Corneal Foreign Body

A corneal foreign body is a particle embedded in or adherent to the corneal epithelium or anterior stroma.

• Common agents: metal fragments (grinding, hammering, drilling), wood, glass, plant matter, sand, insect parts, eyelash fragments.
• Ferrous particles oxidise within hours and leave a rust ring in the stroma, which delays healing and causes a sterile infiltrate.
• Vegetable matter carries a high risk of fungal and bacterial keratitis; contaminated metal can carry Bacillus cereus.
• High velocity particles can penetrate the cornea or enter the globe, so an intraocular foreign body must always be excluded.

• Sudden foreign body sensation, pain, tearing, photophobia, blepharospasm, redness.
• Visible particle on the cornea, often with a surrounding haze and a rust ring after 12 to 24 hours.
• Mild anterior chamber flare and cells (sterile reaction); a dense infiltrate with hypopyon suggests infection.
• Reduced vision if the particle is central.
• Features of globe penetration: full thickness corneal wound, shallow anterior chamber, irregular pupil, iris transillumination defect, lens opacity, low pressure, positive Seidel test.

• History: mechanism, particle type, velocity, whether eye protection was worn, time since injury.
• Visual acuity before any treatment, then slit lamp examination with fluorescein; depth of the foreign body in relation to corneal thickness.
• Evert the upper lid to exclude a retained subtarsal particle.
• Seidel test for leakage; dilated fundus examination for high velocity injuries.
• CT orbits with thin cuts when intraocular foreign body is suspected. Avoid MRI if metal is possible.

• Topical anaesthetic (proxymetacaine 0.5 percent or tetracaine 1 percent) for the procedure only.
• Remove at the slit lamp: irrigate loose particles; lift superficial particles with a moist cotton bud, then dislodge embedded ones with a 25 gauge needle (bevel up, tangential to the surface) or a spud.
• Rust ring: remove at the same visit if it is superficial and not central; use an Alger brush or a burr. A deep or central ring may be left for 24 to 48 hours, when it softens and is easier to remove.
• Treat the residual abrasion: chloramphenicol 0.5 percent drops or 1 percent ointment four times daily for 5 to 7 days, or erythromycin 0.5 percent ointment. Contact lens wearers need an antipseudomonal fluoroquinolone (ofloxacin 0.3 percent or ciprofloxacin 0.3 percent four times daily).
• Cycloplegic for pain and iritis: cyclopentolate 1 percent twice daily for 2 to 3 days. Oral paracetamol 1 g four times daily and ibuprofen 400 mg three times daily with food.
• Do not patch. Never dispense topical anaesthetic for home use.
• Tetanus prophylaxis if immunisation is out of date or the wound is dirty (toxoid 0.5 mL intramuscularly).
• Organic or deep matter: take cultures when infection is suspected and review at 24 hours.
• Suspected penetration: place a rigid shield, no pressure on the eye, nil by mouth, systemic antibiotic (levofloxacin 750 mg or moxifloxacin 400 mg), and urgent surgical exploration.
• Review at 24 to 48 hours to confirm re-epithelialisation. Counsel on protective eyewear.