Cases of amoebic keratitis involving species other than Acanthamoeba are hypothesised to be underdiagnosed and poorly understood. Amoebic keratitis is debilitating and associated with chronic visual impairment. Understanding associated symptoms of non-Acanthamoeba amoebic keratitis could facilitate new diagnostic procedures and enable prompt treatment, ultimately leading to improved patient outcomes. Thus, a review of the literature was undertaken surrounding non-Acanthamoeba amoebic keratitis. Cases were geographically widespread and mostly confined to contact lens wearers ≤ 30 years old exposed to contaminated water sources and/or demonstrating poor lens hygiene. Vermamoeba vermiformis (previously Hartmanella vermiformis) was the most common causative agent, and a moderate number of mixed keratitis cases were also reported. A crucial disease indicator was early onset stromal deterioration/ulcerations, reported in 10 of the studies, usually only occurring in advanced Acanthamoeba keratitis. Mixed infections were the most difficult to treat, often requiring keratoplasty after unsuccessful combination treatment regimens. New diagnostic measures for non-Acanthamoeba amoebic keratitis should consider early onset stromal disease as a key disease indicator. Deep corneal scrapes are also necessary for accurate amoebic identification. Moreover, a combination approach to diagnosis is advised and should involve culture, microscopy and PCR techniques. In vitro drug sensitivity tests should also be conducted to help develop patient-specific treatment regimes.
Keywords: acanthamoeba; amoeba; diagnosis; hartmannella; keratitis; pathogenesis; vahlkampfia; vannella; vermamoeba.