Which organism is associated with contact lens–related keratitis and exposure to tap water?

• A. Acanthamoeba
• B. Naegleria fowleri
• C. Entamoeba histolytica
• D. Toxoplasma gondii

Answer: (A)

Acanthamoeba are free-living amoebae commonly found in tap water and soil. When contact lenses are handled with tap water or stored in water-contaminated solutions, these organisms can be introduced to the corneal surface. In the cornea, Acanthamoeba can cause a painful, often stubborn keratitis that may show characteristic features like ring-shaped corneal infiltrates and radial keratoneuritis. The organism’s ability to form hardy cysts makes it resistant to standard lens disinfection, contributing to difficult treatment.

Other choices are associated with different environments or disease patterns: Naegleria fowleri is linked to hot freshwater exposure and causes a fatal brain infection rather than keratitis; Entamoeba histolytica causes amoebic dysentery from ingestion; Toxoplasma gondii leads to toxoplasmosis, sometimes with ocular involvement but not keratitis related to contact lenses.