3. Diagnosis
Clinical symptoms are often corneal pain and photophobia, which may be disproportionate to the appearance of the eye. Initial findings are often punctate epitheliopathy or scattered subepithelial infiltrates which respond well to steroid therapy. The recognised pathognomonic sign of AK is a radial pattern of perineural infiltrates, often with an associated limbitis. Ring infiltrates are common, with a variable onset from early in the infection until very late. Advanced stages show a central epithelial loss with stromal thinning and occasionally progression to corneal melt. Uveitis and hypopyon may occur in the later stages of the infection. The common disciform epithelial and stromal infiltrate appearance causes Acanthamoeba keratitis to be very commonly initially diagnosed as herpes simplex virus (HSV) keratitis or even fungal keratitis, until treatments for these conditions fail to effectively treat the patient.