Corneal abrasion

Corneal abrasion
A corneal abrasion after staining with fluorescein.
Classification and external resources
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 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 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" 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

Cycloplegics may also reduce a secondary inflammation of the iris known as an iritis. A 2000 review however found no good evidence to support the use of cycloplegics/mydriatics.^[1] Also, as mentioned earlier in this text, the practice of pressure patching should never be used on a person presenting with a corneal abrasion who is also a contact lens wearer. This is due to a susceptibility in this group to develop a gram negative bacterial infection caused by Pseudomonas Aeruginosa, a bacterium that colonizes in the bio films of contact lens users's eyes. An abrasion creates an opportunity for the bacteria to invade that the eye is usually able to successfully thwart. However, pressure patching in addition to providing optimal environmental factors for the bacteria's growth, robs the eye of its natural defenses against such organisms in the form of tears. Tears are oxygen carrying mechanisms that help flush the eye area of the potential threatening bacterial organisms. When an eye is pressure patched, tears are prevented from forming, greatly increasing the chance of the development of severe bacterial keratitis in contact lens wearing individuals with abraded corneas. It is therefore very important that the treating physician obtain a sufficient clinical background on the patient before implementing treatment in these cases. This is a known medical fact and is supported by numerous journals, controlled studies and articles published by such organizations as the American Academy of Optometry, the Center for Disease Control, and the American Ophthalmology Association. ^[2][3] Furthermore, meta-analysis of eleven trials (1014 patients), some including and others excluding contact lens users, favors no patching on the first day of healing (risk ratio (RR) 0.89, 95% Confidence Interval 0.79 to 0.99). There is no significant difference between patching and no patching on the second and third day of healing. The meta-analysis, however, did not discretely analyze differences between contact lens users and non-users.^[4] A soft contact lens can be used in conjunction with a prescription drop (steroid/antibiotic) in order to treat the abrasion and helps with comfort until the abrasion is resolved. 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 edema. These lenses greatly decrease the patient's pain and allow the patient to administer drops. A prospective, randomized, masked, three-arm clinical study of 66 patients comparing 3 different treatment modalities (pressure patching with ofloxacin ointment, therapeutic contact lens with ofloxacin eye drops and ofloxacin ointment alone) found no statistically or clinically significant difference regarding the therapeutic value of the modalities used for traumatic corneal abrasions. The authors concluded that the treatment of choice for traumatic abrasions may be adapted to the needs and preferences of the patient.^[5]

For recurrent corneal erosions, treatment may be had with a laser surgery called phototherapeutic keratectomy. ^[6] Topical anesthetics are not to be used for continued pain control as they can reduce healing and cause secondary keratitis.^[7]

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