A 26-year-old woman developed horizontal diplopia after a road traffic accident. She cannot abduct the left eye fully, there is no enophthalmos and vertical gaze is normal. CT shows a fracture of the left lamina papyracea with medial bowing of the medial rectus. The most likely diagnosis is:

• A Orbital floor blowout fracture
• B Medial orbital wall (lamina papyracea) blowout fracture with medial rectus entrapment ✓
• C Sixth nerve palsy from raised intracranial pressure
• D Direct traumatic myopathy of the lateral rectus

Explanation

The lamina papyracea is the thinnest bony wall of the orbit and may fracture with medial rectus or superior oblique entrapment even when the floor is intact. Entrapment produces horizontal diplopia worst on abduction, and CT confirms the defect with medial rectus displacement into the ethmoid sinus. A sixth nerve palsy gives abduction weakness without any bony defect, and direct lateral rectus injury would spare the characteristic CT finding of a fractured medial wall.

Reference: Scott-Brown's Otorhinolaryngology and Head and Neck Surgery, 8th ed.

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Written and medically reviewed by the StethoPrep medical team.