Causes of keratitis include:

  • Injury. If an object scratches the surface of one of your corneas or penetrates a cornea, keratitis without an infection may result. In addition, an injury may allow bacteria or fungi to gain access to the cornea through the damaged surface, causing infectious keratitis.
  • Contaminated contact lenses. Bacteria, fungi or parasites — particularly the microscopic parasite acanthamoeba — may inhabit the surface of a contact lens or contact lens carrying case. The cornea may become contaminated when the lens is in your eye, resulting in infectious keratitis.
  • Viruses. Viruses such as the herpes viruses (herpes simplex and herpes zoster) and the virus that causes chlamydia may cause keratitis.
  • Contaminated water. Chemicals in water such as those used in swimming pools may irritate the cornea and weaken the delicate surface tissue of the cornea (corneal epithelium), resulting in a chemical keratitis. This is usually short-lived and may last only minutes to hours.

    Bacteria, fungi and parasites in water — particularly in oceans, rivers, lakes and hot tubs — can enter your eyes when you're swimming or bathing and result in keratitis. If you're exposed to these microorganisms, a healthy cornea is unlikely to become infected. But if you've experienced some previous breakdown of the corneal epithelium, such as from wearing a contact lens too long, your cornea may be vulnerable to infection.

Sept. 10, 2015