Acanthamoeba keratitis is an extremely rare but serious eye infection. In the United States, it mostly affects people who wear contact lenses. Prompt diagnosis and treatment can help prevent permanent vision loss, but doctors often first mistake it for another condition.

Acanthamoeba keratitis is a rare eye infection caused by the parasite Acanthamoeba. Doctors first diagnosed it in 1974. The infection develops in your cornea, the transparent layer that covers your iris and pupil. Without prompt diagnosis and treatment, it can lead to permanent vision loss.

People who wear contact lenses are at the highest risk of developing Acanthamoeba keratitis. Experts estimate it affects 1 to 33 contact lens wearers per million per year in developed countries.

Doctors often have trouble diagnosing Acanthamoeba keratitis since it can cause many of the same symptoms as other eye infections. A delay in diagnosis can lead to more severe disease and complications.

Keep reading to learn more bout this rare infection, including its symptoms, risk factors, and ways to prevent it.

Keratitis is inflammation of your cornea. Your cornea is a clear layer of tissue at the front of your eye that covers your pupil and iris. Acanthamoeba keratitis develops when your cornea develops an infection from a single-celled organism called Acanthamoeba.

Acanthamoeba is one of the most common organisms in the environment. It’s found worldwide in soil and water. Most people are exposed to it, but very few become sick. It can live in water sources, such as:

  • ponds
  • swimming pools
  • hot tubs
  • contact lens solutions

In the United States, experts estimate it affects 1 to 2 contact lens wearers per million per year. Despite being rare, the number of cases is increasing each year.

The most common ways people develop Acanthamoeba keratitis is through injury to the cornea or exposure to contaminated water, such as using a nonsterile contact lens solution or being immersed in jacuzzi or pool water.

People who wear contacts are at the highest risk of developing Acanthamoeba keratitis. Up to 85% of people who develop it wear contacts.

Acanthamoeba keratitis mainly affects younger to middle-aged people. Those with compromised immune systems seem to be at an increased risk, but it also affects people with full immune function.

Acanthamoeba keratitis usually affects one eye but, in rare cases, can affect both. Symptoms generally progress slowly over time.

Symptoms of Acanthamoeba keratitis are similar to those of many other eye infections and can include:

It can lead to complications, such as:

  • glaucoma
  • cataracts
  • degeneration of the iris
  • vision loss
  • permanent corneal damage
  • retinal vasculitis, which is the inflammation of retinal blood vessels
When to see a doctor

It’s important to see an eye doctor if you have signs of an eye infection. Your doctor can help you figure out whether your infection is caused by a:

  • bacterium
  • virus
  • parasite
  • fungus

It helps to be honest and upfront with your doctor about how you wear and clean your contacts. Knowing which type of infection you have allows doctors to prescribe the right kind of medication to treat it and gives you the best chance of avoiding long-term complications.

An eye doctor can diagnose Acanthamoeba keratitis. But it’s often difficult to diagnose because of its rarity and since it isn’t recognizable by its symptoms alone.

Doctors initially misdiagnose approximately 75% to 90% of people. In a 2015 study, researchers found nearly half of people diagnosed in Germany over a 10-year period initially received a diagnosis of herpes simplex virus keratitis. But the studies didn’t comment on whether participants shared information with their doctors on how well they maintained their contacts.

Eye doctors usually start the diagnostic process by examining your eye and considering your medical and family history.

If they suspect Acanthamoeba keratitis, they may order:

  • Corneal scraping: During this test, your doctor numbs the area around your eye and scrapes off a small amount of tissue from the surface of your eye with a small blade or brush. They then send the cells to a laboratory for analysis.
  • Confocal microscopy: This procedure involves using a laser to create a detailed image of your cornea. This image can help identify signs of parasites such as Acanthamoeba. It’s less available than corneal scraping, but experts consider it the first-line diagnostic tool when available.

Two medications called diamidines and biguanides are often the first-line therapy. You can apply them directly to your eyes in the form of eye drops.

You’ll usually need to administer the drops every hour for the first few days and then every 3 hours. You’ll likely need to apply drops for 6 months to a year.

These two drugs are effective for about 35% to 86% of people. Most people take them together to overcome drug resistance. The antibiotic neomycin may also be beneficial when combined with other drugs.

If medications fail and the disease progresses to an advanced stage, you may need a corneal transplant. During this surgical procedure, a doctor replaces your cornea with corneal tissue from a recently deceased donor.

You can reduce your chances of developing Acanthamoeba keratitis by avoiding contaminated water or trauma to your cornea.

Most people who develop Acanthamoeba keratitis wear contacts. If you wear contacts, you can take the following steps to decrease your risk:

  • Store and handle your lenses properly.
  • Wash your hands before touching your contacts.
  • Disinfect lenses with sterile products that your eye doctor recommends.
  • Avoid storing or washing your lenses with tap water.
  • Avoid wearing your contacts in the shower, pool, or jacuzzi.
  • Replace your lenses on your prescribed schedule.
  • Avoid using other people’s lenses.
  • Avoid sleeping with your lenses in or wearing them after swimming.
  • Visit an eye care professional for regular checkups.

The outlook for people with Acanthamoeba keratitis is poorer than for many other eye infections. Some people experience corneal scarring and permanent vision loss. Receiving a prompt diagnosis and treatment gives you the best chance of having a good outlook.

In a 2020 study, researchers found the average healing time was 12.5 months in a group of 35 people. People with severe corneal ulcers took an average of 16.2 months to heal.

All the people in the study had reduced quality of life. But people who received a diagnosis within 30 days had a smaller reduction in quality of life and a quicker healing time than those who received a diagnosis more than 30 days after developing symptoms.

Acanthamoeba keratitis is a serious eye infection caused by a single-celled parasite that lives in soil and water. This parasite can cause permanent vision loss if a doctor doesn’t diagnose and treat it promptly.

People who wear contacts have the highest risk of developing Acanthamoeba keratitis. Following good contact lens hygiene can minimize your chances of developing an infection.