Acanthamoeba keratitis is an extremely serious coinfection of acanthamoeba, a common organism found in tap water, and bacterial keratitis. This dangerous condition is closely linked to improper handling of soft contact lenses. (Learn More)

According to the Centers for Disease Control and Prevention (CDC), 40 to 90 percent of contact lens wearers do not follow care instructions for their contacts. Poor hygiene can result in serious infections that could result in vision loss. (Learn More) 

Acanthamoeba keratitis is rare. Because cases of it aren’t required to be reported to state or federal health organizations, the CDC is unsure how many people experience the infection each year. (Learn More)

Symptoms of acanthamoeba keratitis include a red and excruciating eye infection that doesn’t improve with treatment, along with light sensitivity, blurred vision, and long-lasting pain after taking out contact lenses. (Learn More) 

Avoiding the most high-risk contact lens care behaviors, which include using tap water as part of a contact lens care and cleaning regimen, swimming with contacts in, and swapping contacts with someone else, can greatly reduce the risk of contracting acanthamoeba keratitis. (Learn More)

Following contact care lens care instructions and maintaining proper hygiene while handling contact lenses can also help to lower the risk of contracting eye infections. (Learn More) 

Aggressive and early treatment — usually with an antibiotic or topical medicine — is required to treat acanthamoeba keratitis before it results in irreversible vision loss or the need for a corneal transplant. (Learn More)

colored contacts

What Is Acanthamoeba Keratitis? 

Acanthamoeba is one of the most common organisms in the environment, and it rarely causes infections on its own. When infection does occur, it can be very serious and even result in vision loss.

In recent years, acanthamoeba has gained notoriety for increasing reports of acanthamoeba keratitis, which is a coinfection of acanthamoeba with the bacterial keratitis. Keratitis is an eye condition that causes the cornea (the round dome covering the eye’s pupil and iris) to become swollen and inflamed.

This coinfection most commonly occurs in the contact lens case and on the cornea.

Acanthamoeba keratitis is closely linked with contact lens wear — more specifically, poor contact lens care and hygiene. Before the popularity of soft contact lens use, this coinfection was extremely rare.

Contact Lenses Care Facts

Orthokeratology contact lenses

According to the Centers for Disease Control and Prevention (CDC), approximately 45 million people in the U.S. wear contact lenses. Soft contact lenses were first introduced to the market in 1971. Today, about 90 percent of contact lens wearers use soft contact lenses.

It’s estimated that 40 to 90 percent of contact lens wearers do not follow care instructions for their contacts. According to the CDC, 99 percent of contact lens wearers reported at least one contact lens hygiene action that has been associated with an increased risk of eye inflammation or infection.

These statistics may explain why 1 out of every 500 contact lens users is affected by a serious eye infection that could lead to blindness. Acanthamoeba keratitis is included in these vision-threatening infections

How Common Is Acanthamoeba Keratitis? 

The CDC reports that keratitis is responsible for 1 million doctor and hospital visits every year. Acanthamoeba keratitis is a very serious form of keratitis and is more rare. Still, research indicates that year after year, the number of cases of acanthamoeba keratitis increases.

In 2007, the CDC began investigating acanthamoeba keratitis cases, after an outbreak of the infection that led to a recall of contact lens solution. While the organization doesn’t have official records of how many cases of the infection are reported each year since cases of the infection are not required to be reported to state health organizations or the CDC, it did open another 2011 investigation into acanthamoeba keratitis after the number of cases didn’t seem to recede to pre-outbreak levels.

Symptoms of Acanthamoeba Keratitis

perspective of someone with blurry vision

Acanthamoeba keratitis is an extremely serious and painful infection, with symptoms that may include:

  • A red and excruciating eye infection that doesn’t improve with treatment.
  • A feeling that something is stuck on or in the eye.
  • Excessive tearing.
  • Blurred vision.
  • Sensitivity to light.
  • After removing contacts, an unusually long sensation of pain or irritation, along with redness. 

Preventing Acanthamoeba Keratitis: Avoid Risk Factors 

Being careful to avoid certain high-risk behaviors can greatly reduce the risk of developing acanthamoeba keratitis. The most high-risk activities are:

  • Using tap water in any part of contact lens care or hygiene. Acanthamoeba is very common in tap water. Using tap water in any part of a hygiene regimen, including while washing a contact lens case, can introduce the organism into the environment and onto the contact lens.
  • Swimming while wearing contact lenses. Acanthamoeba may be present in swimming water and attach to contact lenses.
  • Swapping contact lenses with someone else. This is unsanitary for many reasons, and the other person’s lenses may be infected.
  • Using saliva to wet contacts. Acanthamoeba may be present in saliva.
  • Using homemade saline solution to disinfect or clean contacts. Homemade solutions are unsterilized and may contain acanthamoeba. Saline solution is not a contact lens disinfectant.

Use Safe Contact Care

person washing hands

Following the care instructions for contact lenses and contact lens solutions will greatly reduce the risk of acanthamoeba keratitis and other eye infections. Follow these guidelines for safe and hygienic contact lens care: 

  • Always wash and dry hands before handling contact lenses.
  • Rub and rinse the surface of the contact lens with contact lens solution.
  • Contact lenses should be cleaned and disinfected with an optometrist-approved, sterile multipurpose or disinfectant product. Saline solution (homemade or store-bought), rewetting drops, and eye moisture treatments are not designed to disinfect lenses.
  • Never use tap water to store or wash contact lenses or contact lens cases.
  • Every time a contact lens case is opened, the solution inside should be discarded.
  • Every time contact lenses are placed inside the case, fresh solution should be used.
  • Lenses should be replaced according to the schedule outlined by the prescribing optometrist.
  • Unless advised to do so by an optometrist, contact lenses should not be slept in.
  • Contact lenses should never be slept in after swimming.
  • Contact lenses should never be placed in the mouth or come in contact with saliva.
  • Optometrists should be seen regularly to evaluate contact lens prescriptions and eye health.
  • If any redness, secretions, visual pain, or blurring is experienced, contact an optometrist or seek immediate medical care. 

Treatment for Acanthamoeba Keratitis 

Antibiotic eye drops are the most common medication used to treat this coinfection, along with a topical cationic antiseptic agent, such as polyhexamethylene biguanide. Treatment may be required for six months to a year, and pain medication may be also necessary.

Aggressive and early treatment is required to treat acanthamoeba keratitis before it results in irreversible vision loss. A corneal transplant may be required if the infection has progressed to advanced stages or is resistant to many forms of medication.


How Could Contact Lens Wearers Be at Risk of Acanthamoeba Infection? A Review. (November 4, 2010). Journal of Optometry.

Acanthamoeba. American Optometric Association (AOA).

Healthy Contact Lens Wear and Care. (July 26, 2018). Centers for Disease Control and Prevention (CDC).

An Update on Acanthamoeba Keratitis: Diagnosis, Pathogenesis, and Treatment. (February 18, 2015) Parasite.

Parasites – Acanthamoeba – Granulomatous Amebic Encephalitis (GAE); Keratitis. (April 20, 2011) Centers for Disease Control and Prevention (CDC).

An Eye on Contact Lens Solutions. (May 30, 2007). Time.

The Danger of Using Tap Water With Contact Lenses. (March 5, 2019). United States Environmental Protection Agency (EPA).

An Overview of Keratitis. March 10, 2019. Verywell Health.

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