Which imaging modality is the investigation of choice for detecting and localising a suspected intraocular foreign body, and why is MRI avoided in certain cases?
- A Ultrasound B-scan; MRI is avoided because it cannot detect glass
- B Plain orbital radiographs; MRI is avoided because of cost
- C Non-contrast CT orbit; MRI is avoided when the foreign body is ferromagnetic because the magnetic field can cause movement and further damage ✓
- D MRI orbit; CT is avoided because of radiation dose to the lens
Correct answer: C. Non-contrast CT orbit; MRI is avoided when the foreign body is ferromagnetic because the magnetic field can cause movement and further damage
Explanation
Thin-section non-contrast CT of the orbits is the modality of choice for suspected intraocular foreign body because it detects metallic, glass, and stone fragments with high sensitivity and precisely localises them. MRI is contraindicated when a ferromagnetic foreign body is suspected, since the magnetic field can displace the fragment and cause additional intraocular injury. Ultrasound is useful adjunctively but is operator dependent and risks globe pressure in an open eye.
Reference: Kanski's Clinical Ophthalmology, 9th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.