Structural correlates of fixation-off sensitivity: Evidences from a case of symptomatic occipital epilepsy with bilateral occipital gliosis

The fixation-off sensitivity (FOS), an epileptic phenomenon induced by elimination of central vision and fixation, is rarely seen in symptomatic occipital lobe epilepsy. The cerebral mechanisms and the structural correlate underlying FOS remain unclear. We describe a 19-year-old male with persistent left sided FOS following perinatal insult. MRI revealed asymmetric changes with more gliosis and ulegyria over the left posterior occipital cortex corresponding to the topographic representation of the macula. We suggest that the extensive denervation of the area representing macula along with the presence of hyperexitable ulegyric cortex is responsible for the phenomenon of FOS.