Characterizing binocular eye-movements in reading in esotropic Duane’s Syndrome

We present a case-study of the eye-movements in reading of an individual with esotropic Duane’s Syndrome, which involves an inability to move one of the eyes away from the nose (abduction), but typically near normal adduction and intermittent diplopia. The participant read some 5000 words of English text, consisting of slightly modified newspaper stories, and their eye-movements were recorded binocularly, using a monocular calibration procedure. The eye-tracking record shows the unaffected right eye moving across the lines of text on both left and right halves of the screen, while the affected left eye only moves in the right – but not the left – half of the screen during reading. The left eye moves concordantly with the right eye in the right half of the screen but only makes small and spatially unrelated (but temporally related) saccades when the right eye fixates text on the left. The participant read slowly and reported no diplopia. These data reveal the constraints on uptake of visual information by Duane's Syndrome readers, and the flexibility required when the unaffected eye fixates in the affected hemifield.