A contact lens wearer presents with a painful red eye with a ring-shaped stromal infiltrate at the mid-periphery. Corneal confocal microscopy shows highly reflective double-walled cysts. The first-line treatment is:
- A Topical moxifloxacin 0.5% every 2 hours
- B Topical voriconazole 1% alternating with natamycin 5%
- C Topical polyhexamethylene biguanide (PHMB) 0.02% with propamidine isethionate (Brolene) every 1–2 hours ✓
- D Topical acyclovir 3% ointment five times daily
Correct answer: C. Topical polyhexamethylene biguanide (PHMB) 0.02% with propamidine isethionate (Brolene) every 1–2 hours
Explanation
The clinical picture — ring infiltrate, contact lens use, double-walled cysts on confocal microscopy — is pathognomonic for Acanthamoeba keratitis. First-line treatment is a biguanide (PHMB 0.02% or chlorhexidine 0.02%) combined with a diamidine (propamidine isethionate/Brolene). These agents target both the trophozoite and the resistant cyst form. Treatment duration is typically 6–12 months. Fluoroquinolones, antifungals, and antivirals are not effective against Acanthamoeba.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.