Flexible optical waveguides for uniform periscleral crosslinking

Abstract

Purpose : Scleral crosslinking (SXL) with a photosensitizer and light is a promising strategy to mechanically reinforce the sclera and prevent the progression of pathologic myopia. Current approaches for light delivery to the sclera are invasive, involving complicated surgery, and do not provide uniform illumination, which could lead to astigmatism. To overcome these challenges, we have developed flexible optical waveguides optimized for efficient, homogeneous light delivery, and demonstrate their application for SXL.

Methods : Waveguides were fabricated from polydimethylsiloxane elastomer. Light is coupled into the waveguide with an input fiber (NA=0.22) connected to a 445 nm laser. Light extraction efficiency from the waveguide to scleral tissue was measured and fit to a theoretical model. To demonstrate SXL ex vivo, fresh porcine eyes were stained with 0.5% riboflavin for 30 minutes. SXL was performed using irradiances of 0,25,50 mW/cm² on equatorial sclera over the entire circumference of the eyeball. SXL with elastomer waveguides was compared to direct laser illumination at the same irradiances. At least 5 eyes were used per condition. Scleral strips were dissected and characterized with tensiometry to measure Young's moduli.

Results : Light delivery with a waveguide of tapered thickness (1.5 to 0.5 mm) enhanced the uniformity of light distribution compared to a flat waveguide (~1 mm), from a coefficient of variation of 28% to just 10%. SXL treatment significantly increased the stiffness of equatorial sclera compared to control. At 8% strain, sclera treated with the waveguides at 50 mW/cm² for 30 min had a modulus of 10.7 ± 1.0 MPa, compared to 5.9 ± 0.5 MPa for no irradiation (two tailed p<0.001). There was no difference in stifness between the proximal and distally treated halves of the sclera, and no difference between SXL with elastomer and with direct illumination (10.2 ± 1.9 MPa).

Conclusions : We have developed flexible polymer-based waveguides for periscleral crosslinking. Our technique enables efficient and homogeneous stiffening of the sclera with minimal invasiveness. Using our waveguides, SXL on fresh porcine eyes resulted in a near 2-fold increase in the Young's modulus of sclera compared to untreated eyes. Further studies with Brillouin imaging will characterize the uniformity of SXL-induced stiffening. In vivo studies using our waveguides on rabbit eyes are underway.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

 

Elastomer waveguides

 

Tensiometry results