A contact lens wearer presents with a rapidly progressive corneal ulcer. Confocal microscopy shows double-walled, spherical cysts with internal granular material. The MOST likely causative organism is:
- A Fusarium solani
- B Acanthamoeba species ✓
- C Pseudomonas aeruginosa
- D Streptococcus pneumoniae
Correct answer: B. Acanthamoeba species
Explanation
Acanthamoeba keratitis almost exclusively affects contact lens wearers and is characterised by severe pain disproportionate to clinical signs, ring infiltrate (Wessley immune ring), and perineural infiltrates. Confocal microscopy is the gold standard for in vivo diagnosis, showing double-walled cysts (trophozoites also visible). Treatment requires prolonged polyhexamethylene biguanide (PHMB) ± chlorhexidine ± propamidine. Fusarium shows feathery white infiltrate with satellite lesions in agricultural workers.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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