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abstract Fixation-off sensitivity (FOS) is a phenomenon induced by elimination of central vision/fixation, and mayeither manifest clinically with seizures or only represent an EEG abnormality. FOS is characterized byposterior or generalized epileptiform discharges that consistently occur after closing of the eyes and lastas long as the eyes are closed. It is most commonly encountered in patients with idiopathic childhoodoccipital epilepsies, but may also be observed in cases of symptomatic or cryptogenic focal and general-ized epilepsies, as well as in asymptomatic non-epileptic individuals. FOS should be differentiated frompure forms of scotosensitivity, in which EEG discharges or epileptic seizures are elicited by darkness, andfrom epileptiform discharges triggered by eye closure, which refer to eye closure sensitivity. AlthoughFOS is probably associated with occipital hyperexcitability its intrinsic epileptogenic potential is pre-sumed to be low. 2012 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rightsreserved.Contents1. Introduction . . . 2222. Historic background. . . . . . . . . . . . . . . . 2223. EEG description and diagnostic aspects 2224. Differential diagnosis. . . . . . . . . . . . . . . 2245. Related conditions . . . . . . . . . . . . . . . . . 2256. Epileptogenicity potential . . . . . . . . . . . 2257. FOS and photosensitivity. . . . . . . . . . . . 2258. Pathophysiology 2258.1. Magnetoencephalography 2258.2. Functional magnetic resonance imaging (fMRI) . . . . . . . . . . . . . . . . . 2258.3. Magnetic resonance spectroscopy . . . . . . . . . 2268.4. Single-photon emission tomography . . . . . . . 2268.5. Transcranial magnetic stimulation (TMS) . . . 2268.6. Visual evoked potentials. 226