Acanthamoeba keratitis (AK) is an infection of the cornea, the clear ‘window’ at the front of the eye.
What is Acanthamoeba keratitis?
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.
Generally speaking, 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
How is AK diagnosed?
Your ophthalmologist will use a standard slit lamp microscope to look for signs of inflammation in your cornea, including specific clinical signs characteristic of AK. This is sometimes followed by a corneal scrape and culture (a process by which some cells from the surface of your cornea are removed and sent to a laboratory for further analysis), or a swab of the cornea to check for Acanthamoeba DNA using a test called “PCR”. Results for both these tests take a few days to come through. In some cases, AK can be detected using a confocal microscope, a powerful scanner that can see Acanthamoeba cysts within the various layers of the cornea. Your ophthalmologist will use these tests together with other clinical signs and symptoms in order to decide on the appropriate treatment plan
Why is it difficult to make a diagnosis?
In the early stages, AK and other microbial corneal infections have similar signs and symptoms, making it difficult to tell immediately which one you may have. This is why a variety of tests and clinical signs are observed. Sometimes diagnosis can change when the doctor receives more information from lab tests. Diagnosis can also change depending on how your eye(s) respond to treatment.
The primary difference between AK and other microbial infections is that it is challenging to treat, due to its resistance to many forms of therapy. Acanthamoeba in the dormant cyst form can survive for long periods of time. AK cannot be treated with antibiotics because it is not a bacterial infection.
How am I going to be treated?
Typically treatment is with antiseptic drops, including PHMB, Chlorhexidine, Brolene or Hexamidine, which have an anti-amoebic effect. Usually you’ll need to take these eye drops every hour for the first few days (including overnight), reducing to 2-hourly by day only, and then less frequently as the treatment progresses. It can be quite difficult to take eye drops through the night during the first few days, but it’s very important to try and stick to the regime outlined by the doctor as best you can.
In addition to the anti-amoebic eye drops, you may be given anti-inflammatories or painkillers to help with the pain. You may also be given a dilating drop early in the infection to stop painful spasms of the coloured part of the eye, the iris. Around 10% of Acanthamoeba infections have dual pathology, which means that another infection, usually bacterial, is also present. If this is the case for you, we may also prescribe you with antibiotics as well as your other drops. Sometimes these are also given to guard against bacterial infection while the eye surface is disrupted in the early stages of the disease. Patients with severe inflammation or scleritis (inflammation of the white part of the eye)are sometimes prescribed steroid eye drops, although not every patient requires these and their use needs to be carefully managed.