Dysthyroid optic neuropathy (DON) in Graves' orbitopathy is MOST commonly caused by which mechanism?
- A Enlarged extraocular muscles compressing the optic nerve at the orbital apex ✓
- B Optic nerve stretch due to proptosis
- C Apical orbital fat compression of the optic nerve
- D Optic disc oedema from elevated IOP due to restricted outflow
Correct answer: A. Enlarged extraocular muscles compressing the optic nerve at the orbital apex
Explanation
In Graves' orbitopathy, DON results from hypertrophied, inflamed extraocular muscles (predominantly the inferior and medial recti) compressing the optic nerve at the orbital apex — the 'crowded apex' syndrome. This can occur without significant proptosis. Optic nerve stretch in severe proptosis is a less common mechanism. Apical fat itself does not primarily compress; it is the enlarged muscle bellies that cause compression. DON is a sight-threatening complication requiring urgent orbital decompression.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.