internuclear ophthalmoplegia
A disorder of the medial longitudinal fasciculus (MLF), the brainstem tract that carries the horizontal gaze signal from the abducens nucleus on one side to the medial rectus subnucleus on the other.
Signs on lateral gaze:
Adduction of the eye on the side of the lesion is impaired.
The abducting eye shows nystagmus.
Convergence is usually preserved, which separates INO from a medial rectus or oculomotor nerve palsy.
More detail
It may be unilateral or bilateral. Demyelination is the commonest cause in young adults and brainstem infarction in older ones.
Sources (5)
- Caloroso, E.E., Rouse, M.W. (1993). Clinical Management of Strabismus. Butterworth-Heinemann.
- Rutstein, R., Daum, K. (1997). Anomalies of Binocular Vision: Diagnosis & Management, Mosby.
- Rowe, F.J. (2012). Clinical Orthoptics. 3rd ed., Wiley-Blackwell.
- Noorden, G.K.V., Campos, E.C. (2002). Binocular Vision and Ocular Motility: Theory and Management of Strabismus. 6th ed., Mosby.
- Leigh, R.J., Zee, D.S. (2015). The Neurology of Eye Movements. 5th ed., Oxford University Press.
Reviewed October 2026
Related terms
Nearby in the glossary
- infravergence
- infraversion
- intermittent strabismus
- internuclear ophthalmoplegia
- intorsion (incyclodeviation)