An ex vivo investigation into the effect of accelerated crosslinking using pulsed and continuous UVA irradiation modes on corneal enzymatic resistance

Abstract

Purpose : Riboflavin-UVA crosslinking (CXL) has become a ubiquitous treatment for halting progressive corneal ectasia. This study examines the increase of corneal enzymatic resistance following the standard CXL protocol (SCXL), and higher UVA intensity CXL protocols, using continuous (HCXL) or pulsed (p-HCXL) UVA irradiation modes.

Methods : Sixty-six enucleated porcine eyes, with corneal epithelium removed, were divided into 6 groups. Group 1 was untreated controls, groups 2-6 received riboflavin/dextran for 30 minutes, group 3 underwent SCXL with 3mW/cm² UVA for 30 minutes (total energy dose 5.4 J/cm²), group 4 underwent HCXL with 30mW/cm² UVA for 3 minutes (5.4 J/cm²), group 5 received high energy dose HCXL with 30mW/cm² UVA for 4 minutes (7.2 J/cm²) and group 6 received high energy dose p-HCXL using 30mW/cm² UVA for 8 min with 1 s on/1 s off (7.2 J/cm²). A pepsin digestion assay was performed on central corneal disks trephined from each treated and untreated cornea. Statistical analysis of corneal disk dry weight after 13 days of digestion (n= 5 per group) and the time required for complete tissue digestion (n = 6 per group), was performed using ANOVA.

Results : The time required for complete digestion was significantly longer for the CXL-treated corneas than the non-irradiated corneas (P < 0.0001). Significant differences in digestion time were also observed between the cross-linked groups such that HCXL (5.4 J/cm²) < SCXL (5.4 J/cm²) < HCXL (7.2 J/cm²) < p-HCXL (7.2 J/cm²) (P < 0.0001). The average dry weight of SCXL (5.4 J/cm²) treated corneas after 13 days of digestion was significantly higher than that of the HCXL (5.4 J/cm² and 7.2 J/cm²) treated corneas (P < 0.0001) and the p-HCXL 7.2 J/cm² treated corneas (P <0.03). No difference in dry weight was detected between the HCXL 7.2 J/cm² and p-HCXL 7.2 J/cm² treatment groups.

Conclusions : Differences in the enzymatic resistance of SCXL and HCXL corneas suggest that there are variations in the intensity and distribution of the cross-links formed within the corneal tissue with different UVA protocols. The precise location and amount of cross-linking needed to prevent disease progression is unknown.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.