Internuclear ophthalmoplegia (INO) is characterized by which specific eye movement abnormality and its pathological basis?

• A Ipsilateral gaze palsy; lesion in the contralateral PPRF
• B Bilateral horizontal gaze palsy; pontine tegmentum infarct
• C Upbeat nystagmus with convergence spasm; midbrain lesion
• D Ipsilateral adduction deficit with contralateral abducting nystagmus; lesion in the ipsilateral MLF between abducens nucleus and oculomotor nucleus ✓

Explanation

INO results from a lesion in the medial longitudinal fasciculus (MLF) on the side of the adduction deficit. The MLF carries axons from the abducens interneurons (CN VI nucleus) to the contralateral oculomotor nucleus (medial rectus subnucleus). A right MLF lesion causes: right eye adduction failure on leftward gaze (right medial rectus cannot abduct), with left eye abducting nystagmus (compensatory). Convergence is typically preserved. Bilateral INO (WEBINO) in a young person strongly suggests MS; unilateral INO in elderly suggests pontine infarct.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.