Acanthamoeba Keratitis

doi:10.1016/S0039-6257(98)00004-6

Survey of Ophthalmology

Volume 42, Issue 6, May–June 1998, Pages 493-508

https://doi.org/10.1016/S0039-6257(98)00004-6 Get rights and content

Abstract

Acanthamoeba species are an important cause of microbial keratitis that may cause severe ocular inflammation and visual loss. The first cases were recognized in 1973, but the disease remained very rare until the 1980s, when an increase in incidence mainly associated with contact lens wear was reported. There is an increased risk when contact lens rinsing and soaking solutions are prepared with nonsterile water and salt tablets. The clinical picture is often characterized by severe pain with an early superficial keratitis that is often treated as herpes simplex infection. Subsequently a characteristic radial perineural infiltration may be seen, and ring infiltration is common. Limbitis and scleritis are frequent. Laboratory diagnosis is primarily by culture of epithelial samples inoculated onto agar plates spread with bacteria. Direct microscopy of samples using stains for the cyst wall or immunostaining may also be employed. A variety of topically applied therapeutic agents are thought to be effective, including propamidine isethionate, clotrimazole, polyhexamethylene biguanide, and chlorhexidine. Various combinations of these and other agents have been employed, often resulting in medical cure, especially if treatment is commenced early in the course of the disease. Penetrating keratoplasty is preferably avoided in inflamed eyes, but may be necessary in severe cases to preserve the globe or, when the infection has resolved, to restore corneal clarity for optical reasons. (Surv Ophthalmol 42:493–508, 1998.

Section snippets

Acanthamoeba in the Environment

Acanthamoeba is a free-living genus of amoeba that is abundant in the environment. It survives in diverse conditions and has been isolated from soil and dust,28, 65, 119, 147 freshwater,65, 87 seawater,33, 137 and air.85, 133 Acanthamoeba is not naturally parasitic and does not require a host, in contrast to many other protozoa that cause disease in humans. It usually feeds on bacteria, fungi, other protozoa, and cyanobacteria (blue-green algae),³⁹ and is found in greatest numbers where other

Biology of Acanthamoeba

The active form, known as the trophozoite (Fig. 1), is 25–40 μm in length, has a single nucleus with a prominent nucleolus, and has a central cytoplasmic contractile vacuole,¹²⁰ the function of which is to expel water. During movement, a hyaline pseudopodium can be seen to slowly extend from the amoeba, and when moving on a surface, small processes called filopodia that extend between the amoeba and the surface appear to play a role in motility.¹²⁸ Many thin processes called acanthapodia

Acanthamoeba in Humans

Because of the widespread distribution of Acanthamoeba, human contact with the organism is inevitable and frequent. In a study based on sampling of air both inside and outside a building, it was estimated that a human inhales on average two Acanthamoeba organisms per day.⁸⁵ Humans may also come into contact with amoebas while swimming in lakes, and also in swimming pools, which have been found to frequently contain Acanthamoeba.21, 35, 101 Another source is domestic tapwater,83, 168 where the

Conclusions

Acanthamoeba keratitis has emerged as a clinical problem only during the last 25 years and has been one of the most difficult corneal diseases to manage successfully. Recently, treatment has become more effective and diagnosis is often made earlier than in the past, due to increased familiarity with the condition. However, a worrisome aspect is that in some countries the disease appears to be increasing in incidence. Additionally, there have been reports of apparent resistance to treatment with

Method of Literature Search

The literature was searched using MEDLINE and using citations in articles thus obtained. Articles that were considered to have made a contribution to the understanding of the disease were included in this review, although some earlier case reports that have already been reviewed in some detail by Auran⁵ were not included. Attention was focused on case series rather than single case reports unless the latter were in some way unique.

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