A 25-year-old man is hit on the left eye by a fist. He develops enophthalmos, restricted upgaze, and diplopia on upward gaze. CT orbit shows a fracture of the orbital floor with herniation of orbital fat and inferior rectus into the maxillary sinus. The mechanism responsible for the restricted upgaze is:

• A Direct injury to the inferior oblique muscle
• B Entrapment of the inferior rectus and periorbital fat in the fracture defect restricting upgaze ✓
• C Oedema of the superior rectus secondary to hydraulic trauma
• D Superior orbital fissure syndrome from haemorrhage

Explanation

Blow-out fracture of the orbital floor occurs when sudden intraorbital pressure increase forces the thin orbital floor (paper plate lamina papyracea on the medial wall, or sinus roof of maxillary sinus for the floor) to fracture. The inferior rectus and periorbit herniate through the defect and become entrapped, mechanically restricting upgaze (not due to muscle paresis but to physical tethering). The positive forced duction test distinguishes mechanical restriction from a neurogenic palsy. Surgical release is required if diplopia persists after oedema resolution.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

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Written and medically reviewed by the StethoPrep medical team.