Pure photosensitive epilepsy is characterized by generalized seizures provoked exclusively by flickering light. According to Jeavons (57), 40% of photosensitive patients have this variety of epilepsy, and television is the most common precipitating factor. Video games may trigger these seizures, although not all such events represent pure photosensitive epilepsy (58,59). Other typical environmental stimuli include discothèque lights and sunlight reflected from snow or the sea or interrupted by roadside structures or trees.

Pure photosensitive epilepsy is typically a disorder of adolescence, with a female predominance. Reviews of the topic have been provided by several authors (51,52,55, 56,60). The seizures are generalized tonic-clonic in 84% of patients (61), absences in 6% of patients, partial motor seizures (possibly asymmetric myoclonus in some cases) in 2.5% of patients, and myoclonic seizures in 1.5% of patients. Subtle myoclonic seizures may go unnoticed until an obvious seizure occurs. The developmental and neurologic examinations are normal. The resting electroencephalogram may be normal in approximately 50% of patients, but spike-and-wave complexes may be seen with eye closure. Intermittent photic stimulation evokes a photoparoxysmal response in virtually all patients. Depending on the photic stimulus and on the patient’s degree of photosensitivity, the clinical response ranges from subtle eyelid myoclonus to a generalized tonic-clonic convulsion.

Pure photosensitive epilepsy is typically conceptualized as a variety of idiopathic generalized epilepsy, but cases occur in which electroencephalography and clinical evidence favors the occipital lobe origin, as predicted by theoretical and animal models (62,63). Recently, there has been increased recognition that IPS can induce clear-cut partial seizures originating in the occipital lobe (64,65). As in more typical photosensitive subjects, environmental triggers include television and video games. Many of these patients
have idiopathic photosensitive occipital lobe epilepsy, a relatively benign, age-related syndrome without spontaneous seizures, although cases with occipital lesions have been reported, including patients with celiac disease. The clinical seizure pattern depends on the pattern of spread. The visual stimulus triggers initial visual symptoms that may be followed by versive movements and motor seizures; however, migraine-like symptoms of throbbing headache, nausea, and, sometimes, vomiting are common and can lead to delayed or incorrect diagnosis.

Jeavons and Harding (61) found that about one-third of their photosensitive patients with environmentally precipitated attacks also had spontaneous seizures similar to those of pure photosensitive epilepsy. Spike-and-wave activity was common in the resting EEG patterns of patients with spontaneous seizures, and only 39% of patients had normal resting electroencephalograms. Photosensitivity may accompany idiopathic generalized epilepsies, especially juvenile myoclonic epilepsy (JME), and is associated with onset in childhood and adolescence, normal intellectual development and neurologic examination, normal EEG background rhythm, and generally good response to treatment with valproate. It also may occur with severe myoclonic epilepsy of infancy (Dravet syndrome) or with disorders associated with progressive myoclonic epilepsy like Lafora disease, Unverricht-Lundborg disease, Kufs disease, and the neuronal ceroid lipofuscinoses (66). Photosensitivity is usual in eyelid myoclonia with absences (EMA) but not in benign occipital epilepsies of childhood of the Gastaut or Panayiotopoulos types (67).

Pure photosensitive epilepsy may be treated by avoiding or modifying environmental light stimuli. Increasing the distance from the television set, watching a small screen in a well-lighted room, using a remote control so that the set need not be approached, and monocular viewing or the use of polarized spectacles to block one eye should provide protection (57,68). Colored spectacles may be useful in selected patients (69,70). Drug treatment is needed if these measures are impractical or unsuccessful, if photosensitivity is severe, or if spontaneous attacks occur. The drug of choice is valproate, which in one study (71) abolished photosensitivity in 54% of patients and markedly reduced it in a further 24%. Lamotrigine, topiramate, ethosuximide, benzodiazepines such as clobazam (72), and levetiracetam (56) also may be useful. Quesney and associates (73) proposed a dopaminergic mechanism in human epileptic photosensitivity based on the transient abolition of photosensitivity with apomorphine, and bromocriptine and parenteral L-dopa are reported to alleviate photosensitivity (74,75). About one-fourth of patients with pure photosensitive epilepsy lose their photosensitivity by 25 years of age (76). Because this resolution usually occurs only in the third decade, withdrawal of treatment too early may lead to seizure recurrence; serial EEG recordings to determine the photosensitivity range may be helpful in assessment and follow-up (56).

