incomitance

Incomitance is a term used in ophthalmology to describe a noncomitant strabismus, a misalignment of the eyes whose magnitude varies with the direction of gaze. In comitant strabismus, the deviation remains essentially the same in all gaze positions. Clinically, incomitance is detected when the angle of strabismus changes with gaze or with different eye movements, and may be accompanied by duction restrictions or asymmetric motility.

Assessment involves systematic motility testing in primary position and in multiple gaze directions, sometimes using a Hess screen, photo grid, or synoptophore. The forced duction test helps differentiate mechanical restriction from neurologic palsy. Imaging such as MRI or CT can identify orbital pathology, muscle restriction, or nerve lesions.

Common causes include cranial nerve palsies (oculomotor III, trochlear IV, abducens VI) producing gaze-dependent misalignment; restrictive or paralytic conditions such as thyroid-associated ophthalmopathy, orbital trauma, fibrosis after inflammation; and less commonly neuromuscular disorders like myasthenia gravis which may produce variable incomitance. The presence of incomitance often indicates an underlying structural or neuromuscular problem rather than a simple binocular coordination issue.

Management targets the underlying cause and the resultant diplopia. Some cases are observed if mild and stable; others require prisms or eye muscle surgery planned with gaze-specific alignment in mind, making incomitant strabismus more complex to treat than comitant cases. Prognosis depends on etiology and response to treatment.