What is acanthamoeba?

Acanthamoeba keratitis is a severe sight-threatening infection of the cornea. Acanthamoeba is a protozoan (single-celled organism) that is very widespread throughout the environment, especially where there is standing water, and it may be present in inadequately treated tap water. It has two forms: the trophozoite, which is active, capable of feeding, moving and reproducing, and which is easily destroyed; and the cyst, which is dormant and difficult to destroy. Acanthamoeba can change between these two forms, depending on whether it is in a favourable or a hostile environment.

Acanthamoeba is normally harmless to humans, but if it is transferred to the eye on a contaminated contact lens it can infect the cornea (the clear window at the front of the eye). Such infections can be difficult to treat owing to the lack or non-availability of anti-amoebic drugs. It is far better to prevent the infection by the use of effective contact lens hygiene, in particular avoiding contact of the lens and lens case with tap water.

Patients with early Acanthamoeba keratitis usually complain of discomfort, redness and light sensitivity of the affected eye. In the later stages the eye can become very painful as the nerves and deeper parts of the cornea become affected.

How is acanthamoeba keratitis managed?

An optometrist who suspects such an infection is advised to refer the patient as an emergency (same day) to the ophthalmologist, who will try to confirm the diagnosis and then prescribe special eye drops given day and night. Often the patient will be admitted to hospital. If there is much scarring of the cornea following the eventual elimination of the infection, and vision is badly affected, a corneal transplant may be recommended.