The specimen is a cornea from a 67 year old Caucasian female from San Diego with history of chronic corneal ulcer (x 6 months) and status post Lasik surgery a few months before. Cultures and smears were all negative. The patient was treated with antibiotics and anti-amebic drugs empirically for 3-6 months. Initially there was clinical suspicion for amebic keratitis despite the negative corneal smear examination.

Amebic keratitis
Consistent with Hartmannella-Acanthamoeba group. 

Histologic sections of the ulcerated cornea show numerous amebic organisms in predominately cyst forms. Very rare trophozoites are seen at the periphery of the cornea along with a rather mild infiltrate of inflammatory cells including eosinophils. The size of the cysts (20-25 microns) and the morphology of  the nuclei ( large and sharply outlined nuclei with dense nucleolus and with a clear space between the two) are consistent with Acanthamoeba , which is the typical species infecting of the cornea. The preponderance of cysts is helpful in excluding Naegleria infection which is in the main differential diagnosis for this case, and is also consistent with the history of treatment with anti-amebic drugs. Infection with the H-A group is usually not associated with swimming, and is usually preceded by disease or trauma, and is often with a more protracted clinical course. It is not known how this patient became exposed to this amebic infection.

Reference: AFIP Atlas of Pathology of Tropical and Extraordinary Diseases.

The Doctor's Doctor-Acanthamoeba

Note: Many thanks to Dr. Jay Packer at Good Samaritan Hospital of Los Angeles for reviewing this case.

Submitted by Si Nguyen, M.D. from Huntington Hospital, Huntington Beach, CA.