Fixation-off, scotosensitive, and other visual-related epilepsies

FOS is a relatively recently described specific mode of precipitation of seizures and paroxysmal EEG abnormalities. Elimination of central vision and fixation, even in the presence of light, induces high-amplitude occipital or generalized paroxysmal discharges. FOS is suggested on routine EEG by abnormalities that consistently occur as long as the patient's eyes are closed but not when the eyes are open. The model example of FOS is early-onset and late-onset BCEOP. Idiopathic and cryptogenic generalized epilepsies with FOS have been described. Scotosensitive epilepsy implies seizures and EEG abnormalities induced by the complete elimination of retinal light stimulation, and most cases described as scotosensitive are probably FOS. FOS has characteristics opposite to those of photosensitive epilepsies, but conversion from one to the other or co-existence may rarely occur. The underlying mechanisms of FOS are not known, but they may be related to an abnormality of the alpha-rhythm generators.