Signs and symptoms of keratitis include:

• Eye redness
• Eye pain
• Excess tears or other discharge from your eye
• Difficulty opening your eyelid because of pain or irritation
• Blurred vision
• Decreased vision
• Sensitivity to light (photophobia)

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.

Factors that may increase your risk of keratitis include:

• Contact lenses. Wearing contact lenses — especially sleeping in the lenses —increases your risk of both infectious and noninfectious keratitis. The risk typically stems from wearing them longer than recommended, improper disinfection or wearing contact lenses while swimming.

Keratitis is 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.

• Reduced immunity. If your immune system is compromised due to disease or medications, you're at higher risk of developing keratitis.
• Corticosteroids. Use of corticosteroid eyedrops to treat an eye disorder can increase your risk of developing infectious keratitis or worsen existing keratitis.
• Eye injury. If one of your corneas has been damaged from an injury in the past, you may be more vulnerable to developing keratitis.

Potential complications of keratitis include:

• Chronic corneal inflammation and scarring
• Chronic or recurrent viral infections of your cornea
• Open sores on your cornea (corneal ulcers)
• Temporary or permanent reduction in your vision
• Blindness