Dr. Jeremy D. Keenan offers pearls for making the tricky Acanthamoeba keratitis (AK) diagnosis. Though rare, it is important to know the signs of this vision-threatening infection, beginning with the epidemiology. The 2 biggest risk factors are contact-lens wear and freshwater exposure, with infection rates typically higher in the summer. Early signs include epitheliopathy, pseudodendrites lacking terminal bulbs, and an epithelial ridge. Because AK is often misdiagnosed as HSV, Dr. Keenan recommends performing a confocal exam to detect AK cysts before starting an HSV suspect on steroids. To be certain, perform a corneal scraping to debulk the lesion and run a smear.