A 25-year-old contact lens wearer presents with severe eye pain, photophobia, and a ring-shaped stromal infiltrate on slit-lamp examination. Corneal scraping stained with calcofluor white shows double-walled cysts. The most likely causative organism is:
- A Fusarium solani
- B Acanthamoeba species ✓
- C Pseudomonas aeruginosa
- D Herpes simplex virus
Correct answer: B. Acanthamoeba species
Explanation
Acanthamoeba keratitis is strongly associated with contact lens use (especially in non-sterile water or swimming while wearing lenses) and presents with severe disproportionate pain, a pathognomonic ring infiltrate, and radial keratoneuritis (inflammation along corneal nerves visible as linear infiltrates). Calcofluor white or acridine orange staining of corneal scrapings reveals the double-walled cysts (trophozoites and cysts). Treatment is with polyhexamethylene biguanide (PHMB) or chlorhexidine combined with propamidine.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.