Acanthamoeba keratitis

Acanthamoeba keratitis is a rare, serious eye infection. It happens when a tiny organism called acanthamoeba infects the cornea at the front of the eye. It's more likely to happen to contact lens wearers, though hygienic contact lens care can help limit the risk.

Acanthamoeba keratitis can be very painful and lead to sight loss if it isn't treated. Get urgent medical help if you experience eye pain, redness and vision changes. The sooner it's diagnosed and treated, the better the outcome is likely to be.

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Acanthamoeba keratitis symptoms

Acanthamoeba keratitis is more likely to happen to contact lens wearers and can occur in one or both eyes. If you wear contact lenses, be aware of the symptoms of an acanthamoeba infection. If you notice symptoms, get urgent medical help because treatment can be more effective with an early diagnosis. Symptoms include:

  • Feeling like there's something in your eye
  • Eye pain, sometimes intense
  • Eye redness
  • Vision changes, for example, blurred vision
  • Visible change to the cornea, for example, looking cloudy or dirty
  • Excessive tearing of the eye (as the eye tries to clear the irritant)
  • Developing a sensitivity to light

An acanthamoeba infection can lead to vision loss due to scarring on the cornea’s surface if it's not treated. Research has found that 25% of the worst cases needed a corneal transplant to treat sight loss (Source: British Journal of Ophthalmology).

In severe cases and the later stages of infection, it can cause complications including:

  • Cataracts - a clouding of the lens
  • Glaucoma - damage to the optic nerve
  • Anterior uveitis - inflammation of the middle of the eye
  • Scleritis - inflammation of the white of the eye

Acanthamoeba keratitis treatment

Treatment of acanthamoeba keratitis is sometimes difficult as the acanthamoeba organism can be resistant to treatment. If you're a contact lens wearer, to stop lens use straight away.

What causes acanthamoeba keratitis?

Acanthamoeba is a single-celled organism commonly found in freshwater in nature, such as lakes, oceans, and soil. It is also found in water supplies like tap water and equipment such as hot tubs and air conditioning units.

The organism can infect the eye through small scrapes or eye injuries, causing corneal infection. The amoebae attach to cells on the outer surface of the cornea. It only causes infection after direct contact with the eye. You can't get it in other ways, for example, drinking water or from contact with someone who has it.

The acanthamoeba organism exists in two types. Acanthamoeba trophozoites are active, can move and reproduce, and are easier to get rid of. The acanthamoeba cyst is dormant and harder to shift.

How can you reduce the risk of acanthamoeba keratitis? If you wear contact lenses, follow good practices when wearing and looking after your lenses. Use fresh contact lens solution, use the correct disinfecting solution to clean lenses, not tap water or saline solution, and keep your lens case clean. Always wash your hands before touching your contact lenses, and don't sleep, swim, or shower in your contact lenses. 

Acanthamoeba keratitis diagnosis

If you notice any symptoms of acanthamoeba keratitis, get urgent help. See an optician or call 111 straight away because an early diagnosis gives the best chance for effective treatment to protect your sight. If you use contact lenses, take them with you; analysing them may help with a diagnosis.

An optometrist or ophthalmologist will use a range of tests to diagnose acanthamoeba keratitis. An optician who suspects acanthamoeba keratitis may refer you urgently to your local hospital eye department or A&E.

Tests to diagnose acanthamoeba keratitis include:

  • Taking a history of your symptoms.
  • A standard slit lamp microscope exam to look closely for signs of inflammation in the cornea.
  • Taking a sample from the eye for laboratory analysis. They may take a small sample of cells from the cornea (corneal scrape) or take a swab to do a PCR (polymerase chain reaction) test.
  • A test called confocal microscopy to see evidence of acanthamoeba in the cornea, using a powerful microscope.

Diagnosis of acanthamoeba keratitis can sometimes be challenging. That's because the symptoms are often similar to other corneal infections, and it's not always easy for doctors to know which infection you have. Laboratory tests may be needed to confirm the diagnosis, or diagnosis might depend on how you respond to treatment.

When to get medical advice

If you have symptoms that could be a sign of acanthamoeba keratitis, get help from an eye doctor straight away. It's best not to delay because getting an early diagnosis can lead to a better outcome.

If you've been diagnosed with acanthamoeba keratitis and notice a change in your symptoms, speak to your ophthalmologist. If your eye pain or redness suddenly gets worse, or your vision suddenly deteriorates, get help urgently, for example attending your local hospital eye department or A&E.

Living with acanthamoeba keratitis

The symptoms of acanthamoeba keratitis can be unpleasant, and early treatment like hourly eye drops can disrupt your regular daily routines. It can be a stressful time, especially because you may be worried about the long-term risk to your sight, and treatment can last many months.

Hopefully, your symptoms will ease, and as your treatment becomes less intense, you'll start to get back to a more normal routine. It can help to speak to other people who've had the condition and get support for coping with the practical and emotional challenges.

Frequently asked questions

Medically reviewed by: The Royal College of Ophthalmologists on 18/10/2022

Edited by: Nick Astbury FRCS FRCOphth FRCP
Clinical Associate Professor

The Royal College of Ophthalmologists champions excellence in the practice of ophthalmology and is the only professional membership body for medically qualified ophthalmologists. The RCOphth is unable to offer direct advice to patients. If you’re concerned about the health of your eyes, you should seek medical advice from your GP, optometrist or ophthalmologist.

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