Wednesday, May 3, 2017

Corneal abrasion

Commonly caused by a foreign body, a corneal abrasion is a scratch on the surface epithelium of the cornea. An abrasion or foreign body in the eye is the most common eye injury. With treatment, the prognosis is usually good.

A corneal abrasion usually results from a foreign body, such as a cinder or a piece of dust, dirt, or grit, which becomes embedded under the eyelid. Even if the foreign body is washed out by tears, it may still injure the cornea.
A small piece of metal that gets in the eyes of workers who don’t wear protective glasses quickly forms an abrasion and then forms a rust ring on the cornea. Abrasions also commonly occur in the eyes of people who fall asleep wearing hard contact lenses. A corneal scratch produced by a fingernail, a piece of paper, or another organic substance may cause a persistent lesion. The epithelium doesn’t always heal properly, and a recurrent corneal erosion may develop, with delayed effects more severe than those of the original injury.
Signs and symptoms
Typically, corneal abrasions produce redness, increased tearing, a sensation of “something in the eye” and, because the cornea is richly endowed with nerve endings from the trigeminal nerve (cranial nerve V), pain disproportionate to the size of the injury. A corneal abrasion may affect visual acuity, depending on the size and location of the injury.
A history of eye trauma or prolonged wearing of contact lenses as well as typical symptoms suggest corneal abrasion. Staining the cornea with fluorescein stain confirms the diagnosis: The injured area appears green when examined with a Wood’s lamp or black light. Slit-lamp examination discloses the depth of the abrasion.
Examining the eye with a flashlight may reveal a foreign body on the cornea; the eyelid must be everted to check for a foreign body embedded under the lid.
Before beginning treatment, a test to determine visual acuity provides a medical baseline and a legal safeguard.
The first steps in treatment include examining the eye and checking visual acuity. If the foreign object is visible, the eye can be irrigated with normal saline solution.
Removal of a deeply embedded foreign body is done with a foreign-body spud, using a topical anesthetic. A rust ring on the cornea must be removed at the slit-lamp examination with an ophthalmic burr, after applying a topical anesthetic. When only partial removal is possible, reepithelialization lifts the ring again to the surface and allows complete removal the next day.
Treatment also includes instillation of a cycloplegic eyedrop and broad-spectrum antibiotic eyedrops in the affected eye every 3 to 4 hours.

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