Corneal collagen cross-linking procedures

Objective: to present corneal collagen corsslinking techniques. Corneal collagen cross-linking (CXL) is a procedure used to slow down or arrest the progression of keratoconus in order to avoid or, at least delay the necessity of keratoplasty. CXL means photopolimerisation of the stromal fibrillar tissue, in order to increase their stiffness and resistance to the corneal ectasia. CXL is a process mediated by photo oxidation between an ultraviolet A light and riboflavin. Evidence reviewed: In the 1970s, Siegel et al. presented that crosslinking reactions where lysyl oxidase catalyzed the formation of crosslinking aldehydes in collagen and elastin. The procedure was later developed in 1990 by Theo Seiler who used a UVA light and a photo sensitizer (typically riboflavin) to strengthen bonds in the cornea. Findings: Instruments used in cross-linking: Initial, Wollensak et al., in 2003, used a 370-nm UV light diodes with a potentiometer regulating the voltage, in the present being available: the XLink TM; the CBM Vega XLink Crosslinking System; the LightLink CXL TM; the UV-X TM 2000 Crosslinking System; the KXL TM System. The procedures used today are: Epi-Off Cross-linking technique (standard procedure); CXL with hypo-osmolar riboflavin solution; Epithelium-on CXL technique; Accelerated cross-linking; Iontophoresis Cross-Linking; Contact Lens-Assisted Cross-Linking; LASIK-Xtra; Topography-guided PRK and CXL; Intrastromal Corneal Ring Segments and CXL; Epithelial Island Cross-Linking; Orthokeratology and CXL. The clinical applications of CXL are: corneal ectasia; corneal infections; chemical burns; bullous keratopathy and other causes of corneal edema; LASIK and CXL; PRK and CXL; intra-corneal stromal rings and CXL; scleral CXL (experimental study). Conclusions and relevance: There are no known side effects for the corneal endothelium, lens and retina. Cross-linking treatment does not exclude the possibility of keratoplasty. Cross-linking is a safe and efficient method of treatment in corneal ectasia in order to stop or arrest the progression of conus Introduction Corneal collagen cross-linking (CXL) means photopolimerisation of the stromal fibrillar tissue, in order to increase their stiffness and resistance to the corneal ectasia, through the combined action of the photosensitizing substance (riboflavin – B2) with the irradiation of the UV light performed with an illuminator in a solid state of UVA kind. History of corneal cross-linking In 1970s, Siegel et al. presented that crosslinking reactions where lysyl oxidase catalyzed the formation of crosslinking aldehydes in collagen and elastin [1,2]. In 1990, Theo Seiler used a UV light and a photo sensitizer (typically riboflavin, Vitamin B2) to strengthen bonds in the cornea [3]. In 1997, Spoerl et al. used a similar principle to attempt an induction of corneal crosslinking (CXL), aiming to increase corneal stiffness [4]. Wollensak et al. [5] demonstrated that following central removal of the epithelium, photosensitizing riboflavin drops were applied and the eyes exposed to UVA light (370 nm, 3 mW/cm2) at a 1 cm distance for 30 minutes. Clinical follow-up showed that keratoconus stopped progressing in all eyes, and in 70% of the eyes a regression of keratometric and refractive values had been observed. Mechanism of action for cross-linking CXL is a process mediated by photo oxidation between UVA light (370 nm) and riboflavin (B2 vitamin). UVA light activates riboflavin into triplet, which in turn produces reactive oxygen species (ROS) Correspondence to: Dr. Cristina Nicula, MD; PhD, Associate Professor, ClujNapoca University Ophthalmology Clinic, Cluj County Hospital No. 3-5, Clinicilor Street, 400006, Cluj-Napoca, Romania, Tel: +40 722 849 575; E-mail: [email protected]