Optimization model for UV-Riboflavin corneal cross-linking

Abstract

Nowadays UV-cross-linking is an established method for the treatment of keraectasia. Currently a standardized protocol is used for the cross-linking treatment. We will now present a theoretical model which predicts the number of induced crosslinks in the corneal tissue, in dependence of the Riboflavin concentration, the radiation intensity, the pre-treatment time and the treatment time. The model is developed by merging the difussion equation, the equation for the light distribution in dependence on the absorbers in the tissue and a rate equation for the polymerization process. A higher concentration of Riboflavin solution as well as a higher irradiation intensity will increase the number of induced crosslinks. However, performed stress-strain experiments which support the model showed that higher Riboflavin concentrations (> 0.125%) do not result in a further increase in stability of the corneal tissue. This is caused by the inhomogeneous distribution of induced crosslinks throughout the cornea due to the uneven absorption of the UV-light. The new model offers the possibility to optimize the treatment individually for every patient depending on their corneal thickness in terms of efficiency, saftey and treatment time.

Rate of riboflavin diffusion from intrastromal channels before corneal crosslinking

“…11,13,15,16 Furthermore, the hypotonic solutions and transepithelial had a higher diffusion coefficient approaching 10D 0 Z 65.0 Â 10 À5 mm 2 /sec, showing an order-of-magnitude increase compared with the diffusion coefficient found for standard corneal CXL.…”

“…13,14 This suggests that changes in the method to administer at the corneal surface are linked to the effectiveness of different riboflavin concentrations and the reservoir of riboflavin available at the corneal surface (eg, layer thickness and dropping intervals). 15 Thus, standardization to the clinical dropping scheme related to the application of riboflavin is important to achieve consistency in the treatment outcome as well as in optimizing the procedure itself.…”

“…Figure 5 shows the related radial averages for the diffusion over time. The numerical analysis used the standard diffusion coefficient (or multiples thereof) of riboflavin seen in previous work 13,15,16 and calculated the best fit to the experimental results. Figure 6 shows the outcomes of the experimental analysis.…”

“…13,15,16 The rotationally symmetrical corneal model has a diameter of 12.0 mm and a thickness of 1.0 mm, and the surgical incision (applied halfway into the stroma) has a 5.7 mm diameter with a rectangular 0.6 mm  0.2 mm cross-section. Analysis was implemented with a finite amount of riboflavin applied to the channel as the initial condition (with no riboflavin present elsewhere at 0 minute) and then diffused over time into the stroma.…”

Corneal Collagen Crosslinking Techniques: Updates

“…The patient is asked to focus on the central light-emitting diode of the UVA device. Saturating the anterior segment with riboflavin blocks the transmission of irradiation to posterior intraocular structures [27] . Topical antibiotic therapy is instilled at the end of the intervention, and a therapeutic lens may be placed for about 48 hours.…”