The orbital apex is the posterior vertex of the pyramidal orbit, where the optic canal (transmitting CN II and ophthalmic artery) and the superior orbital fissure (transmitting CN III, IV, V1 ophthalmic division, and VI, plus the ophthalmic veins) converge in a small crowded space formed by the sphenoid body and greater and lesser wings. The annulus of Zinn (common tendinous ring) originates here and forms the origin of all four rectus muscles.
Orbital apex syndrome is the combination of optic neuropathy (optic canal involvement) and oculomotor palsy (superior orbital fissure involvement) from a single lesion at the orbital apex. Causes include tolosa-hunt syndrome (idiopathic granulomatous inflammation), sinus mucocele extension, sphenoid sinusitis, metastasis, and cavernous sinus thrombosis. The syndrome requires urgent MRI to distinguish treatable inflammatory causes from neoplastic ones. Orbital apex decompression in thyroid eye disease relieves optic nerve compression when visual field loss occurs from apical orbital fat congestion.
A lesion compressing the orbital apex simultaneously affects the optic canal (producing optic neuropathy with decreased VA and colour vision) and the superior orbital fissure (producing oculomotor palsy with ptosis, ophthalmoplegia, and V1 sensory loss); urgent MRI with gadolinium distinguishes inflammatory (tolosa-hunt) from neoplastic causes and guides systemic corticosteroid or surgical treatment.
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