Keratitis

Schematic of the structure of the eye showing the cornea, the site of inflammation in keratitis. Source: NEI/NIH.

Types

Keratitis refers to inflammation of the cornea which is the clear covering over the pupil and iris. The disease process can be superficial (involving only the outer layers of the cornea) or can be interstitial (affecting deeper layers). Superficial keratitis usually does not result in corneal scar formation after healing, whereas scars can form in interstitial types, resulting in a permanent decrease in vision.

Keratoconjunctivitis refers to inflammation of the cornea and the conjunctiva, the membrane that covers the white part of the eye and lines the inside of the eyelids.

Signs and Symptoms

Clouding of the cornea from keratitis caused by congenital syphilis. Source: CDC/Susan Lindsley, VD.

Keratitis can cause the following symptoms:

• Eye pain
• Blurred vision
• Eye redness
• Photophobia (sensitivity to light)
• Excessive tearing
• Foreign body sensation in the eye
• Decreased vision
• Blepharospasm (involuntary tight closing of the eyes)

Symptoms may last from days to months depending on the cause of the keratitis and the treatment modalities used.

Causes

Infections are the most common cause of keratitis. The list of microbes that can cause the disease is long. Bacteria account for 65% to 90% of infectious causes of keratitis. Some of the more common pathogens (microbes that cause disease) include the following:

Keratitis caused by Acanthamoeba. Source: CDC.

• Bacteria
  • Staphylococcus species
  • Streptococci
  • Pseudomonas species
  • Enterobacteriaceae
• Viruses
  • Herpes simplex virus
  • [[Herpes zoster virus
  • Measles
  • Vaccinia from smallpox vaccination
  • Epstein-Barr virus
• Fungi
  • Candida species
  • Aspergillus
  • Fusarium
• Parasites
  • Onchocerciasis
  • Acanthamoeba
  • Trypanosomiasis

Keratitis can also develop from non-infectious causes. These include the following:

• Cogan syndrome, a disease causing inflammation of the blood vessel (vasculitis) with keratitis and inner ear disease.
• Fuch dystrophy, a slowly progressive disease, usually affecting both eyes, causing loss of cells and damage to the cornea.
• Abnormal development of the cornea, such as keratoconus.
• Iridocorneal endothelial syndrome, which leads to changes in the iris, swelling of the cornea, and development of glaucoma.
• Lattice dystrophy, an accumulation of amyloid proteins in the front of the eye and cornea.
• Photokeratitis, due to intense ultraviolet radiation exposure such as in snow blindness or welder's arc eye.
• Stevens-Johnson syndrome (a rare, severe type of allergic reaction sometimes which can be caused by certain types of antibiotics) occasionally affects the cornea.

Diagnosis

Keratitis is usually diagnosed based on the clinical symptoms of pain and/or redness in the eye along with close examination of the cornea by an eye specialist. In addition, scrapings or biopsies of the cornea can be taken for staining and culture to search for any microbial pathogens causing the illness.

Treatment

In infectious causes of keratitis, treatment is tailored to the causative agent. In bacterial keratitis, several antibiotics can be either applied topically to the eye, or given systemically by vein. Antibiotics have also been delivered to the cornea by continuous irrigation ^[1] and by the use of soft contact lenses or corneal shields.^[2] Other antimicrobial agents can be used for fungal, viral, or parasitic infections.

Topical steroid drops may help in some cases of keratitis. Their use in infectious causes remains controversial, since steroids can decrease the body's immune response to infections.^{[3] [4]}

In severe cases of keratitis leading to significant impairment of vision, a corneal transplant may be necessary to improve sight.^[5]

Prevention

Some cases of keratitis can be caused by microbes that are introduced into the eye by contact lenses through the use of contaminated contact lens solutions or improper home sterilization methods.

