Incyclotorsion is a term applied to the inward, torsional (rotational) movement of the eye, mediated by the superior oblique muscle of the eye. The superior oblique muscle is innervated by cranial nerve IV (trochlear nerve).
Incyclotorsion may also be used to describe one part of the condition of the eye when a patient has a cranial nerve III (oculomotor nerve) palsy. The oculomotor nerve supplies the inferior oblique muscle (along with four other eye muscles - superior rectus, medial rectus, inferior rectus and the striated muscle of levator palpebrae superioris), and when this muscle is non-functional (as in oculomotor palsy) the eye incyclotorts; i.e. twists/rotates inward.