A contact lens wearer presents with a painful red eye and a corneal infiltrate with a hypopyon. Confocal microscopy shows highly reflective double-walled cysts. The MOST likely pathogen is:

• A Pseudomonas aeruginosa
• B Aspergillus fumigatus
• C Herpes simplex virus
• D Acanthamoeba species ✓

Explanation

Acanthamoeba keratitis in contact lens wearers classically presents with severe pain disproportionate to clinical signs, ring infiltrate (late sign), and perineural infiltrates (pathognomonic). Confocal microscopy is diagnostic, showing the characteristic double-walled (trophozoite and cyst) reflective structures at the epithelial and anterior stromal levels. Pseudomonas causes rapidly progressive bacterial keratitis with aggressive suppuration. Aspergillus shows feathery grey infiltrates and satellite lesions. HSV shows dendritic ulcers.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.