Acanthamoeba keratitis (AK), is a devastating, extremely painful eye infection that affects the cornea (the window of the eye). It is mainly found in association with contact lens wearers with specific behaviours, putting these people more at risk – although there are cases of this disease in non-contact lens users. AK can lead to severe vision loss with around 50% of patients needing corneal transplantation or becoming blind, and for around 5-10% of patients can also result in enucleation (removal) of the eye. AK is frequently misdiagnosed, and the associated pain can be widely underestimated by various clinicians.

AK is often characterized by pain out of proportion and the late clinical appearance of a stromal ring-shaped infiltrate. This condition is both difficult to diagnose and difficult to treat therapeutically and almost always needs some sort of surgical intervention.

AK can affect one eye (unilateral) or both eyes (bilateral). A rare and painful complication of AK is Acanthamoeba scleritis also known as ASK, which affects around 10–18% of patients. In extreme cases the Acanthamoeba can cause a systemic infection beyond the eye, even causing granulomatous Acanthamoeba encephalitis (GAE) of the brain.

Acanthamoeba is suspected to cause pathology through using small cuts or abrasions in the cornea to invade the eye. This is probably due to some trauma to the eye and exacerbated by wearing contact lenses, and the parasite takes advantage of these factors, using the natural bacteria found on the surface of the eye as a food source.

This picture shows the different layers of a cornea with AK (reaction of the parasite)

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

AK can lead to severe vision loss with around 50% of patients becoming blind, need corneal transplantation, and can also result in enucleation of the eye for 5-10% of patients. AK is frequently misdiagnosed and the associated pain is underestimated by various clinicians.

AK is often characterized by pain out of proportion to findings and the late clinical appearance of a stromal ring-shaped infiltrate. This disease is both difficult to diagnose and difficult to treat therapeutically and almost always needs some sort of surgical intervention. 

AK can affect one eye (unilateral) or both eyes (bilateral). A rare and painful complication of AK is Acanthamoeba scleritis also known as ASK, which affects ~10–18% of patients. In extreme cases the Acanthamoeba can cause a systemic infection beyond the eye, even causing granulomatous Acanthamoeba encephalitis (GAE) of the brain. 

The way the acanthamoeba works is using small cuts or abrasions in the cornea to invade the eye, probably due to wearing contact lenses or trauma to the eye, by taking advantage of that while using the bacteria on the eye as food.