The anatomical and functional features of the medial longitudinal fasciculus (MLF) are discussed in BCSC Section 5, Neuro-Ophthalmology. The MLF integrates the nuclei of the cranial nerves governing ocular motility and has major connections with the vestibular nuclei. An intact MLF is essential for production of conjugate eye movements. Lesions of the MLF result in a typical pattern of dysconjugate movement called internuclear ophthalmoplegia (INO). Abnormalities of this pathway are frequently seen in patients with demyelinating disease, but they may also occur in patients who have had cerebrovascular accidents or brain tumors.
On horizontal versions, the eye ipsilateral to the MLF lesion adducts slowly and incompletely or not at all, whereas the abducting eye exhibits a characteristic horizontal jerk nystagmus (see Chapter 13). Both eyes adduct normally on convergence. Skew deviation may be present, in addition to exotropia.
If exotropia persists, medial rectus muscle resection and unilateral or contralateral lateral rectus muscle recession (to limit exotropia in lateral gaze) can help eliminate diplopia, particularly in bilateral cases.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.