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What is keratitis?

Keratitis is a medical term for inflammation of the cornea. Symptoms include rapid onset of pain and redness of the eye, itching, blurred vision, tearing or discharge from the eye, and sensitivity to light.

Keratitis resulting from an infectionis among the leading causes of preventable blindness worldwide. The disease occurs far more frequently in developing countries, with the total number of cases globally estimated at 500,000 a year. The number of cases in the United States range between 25,000 and 30,000 annually.

What causes keratitis?

The most common cause of keratitis is injury or infection, but keratitis may also be noninfectious and develop from a wide range of other conditions.

Corneal infections rarely occur in the normal eye. Viral, fungal, parasitic and bacterial infections are more common after a minor injury or insult to the surface of the cornea.  They are a result of an alteration in the cornea’s defense mechanisms that allows bacteria or other microorganisms to invade when an epithelial defect (such as a scratch of the cornea) is present. These organisms may come from the tear film or as a result of foreign bodies, contact lenses or irrigating solutions. The process of corneal destruction can take place rapidly (within 24 hours in the case of virulent organisms), requiring quick recognition and initiation of treatmentto prevent vision loss.

Corneal infections are caused by a wide variety of microorganisms, including bacteria, viruses, fungi and protozoa.  Bacteria are the most frequent cause of infectious keratitis. The most common groups of bacteria responsible for bacterial keratitis are  Streptococcus, Pseudomonas, Enterobacteriaceae (including Klebsiella, Enterobacter, Serratia, and Proteus), and Staphylococcus species.

Other contributing factors, that may impact the severity of the case include, the degree of trauma, the presence of underlying ocular surface disease, the use of topical steroids or contact lenses,  host immune response, and the time it took to diagnosis and begin treatment 

What are the risk factors for keratitis?

The most common risk factors for keratitis include:

  • Contact lenses—Wearing contact lenses increases your risk of both infectious and noninfectious keratitis. This is in part from not disinfecting lenses properly, wearing contact lenses while swimming, wearing them longer than recommended, or using water or homemade solutions to store and clean lenses. Keratitis is much more common in people who use extended-wear contacts, or wear contacts continuously, than in those who use daily wear contacts and take them out at night.
  • Impaired or reduce immunity—If your immune system is weakened either from local or systemic disease (i.e. cancer, diabetes, or autoimmune diseases such as lupus or rheumatoid arthritis) or through  use of medications (anticancer medications or oral steroids) your risk of developing keratitis is higher.
  • Use of topical corticosteroids—The use of corticosteroid eye drops to treat other ocular disease increases your risk of developing keratitis or worsening an existing case.
  • Neurotrophic keratitis—This corneal degenerative disease is characterized by a reduction or absence of corneal sensitivity. The most common ocular conditions associated with neurotrophic keratitis are herpes zoster keratitis and simplex, topical anesthetic abuse, chemical and physical burns to the eye, contact lens over-wear/abuse, topical drug toxicity, irradiation to the eye, and previous corneal surgery.
  • Eye injury/ocular traumaIf one of your corneas is injured severely or has been damaged from an injury in the past, you may be more vulnerable to developing keratitis.  If you live in a warm, humid climate or are involved in agricultural work, your risk of keratitis is increased, particularly if your trauma involved organic plant material. (Plant material can scratch the corneal epithelium and chemicals from the plant can cause  inflammation, which may lead to an infection).

What is the treatment for infectious keratitis from bacteria?

Promptinitiation of antimicrobial therapy is the most appropriate treatment. Both  American Academy of Ophthalmology (AAO) and  World Health Organization (WHO) current guidelines recommend broad spectrum topical antimicrobials for initial treatment of suspected bacterial corneal ulcers.  Antibacterial eye drops are usually effective against most forms of bacterial keratitis. More severe infections may require non-commercially available fortified topical antibiotic formulations.  Generally, oral antibiotics are unnecessary in bacterial keratitis. In some cases, your cornea specialist may need further tests at a cellular level to diagnose the nature of the infection.   

What are other types of infectious keratitis?

Fungal keratitis (or keratomycosis) refers to an infection of the cornea caused by any of the multiple fungi capable of invading the ocular surface. The most common species responsible for fungal keratitis are Candida, Fusarium, and Aspergillus species.The infection typically develops slowly and  can be hard to differentiate from  more common bacterial infections. Keratomycosis is relatively uncommon in the Western world and most often originates in tropical or semi-tropical regions where climate, agricultural work and outdoor lifestyle may be important predisposing factors. While there is no concensus on the ideal regimen, topical antifungal drops and systemic antifungal agents can be used to treat the disease.

Herpes Simplex Virus (HSV) is the most common cause of viral infectious keratitis. HSV causes a spectrum of ocular diseases with many clinical manifestations. It is the most frequent cause of corneal blindness in the United States and the most common source of infectious blindness in the Western world. The prognosis for HSV keratitis, however, is generally favorable with aggressive treatment. These may  be followed by  reactivations and possibly multiple episodes of stromal keratitis (infection within the stroma of the cornea) lasting for months or years.  Treatment  generally involves topical antiviral agents and/or systemic antiviral agents.

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