A patient with a lesion in the right paramedian pontine reticular formation (PPRF) will show:

• A Inability to adduct the right eye (internuclear ophthalmoplegia)
• B Upward gaze palsy with Parinaud's syndrome
• C Pendular nystagmus in all directions
• D Conjugate horizontal gaze palsy to the right side (eyes deviated to the left at rest) ✓

Explanation

The PPRF is the horizontal gaze center in the pons. It contains burst neurons that drive ipsilateral conjugate horizontal gaze. A destructive lesion of the right PPRF produces a conjugate horizontal gaze palsy to the right — the patient cannot look toward the side of the lesion, and eyes deviate away (to the left) at rest due to unopposed left PPRF activity. INO (internuclear ophthalmoplegia) results from a lesion in the medial longitudinal fasciculus (MLF), not PPRF. Parinaud's syndrome involves the dorsal midbrain.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.