Corneal abrasion

What it is

A corneal abrasion is an epithelial defect of the cornea, usually due to trauma from fingernails, paper or twigs, or to a contact lens. It is also one of the things to look for after blunt trauma to the eye, such as a fist, where a hyphaema may be seen with it.

How it presents

Pain, redness, tearing, photophobia and a foreign body sensation.

How it is diagnosed

The de-epithelialized area stains with fluorescein dye on slit lamp examination, and the pain is relieved by a topical anesthetic. The abrasion must be told apart from a corneal ulcer:

• Time course: the abrasion is acute and instantaneous, the ulcer is subacute over days.
• History of trauma: common with the abrasion, rare with the ulcer.
• The cornea: clear in the abrasion, a white necrotic area in the ulcer.
• Iris detail: clear in the abrasion, obscured in the ulcer.
• Corneal thickness: normal in the abrasion, the ulcer may have a crater defect with thinning.
• Extent: the abrasion stays in the epithelium, the ulcer shows extension into the stroma.

The same two tests carry the negative. In an eye with pain the slit-lamp examination with fluorescein staining and tonometry, whose normal is 12-22 mmHg, are the key steps, and persistence of pain despite an ocular anesthetic, with a normal fluorescein examination, suggests anterior uveitis, scleritis or acute angle-closure glaucoma instead.