Corneal abrasion

Corneal abrasion
Classification and external resources
A corneal abrasion after staining with fluorescein.
ICD-10	S05.0
ICD-9	918.1
DiseasesDB	3108
eMedicine	oph/247 emerg/828

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.

Symptoms and signs

Symptoms of corneal abrasion include pain, photophobia, a foreign-body sensation, excessive squinting, and a reflex production of tears. Signs include epithelial defects and edema, and often conjunctival injection, swollen eyelids, large pupils and a mild anterior-chamber reaction. The vision may be blurred, both from any swelling of the cornea and the excess tears. Crusty build up 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 jabbing a finger into an eye, walking into a tree branch, getting grit in the eye and then rubbing the eye or being hit with a piece of projectile metal. 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 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.

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.

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

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 sometimes a topical cycloplegic to reduce pain and improve comfort.^{[citation needed]}. A single large study by John W King, et al.; showed that only 0.7% of corneal abrasions actually become infected without antibiotic drops, questioning the necessity of such practice.^[1] The cycloplegic may also reduce a secondary inflammation of the iris known as an iritis.^{[citation needed]} A 2000 review however found no good evidence to support the use of cycloplegics/mydriatics.^[2] It is often believed that eye pads used in "pressure patching" may improve comfort and promote healing by preventing repeated eyelid blinking that may cause further physical distruption to the cornea.^{[citation needed]} Controlled studies have however not supported this assertion.^[3][4]

Due to the introduction of newer contact lens materials, mainly silicone 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 fitted tightly (providing minimal movement) with a low risk of corneal hypoxia and oedema. 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.

Topical anesthetics are not to be used for continued pain control as they can reduce healing and cause secondary keratitis.^[5]

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.

References

1. ^ Canadian Family Physician, VOL 39, Nov, 1993 pages 2349-2352
2. ^ "BestBets: Mydriatics in corneal abrasion". http://www.bestbets.org/bets/bet.php?id=169. 
3. ^ Arbour JD, Brunette I, Boisjoly HM, Shi ZH, Dumas J, Guertin MC (March 1997). "Should we patch corneal erosions?". Arch. Ophthalmol. 115 (3): 313–7. PMID 9076201. 
4. ^ "UpToDate Inc.". http://www.uptodate.com/online/content/topic.do?topicKey=priophth/2242&selectedTitle=1~30&source=search_result#14. 
5. ^ "eMedicine - Corneal Abrasion : Article by Arun Verma". http://www.emedicine.com/oph/TOPIC247.HTM.