Acanthamoeba keratitis, first recognized in 1973, is a rare, vision threatening, parasitic infection seen most often in contact lens wearers. It is often characterized by pain out of proportion to findings and the late clinical appearance of a stromal ring-shaped infiltrate. It is both difficult to diagnose and difficult to treat.
Acanthamoeba keratitis is characterized by pain out of proportion to findings. In one study, 95% of patients complained of pain. Patients may also complain of decreased vision, redness, foreign body sensation, photophobia, tearing, and discharge. Symptoms may wax and wane; they may be quite severe at times.
Risk factors include contact lens wear, exposure to organism (often through contaminated water), and corneal trauma. Low levels of anti-Acanthamoeba IgA in tears has also been shown to be a risk factor. It is thought that over 80% of Acanthamoeba keratitis appears in contact lens wearers. In one study, 75% of the patients were contact lens wearers; 40% wore daily soft lenses, 22% wore rigid gas permeable lenses, and 38% wore extended wear or other lenses.
Medical treatment for Acanthamoeba keratitis is still evolving. Success has been reported with various combinations of antibiotic, antiviral, antifungal, and antiparasitic drugs. Many of these topical treatments are not commercially available in the United States and need to be specially ordered. Different regimens include combinations of diamidines, biguanides, antibiotics and antifungals. Some topical preparations of diamidines are propamidine-isethionate, hexamidine-diisethionate, and dibromopropamidine. Biguanides include polyhexamethylene biguanide (PHMB), chlorhexidine. Neomycin-polymyxin B-gramicidin is thought to kill bacteria which provides a food source for the acanthamoeba. Antifungals include topical and oral preparations of voriconazole as well as ketoconazole, miconazole and clotrimazole .
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