Acanthamoeba Eye Parasite

Acanthamoeba  Eye Parasite

What is Acanthamoeba?

Acanthamoeba (pronounced ah-canth-ah-me-baa) literally means spiny amoeba, and that’s exactly what Acanthamoeba spp. are—single celled amoebae that produce spiny pseudopodia as they move slowly along. About five times the size of a human red blood cell, acanthamoebae are large as microbes go, but still much too small to be seen with the naked eye. The most common amoebae in fresh water and soil, Acanthamoeba spp. sometimes cause human infections.

In water, moist soil, mud, and decaying organic material, acanthamoebae feed on bacteria and other microscopic organisms. In water supply systems, these amoebae live in the biofilm of organisms that proliferate on the inside surfaces of pipes, grazing on the other organisms in the biofilm. When the environment gets dry, they wrap themselves up inside a tough cyst wall and wait for the moisture and the food to return. They’re resistant to drying, chlorine, and many antiseptics. They are tough and ubiquitous.

Why is acanthamoeba important?

Though the natural environment for Acanthamoeba spp. is moist decaying organic material, at least six different species are capable of feeding on living tissue. Given the chance, these amoebae will invade human tissues and cause disease—the most common way that they do this is through the cornea of an eye from a contact lens. The destruction of the cornea, acanthamoeba keratitis, can result in the need for corneal transplant, and sometimes even surgical removal of the eye.

A rare cause of eye infections before the days of contact lenses, Acanthamoeba spp. were given a new opportunity when people started regularly putting lenses in their eyes. Tap water is usually the vehicle for the amoeba:

  1. Washing lenses and lens cases with tap water, and homemade saline made with tap water, allows Acanthamoeba spp. to adhere to contact lenses.
  2. Improper lens care, particularly conditions in which bacteria proliferate on lenses and in cases and solutions, provides the amoebae with a food supply. They multiply.
  3. Amoebae adhere to contact lenses—they are able to adhere to some lens materials more readily than others.
  4. Amoebae are transferred into the eye on the contact lens.
  5. Even the tiniest scratch or abrasion on the surface of the cornea allows the amoebae to get inside the eye, where they multiply and destroy tissue. A painful and vision destroying infection ensues.

Avoid acanthamoeba eye infection

Even though acanthamoeba keratitis is much more common than it used to be, it is still rare even among contact lens wearers. To avoid this devastating infection:

  • Never allow lenses or cases to come in contact with tap water.
  • Never swim with contact lenses in, even in a chlorinated swimming pool.
  • Don’t shower with contact lenses in your eyes.
  • Never wear contact lenses when your eyes are irritated or if you suspect you have even a tiny scratch.
  • Do not keep lenses or solutions past their expiry date.
  • Do not wear lenses for longer periods than your eye professional recommends.
  • Always carefully follow your eye professional’s instructions for cleaning contact lenses.
  • A lens cleaning routine that requires rubbing is preferable to one that only requires soaking.

Contact lenses and lens care disinfectants are improving; however, contact lens wearers still have to be careful. Taking the precautions listed above should keep this opportunistic amoeba where it belongs—in the environment.

Related content:

Contact Care

Read about other protozoan parasites of humans:

A Parasite in the Blood Supply

Toxoplasma gondii


Drisdelle, Rosemary. “Preventing Infections with Proper Lens Care.” Optical Prism. Mar (2007): 32-36.

Drisdelle, Rosemary. “The Amoeba that Loves Eyes.” Optical Prism. March (2004): 24-26.

Roberts, Larry S. and John Janovy Jr. Foundations of Parasitology 6th ed. Boston: McGraw Hill, 2000.