Visual field deficit due to downward displacement of optic chiasm.

Visual disturbance in hydrocephalus is typically due to raised intracranial pressure. We describe a patient who presented with marked loss of peripheral visual fields, but without features suggestive of raised intracranial pressure. MR scan showed an enlarged third ventricle and a downward displacement of the optic chiasm, Chiari II malformation. These radiological changes and the visual field deficits reversed after endoscopic third ventriculostomy and foramen magnum decompression. These observations support the view that the treatment of the hydrocephalus in such patients can help to reverse the change in the position of the optic chiasm and the visual field deficits.