Acanthamoeba keratitis is a very serious eye infection. It affects the cornea (the clear lens that covers your pupil) and can have very serious effects on your vision. Here's what you need to know about this sight-threatening infection.

What is acanthamoeba?

Acanthamoeba is a particularly nasty parasite that is found in soil and fresh water. Acanthamoeba is dangerous because it's an expert at thwarting your body's immune response; it forms a cyst around itself to protect it from your white blood cells. It can cause a wide variety of diseases in humans, depending on how it enters your body. When it enters your eyes, it causes acanthamoeba keratitis.

How does an acanthamoeba get into your eye?

Acanthamoeba is usually associated with contact lens use: about 95% of all cases occur in people who regularly wear contact lenses. If you wear contact lenses, some of your bad habits are increasing your risk of getting this parasite in your eye:

• Rinsing your contact lenses with tap water instead of contact lens solution;
• Swimming in lakes or pools while wearing contact lenses;
• Taking a shower while wearing contact lenses;
• Not washing your hands before touching your contact lenses.

Getting the parasite in your eye isn't enough to allow it to cause an infection; you also need small abrasions on the surface of your cornea to give acanthamoeba a direct route into your tissues. These abrasions can form as a result of improper contact lens use. Here are some common mistakes that you might be making that may be damaging your eye and putting you at a greater risk of acanthamoeba keratitis:

• Going to bed without taking your contact lenses out;
• Wearing your contact lenses for longer than your optometrist recommends;
• Not replacing your lenses when you're supposed to, for example, by wearing daily disposable lenses for more than one day;
• Wearing expired lenses.

Using your contact lenses properly will help lower your risk of damage to your cornea, which makes it harder for acanthamoeba to get into your tissues. Talk to your optometrist about the proper ways to wear and care for your preferred brand of contact lenses.

What are the signs of this infection?

The main sign of this infection is severe pain in the affected eye. The pain is often much worse than the appearance of the eye would suggest, which makes it hard for optometrists to diagnose the problem. Other symptoms can also occur, such as sensitivity to light, very watery eyes, or cloudy vision. The infection can also cause ulcers to form on the surface of your cornea. If you notice any of these signs, see your optometrist right away. The infection will only get worse if you don't get help.

How is it treated?

It's hard for optometrists to treat this infection since acanthamoeba is so resilient. The first treatment option is usually medicated eye drops; these need to be used as frequently as once per hour. Some people need both eye drops and pills to kill the parasite. The damaged surface of your cornea may need to be scraped away to give the tissues underneath a chance to heal.

This infection can cause scarring on the cornea. If the scarring is severe, your vision will be severely impacted, and you may need a corneal transplant.

What is the prognosis?

Your prognosis is good if the infection is caught and treated early: it's likely that you will retain good vision at the end of your treatment.

Acanthamoeba keratitis is a very serious infection, and if it's not caught early, it can destroy your vision. If you wear contact lenses and have very sore eyes, you might have this infection, so see an ophthalmologist right away.