A Puzzling Ocular Motility Disorder: Apparent Up-Gaze Fatigability in a Patient With Oculomotor Nerve Compression.

We report the case of a woman who developed right third nerve dysfunction with synkinesis and ocular neuromyotonia secondary to a compressive arterial aneurysm. Surprisingly, our examination showed a downward drift of the right eye in sustained up-gaze resulting in transient hypotropia, suggesting either fatigability of the superior rectus or contraction of the inferior rectus. We believe this ocular motility pattern is secondary to a co-contraction of the inferior rectus in up-gaze caused by synkinesis (explaining the downward drift), followed by failure of the inferior rectus to relax upon return to primary position caused by ocular neuromyotonia (explaining the hypotropia).