Any material that gets into the eye such as dust or sand, is a foreign body.
Superificial foreign bodies usually stick to the front of the eye in the conjunctiva and the cornea, and do not usually enter the eye itself.
Penetrating foreign bodies enter the eye through the cornea or the sclera. They are usually travelling at a high velocity and are often made of metal.
A patient may not remember a foreign body entering the eye, therefore it is always important to exclude one when a patient presents with a red eye.
Foreign bodies can blow onto the surface of the eye and lead to a prickling sensation, watering and a red eye.
Local anaesthetic drops such as proxymetacaine 0.5% should be instilled into the eye so that the foreign body can be removed easily. Small loose foreign bodies can be removed by irrigating the eye with plenty of water, and possibly using a cotton bud.
Subtarsal foreign bodies (under the upper eyelid) can be removed by asking the patient to look down. A cotton bud can be placed horizontally on the upper eyelid, and gently, the eyelid can be turned over the cotton bud handle so that the foreign body can be removed.
If the foreign body is made of iron then there may be a residual 'rust ring' on the cornea after it has been removed. This should be left on for about 2 days for it to soften and then removed by an Ophthalmologist. These 'rust rings' usually cause a corneal abrasion which should be managed appropriately.
As mentioned above, any penetrating foreign body in the cornea or sclera must be travelling at a high velocity, such as metal from explosions or machinery. The patient sometimes feels the foreign body entering the eye, but a very small one may go in unnoticed. It is important to establish the point of entry of foreign body on examining the eye, to establish its severity. If a foreign body reaches the lens, a cataract can develop within a few hours. If unsure, an X-ray of the orbit or a CT scan can be done to establish the location of the foreign body.
These intraocular foreign bodies must be removed under surgery.
Text taken from Kennerley Bankes ‘Clinical Ophthalmology’, ABC of eyes 4th edition, Basic Ophthalmology 9th edition (Richard A. Harper)
Image 1 - Cutting metal. Taken from http://www.cuttingtoolssite.com/wp-content/uploads/2011/04/metal-cutting.jpg
Image 2 - Foreign body on the cornea http://upload.wikimedia.org/wikipedia/commons/2/21/Foreign_body_in_eye.jpg
Image 3 - instilling local anaesthetic. Taken from http://webeye.ophth.uiowa.edu/eyeforum/images/glaucoma/instil.jpg
Image 4 - irrigating the eye. Taken from http://www.google.co.uk/imgres?imgurl=http://www.vision-and-eye-health.com/images/Irrigation2.jpg&imgrefurl=http://www.vision-and-eye-health.com/eye-health-protection.html&usg=__QQTyhp8LnaXXz8bNvgp2IXoXNJg=&h=134&w=134&sz=5&hl=en&start=35&zoom=1&um=1&itbs=1&tbnid=_jeuK71Yz-sjrM:&tbnh=92&tbnw=92&prev=/images%3Fq%3Dirrigating%2Bthe%2Beye%26start%3D20%26um%3D1%26hl%3Den%26sa%3DN%26ndsp%3D20%26tbm%3Disch&ei=jV2tTdeCDMKq8AOdmeHyAQ
Image 5 - subtarsal foreign body http://www.tedmontgomery.com/the_eye/eyephotos/pics/SubtarsalForeignBody.jpg
Image 6 - Corneal rust ring. Taken from http://www.tedmontgomery.com/the_eye/eyephotos/pics/CornealFBRustRing.jpg
Image 7 - Intraocular foreign body. Taken from http://www.osnsupersite.com/images/OSN/200910a/agarwal50F1.jpg
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