Photoactivated chromophore for keratitis-corneal cross-linking (PACK-CXL) has progressed a great deal since it was first developed (1) as a treatment for infectious keratitis and corneal ulcers. At first, PACK-CXL utilised the same the technical settings as the original CXL-for-ectasia method, the ?Dresden protocol? (2), delivering 5.4 J/cm² of UV energy to the riboflavin-saturated region of the cornea where the infection was present. But it soon became clear that a number of factors meant that higher fluences needed to be delivered: ulcers are opaque, and this makes the effect of PACK-CXL somewhat superficial. For deeper pathogen killing in infectious keratitis ulcers, higher fluences need to be delivered (3).
A recent study by Awad et al. (4) has shown in in rabbits that high fluence PACK-CXL (30 mW/cm²) is as effective as voriconazole for the treatment of fungal keratitis. Compared with voriconazole therapy, high-fluence PACK-CXL not only decreased corneal inflammatory signs و accelerated healing, but it also decreased the incidence of corneal perforation and intraocular inflammation. In other words, high (30 mW/cm²) UV-A fluence is associated with better outcomes regarding not only clinical improvement measures, but also the pathological features of inflammation.
References
1. Said DG, Elalfy MS, Gatzioufas Z, et al. Collagen cross-linking with photoactivated riboflavin (Pack-cxl) for the treatment of advanced infectious keratitis with corneal melting. Ophthalmology. 2014;121(7):1377-1382.
2. Wollensak G, Spoerl E, Seiler T. Riboflavin/ultraviolet-a-induced collagen crosslinking for the treatment of keratoconus. Am J Ophthalmol. 2003;135(5):620-627.
3. Kling S, Hufschmid FS, Torres-Netto EA, et al. High fluence increases the antibacterial efficacy of pack cross-linking. Cornea. 2020;39(8):1020-1026.
4. Awad R, Hafezi F, Ghaith AA, et al. Comparison between three different high fluence UVA levels in corneal collagen cross-linking for treatment of experimentally induced fungal keratitis in rabbits. European Journal of Ophthalmology. Published online April 6, 2022:112067212210922.
