Brillouin Microscopy measurement of the anisotropic properties of the cornea

Abstract

Purpose : Brillouin Microscopy has been used in the past several years to characterize cornea mechanical properties both ex vivo and in vivo. Specifically, the technique is employed to observe changes in cornea mechanical properties due to keratoconus or following crosslinking.
So far, Brillouin measurements have been limited to a single geometry, thus, reporting information about corneal modulus along a single direction. The cornea, however, is known to be transversely anisotropic due to the architectural organization of the collagen in the stroma. Here, we use Brillouin microscopy to study the directionally-dependent biomechanical properties of the cornea with three-dimensional spatial resolution.

Methods : Porcine eyes were obtained from a local slaughterhouse within 2 hours of death and each cornea debrided of its epithelium. The eye globe was mounted on a Brillouin Confocal Microscope using a customized rotational stage. The globe was rotated to 40^○ of the incidence laser and a central corneal sliver of 1 mm was scanned. Following, the globe was rotated to 0^○ of the incidence laser and the scan was repeated. The resulting Brillouin maps were compared for differences in modulus between identical eyes at different angles.

Results : Brillouin Confocal Microscopy measured a distinction in modulus between identical corneas measured at different angles, thereby, demonstrating strong mechanical anisotropy. Figure 1 depicts the difference in Brillouin shift within a singular cornea measured at 0^○ and 40^○. As expected, the 40^○ angled scans resulted in a higher modulus than the 0^○ scan given the structural organization of collagen fibers.

Conclusions : Brillouin Confocal Microscopy was successfully able to measure the anisotropic properties of the cornea. Moving forward, these results will be obtained at different levels of corneal hydration to quantify and differentiate the sensitivity of the technique to corneal water content.

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

 

Representative Brillouin maps (1mm x 1mm) of identical corneas angled at 0 and 40 degrees respectively. A higher Brillouin shift correlates to a higher Brillouin modulus. The corneal maps are positioned anterior up.