A 30-year-old contact lens wearer presents with severe ocular pain, photophobia, and a ring-shaped mid-peripheral stromal infiltrate. He reports his contact lens case contaminated with tap water. Confocal microscopy shows double-walled cysts. The most appropriate treatment is:
- A Topical voriconazole 1% with natamycin 5%
- B Topical polyhexamethylene biguanide (PHMB) 0.02% combined with propamidine isethionate (Brolene) 0.1% ✓
- C Topical moxifloxacin 0.5% every hour
- D Topical acyclovir 3% ointment five times daily
Correct answer: B. Topical polyhexamethylene biguanide (PHMB) 0.02% combined with propamidine isethionate (Brolene) 0.1%
Explanation
Acanthamoeba keratitis is diagnosed by double-walled cysts on confocal microscopy (in vivo confocal) or culture on non-nutrient agar with E. coli overlay. The ring infiltrate (immune ring/Wessely ring) is characteristic. Treatment requires prolonged (6–12 months) combination anti-amoebic therapy with biguanides (PHMB 0.02% or chlorhexidine 0.02%) targeting trophozoites AND aromatic diamidines (propamidine/hexamidine) to cover cysts. Antifungals and antibacterials have no effect; acyclovir is for herpes.
Reference: Khurana Comprehensive Ophthalmology, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.