These guidelines can help contact lens users reduce the risk of eye infections:

• Visiting an eye care provider for regular eye examinations.
• Wearing and replacing contact lenses according to the schedule prescribed by an eye care provider.
• Removing contact lenses before any activity involving contact with water, including showering, using a hot tub, or swimming.
• Cleaning contact lenses according to the manufacturer's guidelines and instructions from an eye care provider.
  • Using fresh cleaning or disinfecting solution each time lenses are cleaned and stored. Never reusing or topping off old solution.
  • Never using saline solution and rewetting drops to disinfect lenses. Neither solution is an effective or approved disinfectant.
• Storing reusable lenses in the proper storage case.
  • Rinsing storage cases with sterile contact lens solution (never using tap water) and leaving them open to dry after each use.
  • Replacing storage cases at least once every three months.
• Washing hands with soap and water and drying them before handling contact lenses.
• Extended-wear contact lens users may have special concerns. It is a good idea for them to discuss these with their eye care provider.

Chances of Developing Keratitis

Some infectious causes of keratitis can be spread to the eye by the hands. For example, in people who receive the smallpox vaccine, touching the resulting blister that forms at the vaccination site, then touching their eye, can spread the infection. Occasionally, infection can occur from foreign bodies that have lodged in the eye.

One of the most important ways of developing keratitis, however, is through the use of contact lenses.

Contact lenses

Contact lenses can be a vehicle for the introduction of microbes into the eye, either through the use of contaminated contact lens solutions,^[6] or through improper cleaning and sterilization methods used at home. Contact lenses, particularly those worn overnight, can present an ideal environment for microbes to infect the cornea. This is because contact lenses reduce the amount of oxygen that reaches the cornea. The lens can also trap organisms against the cornea.

Two more common organisms that can cause keratitis in contact lens wearers include Acanthamoeba, a free-living parasite, and Fusarium a fungus. Outbreaks of keratitis caused by these microbes have occurred in the United States.^{[7] [8] [9]}

Clinical Trials

Clinical research studies are underway in keratitis and other eye diseases. For more information and a list of clinical trials, visit ClinicalTrials.gov.

Expected Outcome

Severe and prolonged inflammation of the cornea can lead to scarring of deeper layers of the organ. The result can be loss of vision and blindness. In such cases a corneal transplant may be necessary.

References

1. ↑ Meallet MA. Subpalpebral lavage antibiotic treatment for severe infectious scleritis and keratitis. Cornea. 2006 Feb;25(2):159-63. Abstract
2. ↑ O'Brien TP, Sawusch MR, Dick JD, Hamburg TR, Gottsch JD. Use of collagen corneal shields versus soft contact lenses to enhance penetration of topical tobramycin. J Cataract Refract Surg. 1988 Sep;14(5):505-7. Abstract
3. ↑ Leibowitz HM, Kupferman A. Topically administered corticosteroids: effect on antibiotic-treated bacterial keratitis. Arch Ophthalmol. 1980 Jul;98(7):1287-90. Abstract
4. ↑ Suwan-Apichon O, Reyes JM, Herretes S, Vedula SS, Chuck RS. Topical corticosteroids as adjunctive therapy for bacterial keratitis. Cochrane Database Syst Rev. 2007 Oct 17;(4):CD005430. Abstract
5. ↑ Al-Fawaz A, Wagoner MD; King Khaled Eye Specialist Hospital Corneal Transplant Study Group. Penetrating keratoplasty for trachomatous corneal scarring. Cornea. 2008 Feb;27(2):129-32. Abstract
6. ↑ FDA News. Advanced Medical Optics voluntarily recalls Complete MoisturePlus contact lens solution. May 26, 2007. News Release
7. ↑ CDC. Acanthamoeba Keratitis --- Multiple States, 2005--2007. MMWR. 2007 May 26;56(Dispatch):1-3. Full Text
8. ↑ CDC. Acanthamoeba keratitis in soft-contact-lens wearers. MMWR. 1987 Jul 3;36(25):397-8, 403-4. Full Text
9. ↑ CDC. Fusarium Keratitis - Multiple States, 2006. MMWR. 2006 Apr 10;55(Dispatch):1-2. Full Text

External Links

Centers for Disease Control and Prevention (CDC)

• Acanthamoeba Keratitis
• Fusarium Keratitis

Medline Plus

• Corneal Ulcers and Infections
• Interstitial Keratitis