A foreign body on the cornea

Essentials

All foreign bodies, including the rust ring caused by a metal foreign body should be removed.
In the case of a high-energy injury, other injuries, such as a penetrating eye injury, must be excluded. (Ocular injuries)

A foreign body on the cornea causes pain or is otherwise felt as if it were under the upper lid. In addition, the eye usually becomes watery and red.
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.

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.

After removing the foreign body, an antimicrobial ointment is applied to the eye and used 3–4 times a day for 5 days.
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.

If a foreign body or a rust ring cannot be removed, a large amount of antimicrobial ointment may be applied to the eye and it may be covered with an eye patch for the night and the removal may be retried the next day. If a significant amount of rust is still 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 antimicrobial ointment is used which is why it should be administered amply for first aid.