A patient sustains a blow to the cheek and presents with enophthalmos, diplopia on upgaze, and infraorbital nerve hypaesthesia. CT face shows fracture of the orbital floor with herniation of orbital contents into the maxillary sinus. The mechanism causing diplopia in this injury is:
- A Direct optic nerve contusion
- B Hematoma compressing the oculomotor nerve in the cavernous sinus
- C Entrapment of the inferior rectus muscle or its fascial slings in the orbital floor fracture defect ✓
- D Dislocation of the eyeball anteriorly causing lens subluxation
Correct answer: C. Entrapment of the inferior rectus muscle or its fascial slings in the orbital floor fracture defect
Explanation
In a 'blowout' fracture of the orbital floor, increased intraorbital pressure from the blunt blow causes the thin orbital floor (formed by the maxillary and palatine bones) to fracture inward. The inferior rectus muscle and its surrounding fascial planes herniate into or become entrapped in the fracture gap, mechanically restricting upward gaze and causing binocular vertical diplopia on upgaze. Enophthalmos results from increased orbital volume. Infraorbital nerve hypaesthesia is due to the nerve running in the infraorbital canal immediately beneath the orbital floor.
Reference: Dhingra Diseases of Ear, Nose and Throat, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.