Corneal abrasion
Corneal abrasion is a medical condition involving the loss of the surface epithelial layer of the eye's cornea.

# Etiology
Corneal abrasions are generally a result of trauma to the surface of the eye.  Common causes include jabbing a finger into an eye or walking into a tree branch.  A foreign body in the eye may also cause a scratch if the eye is rubbed. Injuries can also be incurred by "hard" contact lenses that have been left in too long.  Damage may result when the lenses are removed, rather than when lens is still in contact with the eye.

# Symptoms and signs
Symptoms of corneal abrasion include pain, photophobia, a foreign-body sensation, and a reflex production of tears. Signs include epithelial defects and edema, and often conjunctival injection, swollen eyelids, and a mild anterior-chamber reaction. The vision may be blurred, both from any swelling of the cornea and the excess tears.

# Diagnosis
Although corneal abrasions may be seen with ophthalmoscopes, slit lamp microscopes provide higher magnification which allow for a more thorough evaluation. To aid in viewing, a fluorescein stain that fills in the corneal defect and glows with a cobalt blue-light is generally instilled first.
A careful search should be made for any foreign body, in particular looking under the eyelids. Injury following use of hammers or power-tools should aways raise the possibility of a penetrating foreign body into the eye, for which urgent ophthalmology opinion should be sought.

# Treatment
Although small abrasions may require no specific treatment, larger abrasions are typically treated for a few days with a topical antibiotic to prevent infection and a topical cycloplegic to reduce pain and improve comfort. The cycloplegic will also reduce a secondary inflammation of the iris known as an iritis. Eye pads used in "pressure patching" may also improve comfort and promote healing by preventing repeated eyelid blinking that may cause further physical distruption to the cornea, but they are generally not applied in contact lens wearers or when the abrasion is caused by vegetative material, such as a tree branch, or a finger nail. These conditions may pose the threat of a fungal infection and the warm, moist environment provided by pressure patching increases this possibility.
Due to the introduction of newer contact lens materials, mainly silicon hydrogels, pressure patch treatment is being phased out and replaced by "bandage contact lenses".  These newer materials provide much more oxygen to the cornea and can be fit tightly (providing minimal movement) with a low risk of corneal hypoxia and edema.  These lenses greatly decrease the patients pain and allow the patient to administer drops.
For recurrent corneal erosions, treatment may be had with a laser surgery called phototherapeutic keratectomy.

# Complications
Complications are the exception rather than the rule from simple  corneal abrasions. It is important that any foreign body is identified and removed, especially if containing iron as rusting will occur.
Occasionally the healed epithelium may be poorly adherent to the underlying basement membrane in which case it may detach at intervals giving rise to recurrent corneal erosions.