acanthamoeba keratitis

What is Acanthamoeba Keratitis?

Image: an eye with Acanthamoeba Keratitis © Dr. Taher Eleiwa

Acanthamoeba Keratitis (AK)
is a severe eye infection that can cause excruciating pain and damage to the cornea, often resulting in vision loss or even blindness.

The cornea is the transparent layer at the front of the eye. AK occurs when a microscopic organism called Acanthamoeba infects the cornea. This amoeba is commonly found worldwide in water, including lakes, rivers, hot springs, oceans, tap water and even bottled water. It can also be present in soil and dust.

Although it is more common in contact lens wearers (est. 150 million people wearing daily, weekly, and monthly contact lenses), anyone can develop AK, especially those who have experienced trauma to the eye or have come into contact with contaminated water.

AK can affect one eye (unilateral) or both eyes (bilateral).

The amoeba enters the eye through small scrapes that can be caused by contact lenses, minor eye injuries or trauma to the eye. Contact lens material can absorb water and provide a hospitable environment for the parasite to grow.

Acanthamoebas use the natural bacteria found on the surface of the eye as a food source. Then, once inside the cornea, it is extremely difficult to eradicate. This makes it challenging to treat without causing damage to the eye through toxicity.

Image 1: Scanning electron micrograph (SEM) of two Acanthamoeba trophozoites approaching an indent in a contact lens, © Fiona L Henriquez, Adam Hammerschmid. University of the West of Scotland (UWS), U.K
Image 2: The different stages of infection. © Fiona L Henriquez. University of the West of Scotland (UWS), U.K

Explanation of the different stages of Infection based on image 2:

Stage 1: Acanthamoeba is attached to the contact lens
Stage 2: Acanthamoeba feeds on bacteria (grey rods) that are present on contact lens and also secretes proteases (black dots) to help feeding
Stage 3: Acanthamoeba attaches itself to epithelial layer through receptors. Proteases continue to digest external environment, including epithelial cells
Stage 4: Damaged epithelial cells release signals to recruit immune cells. Immune cells release cytokines that cause inflammation (dotted line)

Stage 5: Acanthamoeba damages the epithelium and membrane
Stage 6: Destruction of the Stroma
Stage 7: Radialneuritis

One of the most concerning aspects of AK is the potential for severe vision loss. In fact, approximately 50% of patients with AK will need to undergo corneal transplantation or may even become blind. For some patients (5-10%) enucleation (removal of the affected eye) may be necessary.
It is important for individuals to take preventative measures to avoid contracting AK.

This infection often presents with ocular pain that is underestimated by the medical community. Patients feel that they are neither heard nor believed because the presenting symptoms do not correlate with the severity of the pain. Unfortunately, AK is frequently misdiagnosed, leading to more severe infection and damage to the eye. Early diagnosis and treatment are crucial in preventing severe complications associated with AK.

There are different stages of AK, ranging from mild to severe. The first stage is often characterized by redness, pain, and sensitivity to light. The second stage may involve the formation of a ring-shaped ulcer on the cornea, leading to blurred vision and even vision loss. The third and final stage can result in scarring of the cornea, which can be permanent.

A rare but painful complication of AK is Acanthamoeba scleritis (ASK), which affects around 10–18% of patients. In extremely rare cases, the acanthamoeba can cause a systemic infection beyond the eye, even causing granulomatous Acanthamoeba encephalitis (GAE) of the brain.

Cycle of Acanthamoeba

The life cycle of Acanthamoeba is typically divided into two stages: the trophozoite stage and the cyst stage.

During the trophozoite stage, the amoebas are active and mobile, feeding on bacteria and other small organisms in its environment. This is when you might experience a lot of pain, light sensitivity and/or sometimes a deterioration in vision.

Image 3: Throphozoite
Images 3 – Trophozoite –  supplied and used with permission from Dr. Christopher A. Rice (Purdue University). Preparation of cells and Scanning Electron Microscopy (SEM) imaging of amoeba was performed by A. Cassiopeia “Cassie” Russell (University of Georgia) on Dr. Peter Bush’s Field Emission Scanning Electron Microscope (FESEM) with Oxford Energy-dispersive X-ray Spectrometer (EDS) – Hitachi SU70 (University at Buffalo)

In the cyst stage, the amoebas are passive as they have formed protective double-walled cells that allows them to survive in harsh environments with low nutrients or high toxicity. This can happen due to changes in pH levels or exposure to therapeutic agents.

Images 4 – Cyst –  supplied and used with permission from Dr. Christopher A. Rice (Purdue University). Preparation of cells and Scanning Electron Microscopy (SEM) imaging of amoeba was performed by A. Cassiopeia “Cassie” Russell (University of Georgia) on Dr. Peter Bush’s Field Emission Scanning Electron Microscope (FESEM) with Oxford Energy-dispersive X-ray Spectrometer (EDS) – Hitachi SU70 (University at Buffalo)

The amoeba attacks the cornea in the active form as a trophozoite causing inflammation, damaging especially the nerves (extreme pain) and causing light sensitivity. As soon as the conditions become unpleasant for the amoeba by applying drugs, it turns into a protected cyst. Now it can even survive lack of food, or any medical treatment known so far. When the drug pressure is reduced the amoeba turns into active trophozoite again.

This illustration shows the different layers of a cornea with AK and the reaction of the parasite.

Image 5: Different layers of the cornea with acanthamoeba

Image 5: source © Ronnie Mooney, Roderick Williams and Fiona L Henriquez. University of the West of Scotland, U.K. New solutions in the prevention and treatment of Acanthamoeba keratitis By Ronnie Mooney, Roderick Williams and Fiona L Henriquez.

