In the United States, it is nearly always associated with contact lens use, as Acanthamoeba can survive in the space between the lens and the eye. For this reason, contact lenses must be properly disinfected before wearing, and should be removed when swimming or surfing.
However, elsewhere in the world, many cases of Acanthamoeba present in non-contact lens wearers.
To detect Acanthamoeba on a contact lens in a laboratory, a sheep blood agar plate with a layer (a lawn) of E. coli is made. Part of the contact lens is placed on the agar plate. If Acanthamoeba are present, they will ingest the bacteria, leaving a clear patch on the plate around the area of the lens. Polymerase chain reaction can also be used to confirm a diagnosis of Acanthamoeba keratitis, especially when contact lenses are not involved. Acanthameoba is also characterized by a brawny edema and hazy view into the anterior chamber. Late stages of the disease also produces a ring shaped corneal ulcer.
Signs and symptoms include severe pain, severe keratitis (similar to stromalherpetic disease), corneal perineuritis, and ring ulcer (late in the disease process).
^JOHN D.T. (1993) Opportunistically pathogenic free-living amebae. In: J.P. Kreier and J.R. Baker (Eds.), Parasitic Protozoa. Vol. 3. Academic Press, New York, pp. 143–246.
^Badenoch, PR; Adams M, Coster DJ (February 1995). "Corneal virulence, cytopathic effect on human keratocytes and genetic characterization of Acanthamoeba". International Journal for Parasitology25 (2): 229–39. doi:10.1016/0020-7519(94)00075-Y. PMID7622330.|accessdate= requires |url= (help)
^Sharma, S; Garg, P; Rao, GN (2000). "Patient characteristics, diagnosis, and treatment of non-contact lens related Acanthamoeba keratitis.". The British journal of ophthalmology84 (10): 1103–8. doi:10.1136/bjo.84.10.1103. PMC1723254. PMID11004092.