A foreign body on the cornea

Essentials

  • All foreign bodies, including the rust ring caused by a metal foreign body should be removed.

Symptoms

  • A foreign body on the cornea is felt as if it were under the upper lid.
  • A metal foreign body rapidly corrodes (picture (Foreign body on the cornea with rust ring)). All the rust must be removed because it causes irritation and may cause corneal scarring.
  • After the foreign body has been removed, the feeling of a foreign body continues for 1–2 days until the epithelium of the cornea has regenerated.
  • If the foreign body was situated in the central part of the cornea, the patient may be left with a permanent visual impairment. The restoration of normal visual acuity takes longer than epithelization in foreign body injuries of the central cornea because the new epithelium is not as transparent to light as mature epithelium.

Techniques for foreign body removal

  • The patient lies supine.
  • The eye is anaesthetized with a local anaesthetic (oxybuprocaine, tetracaine) dropped into the eye.
  • Use a magnifying glass. Use the blunt tip of a foreign body needle to remove the foreign body and rust.
  • Rust formed around a metal chip needs to be removed.
  • The removal of foreign bodies located peripherally on the cornea is often more painful than the removal of centrally located ones.

Further treatment

  • If no significant erosion remains, a single dose of an oculentum is sufficient. If the recovery of the cornea is delayed, local antibiotics should be used.
  • Use antibiotic (e.g. chloramphenicol) drops or an oculentum (3–4 times a day for 3–4 days) for the treatment of an erosion.
  • Patching the eye does not accelerate the healing of a corneal erosion [Evidence Level: A] but it may be used to reduce pain caused by eyelid movements.
  • Recurrent erosion is most commonly caused by delayed healing of the original ulcer which prevents firm attachment of the new epithelium. This may be caused by an abnormality of the basement membrane, blinking over the ulcer or the prescription of a local anaesthetic to treat the ulcer.

Indications for referral to an ophthalmologist

  • If a foreign body or a rust ring cannot be removed the eye may be covered with a greasy dressing for the night and the removal may be retried the next day. If a significant amount of rust is left the patient should be referred to an ophthalmologist within 1–2 days (not necessarily in the evening or during the weekend).
  • The rust is easier to remove if an oculentum is used which is why it should be administered amply for first aid.

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