A contact lens wearer presents with a painful red eye, ring infiltrate at mid-peripheral cornea, and radial perineuritis (pain with periocular pressure). The most likely diagnosis and first treatment step is:

• A Pseudomonas keratitis; intensive topical fluoroquinolone therapy
• B Herpes simplex keratitis; topical acyclovir 3% ointment
• C Fungal keratitis; topical natamycin 5%
• D Acanthamoeba keratitis; polyhexamethylene biguanide (PHMB) and propamidine isethionate (Brolene) ✓

Explanation

The combination of contact lens wear, ring-shaped stromal infiltrate (immune ring), and radial perineuritis (pain along corneal nerves — pathognomonic finding) is characteristic of Acanthamoeba keratitis. Treatment requires prolonged (minimum 3-6 months) combination anti-amoebic therapy: a biguanide (PHMB 0.02% or chlorhexidine 0.02%) plus a diamidine (propamidine 0.1% / hexamidine 0.1%). Steroids are contraindicated in the acute phase as they promote cyst transformation. Confocal microscopy can confirm by visualizing cysts in the stroma.

Reference: Khurana Comprehensive Ophthalmology, 7th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.