What clinical feature most strongly suggests Acanthamoeba keratitis over bacterial keratitis?

• A. Ring infiltrate
• B. Painless eye redness
• C. Disproportionate severe pain with minimal exam findings
• D. Rapid improvement with antibiotics

Answer: (C)

Pain out of proportion to what you can see on exam is the strongest clue for Acanthamoeba keratitis. The organism tends to invade corneal nerves and deeper tissues, so patients often experience severe, disabling pain that seems disproportionate to only mild surface findings early on. In bacterial keratitis, pain typically correlates with visible surface damage and infection signs like epithelial loss, discharge, and redness. Ring infiltrates or other later signs can appear with Acanthamoeba, but they aren’t as reliable early indicators. A rapid improvement with antibiotics would argue against Acanthamoeba, so the standout feature is the extreme pain relative to minimal corneal findings.