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. It is 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.

The cornea, a clear layer at the front of the eye, is vulnerable to Acanthamoeba Keratitis (AK) when infected by a tiny organism called Acanthamoeba. This amoeba is widely prevalent in water sources worldwide, such as lakes, rivers, hot springs, oceans, tap water, and even bottled water, and can also be found in soil and dust.

While AK is more common among contact lens wearers (approximately 150 million people using contacts for medical or cosmetic reasons, including daily, weekly, and monthly users), it can affect anyone, especially those with eye trauma history or exposure to contaminated water.

One of the most concerning aspects of AK is the potential for severe vision loss. In fact, approximately 41% of AK cases eventually require a corneal surgical procedure or even become blind. Most cases are unilateral (affecting one eye) while there is 4% to 11% for bilateral (affecting both eyes)There is a high enucleation rate of 6%. So some AK patients choose to remove their eye. 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 keratitis (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.

ESTIMATED CASES

AK, a severe ocular infection that can lead to vision loss, is on the rise worldwide. The increased use of contact lenses for convenience, sports, costumes, and social media is contributing to a higher risk and developing Acanthamoeba Keratitis.

A recent study revealed an average of 2.9 AK cases per million globally, resulting in over 23,500 new infections annually. However, the infection rates vary by country, with the UK, Portugal, Egypt, India, and New Zealand having the highest per capita numbers, 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

CYCLE OF ACANTHAMOEBA

The life cycle of Acanthamoeba is typically divided into two stages:

TROPHOZOITE 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)

CYST STAGE

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)

HOW DOES IT HAPPENS

Acanthamoeba has a great affinity for the attachment to the corneal epithelium and to contact lenses.

Then 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:
EARLY INFECTION
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)
LATE INFECTION
Stage 5: Acanthamoeba damages the epithelium and membrane
Stage 6: Destruction of the Stroma
Stage 7: Radialneuritis

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.
Image 5:
(1) Acanthamoeba can enter the eye by attaching to contact lenses.
(2) the depleted immune activity allows binding to the epithelial layer.
(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.

WHAT ARE THE SYMPTOMS?

You may experience:

Eye pain from mild to excruciating
Red eye
Foreign body sensation
Blurred vision or complete loss of vision.
Sensitivity to light from mild to extremely high
Excessive tear production
Irritation or grittiness
Headache
Inability to wear contact lenses

These symptoms can have a substantial impact on 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.
ADVOCATE, if available, 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.

HOW TO PREVENT IT

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

DIAGNOSIS

69%

Misdiagnosed

38%

Herpes keratitis

20%

Bacterial Infection

Unfortunately when it comes to properly diagnose AK, statistics show that around 69% of AK Warriors worldwide are being misdiagnosed amongst others herpes, bacterial, viral, or fungal pathogens. Even more concerning is that over 38% of AK cases are misdiagnosed as herpes simplex, this can lead to the administration of corticoids and steroids, worsening the infection and the situation, and 20% as bacterial infection.

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.

TREATMENT

Despite the disturbing symptoms the first priority of AK treatment is to eradicate the parasite. The corneal specialist will prescribe anti amoebic eye drops to attack the amoeba along with possible 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.

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.

More information from a healthcare professional you can find here.