Corneal abrasion

Corneal abrasion
File:Human cornea with abrasion highlighted by fluorescein staining.jpg A corneal abrasion after staining with fluorescein.
Classification and external resources
Specialty
ICD-10	S05.0
ICD-9-CM	918.1
DiseasesDB	3108
eMedicine	oph/247 emerg/828
Patient UK	Corneal abrasion

For corneal abrasions in dogs and cats, see Corneal ulcers in animals.

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

Signs and symptoms

Signs and symptoms of corneal abrasion include pain, trouble with bright lights, a foreign-body sensation, excessive squinting, and reflex production of tears. Signs include epithelial defects and edema, and often conjunctival injection (a tear in the surface of the cornea with possible intruding foreign matter), swollen eyelids, large pupils and a mild anterior-chamber reaction. The vision may be blurred, both from any swelling of the cornea and from excess tears. Crusty buildup from excess tears may also be present.

Cause

Corneal abrasions are generally a result of trauma to the surface of the eye. Common causes include being poked by a finger, walking into a tree branch, and wearing old contact lenses. A foreign body in the eye may also cause a scratch if the eye is rubbed. Injuries can also be incurred by "hard" or "soft" contact lenses that have been left in too long. Damage may result when the lenses are removed, rather than when the lens is still in contact with the eye. In addition, if the cornea becomes excessively dry, it may become more brittle and easily damaged by movement across the surface. Soft contact lens wear overnight has been extensively linked to gram negative keratitis (infection of the cornea) particularly by a bacterium known as Pseudomonas aeruginosa which forms in the eye's biofilm as a result of extended soft contact lens wear. When a corneal abrasion occurs either from the contact lens itself or another source, the injured cornea is much more susceptible to this type of bacterial infection than a non-contact lens user's would be. This is an optical emergency as it is sight (in some cases eye) threatening. Contact lens wearers who present with corneal abrasions should never be pressure patched because it has been shown through clinical studies that patching creates a warm, moist dark environment that can cause the cornea to become infected or cause an existing infection to be greatly accelerated on its destructive path.

Corneal abrasions are also a common and recurrent feature in people who suffer specific types of corneal dystrophy, such as lattice corneal dystrophy. Lattice dystrophy gets its name from an accumulation of amyloid deposits, or abnormal protein fibers, throughout the middle and anterior stroma. During an eye examination, the doctor sees these deposits in the stroma as clear, comma-shaped overlapping dots and branching filaments, creating a lattice effect. Over time, the lattice lines will grow opaque and involve more of the stroma. They will also gradually converge, giving the cornea a cloudiness that may also reduce vision. In some people, these abnormal protein fibers can accumulate under the cornea's outer layer—the epithelium. This can cause erosion of the epithelium. This condition is known as recurrent epithelial erosion. These erosions: (1) Alter the cornea's normal curvature, resulting in temporary vision problems; and (2) Expose the nerves that line the cornea, causing severe pain. Even the involuntary act of blinking can be painful.

Boehm Syndrome defines erosion events that occur only during periods of sleep.

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 always raise the possibility of a penetrating foreign body into the eye, for which urgent ophthalmology opinion should be sought.

Treatment

Medications

Topical antibiotics may be reasonable.

One review has found that eye drops to freeze the surface of the eye such as tetracaine improve pain; however, their safety is unclear. Another review did not find evidence of benefit and concluded there was not enough data on safety.

NSAID eye drops are also useful. A 2000 review found no good evidence to support medications that paralysis the iris.

Patching

A meta-analysis favors no patching on the first day of healing. There is no significant difference between patching and no patching on the second and third day of healing.

Recurrent disease

There is not good evidence for the treatment of recurrent disease. Special content lenses do not appear very useful.

Complications

Complications are the exception rather than the rule from simple corneal abrasions. It is important that any foreign body be 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.