Keratitis is most often caused by which organism?

• A. Acanthamoeba sp.
• B. Naegleria fowleri
• C. Loa loa
• D. Onchocerca volvulus

Answer: (A)

Keratitis is most often caused by Acanthamoeba species. These free-living amoebae can invade the cornea, especially in contact lens wearers or after exposure to contaminated water, solutions, or trauma. Clinically, Acanthamoeba keratitis often presents with severe eye pain, redness, and vision changes, and may show characteristic ring-shaped stromal infiltrates and keratoneuritis. The organism is notoriously difficult to diagnose and requires specific laboratory methods (such as corneal scrapings examined for amoebae or culture on non-nutrient agar with bacteria).

Naegleria fowleri chiefly causes primary amoebic meningoencephalitis, not keratitis. Loa loa and Onchocerca volvulus are parasitic nematodes that affect the eye in other contexts (loiasis and river blindness, respectively), but they are not the most common causes of infectious keratitis.