Acanthamoeba Keratitis is a vision-threatening infection most commonly found in contact lens wearers. In late stages, it presents as characteristic ring abscess in the eye. Other risk factors of Acanthamoeba Keratitis are exposure to contaminated water and trauma to cornea. The differential diagnosis Acanthamoeba Keratitis are: - Corneal erosion - Herpes simplex keratitis - Marginal keratitis - Viral keratitis - Bacterial keratitis - Fungal keratitis - Sterile keratitis Source: https://eyewiki.aao.org/Acanthamoeba_Keratitis