Which organism is linked to rinsing contact lenses with tap water and can cause severe keratitis?

• A. Acanthamoeba
• B. Naegleria fowleri
• C. Giardia lamblia
• D. Entamoeba histolytica

Answer: (A)

Rinsing contact lenses with tap water is a classic setup for infection by Acanthamoeba, a free-living amoeba that can contaminate lenses and the ocular surface. This organism exists in both active trophozoite and hardy cyst forms, and tap water doesn’t reliably eliminate it. Cysts can survive disinfection and once a lens harboring Acanthamoeba touches the cornea, the organism can invade the eye, leading to severe keratitis that can be very painful, progressively vision-threatening, and difficult to treat. This makes Acanthamoeba the organism most strongly linked to lens hygiene practices involving tap water.

The other organisms listed are associated with different diseases and routes of infection. Naegleria fowleri is known for causing a rapidly fatal brain infection after nasal exposure to warm freshwater, not keratitis. Giardia lamblia and Entamoeba histolytica cause intestinal illnesses (giardiasis and amebic dysentery, respectively) and are not tied to eye infections from contact lens use.