The Natural History of Acanthamoeba Keratitis: A Systematic Literature Review

Abstract

Introduction: Acanthamoeba keratitis (AK) was first identified in 1972 and the first patient cured with propamidine was reported in 1985. Treatment outcomes, before the advent of the first effective anti-amoebic treatment, were known to be poor and often required therapeutic keratoplasty (TK) but have not been evaluated in detail. Analysis of these outcomes has value for several reasons: it gives an historical perspective, describes the natural history of AK when the disease was minimally modified by the early treatments and provides a benchmark against which current treatments can be compared and how these have changed the therapeutic results. Methods: We conducted a systematic literature review for the period 1970–1995 using PRISMA guidelines. The population of interest comprised patients with AK treated without products having established anti-amoebic activity against both trophozoites and cysts (biguanides or diamidines). The outcomes of interest were medical cure, TK and enucleation. Proportions and 95% confidence intervals were estimated. Results: Fifty-six case reports were eligible. Risk factors for AK were reported in 44/56 patients: contact lens wear in 30/44 (68.2%) and trauma in 14/44 (31.8%). The mean time from presentation to diagnosis was 7.3 weeks (standard deviation 9.3 weeks); 13/56 (23.2%) were diagnosed within 4 weeks. Topical treatments given to patients included corticosteroids (85.2%), antibiotics (85.2%), antivirals (72.2%) and antifungals (51.8%). Final visual acuity was ≥ 20/40 in 17/33 (51.5%) patients with no missing data. Medical cures were reported in 11/56 patients (19.6%), TK in 38/56 (67.9%), other surgery in 4/56 (7.1%) and enucleation in 3/56 (5.4%). Conclusion: This study suggests that, before the availability of propamidine as the first effective treatment for AK, the clinical outcome of these patients was poor with only a few patients cured without surgery. These findings should be interpreted with caution because they rely on case reports and series that are subject to inherent bias.