Challenges in Acanthamoeba Keratitis: A Review

Abstract

To review challenges in the diagnosis and management of Acanthamoeba keratitis (AK), along with prognostic factors, in order to help ophthalmologists avoid misdiagnosis, protracted treatment periods, and long-term negative sequelae, with an overarching goal of improving patient outcomes and quality of life, we examined AK studies published between January 1998 and December 2019. All manuscripts describing clinical manifestations, diagnosis, treatment, prognosis, and challenges in short- and long-term management were included. The diagnosis of AK is often challenging. An increased time between symptom onset and the initiation of appropriate therapy is associated with poorer visual outcomes. The timely initiation of standardized antiamoebic therapies improves visual outcomes, decreases the duration of treatment, and reduces the chances of needing surgical intervention. In clinical practice, AK diagnosis is often missed or delayed, leading to poorer final visual outcomes and a negative impact on patient morbidity and quality of life.

Keywords: Acanthamoeba keratitis; in vivo confocal microscopy; misdiagnosis; prognosis; therapy.

Figure 1

Representative images of the clinical evolution of Acanthamoeba keratitis (AK): early phase AK showing epithelial keratopathy (A, stage I) [3], stromal involvement and sterile hypopyon (B, stage II) [15], epithelial defect and ring stromal infiltrate (C,D, stage III) [11], and corneal scarring with deep and superficial neovascularization (E,F).

Figure 2

In vivo confocal microscopy image of Acanthamoeba keratitis involving superficial and deeper corneal layers. The typical “starry sky” appearance is depicted: Acanthamoeba spp. cysts appear as oval or round, double-walled, highly refractile structures with a polygonal inner wall and a total size of 12–25 microns [23].

Figure 3

Proposed therapeutic strategy for Acanthamoeba keratitis. An initial aggressive approach to treatment involves hourly topical eye drops (polyhexamethylene biguanide (PHMB) 0.02% and propamidine isethionate 0.1%), followed by tapering to maintenance therapy using PHMB and propamidine 3–4 times per day for 6 weeks. A stable clinical exam after a 2-week antiamoebic free period reduces the risk of medication toxicity and can also unmask the continued presence of trophozoites or cysts. If the infection is still present, the treatment protocol must be repeated. Topical low-dose and low-frequency steroid eye drops (such as loteprednol etabonate and fluorometholone acetate) have been suggested in cases of severe ocular pain, limbitis, or scleritis, and must be used with extreme caution. Topical steroids should only be used with concomitant antiamoebic therapy.