Synopsis
Distinguish internuclear disconnection, nuclear and infranuclear ocular-motor palsy, and supranuclear gaze disorders from the pattern of saccades, pursuit, vestibulo-ocular responses and accompanying brainstem signs.
- Horizontal conjugate gaze requires coordinated activity between the pontine horizontal gaze centre, ipsilateral sixth-nerve nucleus and the contralateral third-nerve medial rectus subnucleus linked by the medial longitudinal fasciculus.
- Internuclear ophthalmoplegia causes impaired adduction of the eye on the side of the medial longitudinal fasciculus lesion with abducting nystagmus of the other eye during horizontal gaze.
- Convergence may be preserved in a classic posterior internuclear lesion, but variable convergence neither proves nor excludes the diagnosis and depends on lesion extent and examination technique.
Key red flags
Adduction failure on one side with abducting nystagmus of the fellow eye during horizontal gaze supports an ipsilateral medial longitudinal fasciculus lesion, often ischaemic when onset is abrupt.
Investigation priorities
Define conjugacy, direction, speed, range and nystagmus to separate internuclear, gaze-centre, nerve and junctional patterns.
Management branches
A conjugate gaze abnormality or internuclear pattern starts abruptly, especially with vertigo, ataxia, dysarthria, weakness or sensory change.
- Establish last known well, perform ABCDE and glucose and document pupils, eye positions, horizontal and vertical range, nystagmus, face, bulbar function, limbs, sensation and coordination.
- Contact the stroke service for urgent CT, vascular imaging and MRI planning; do not dismiss disabling diplopia because FAST is negative or non-contrast CT appears normal.