Persistence of acanthamoeba antigen following acanthamoeba keratitis

Aim-To investigate the hypothesis that persistent corneal and scleral infla mmation following acanthamoeba keratitis is not always caused by active amo ebic infection but can be due to persisting acanthamoebic antigens Methods-24 lamellar corneal biopsy and penetrating keratoplasty specimens w ere obtained from 14 consecutive patients at various stages of their diseas e and divided for microscopy and culture. Histological sections were immuno stained and screened for the presence of Acanthamoeba cysts by light micros copy. Cultures were carried out using partly homogenised tissues on non-nut rient agar seeded with E coli. Clinical data were obtained retrospectively from the case notes of these patients. Results-Of the 24 specimens, 20 were obtained from eyes that were clinicall y inflamed at the time of surgery. Acanthamoeba cysts were present in 16 (8 0%) of these 20 specimens, while only five (25%) were culture positive. Aca nthamoeba cysts were found to persist for up to 31 months after antiamoebic treatment. Conclusion-These findings support the hypothesis that Acanthamoeba cysts ca n remain in corneal tissue for an extended period of time following acantha moeba keratitis and may cause persistent corneal and scleral inflammation i n the absence of active amoebic infection. In view of these findings, prolo nged intensive antiamoebic therapy may be inappropriate when the inflammati on is due to retained antigen rather than to viable organisms.