The Natural History of Acanthamoeba Keratitis: A Systematic Literature Review

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.

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.

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%).

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.