What is Acanthamoeba keratitis?
Acanthamoeba keratitis is a rare disease in which amoebae of the genus Acanthamoeba attack the clear front (cornea) part of the eye and affects about 100 people in the United States each year. Acanthamoeba are protozoa found almost everywhere in soil and water and can cause infections of the skin, eyes, and central nervous system.
Acanthamoeba infection of the cornea is difficult to treat with conventional medicines, and Acanthamoeba keratitis (AK) can cause enduring visual impairment or blindness, due to damage to the cornea or other structures important to vision. Recently, AK has been recognized as an orphan disease and a subsidized project, Orphan Diseases Acanthamoeba Keratitis (ODAK), has tested the effects of a wide range of drugs and biocides on AK.
Symptoms of Acanthamoeba keratitis
The symptoms of Acanthamoeba keratitis can be very alike to the symptoms of other eye infections. These symptoms, which can last for several weeks or months, can include:
- Eye pain
- Redness of the eyes
- Blurry vision
- Sensitivity to light
- Sensation of something in the eye
- Excessive tearing
Patients should consult with their ophthalmologist if they have any of the above symptoms. Acanthamoeba keratitis will eventually cause severe pain and possible vision loss or blindness if left untreated.
Risk factors for Acanthamoeba keratitis
Risk factors include contact lens wear, exposure to organisms (often through contaminated water), and corneal trauma. Low levels of Anti-Acanthamoeba IgA in tears have also been shown to be a risk factor. More than 80% of Acanthamoeba keratitis is believed to occur in contact lens wearers. In one study, 75% of the patients were contact lens wearers; 40% wore soft lenses daily, 22% wore rigid gas permeable lenses, and 38% wore extended wear lenses or others.
Diagnosis of Acanthamoeba keratitis
The emergence of Acanthamoeba keratitis as a serious pathogen in ophthalmology coincided with the expansion of soft contact lens wear in the 1980s. Acanthamoeba generally gains access to the cornea due to contact lens-associated epithelial involvement and has been shown to grow in contact lens cases and some contact lens solutions. Acanthamoeba has been detected in contaminated water supplies, hot tubs, and spinning pools.
Culture, staining, confocal microscopy, polymerase chain reaction, and clinical suspicion can be used to make a diagnosis. Although scrapings and cultures can be negative in disease largely confined to the stroma, epithelial debridement is extremely helpful. When limited to the epithelium, debridement with a Kimura spatula or other suitable instrument decreases the amoebic load and is therapeutic. Because some initial biopsies and cultures are inconclusive, larger samples aid in diagnosis.
Samples should be grown on non-nutritive agar coated with E. coli (or other coliform). Corneal scrapings should also be submitted for microscopy. Scrapings can be stained with Giemsa or calcafour white. Topical therapy begins immediately after debridement. When questioning whether the end point of treatment has been reached, repeat cultures and scrapes is invaluable.
Treatment for Acanthamoeba keratitis
Early treatment of Acanthamoeba keratitis lessens long-term visual sequelae. Unfortunately, the treatment of firm Acanthamoeba keratitis remains frustrating, as the diagnosis of the condition is often indefinable. Too often, patients endure weeks of topical steroid treatment before diagnosis. The possibility of visual loss despite months of continuous topical therapy is an unfortunate potential outcome.
While developing therapies such as alkylphosphocholines (miltefosine), newer guanadines, other antibiotics, and other chemotherapeutics hold potential for difficult-to-treat infections (Eye. 2003; 17: 893-905), many of these remedies have not been well labelled, nor are they, they are currently available to the practicing ophthalmologist. So, as combination of topical therapy with biguanide and diamidine remains the backbone of treatment for Acanthamoeba keratitis.
Postoperative complications after penetrating keratoplasty include reappearance of Acanthamoeba infection, as well as all other possible postoperative complications (such as infection, glaucoma, waterfalls, wound leakage, rejection, astigmatism).
For the most part, contact lens wearers should take precautions when cleaning lenses, they should never use tap water and saline to clean. As the treatment is toxic and lengthy, they should visit you if they discover any signs of inflammation. And those without glasses should not wash their eyes with lake or sea water.