Figure 5:
(1) Acanthamoeba can enter the eye by attaching to contact lenses, (2) the depleted immune activity allows binding to the epithelial layer and (3) the amoeba can begin to feed on the epithelial cells. (4) Micro-abrasions on the epithelial layer provide an opportunity for the amoeba to access the Bowman’s membrane and stroma of the patient. (5) Drug pressure can instigate encystation of the parasite, (6) which can then begin reinfection upon removal of this pressure.


You may experience:

  • Eye pain (which can be excruciating – but may be painless in the early stages)
  • Red eye
  • Sensation of something in the eye – foreign body sensation
  • Blurred, poor vision or total vision loss
  • Sensitivity to light from mild to extremely high
  • Excessive tear production
  • Irritation or grittiness
  • Headache
  • Inability to wear contact lenses

These symptoms can be quite severe and significantly affect a person’s quality of life.

If you suspect that you might have AK, it is important to seek medical attention right away. Here are some steps you can take:

  • Stop wearing contact lenses.
  • Consult an eye doctor as soon as possible.
  • Let them know if you are a contact lens user and have been in contact with water.
  • Take the contact lenses, casing, and solution with you for possible analysis.
  • If available, advocate for an early confocal scan to confirm the diagnosis. Time is of the essence!

Remember, early diagnosis and treatment are key to preventing serious complications from AK.

Risks and Prevention

AK is a serious eye infection caused by a free-living amoeba that is commonly found in soil, bodies of water, and tap water. This means that activities such as showering, bathing, swimming in pools, lakes, ponds, oceans, and even rinsing contact lenses or cases with tap water can put you at risk of contracting AK. Any contact of an injured or scratched eye with dirt or water increases the risk of an AK infection.

Contact lens wearers are especially susceptible to AK because contact lenses can cause small defects on the cornea or trap the parasite between the contact lens and the eye. Therefore, it is crucial to never let water touch your contact lenses. In addition, it is important to follow proper contact lens hygiene and cleaning procedures to further reduce the risk of AK infection.

Water and Contact Lenses don’t mix
  • Never use water to store or rinse your contact lenses
  • Never sleep wearing your contact lenses
  • Never shower wearing your contact lenses
  • Never swim wearing your contact lenses

Read more Contact Lens User

Misdiagnosis of Acanthamoeba Keratitis

Misdiagnosis can be a major hurdle for AK Warriors (patients) who are already dealing with the challenges of AK. Unfortunately, statistics show that around 80% of AK Warriors worldwide are being misdiagnosed with bacterial, viral, or fungal pathogens. Even more concerning is that over 50% of AK cases are misdiagnosed as herpes simplex. This can lead to the administration of corticoids and steroids, worsening the infection and the situation.

While there may be similarities in symptoms with other infections, the treatments are vastly different. It is crucial to get the correct diagnosis for AK quickly. Because of misdiagnoses the recognition of AK often takes days, weeks, months, or even over a year, during which time the amoeba can continue to multiply or hide deeper in the cornea.

It is important for healthcare providers to be aware of the prevalence of misdiagnoses and to thoroughly investigate any corneal inflammation particularly with contact lens users. This will ensure the best possible outcome for patients.


80% of AK cases are misdiagnosed


Half of the misdiagnoses with Herpes Simplex Virus

Estimated case numbers of Acanthamoeba Keratitis

AK is a severe and sight-threatening ocular infection that is becoming more prevalent worldwide. As more people wear contact lenses for various reasons – convenience, sport activities, costume parties and social media trends – the risk of exposure to acanthamoeba and obtaining keratitis increases.

According to a recent study, there are on average 2.9 AK cases per million globally, resulting in over 23,500 new infections each year. However, the infection rate varies from country to country, with the highest numbers per capita occurring in the UK, Portugal, Egypt, India, and New Zealand, followed by Canada, the Netherlands, Italy, Singapore, and Australia.

Image source: The estimated annual incidence of Acanthamoeba keratitis by regions (as defined by the UN). The figure used with permission from co-author Xu. Source: Yuheng Zhang, Xizhan Xu, Zhenyu Wei, Kai Cao, Zijun Zhang, Qingfeng Liang, The global epidemiology and clinical diagnosis of Acanthamoeba keratitis


Despite the disturbing symptoms the first priority of AK treatment is to eradicate the parasite. The corneal specialist will prescribe antiseptic eye drops to attack the amoeba along with other eye drops and oral medication. The initial phase of treatment involves using the drops every hour 24/7.

In the second phase these eye drops are used during waking hours. The duration of this whole process depends on the severity of the infection, the availability of the drugs and the experience of the specialist. This can take from six months up to one year or even longer. However, in some cases medication may be stopped to see how the eye reacts before restarting treatment in case of a relapse.

Once the amoeba has been eradicated, the specialist’s next priority is to help restore vision. This may involve procedures such as cataract surgery or corneal transplantation. The outcome of treatment varies greatly, ranging from clear vision, to vision loss or eye removal. The journey is characterized by many ups and downs, with the intense drop regime, excruciating pain, and many eye appointments, leaving little space for daily life. AK affects not only the eye, but also the mental and emotional health of the patient.

Possible Aftermath

Following treatment for AK, the patient will need to take extra care of their eyes to prevent any further damage or reinfection. The patient may need to continue using eye drops or other medications for several months or even years after the initial infection. The doctor may also recommend wearing special contact lenses or glasses to protect the eyes.

Unfortunately, AK can have severe consequences even after the amoeba is eradicated. Despite medical treatment and surgery, there may be long-term or permanent damage, leading to vision loss, blindness or removal of the eye.

The secondary conditions can, in addition to the eye, also affect the head (nerve pain, teeth, ears) and the organs (kidneys, liver, stomach). Quite often AK Warriors suffer psychological trauma requiring professional help.

A detailed list of secondary conditions can be found here.