Acanthamoeba species are protozoa (unicellular eukaryotes) that can cause an isolated infection of the human cornea as their primary disease in humans. Other conditions have been described, such as disseminated dermatitis, visceral infestation, and encephalitis unrelated to ocular disease. The Acanthamoeba life cycle includes a motile trophozoite form (15–45 μm in diameter) and a dormant cyst form (10–25 μm in diameter) (Fig 10-7). The cysts are double-walled and very hardy, resistant to most environmental extremes and toxins, including chlorine. Classification of Acanthamoeba species has been based on morphology, but molecular methods are more accurate and increasingly utilized.
Microsporidia are obligate intracellular parasites and, recently, have also been linked to the Fungi kingdom. Of the phylum Microspora, the following genera have been implicated in human infection: Nosema, Encephalitozoon, Pleistophora, Vittaforma, Trachipleistophora, Enterocytozoon, and unclassified microsporida.
Leishmania is a genus of flagellate protozoa. Cutaneous leishmaniasis is transmitted by the bite of its vector, the female sandfly, in endemic areas of tropical Asia, Africa, and Latin America. An infected eyelid ulcer may become granulomatous. Scrapings or biopsy material obtained from the ulcer can show intracellular parasites by Giemsa or immunofluorescent stains. The parasites can sometimes be isolated on blood agar or insect tissue culture medium.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.