Reports of self-induced epileptic attacks using visual sensitivity antedated the discovery of the photoparoxysmal EEG response (77). Regarded as rare, self-induction was reported particularly in mentally retarded children and adolescents, with a female preponderance (51,52,78,79). More recent information, however, shows that although some affected patients are retarded, most are not (80, 81, 82). When carefully sought, the syndrome is not rare; it was found in approximately 40% of photosensitive patients studied by Kasteleijn-Nolst Trenité and coworkers (80). The electroencephalogram usually shows spontaneous generalized spikes or spike-and-wave complexes, and approximately 75% of patients are sensitive to IPS. The self-induced seizures are usually myoclonic, especially with palpebral myoclonus, or absences, and some patients have EMA. Patients induce seizures with maneuvers that cause flicker, such as waving a hand with fingers spread apart in front of their eyes or gazing at a vertically rolling television image. Monitoring (82,83) shows that these behaviors, once thought to be part of the seizure, precede the attacks and are responsible for inducing them. The compulsive nature of this behavior has been observed often and has been likened to self-stimulation (84) in experimental animals. Patients have reported intensely pleasant sensations and relief of stress with self-induced photosensitive absence seizures (81,82). Frank sexual arousal has been described (85,86). Patients are often unwilling to give up their seizures, and noncompliance with standard, well-tolerated antiepileptic drugs is common (80,81). Treatment is difficult, however, even in compliant patients (79). Drugs that suppress self-stimulation in animals, such as chlorpromazine and pimozide, may block the pleasurable response without affecting the response to IPS and have partially reduced or completely terminated self-induction (79,87). The effectiveness of valproate in reducing or abolishing photosensitivity has resulted in virtual disappearance of this form of self-induction, which is now encountered in patients for whom the drug has not been prescribed and in those with inadequate drug levels for any reason. Many patients appear not to want treatment for their self-induced attacks.

Absences, myoclonus, or, more rarely, tonic-clonic seizures may occur in response to epileptogenic patterns. These are striped and include common objects such as the television
screen at short distances, curtains or wallpaper, escalator steps, and striped clothing. Pattern sensitivity is seen in approximately 70% of photosensitive patients tested with patterned IPS in the EEG laboratory, but sensitivity to stationary striped patterns affects only about 30% of photosensitive patients (37). Clinical pattern sensitivity is, however, rare, and patients often may not make the association, the family may be unaware of it, and physicians may not inquire about it.

Wilkins and coworkers (36,38,88, 89, 90) studied the properties of epileptogenic patterns, isolating visual arc size, brightness, contrast, orientation, duty cycle, and sensitivity to movement and binocularity. They concluded that the seizures involve excitation and synchronization of a sufficiently large number of cells in the primary visual cortex with subsequent generalization. We can compare this with the previously described animal experiments and Wieser’s theory. Pattern sensitivity optimally requires binocular viewing, and treatment may be aided by avoidance of environmental stimuli (admittedly often impractical) as well as by alternating occlusion of one eye with polarizing spectacles and increased distance from the television set. Spontaneous attacks or a high degree of pattern sensitivity requires antiepileptic drug treatment, as described earlier.

Although eye closure may evoke paroxysmal activity in photosensitive patients, especially those with EMA, seizures induced by eye closure are unusual. They are rare in patients not sensitive to simple flash IPS. Seizures with eye closure are typically absences or myoclonic attacks and are not specific for any one cause. They must be distinguished from rare seizures occurring with eyes closed or with loss of central fixation. Panayiotopoulos and colleagues (67,91) studied these extensively and described syndromes in which they occur.

Photosensitive patients may induce seizures with maneuvers that do not produce flicker. These attacks are similar to flicker-induced seizures, but the inducing behaviors are not. Pattern-sensitive patients may be irresistibly drawn to television screens, which they must approach closely to resolve the epileptogenic pattern of vibrating lines, or they may spend hours gazing through venetian blinds or at other sources of pattern stimulation. Those sensitive to eye closure have been observed to use forceful slow upward gaze with eyelid flutter (92,93) to induce paroxysmal EEG discharge and, at times, frank seizures. These patients are often children, who describe the responses as pleasant: “as nice as being hugged, but not as nice as eating pudding,” (C.D. Binnie, personal communication). We have observed that these tonic eyeball movements are always associated with spike-and-wave activity in children. As they mature, their eyeball movements may persist but no longer elicit epileptiform activity and can be likened to a tic learned in response to positive reinforcement. These observations and the compulsive seizure-inducing behavior of many such patients suggest that, as in flicker-induced seizures, the self-induced attacks give pleasure or relieve stress. Experience suggests that treatment is similarly difficult (79).