A patient with a demyelinating lesion at the right medial longitudinal fasciculus (MLF) at the level of the pons would demonstrate which characteristic eye movement abnormality?

• A Left internuclear ophthalmoplegia: adduction failure of the left eye on right gaze, abduction nystagmus of the right eye
• B Bilateral gaze palsy toward the right
• C Right abducens nerve palsy with no adduction nystagmus
• D Right internuclear ophthalmoplegia: adduction failure of the right eye on left gaze, abduction nystagmus of the left eye ✓

Explanation

The MLF carries signals from the contralateral PPRF/abducens internuclear neurons to the ipsilateral medial rectus subnucleus of CN III. A right MLF lesion disrupts adduction of the right eye (ipsilateral to the lesion) during conjugate left gaze, while the left eye abducts normally but shows nystagmus (abduction nystagmus). This is right INO. Convergence is typically preserved because it uses a different pathway. In MS, bilateral INO ('Wall-eyed bilateral INO', WEBINO) may occur.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.