Acanthamoeba keratitis (AK) is an infection of the cornea, the clear ‘window’ at the front of the eye, that can be very painful. The infection is caused by a microscopic organism called acanthamoeba, which is common in nature and is usually found in bodies of water (lakes, oceans and rivers) as well as domestic tap water, swimming pools, hot tubs, soil and air.
Many different species of acanthamoeba exist. Acanthamoeba organisms do not generally cause harm to humans (we come into contact with them when we wash, swim, drink water etc), but they can cause a serious eye disease if they infect the cornea. Not all species of acanthamoeba have been found to cause corneal infections. AK is most common in people who wear contact lenses, but anyone with a corneal injury is susceptible to developing the infection.
Acanthamoeba has a life cycle of two stages: an active form (when the organism feeds and replicates), and a dormant form (when the acanthamoeba protects itself from attack by developing into a cyst).
In the early stages of the disease, the cornea can become irregular due to the infection and inflammation, which can affect your vision.
You may also have light sensitivity (also termed photophobia), which is a symptom of the inflammation and infection in your cornea.
Tears are a natural reaction to disruption of the corneal surface and are a reflex response to the infection.
AK can be extremely painful, although not all patients experience intense pain
Around 85% of cases of AK have been associated with contact lens wear.
There are a number of different factors which are known to increase the risk of contracting AK. The biggest risk factor is exposure to water (generally through swimming or showering in contact lenses, rinsing or storing lenses in water and handling lenses with unwashed or wet hands). Improper contact lens hygiene, including not disinfecting lenses properly and not cleaning and changing contact lens cases regularly have also been shown to increase the risk of infection. Those who do not wear contact lenses may still contract AK, although it has a much rarer incidence than in contact lens wear.
Due to the way that UK domestic water is stored and supplied, incidence of the disease is generally higher in the UK than in other parts of the world. Studies suggest that AK affects around 2 in 100,000 contact lens wearers per year in the UK, which is around 20 times less than the number of daily wear soft contact lens wearers with bacterial infections. Since 2011, Moorfields Eye Hospital and other centres in the UK and USA have reported a three-fold increase in the number of cases of disease, although it still remains rare.
Acanthamoeba keratitis (AK) can be extremely painful, although not all patients experience intense pain. The cornea is one of the most sensitive organs, with the highest density of pain receptors in the body. This means that any injury to the cornea can be very painful. Pain can also be triggered by the body’s immune response to the infection in your cornea - this is called an inflammatory response and may be one of the reasons your eye is red as well as painful. The medicines used to treat AK can be quite harsh and, in some cases, can also irritate the surface of your cornea. Your doctor will try to strike a balance between effective treatment of the infection and preventing further irritation on the corneal surface.
Light sensitivity (also termed photophobia) is a symptom of the inflammation and infection in your cornea because the cornea, which is usually clear, turns cloudy and scatters the light around. You may also have light sensitivity because you have been given an eye drop that temporarily widens the pupil, the hole through which light enters the eye. Sometimes the iris (the coloured part of the eye) can go into spasm when the cornea is infected, which can also cause pain, so these drops may help relieve the pain but may also make you more light sensitive. Tears are a natural reaction to disruption of the corneal surface and are a reflex response to the infection. They act to remove irritants from the surface of the eye.
In the early stages of the disease, the cornea can become irregular due to the infection and inflammation, which can affect your vision. This can occur quite suddenly, and you should inform your ophthalmologist as soon as possible if this happens to you. As the infection responds to treatment, patients can notice their vision improve as the inflammation reduces and the surface heals. In later stages of the disease, scarring on the front of the cornea, resulting from long-term inflammation, is usually the reason for vision loss. In some patients, scarring can be quite extensive and may need further therapy (e.g. a cornea transplant) to rehabilitate vision once the infection is over. A degree of permanent vision loss occurs in around a quarter of cases.
At Moorfields Eye Hospital, we have only seen cases of bilateral AK (affecting both eyes) where the patient has been infected in both eyes at the same time rather than it spreading from one eye to the other.
Acanthamoeba is an opportunistic organism in that it is widespread in the environment, but fortunately only rarely invades human tissue to cause disease. It’s extremely unlikely for acanthamoeba to spread from person to person. There are some extremely rare strains of acanthamoeba that can affect the brain; most of these cases occur in immunocompromised patients and are not related to contact lens wear. However, it’s still a good idea to take sensible precautions to ensure that other bacteria or germs do not spread between your eyes or from your nose/mouth to your eyes. Always wash your hands and dry them thoroughly before and after putting in your eye drops. Also make sure that you don’t touch your eye with the dropper or bottle top when applying eye drops.
Around 25% of cases of AK seen at Moorfields result in a corneal transplant. There are different types of transplant – and these carry different risks. Some are carried out to improve your vision at the end of infection. Other transplants are carried out, on actively inflamed eyes, as part of therapy.
The therapeutic transplants are usually for corneal perforations, although the success rate of these is poorer than the transplants to improve vision, therefore the procedure is rarely used unless absolutely necessary.
There is also a risk of a recurrence of AK post-surgery and this is one reason why corneal transplants are generally delayed until the eye has been infection free for some time. Your doctor will discuss what’s right for you and separate information will be provided if you are a possible candidate for a corneal transplant.
For patients who have poor vision but do not require a transplant, vision can be improved using a rigid contact lens. Your ophthalmologist will discuss all options with you at the appropriate time.
In order to provide you with the best care, we need to re-review your situation, especially any changes since your last appointment, as it may have an effect on your current treatment.
The UK’s Medicines and Healthcare Products Regulatory Agency (MHRA) suggest all contact lens-wearing patients report their case of acanthamoeba keratitis via their Yellow Card reporting scheme. It is important for people to report problems experienced with medical devices as these are used to identify issues which might not have been previously known about. The MHRA will review the product if necessary and take action to minimise risk and maximise benefit to the patients. You can do this at yellowcard.mhra.gov.uk. Other countries have similar reporting schemes, so please check with your doctor for details.
You may find some other information about AK on the internet, but please bear in mind that much of this information may be inaccurate or out of date. Instead, please share this leaflet, (which is regularly reviewed and updated) with friends/family and others, to help them understand AK better.
There are also a number of social media forums where AK patients from all over the world talk and provide support to each other. Talk to your doctor if you require more detailed information about your specific case to give to your employer.
There are regular informal meet ups for acanthamoeba keratitis (AK) patients and their friends and families in London, which are also live streamed online for those who do not live nearby. We try and arrange this meeting once a year outside of working hours, and often have expert speakers and group discussions on how to raise awareness of AK, or how to participate in research.
There are several promising new drugs being developed, but it is likely to be years before they are used on patients.
There are a number of studies currently being undertaken by centres including Moorfields Eye Hospital and the UCL Biomedical Research Centre (BRC) to better diagnose, treat and prevent acanthamoeba keratitis. A clinical trial is also currently underway to develop the first properly licensed treatment for the infection.
More information on diagnosis and treatment of AK
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