The inferior rectus depresses the abducted eye and is associated with the lower eyelid retractors, explaining why inferior rectus palsy produces lower eyelid elevation (apparent lower lid retraction) on the affected side. Orbital floor blowout fractures can trap the inferior rectus in the fracture, producing mechanical limitation of upgaze — enophthalmos and diplopia in upgaze are the hallmarks of orbital floor entrapment.
| Origin | Common tendinous ring (annulus of Zinn) at the orbital apex |
|---|---|
| Insertion | Inferior sclera 6.5 mm from the limbus — the thickest of the four rectus muscles |
| Nerve Supply | Inferior division of CN III |
| Blood Supply | Ophthalmic artery |
| Actions | Depression (primary when abducted); External rotation (extorsion); Adduction |
|---|
Inferior rectus entrapment in orbital floor fractures produces a positive forced duction test (inability to passively elevate the eye against the fibrotic entrapped muscle) distinguishing it from neurogenic superior rectus palsy (negative forced duction).
Orbital floor fractures trap the inferior rectus producing upgaze limitation confirmed by the forced duction test. Surgical repair of the orbital floor releases the trapped muscle. White-eyed blowout fracture in children produces acute-onset upgaze limitation with vagal symptoms (nausea, vomiting, bradycardia) from the vagal reflex of the trapped rectus — a surgical emergency requiring same-day release.
Not directly palpable. Assessed by gaze testing and forced duction test under anaesthesia.
Inferior rectus muscle trapped in orbital floor blowout fracture producing mechanical upgaze limitation requiring surgical floor repair and muscle release.
