Successful Treatment of Acanthamoeba Keratitis According to New Protocol with Polihexanide 0.08% Therapy: Case Report

<b>Background and Clinical Significance:</b> Acanthamoeba keratitis (AK) is a rare but serious corneal infection that can lead to severe visual impairment or blindness if not promptly treated. The condition is primarily associated with contact lens use but can also occur due to ocular trauma or environmental contamination. The most frequently used treatment options include biguanides and diamidines, though dosing protocols remain empirical and vary widely among clinicians. Recent research has explored a new standardized protocol with 0.08% polihexanide (polyhexamethylene biguanide, PHMB) as a monotherapy for AK, offering improved efficacy and better corneal penetration. <b>Case Presentation</b>: This case report describes a 35-year-old female contact lens wearer who presented with redness, pain, photophobia, and vision loss in her right eye. Upon referral, a slit-lamp examination revealed stromal infiltrates and perineural involvement, with in vivo confocal microscopy (IVCM) confirming Acanthamoeba cysts. The patient was treated with a new standardized intensive regimen of polihexanide 0.08% monotherapy, leading to rapid clinical improvement. Corneal infiltrates were significantly reduced, and the best-corrected visual acuity (BCVA) improved from 0.4 logMAR to 0.15 logMAR. Resolution with only discrete stromal haze was achieved over the following months, without recurrence. <b>Conclusions:</b> This case highlights the potential of polihexanide 0.08% monotherapy as an effective treatment for AK in a new standardized treatment protocol.