A lesion of the right paramedian pontine reticular formation (PPRF) causes:

• A Loss of rightward saccades with preserved pursuit, causing gaze deviation to the LEFT
• B One-and-a-half syndrome with loss of rightward gaze AND ipsilateral INO
• C Bilateral horizontal gaze palsy due to crossing of all horizontal gaze pathways at the PPRF
• D Loss of all rightward conjugate eye movements (saccades and pursuit) — ipsilesional gaze palsy with eyes deviated toward the LEFT ✓

Explanation

The PPRF (paramedian pontine reticular formation) is the horizontal gaze center in the pons; it controls ipsilateral horizontal saccades by sending excitatory signals to the ipsilateral CN VI nucleus (which moves the ipsilateral lateral rectus and, via the MLF, the contralateral medial rectus). A destructive right PPRF lesion impairs all rightward eye movements — both saccades (the PPRF generates burst firing for saccades) and pursuit (PPRF receives pursuit commands from the ipsilateral cerebello-ponto pathway). The eyes are deviated toward the left (away from the lesion), as intact left PPRF drives eyes leftward unopposed. This contrasts with a frontal eye field (FEF) lesion, where eyes deviate toward the lesion side (ipsilateral). One-and-a-half syndrome requires additional ipsilateral MLF involvement (combined PPRF + MLF lesion).

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.