The proof-of-principle study included 5 corneas that were therapy-resistant to any conventional type of treatment. In all five cases, the corneal infection calmed down within days to weeks and all eyes could be saved. In the same year, the effect of riboflavin/UV-A irradiation was shown on several bacteria and fungi in vitro, with a killing rate of almost 98% within 30 minutes for the most common strains responsible for bacterial keratitis like Methicillin resistant Staph aureus and Pseudomonas aeruginosa. A case series and a clinical phase 1 study performed by Makdoumi et al showed the beneficial effect of PACK-CXL (photoactivated chromophore for the treatment of infectious keratitis-corneal collagen crosslinking) in 15 eyes of 15 patients with early onset corneal ulcers. Here, PACK-CXL was even used as the primary therapy, whereas controls received maximal conventional therapy (medication). Again, PACKCXL alone was beneficial in the outcome in all eyes investigated. Between 2010 and 2013, a randomized prospective clinical trial was performed examining the effect of adjuvant PACK-CXL therapy in advanced corneal ulcers with associated melting. Even in these far advanced cases with impending perforation, the additional effect of PACK-CXL was significant, with a drop in the ulcer-related complication rate from 23% (controls) to 0%. A number of smaller reports and case series have shown the effect of PACK-CXL on other bacterial, and also fungal infections.