WST11-D and Near Infra Red (NIR) light induces ex-vivo and in-vivo corneal stiffening using low energy and short irradiation time

Abstract

Purpose : Controversy exists regarding the efficacy of shortened corneal cross-linking (CXL) protocols. We previously described the safety and efficacy of WST11-D/NIR in corneal stiffening using parameters similar to the Dresden protocol for Riboflavin/UVA CXL. This ex-vivo and in-vivo laboratory study sets out to determine the stiffening effect of shortened WST11-D/NIR protocols with 1, 5 and 30 minutes of NIR irradiation in a rabbit model.

Methods : Corneas of 3 months old, male, New Zealand White rabbits were treated in-vivo (n=24) and ex-vivo (n=54) using three irradiation times and biomechanically tested immediately (ex-vivo) or one month after treatment (in-vivo). One cornea of each pair was mechanically de-epithelialized and topically impregnated with 2.5 mg/ml WST11 (Steba-Biotech, France) combined with dextran-500 (WST11-D) for 20 minutes. Next, irradiation with NIR light at 10mW/cm² was applied for either 30 minutes (n_in=3, n_ex=11), 5 minutes (n_in=6, n_ex=5) or 1 minute (n_in=3, n_ex=11) using a diode laser at 755nm (CeramOptics, Israel). Untreated fellow eyes served as controls. Corneal strips, 4±0.2mm in width, underwent biomechanical stress-strain measurements using a biomaterial tester (Minimat, Rheometric Scientific GmbH, Germany) to obtain the tangent modulus. Results were compared by paired Student-T tests and linear mixed modelling using SPSS (IBM Corp., Armonk, NY).

Results : Ex-vivo treatment resulted in a similar significant increase (>100%) in Young’s modulus (p<0.001) for all three irradiation protocols, figure 1. One month after in-vivo treatment Young’s modulus increased significantly after 30 and 5 minutes of irradiation (125% and 35% respectively, p<0.05) but did not increase significantly after 1 minute of irradiation, figure 2.

Conclusions : Shortening NIR irradiation time to 5 minutes without increasing total delivered energy results in significant corneal stiffening both ex-vivo and in-vivo. Differences between ex-vivo and in-vivo stiffening may result from living tissue behavior, making 1 minute irradiation in-vivo not sufficient. This novel ultra-fast treatment with reduced irradiation time and overall irradiation energy may provide a safe alternative to Riboflavin/UVA CXL for the treatment of corneal ectasia.

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

 

Fig. 1 Young’s Modulus, ex-vivo experiments.

 

Fig. 2 Young’s Modulus, in-vivo experiments.