Acanthamoeba Keratitis:
What Contact Lens Wearers
Need To Know

By Edward S. Bennett, OD

Acanthamoeba eye infections in contact lens wearers are rare but serious, and they often start because of improper lens handling and poor hygiene.

To avoid Acanthamoeba keratitis, contact lens wearers should follow wearing and cleaning instructions from both manufacturers and eye doctors very closely, to reduce the possibility of ever having this type of eye infection.

Prevention is always the best approach, because Acanthamoeba keratitis can be extremely difficult to treat; in fact, sometimes these infections require a corneal transplant, which is a serious surgical procedure.

What Are Acanthamoeba?

Acanthamoeba are naturally occurring amoeba (tiny, one-celled animals) commonly found in water sources, such as tap water, well water, hot tubs, and soil and sewage systems.

If these tiny parasites infect the eye, Acanthamoeba keratitis results.

The condition first was diagnosed in 1973, with about 90 percent of cases involving contact lens wearers. But overall the risk of Acanthamoeba keratitis is quite low, with only about two cases reported per million contact lens wearers.

Acanthamoeba Outbreaks Among Contact Lens Wearers

In recent years, however, the U.S. Centers for Disease Control (CDC) and other researchers have noted certain, sometimes isolated instances of higher numbers of Acanthamoeba keratitis cases among contact lens wearers.

As an example, the CDC in 2007 released several public health warnings regarding the eye infection in association with use of the contact lens solution Complete MoisturePlus, manufactured by Abbott Medical Optics (AMO) — formerly Advanced Medical Optics.

The CDC said a sevenfold increase in the risk of developing Acanthamoeba keratitis associated with use of the contact lens solution prompted AMO to withdraw Complete MoisturePlus from the market.

The contact lens solution itself was not contaminated, but it seemed to be ineffective in preventing Acanthamoeba keratitis. [Read more about fungal eye infections associated with use of another contact lens solution.]

What Causes Acanthamoeba Keratitis?

Factors and activities that increase the risk of contracting Acanthamoeba keratitis include using contaminated tap or well water on contact lenses, using homemade solutions to store and clean contacts, wearing contact lenses in a hot tub and swimming or showering while wearing lenses.

Contact lens wearers need to us good hygiene to prevent eye infections caused by Acanthamoeba, an amoeba shown here greatly magnified. (Photo: U.S. Centers for Disease Control and Dr. George Healy)

A dirty lens case also can be a source of Acanthamoeba infection.

In addition, some scientists theorize that new U.S. Environmental Protection Agency regulations aimed at reducing carcinogenic (potentially cancer-causing) products such as disinfectants in the water supply may have inadvertently boosted microbial risks, including an increased likelihood of finding Acanthamoeba in water supplies.

Other researchers associate recent increases in keratitis cases with the introduction of lens care systems that do not fully emphasize the need to clean contact lenses upon removal.

But regardless of the cause of the increase, Acanthamoeba can be killed easily, especially when rubbed off the lens surface during cleaning. In the end, good contact lens hygiene is the best way to prevent Acanthamoeba keratitis.

How Do You Know if You Have Acanthamoeba Keratitis?

Symptoms of Acanthamoeba keratitis include redness and eye pain after removing your contact lenses, as well as tearing, light sensitivity, blurred vision and a feeling that something is in your eye.

Advanced Acanthamoeba keratitis can cause a white "ring" to cover the iris, as well as redness in the white of the eye. (Also read about conjunctivitis, another cause of eye redness.)

With these types of symptoms, you should always contact your eye doctor. But keep in mind that Acanthamoeba keratitis is often difficult for your eye doctor to diagnose at first, because its symptoms are similar to those of other eye infections.

Diagnosis of keratitis often occurs once it is determined that the condition is resistant to antibiotics used to manage other infections. A "ring-like" ulceration of your corneal tissue may also occur.

Unfortunately, in most cases of Acanthamoeba keratitis, permanent vision loss occurs. Once you have this type of eye infection, the CDC says that corneal transplant surgery often is necessary to recover lost vision.

How Can You Reduce the Risk of Getting Acanthamoeba Keratitis?

There are several easy ways to greatly reduce the chance of getting this sight-threatening condition — and, in fact, any type of eye infection:

1. Follow your eye doctor's recommendations regarding care of your contact lenses. Use only products that he or she recommends.
2. Never use tap water with your contact lenses. Do not swim, shower or use a hot tub while wearing them. If you do decide to wear your lenses while swimming, wear airtight swim goggles and afterward dispose of the lenses immediately.
3. Be sure to soak your lenses in fresh disinfecting solution every night. Don't use a wetting solution or saline solution that isn't intended for disinfection.
4. Always wash your hands before handling your lenses.
5. Unless you are wearing disposable contact lenses that are replaced daily, always clean the lenses upon removal, or at a minimum, rub the lenses with your multipurpose solution and rinse the solution off of the lens.

Take Care of Your Contact Lens Case

Cleanliness and proper care are equally important for contact lens cases.

Besides using good hygiene when handling contact lenses, clean and sterilize your lens cases, to avoid Acanthamoeba contamination. (Read more about soft contact lens care.)

Many eye doctors recommend that you at least clean your contact lens case with hot tap water and leave it out to air dry when not in use.

Replace your case at least every three months, and preferably every month.

If you want to do a more thorough cleaning, scrub your case with a clean toothbrush, rinse with sterile, disinfecting solution and then let it air dry.

The case can be sterilized weekly, either by boiling it in hot water or microwaving it (in dry form) for three minutes.

Again, prevention is your best defense against Acanthamoeba keratitis. Always use good hygiene during contact lens use and care. And if you notice any unusual eye symptoms that might indicate an infection, immediately consult your eye doctor.

[Page updated December 2008]