A Case of Functional (Psychogenic) Monocular Hemianopia Analyzed by Measurement of Hemifield Visual Evoked Potentials
A 14-year-old boy who was born deaf was referred to the emergency room at Kochi University Hospital on 30 January 2013 with a history of monocular temporal hemianopia of the right eye following headache, nausea and ague. He visited our department for the first time the next day. His visual acuity was 1.2 and 1.5 in the right and left eye, respectively. His intraocular pressure was normal, as were the anterior segment and macular as revealed by optical coherence tomography. No relative afferent pupillary defect was apparent, and a color perception test (Ishihara color test) was normal. Goldmann perimetry revealed a vertical monocular temporal hemianopia of the right eye (fig. ); this was also detected with a binocular visual field test. Computed tomography, magnetic resonance imaging (MRI) and MR angiography of the brain including the optic chiasm as well as orbital MRI revealed no apparent abnormality. On the basis of these findings, we diagnosed the patient's condition as functional monocular hemianopia.\nAt a follow-up 1 week later, the patient still manifested monocular temporal hemianopia of the right eye as revealed by Goldmann perimetry as well as a hemifield defect as revealed by the binocular field test. Pattern VEPs were then measured with a VikingSelect instrument (Natus Medical Inc., San Carlos, Calif., USA). The stimuli were checkerboard patterns with an individual check size of 1.5 degrees. The stimulus monitor was a cathode-ray tube of 14.3 × 18.5 degrees and the hemifield was of half size. The measurement distance was 100 cm and the reversal frequency was 0.7 Hz (transient VEP). Pattern VEPs according to the International Society for Clinical Electrophysiology of Vision (ISCEV) standard were within the normal range []. The latency and amplitude were 111.5 ms and 13.4 μV for the right eye and 107.5 ms and 11.9 μV for the left eye, respectively (fig. ). The hemifield pattern VEPs for the right eye were symmetrical, with a latency and amplitude of 114.0 ms and 9.1 μV for stimulation of the temporal field and 109.5 ms and 8.9 μV for stimulation of the nasal field, respectively (fig. ).\nOne month later, the visual field defect of the patient spontaneously disappeared.