Low frequency ultrasound-mediated transcorneal delivery of riboflavin for corneal collagen crosslinking in treating keratoconus

Abstract

Purpose : To investigate the feasibility of using low-frequency US to break through the epithelial barrier for the delivery of riboflavin to corneal stroma. To determine the effect of US-mediated delivery of riboflavin in ultraviolet A collagen crosslinking (UVA-CXL) on the biomechanical property of ex-vivo porcine cornea.

Methods : Riboflavin solution (0.5%) was applied to the fresh porcine corneal surface for 30 min as shown in Fig 1. In US-treated group (n=10), fresh porcine eyes with intact epithelium were treated with low-frequency US continuously. Temperature increase was maintained to be less than 1°C. In Epi-on control group (n=10), no US was applied while epithelium remains intact. In the Epi-off control group (n=10), epithelium was removed to mimic the conventional practice for corneal riboflavin delivery. Fluorophotometer(OcuMetrics) was used to quantify the amount of stromal riboflavin by the detection of fluorescence intensity. Half of each group received UVA irradiation (365nm,3mW/cm²,30min) for CXL.Young’s modulus of the corneal strip was measured by rheometer (TA, G2) to determine the change in corneal stiffness post CXL.

Results : The fluorescence intensity in the cornea of US-treated group was at least two orders of magnitude higher than Epi-on group. Fig.2A and 2B indicate that the amount of riboflavin transported to the cornea by US treatment is similar to that attained by scarping off the corneal epithelium in Epi-off group. The values of Young’s modulus of US-treated and Epi-off samples were increased by UVA-CXL by 1.40 and 1.44 fold, respectively, which was in contrast to the negligible difference observed in the Epi-on samples (Fig.2C).

Conclusions : Low frequency US enhanced the absorption of riboflavin in corneal stroma via transcorneal route in the absence of thermal effect. US-mediated delivery of riboflavin to the cornea is sufficient to enable effective CXL by UVA for increasing the stiffness of porcine cornea.The study supports that low-frequency US may provide a less invasive alternative to modulate transcorneal barrier for delivering riboflavin into corneal stroma, potentially benefiting the treatment of keratoconus.

This is a 2021 ARVO Annual Meeting abstract.

 

Fig. 1.The set-up of ex-vivo.

 

Fig. 2. Riboflavin absorption in corneas (****p<0.0001)(A), the absorption effect visualized under UVA excitation(B), Young’s modulus of corneas between CXL and Non-CXL(C).