The effect of corneal cross-linking on biomechanical properties in human eye-banked corneas using nano-indentation microscopy

Abstract

Purpose : To evaluate the effect of corneal cross-linking (CXL) on corneal biomechanical properties by assessing corneal elasticity at different locations within the corneal stroma using nano-indentation microscopy, and to explore to what extent age affects CXL treatment.

Methods : A total of twelve pairs of human eye-banked corneas (24 corneas) were used in the study. The mean age of donors was 48.5 years (ranging from 26 to 71 years), and included 7 females and 5 males. Corneas were divided into three age groups (26-41, 42-57 and 58-71 years) to investigate the effect of donor age on CXL treatment. Corneal epithelial debridement was carried out in all 24 corneas. For each pair, the right corneas were cross-linked using accelerated CXL (9.86mW/cm²) for 9 minutes after applying riboflavin 1% solution (10 mg riboflavin-5-phosphate in 10 mL dextran 20% solution) for 30 minutes, and then riboflavin was applied at 3-minute intervals during UVA irradiation, while the left corneas served as controls and were not exposed to either UVA irradiation or riboflavin. Corneal elasticity (kPa) at the anterior, mid and posterior corneal stroma was measured for all corneas using nano-indentation microscopy.

Results : Repeated measures ANOVA showed a significant difference in stromal elasticity across both treatment groups (p<0.0001, multivariate partial eta squared=0.71). The change in corneal elasticity following CXL was statistically significant in the anterior and mid stroma (p<0.05), however the change was not significant in the posterior stroma (p=0.09). There was a positive but weak correlation between the age and corneal elasticity in all three depths within the corneal stroma, with a tendency for the elasticity of the anterior stroma to be more correlated to age for both cross-linked (Pearson r=0.32, p=0.32) and uncross-linked corneas (r=0.51, p=0.09) when compared to their adjacent mid and posterior stroma.

Conclusions : CXL treatment showed effectiveness in enhancing stromal strength, and the effect is concentrated in the anterior and mid stroma with minimal impact on the posterior stroma. Nano-indentation is a useful tool to providing a better understanding of CXL treatment outcomes. It offers the ability to assess CXL effect at different locations within the corneal stroma, which will allow developing a method that is effective in estimating biomechanics after different CXL protocols.

This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.