Acanthamoeba keratitis

ACANTHAMOEBA KERATITIS

• Acanthamoeba castellani is the most common cause.
• Does not require a human host to complete the life cycle —free living amoeba
• In human, acanthamoeba causes:

1. Keratitis
2. Granulamatous encephalitis
3. Fulminant meningoencephalitis

1. Contact lens wearers using home-made saline is the most common cause in developed countries
2. Trauma with contaminated vegetable matter — mcc in developing countries
3. Other causes – exposure to contaminated water especially fresh water sources, swimming pools or hot tubs
4. Opportunistic infection in herpetic, bacterial and neuroparalytic keratitis and bullous keratopathy
5. Common in immune compromised and debilitated persons which may result in granulomatous amoebic encephalitis

Clinical features

• Patient presents with very severe pain.

1. Initial lesions (Epithelial lesions):

• Typical reticular pattern due to radial keratoneuritis (Radial perineuritis).
• At this stage it is commonly mistaken for herpes simplex keratitis because of pseudodendritic epithelial lesion (dendritic ulcer morphology)

2. Advanced cases (Stromal involvement):

• Over a period of weeks stromal signs develop with central or paracentral ring shaped lesion with stromal infiltrate & an overlying epithelial defect, ultimately presenting as ring abscess.

1. KOH mount
2. Calcoflur white stain
3. Lactophenol cotton blue stain
4. Culture on non- nutrient agar (E.coli)

Treatment

• Started with a combination of anti-amoebic & trophozoicidal drugs, 0.02% polyhexamethylene biguanide PHMB (Drug of choice),propamidine & neomycin.
• Some clinicians use topical chlorhexidine instead of PHMB as an alternative cystocidial agent.