Acanthamoeba keratitis

A problem for contact lens users that is here to stay

Keratitis due to acanthamoeba infection has now been recognised in Europe, Asia, Australia, the Americas, and parts of Africa. The cause is a free living protozoan found not only in soil and pond water but also in mains water supplies. It survives in adverse conditions by forming resistant cysts, which may contain legionellas and other bacteria. These cysts are impervious to inorganic chlorine at up to 50 ppm. The trophozoites are sensitive to chlorine at 2 ppm, but even this concentration is well in excess of that in public water supplies (<1 ppm). A strength of between 3 and 8 ppm is found, however, in chlorine generating disinfecting solutions for contact lenses.1

The cysts, so difficult to destroy, may be incorporated in the biofilm within water pipes and on contact lenses and may be cultured from both sites. Enhancement techniques may be required--especially when cultures are made from corneal scrapings or biopsy specimens--because earlier drug treatment may have induced temperature sensitivity and a shift into a “dormant” cyst stage.

Infection of the cornea with acanthamoeba without a contact …