What type of x-ray (x-ray) is ordered to detect a foreign body in the eye?

CT Orbits Is the Preferred Imaging Modality for Detecting Foreign Bodies in the Eye

CT of the orbits without contrast is the most appropriate imaging study for detecting foreign bodies in the eye, with a sensitivity of 94.9% for metallic and glass foreign bodies. 1

Imaging Options for Orbital Foreign Bodies

First-Line Imaging:

• CT Orbits (without contrast):
  • Gold standard for detecting orbital foreign bodies
  • Superior for identifying both metallic and glass foreign bodies
  • Provides excellent visualization of orbital structures
  • Can detect associated injuries including fractures and soft tissue damage
  • Allows for precise localization of the foreign body

Alternative/Adjunctive Imaging:

• Plain Radiography (X-ray) of the Orbit:

  • Limited utility in modern practice
  • May be used as an initial screening tool only for metallic foreign bodies
  • Insufficient sensitivity for comprehensive evaluation
  • Has been largely replaced by CT in clinical practice 1
  • Sensitivity varies significantly by foreign body size (46% for small, 76% for medium, 93% for large objects) 2

• MRI Orbits:

  • Contraindicated when metallic foreign bodies are suspected due to risk of movement and further injury 1, 3
  • Superior for detecting wooden foreign bodies (which may appear as air on CT)
  • Should be used only after metallic foreign bodies have been excluded

Clinical Considerations

Important Factors Affecting Imaging Choice:

1. Foreign body composition:

   • Metallic objects are best detected by CT
   • Wooden objects may be better visualized on MRI (but only after metallic objects are excluded)

2. Location considerations:

   • Lower lateral quadrants of the orbit have the lowest detection sensitivity (53%)
   • Upper medial quadrants have the highest detection sensitivity (88%) 2

3. Size of foreign body:

   • Smaller objects are more difficult to detect
   • CT remains superior to plain radiography for small objects

Potential Pitfalls:

• False negatives with plain radiography: Plain X-rays can miss foreign bodies, particularly small ones or those in certain locations 4, 2
• MRI safety concerns: Never perform MRI when a metallic foreign body is suspected as it can cause movement of the object and worsen injury 3
• CT limitations: While highly sensitive (94.9%), CT is still not 100% sensitive, especially for very small or wooden foreign bodies 1

Management Algorithm

1. For suspected foreign body in eye:

   • Proceed directly to non-contrast CT of the orbits
   • Thin-section imaging with multiplanar reconstructions is optimal

2. If CT is negative but clinical suspicion remains high:

   • Consider ultrasound by an experienced operator (if no open globe injury)
   • Consider MRI only after metallic foreign body has been excluded by CT

3. If metallic foreign body is confirmed:

   • Urgent ophthalmologic consultation for removal
   • Absolutely avoid MRI

CT orbital imaging without contrast remains the definitive study for evaluating suspected foreign bodies in the eye, offering the best combination of sensitivity, safety, and ability to detect associated injuries.