A patient develops a 'one-and-a-half syndrome' (conjugate gaze palsy to one side plus ipsilateral internuclear ophthalmoplegia). The anatomical lesion responsible is located in the:
- A Ipsilateral PPRF and ipsilateral MLF (paramedian pontine reticular formation and medial longitudinal fasciculus on the same side) ✓
- B Contralateral PPRF and MLF
- C Ipsilateral frontal eye field
- D Bilateral cortical lesions in parietal lobes
Correct answer: A. Ipsilateral PPRF and ipsilateral MLF (paramedian pontine reticular formation and medial longitudinal fasciculus on the same side)
Explanation
One-and-a-half syndrome results from a unilateral pontine lesion affecting both the PPRF (parapontinne reticular formation) or abducens nucleus (causing ipsilateral horizontal gaze palsy — the 'one') AND the ipsilateral MLF (causing ipsilateral internuclear ophthalmoplegia — the 'half'). The net result is that only the contralateral eye can abduct (with nystagmus), while the ipsilateral eye cannot move horizontally in either direction. Common causes include MS, pontine infarct, or pontine glioma.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.