Acanthamoeba keratitis most commonly presents with pain disproportionate to clinical signs. The pathological basis for this severe pain is:

• A Release of proteolytic enzymes that directly stimulate corneal nociceptors
• B Corneal hypoxia from heavy stromal infiltrate blocking oxygen diffusion
• C Secondary aqueous flare and anterior chamber inflammation causing ciliary spasm
• D Preferential invasion of corneal nerves (perineural infiltration) by Acanthamoeba trophozoites ✓

Explanation

Acanthamoeba keratitis characteristically causes severe pain that is disproportionate to the degree of visible corneal inflammation — often described as the 'hallmark' of the condition. This is because Acanthamoeba trophozoites preferentially invade and track along corneal nerves (perineural infiltration), which is well demonstrated on confocal microscopy as trophozoites surrounding or adjacent to corneal nerve fibers. This direct neural invasion triggers intense pain signals. A 'pseudodendrite' pattern in the epithelium along nerve fiber distribution may be seen early. The ring infiltrate (Wessely immune ring) appears later as a characteristic but not earliest sign.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.