[Voluntary control of unilateral strabismus sursoadductorius]

Strabismus with unilateral elevation in adduction is an upward deviation of the adducting eye of unknown, not necessarily paretic origin. The term "old trochlear palsy" may be erroneous since the hypertropia is not necessarily larger in downward gaze and a causative lesion can usually not be identified. We describe here a marked voluntary influence on unilateral elevation in adduction, in situations that exclude binocular fusion.

Two patients with an elevation in adduction of the right eye and a positive head-tilt phenomenon, a 21-year-old and a 28-year-old man, were able to vary their vertical angle of squint at will. Even under artificial conditions that exclude binocular fusion (alternate cover test, dark-red glass test) could they change their right-over-left deviation, Patient 1 between 4 and 20 degrees and Patient 2 between 0 and 15 degrees. Under natural viewing conditions both patients had binocular vision with stereopsis that decompensated only when they looked to the left.

We assume that our two patients had a "motor memory" that stores the muscle innervation for parallel eyes, i.e. the innervation suitable for binocular vision, and that the patients made use of or neglected this memory at will. In general, our observations suggest that a variable recourse to such a motor memory explains why, in patients with unilateral elevation in adduction, the angle of squint often changes. A voluntary access to this memory may, however, be exceptional.