Acanthamoeba keratitis is the most serious infective keratitis associated with contact lens wear. Although it is uncommon (Pseudomonas aeruginosa is the most common organism involved in contact lens associated infection followed by other bacteria), it is difficult to treat and may be mis-diagnosed as herpertic keratitis at the early stage. The examiner will expect the candidates to know this organism well as well as the associated clinical signs.

In the examination, you may be given slide showing cornea infected with acanthamoeba or simply ask to discuss the management of a patient with contact lens related corneal infection.

cyst	trophozoite

Acanthamoeba exists in two forms: cyst (which is double-walled) and trophozoite. Both may be seen in corneal scrap or biopsy. 

A specimen of cornea showing acanthamoeba cysts and trophozoite.  Click on the picture to see if you have found the organisms.

Common viva questions:

• How can you identify acanthamoeba in cornea? (Using special stains, see the section on stains for microbes; culture using nutrient poor agar overlay with E.coli and  immunofluorescent staining on the corneal scrap. Confocal microscopy may be used to identify acanthamoeba in cornea..)
• What factors and signs may alert you to the possibility of acanthamoeba keratitis?
• What are the treatment options for acanthamoeba keratitis?