Fixating with the paretic eye: evidence of “fixation duress” on PET imaging

A 71-year-old man presented with a one-month history of binocular vertical diplopia. On examination, visual acuity was 20/25 OD and 20/20 OS. He had an 8-diopter right hypotropia in primary gaze that worsened with right gaze and with left head tilt, in keeping with a left superior oblique (SO) palsy. Cover testing demonstrated an upward refixation movement of the right eye, indicating preferential fixation with his paretic left eye....