On presentation, all pre-existing treatment was stopped for 48 hours and corneal scrapes for direct smears and cultures using blood agar, chocolate agar, thioglycolate broth and sabouraud dextrose agar were done. Initial antimicrobial therapy for both groups consisted of fortified vancomycin eye drops 50 mg/ml, fortified ceftazidime eye drops 50 mg/ml hourly, and the antifungal agent itraconazole 100 mg orally twice per day. This regimen was subject to change according to microbiology culture sensitivities and/or results.

Patients allocated to the PACK-CXL group were assessed and treated by PACK-CXL within 2 days of treatment initiation. Topical anaesthesia was achieved using 0.4% benoxinate hydrochloride drops. Epithelium was removed up to 9 mm diameter. Corneal thickness of the area to be treated was measured (without epithelium) aiming for a starting thickness of no less than 350μm. Corneas thicker than 500μm were dehydrated to reduce thickness by using 70% Glycerol drops applied topically at intervals of 2-3 seconds for a total of five minutes. A schematic representation of PACK-CXL protocol is provided in Figure 1. Iso-osmolar riboflavin drops were instilled topically on the cornea at regular intervals of 2 minutes for a total period of 30 minutes. Thickness was also re-measured every 5 min to ensure that it remained below 500µm during instillation of riboflavin. The cornea was illuminated using a UVX, UV-A 365 nm with an irradiance of 3 mW/cm2 for 30 minutes and a total dose of 5.4 J/cm2 during

Topical anaesthesia was achieved using 0.4% benoxinate hydrochloride drops. Epithelium was removed up to 9 mm diameter. Corneal thickness of the area to be treated was measured (without epithelium) aiming for a starting thickness of no less than 350μm. Corneas thicker than 500μm were dehydrated to reduce thickness by using 70% Glycerol drops applied topically at intervals of 2-3 seconds for a total of five minutes. A schematic representation of PACK-CXL protocol is provided in Figure 1. Iso-osmolar riboflavin drops were instilled topically on the cornea at regular intervals of 2 minutes for a total period of 30 minutes. Thickness was also re-measured every 5 min to ensure that it remained below 500µm during instillation of riboflavin. The cornea was illuminated using a UVX, UV-A 365 nm with an irradiance of 3 mW/cm2 for 30 minutes and a total dose of 5.4 J/cm2 during which riboflavin was instilled every 2 min and corneal pachymetry performed every 5 min. PACK-CXL was performed in a 9

Ulcer dimensions will be studied on slit lamp and AS-OCT.