Causes

Causes of keratitis include:

• Injury. If any object scratches or injures the surface of your cornea, noninfectious keratitis may result. In addition, an injury may allow microorganisms to gain access to the damaged cornea, 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. Over-wearing your contact lenses can cause keratitis, which can become infectious.
• Viruses. The herpes viruses (herpes simplex and herpes zoster) may cause keratitis.
• Bacteria. The bacterium that causes gonorrhea can cause keratitis.
• Contaminated water. Bacteria, fungi and parasites in water — particularly in oceans, rivers, lakes and hot tubs — can enter your eyes when you're swimming and result in keratitis. However, even if you're exposed to these bacteria, fungi or parasites, a healthy cornea is unlikely to become infected unless there has been some previous breakdown of the corneal surface — for example, wearing a contact lens too long.