivity after withdrawal of medication. The wider the range, the more the patient is at risk of getting visually evoked seizures in daily life (Kasteleijn-Nolst Trenite 1989). Complications of convulsive seizures induced by visual stimulation are the same as those of spontaneous convulsive seizures, and may exceptionally be severe or lethal.

Management
Management of reflex epilepsy of all types requires consideration of stimulus avoidance, stimulus alteration, antiepileptic drugs, and combinations of these. General measures applicable to epilepsy also apply, such as avoidance of sleep deprivation and excessive alcohol use, and these are especially important in juvenile myoclonic epilepsy, which is often associated with photosensitivity. Covanis and colleagues (Covanis et al 2004) have recently reviewed this subject. Management of visual sensitive epilepsy also involves a role for society in preventing the broadcast of predictably dangerous television screen content and in appropriate labeling of screen games and other flashing material, such as artistic exhibits. Not every screen-triggered seizure can be prevented, but many isolated seizures, as well as mass outbreaks are preventable, and can be expected if broadcast guidelines are not implemented or if they are not followed. Official guidelines exist in some countries, notably in Japan and in Europe.

Patients with pure photosensitive epilepsy may be interested in treatment without drugs. The effectiveness of these measures will depend on the individual’s degree of photosensitivity, awareness of subtle signs and symptoms when exposed to potentially provocative stimuli, and on patient compliance. Patients can benefit from simple measures to avoid stimuli, such as discotheques and other evident sources of flashing lights. They should also be taught to cover one eye and turn away from the stimulus if they notice myoclonic jerks or eyelid or face twitching. Some video games are more provocative of abnormal activity than others, such as those with lots of motion and flickering (Ricci and Vigevano 1999), and avoidance of prolonged play is suggested. Stimulus modification involves measures such as wearing sunglasses or specifically tinted lenses (Covanis et al 2004), watching a small television set in a well-lit room, and using a remote control to avoid approaching the television set. Alternate eye patching or polarizing eyeglasses that permit blocking light to one eye to avoid binocular viewing are useful and also helpful for patients with pattern sensitivity, especially because environmental pattern stimulation can be difficult to avoid in everyday life. Combined tinted and polarized glasses were found useful in a small study (Kepecs et al 2004). Patients in countries with 50 Hz household alternating current should use 100 Hz television sets. Adaptive electronic filters have been useful (Takahashi et al 2002).

Patients for whom these measures are impractical or ineffective will require treatment with antiepileptic drugs. Valproate is the current drug of choice, and lamotrigine has been reportedly useful (Burrow et al 2001). These drugs suppress photosensitivity and pattern sensitivity. Benzodiazepines such as clobazam (not available in the United States), and ethosuximide may be useful adjuncts. Levetiracetam has also been suggested, but no long-term clinical studies are yet available. These drugs can also be combined with the measures described above.

Self-induced visual-evoked seizures may be highly difficult to treat. The attacks may be intensely pleasurable. Some patients who note a refractory period after a convulsive reflex seizure will induce an attack to avoid a later one at a less convenient or safe time. Noncompliance with drug or nondrug treatment is common. There is clear secondary gain for some patients and formal psychiatric evaluation is usually indicated.

Pregnancy
Not applicable.

Anesthesia
Not applicable.

References Cited
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ILAE.
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Abbreviations
EEG:electroencephalogram

McKusick MIM number
132100

Associated Disorders
Photosensitive epilepsy

Major Keyword Descriptors
asymmetric myoclonus
environmental light stimulation
flicker sensitivity
generalized tonic-clonic seizures
intermittent photic stimulation
myoclonic seizures
partial motor seizures
partial seizures
pattern sensitive epilepsy
photosensitivity
pure photosensitive epilepsy
red-cyan flicker
reflex epilepsy syndrome
reflex seizures
seizures with eye closure
self-induced seizures
simple reflex epilepsy
stroboscopic stimulation
television-induced seizures
visual sensitive epilepsy

Minor Keyword Descriptors
absences
convulsions
epilepsy
eye closure
flickering light
hyperexcitability
isoluminant
Papio papio
seizures
stripes
television
video games
visual stimuli

Age of Presentation
06-12 years
13-18 years

Age of Typical Presentation
06-12 years
13-18 years

Population Group(s) Preferentially Affected
none selectively affected

Occupation Group(s) Preferentially Affected
none selectively affected

Sex
female>male, >1:1

Family History
family history may be obtained
family history typical

Heredity
heredity may be a factor
heredity typical

Glossary
photosensitive epilepsy: epileptic syndrome characterized by generalized seizures induced by flickering or other changes in light stimulation.

Permuted Topic, Synonyms, Variants
Visual-sensitive epilepsies

Related Topics
Childhood absence epilepsy
Epilepsy
Epilepsy with myoclonic absences
Eyelid myoclonia with and without absences
Idiopathic photosensitive occipital lobe epilepsy

Differential Diagnosis
pattern sensitive epilepsy
idiopathic generalized epilepsies
juvenile myoclonic epilepsy
eyelid myoclonia with absences
severe myoclonic epilepsy of infancy
Dravet syndrome
degenerative gray matter encephalopathies
Lafora disease
Unverricht-Lundborg disease
Kufs disease
neuronal ceroid lipofuscinoses
progressive myoclonus epilepsies
photic cortical reflex myoclonus
idiopathic occipital lobe epilepsies
Panayiotopoulos type epilepsy
Gastaut type epilepsy
nonepileptic events
migraine

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