Keratitis is inflammation of the cornea, the clear window of the front of the eye. The cornea is an incredibly unique tissue in the body, in that it is perfectly transparent, and allows light to pass through to help us see. It is incredibly fragile, and depends greatly on the mechanisms in place which protect it from the harsh outside environment. When the cornea becomes injured, or when forces external to the cornea drive inflammation around it, scarring can occur, which is often permanent – this is the number one cause of blindness in the world.
Decreased vision, often described as blurry or hazy, is a frequent complaint of patients with keratitis. When inflammation affects the front surface of the cornea, it is usually associated with tremendous sharp pain and light sensitivity, sometimes along with redness and tearing. Inflammation of deeper levels of the cornea may present with only blurring, but may equally threaten with permanent vision loss.
There are many triggers of corneal inflammation, and the most frequent is infection, notably the herpes virus. Autoimmune diseases, particular those with components involving vasculitis, or inflammation of blood vessels, can cause inflammation especially around the outside edges of the cornea, known as peripheral keratitis. Additionally, problems such as dry eye and abnormal eyelid function, which lead to poor corneal health, can lead to keratitis by making the corneal more susceptible to infection or other types of inflammation. Contact lens abuse and poor lens hygiene are also common causes of corneal inflammation via secondary infection.
Herpes is mostly known as the virus which causes painful sores in and around the mouth, as well as a sexually transmitted disease. It is actually quite common, with most people in a given population being exposed to it at some point in their life. Usually it lies dormant in nerves throughout the body, and can become “activated” during moments of illness, stress, or just bad luck. It travels through these nerves that can also connect to and affect several parts of the eye, including the cornea, and can cause devastating inflammation and scarring.
Aside from herpes, bacterial and fungal infections can cause severe keratitis requiring aggressive treatment and sometimes surgery. Diseases which affect the eyelids, such as thyroid disease or rosacea, can lead to a compromised corneal surface, and secondary infection. Severe systemic allergies involving the eyes can also involve inflammation of the cornea. Auto-immune diseases, especially rheumatoid arthritis and types of vasculitis, can be a risk factor for developing keratitis and dangerous thinning of the cornea which may also require surgery.
Keratitis is diagnosed by slit lamp examination by an ophthalmologist. History of illness and review of systems is always important in any inflammatory condition. The cause of keratitis, however, may need further work up, which may require blood work, culture of ocular fluid or tissue, or even biopsy.
Scarring is the most frequent complication, and this may result in severe decrease in vision if the scar is located centrally in the visual axis. Infectious keratitis that is not promptly treated can progress through the entire thickness of the cornea, or begin to involve neighboring sclera, possibly leading to spread of infection inside the eyeball or perforation, or both, and possible loss of the eye. Thinning of the peripheral edges of the cornea may lead to irregular astigmatism, and if severe, can also lead to perforation, which can also lead to infection, and possible loss of the eye.
Aggressive eradication of infection is the most important step in treating infectious keratitis, which may involve around-the-clock use of antibiotic eye drops. Cycloplegic (dilating) drops can be used for relief from light sensitivity. Hospitalization is sometimes needed for those patients who are not able to properly administer drops themselves, or when systemic antibiotics are used. Viral keratitis is best treated with use of systemic antiviral medication, along with topical antiviral drops or ointment, and addition of corticosteroid drops once surface disease is resolved. Fungal keratitis is treated in a similar fashion, however, corticosteroids should never be used to help resolve inflammation or scarring in these cases.
Non-infectious keratitis is best treated with topical corticosteroid, with close observation when there is significant thinning to make sure the wound does not worsen. Use of steroids in ulcerative (thinning) keratitis is controversial for this reason; however the underlying cause for thinning – inflammation – must be kept in mind, and treated. Topical antibiotics are given when superficial corneal damage exists as prophylaxis against infection. Severe disease, especially that driven by known autoimmune disease, may require oral or intravenous corticosteroids or immunomodulatory therapy.
Surgical therapy may be useful in acute keratitis. Peripheral ulcerative keratitis may benefit from simple dissection of conjunctiva around the active inflammation. Corneal glue applied to severely thinned or perforated areas, along with a contact lens bandage, can help wounds regain structural integrity. Removal of superficial corneal layers may rid the burden of severe infection or scarring, however corneal transplant may be necessary for aggressive ulcers non-responsive to therapy or for central scarring left behind by treated keratitis. Some research is being done to see if a surgical method involving riboflavin and ultraviolet light may be helpful in treating corneal infections.
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