The Resistance of Riboflavin/UV-A Corneal Cross-Linking to Enzymatic Digestion Is Oxygen-Independent

Author:

Hafezi Nikki L.12ORCID,Aydemir M. Enes1,Lu Nan-Ji12,Torres-Netto Emilio A.13,Hillen Mark1,Koppen Carina2ORCID

Affiliation:

1. ELZA Institute, Dietikon, Switzerland;

2. Dept. of Ophthalmology, Antwerp University Hospital, Edegem, Antwerp, Belgium; and

3. Laboratory for Ocular Cell Biology, Center for Applied Biotechnology and Molecular Medicine, University of Zurich, Zurich, Switzerland.

Abstract

Purpose: Corneal cross-linking (CXL) with riboflavin and UV-A induces several effects in the cornea, including biomechanical stiffening, generation of reactive oxygen species, and increased resistance to enzymatic digestion. Whereas the biomechanical stiffening effect is oxygen-dependent, little is known about the effect of oxygen on the resistance to enzymatic digestion. Here, we examined CXL-induced enzymatic resistance in the absence of oxygen. Methods: Ex vivo porcine corneas (n = 160) were assigned to 5 groups. Group 1 was the control group (abrasion and riboflavin application). Groups 2 and 3 received accelerated 10 and 15 J/cm2 high-fluence CXL protocols in the presence of oxygen (9′15″ @ 18 mW/cm2 and 8′20″ @ 30 mW/cm2, respectively), whereas groups 4 and 5 received accelerated 10 and 15 J/cm2 high-fluence CXL protocols in the absence of oxygen (oxygen content less than 0.1%). After CXL, corneas were digested in 0.3% collagenase A solution. Mean time until complete dissolution was determined. Results: The mean times to digestion in groups 1 through 5 were 22.31 ± 1.97 hours, 30.78 ± 1.83 hours, 32.22 ± 2.22 hours, 31.38 ± 2.18 hours, and 31.69 ± 2.53 hours, respectively. Experimental CXL groups showed significantly higher (P < 0.001) resistance to digestion than nonirradiated controls. There was no significant difference in time to digestion across all experimental CXL groups, irrespective of fluence delivered or the absence of oxygen. Conclusions: The resistance to digestion in accelerated high-fluence riboflavin/UV-A CXL is oxygen-independent, which is of particular importance when developing future optimized CXL protocols for corneal ectasia and infectious keratitis.

Funder

Light for Sight Foundation

Publisher

Ovid Technologies (Wolters Kluwer Health)

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