A 35-year-old woman presents with bilateral exophthalmos, lid retraction, lid lag on downgaze, and periorbital oedema. She has a history of hyperthyroidism treated with carbimazole. Thyroid function tests are currently normal. The most appropriate first-line investigation to assess orbital involvement is:
- A CT or MRI of the orbit ✓
- B B-scan ultrasonography
- C Visual evoked potentials
- D Intraocular pressure in upgaze
Correct answer: A. CT or MRI of the orbit
Explanation
Thyroid-associated orbitopathy (Graves ophthalmopathy) causes enlargement of the extraocular muscles (especially inferior and medial recti) and orbital fat expansion leading to proptosis, lid retraction, and restrictive strabismus. CT or MRI of the orbit is the investigation of choice to assess muscle belly enlargement (sparing tendon insertion — distinguishing from orbital myositis), optic nerve compression at the apex, and degree of proptosis. Clinical activity score (CAS) guides treatment decisions.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.