intorsion

Intorsion is a cyclotorsional movement of the eye about the visual axis in which the top of the eye rotates toward the nose. It is the inward rotation component of ocular torsion, with extorsion being the opposite outward rotation. Intorsion can occur as part of normal binocular viewing or as part of various eye-movement or misalignment disorders.

Physiology and mechanism: The superior oblique muscle is the primary driver of intorsion, with additional contribution from other extraocular muscles in different gaze positions. Intorsion can be produced during adduction and is often assessed together with vertical and horizontal eye movements to understand a patient’s motility pattern. Pathologic torsion refers to torsional misalignment beyond normal physiologic variation and can lead to visual symptoms such as torsional diplopia.

Clinical significance and assessment: Abnormal intorsion or extorsion can cause cyclodiplopia, a misalignment of the two eyes that worsens with certain gaze positions. Clinically, torsion is evaluated with tests such as the double Maddox rod test, which measures torsional deviation in degrees, and by fundus examination, where the optic disc and retinal vessels may appear rotated. Imaging and photographic methods can also document ocular torsion.

Causes and management: Physiologic torsion occurs during normal fixation. Pathologic torsion may arise from cranial nerve palsies (notably trochlear nerve palsy affecting the superior oblique), skew deviations, trauma, or certain forms of strabismus. Treatment targets the underlying cause and may include prism correction or surgical adjustment of the oblique or other extraocular muscles to reduce torsional misalignment and associated diplopia. Regular follow-up assesses whether torsion changes with gaze, head position, or treatment.