Spatially-resolved measurement of corneal water content using Brillouin microscopy: A first pilot study of Fuchs’ patients

Abstract

Purpose : To evaluate Brillouin microscopy for sensitive measurement of corneal tissue water content.
Water concentration in corneal stroma is altered in many eye diseases and after procedures such as photorefractive surgery or corneal graft surgery. Existing clinical techniques such as pachymetry cannot directly quantify corneal water concentration. Experimental techniques such as confocal Raman spectroscopy currently lack sensitivity. Recent studies have established that Brillouin spectroscopy measurements are modulated by water concentration. Here, we explore whether Brillouin microscopy can be used for spatially-resolved mapping of corneal water content in patients with Fuchs’ endothelial dystrophy.

Methods : We mapped the Brillouin frequency shift across the corneas of several patients diagnosed with Fuchs’ endothelial dystrophy using a clinical Brillouin imaging system (780-nm laser, 5 mW).

Results : In patients with Fuchs’ endothelial dystrophy (n = 7), we observed significant centralized reduction in Brillouin frequency shift (see Figure 1) compared to normal subjects (n = 8). The mean Brillouin shift in the central region (defined as the zone < 1 mm from the corneal apex) was 5.731 ± 0.015 GHz (mean ± std. dev.) for normal subjects, and 5.651 ± 0.038 GHz for Fuchs’ patients (p = 0.00009, unpaired t-test), corresponding to approximately 3.6% higher water content (percentage change of weight fraction) in the Fuchs’ group compared to the normal group. These results are consistent with the centralized edema that is characteristic of Fuchs’.

Conclusions : Brillouin microscopy allows for non-contact mapping of corneal water content (weight fraction) with a sensitivity of approximately ±0.3%. This technique could be useful for assessment of dystrophy-suspect corneas, or possibly for monitoring grafts after transplantation. It may also prove beneficial for understanding the role that water content plays in different corneal diseases.

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

 

Representative examples of Brillouin maps (top) and corneal topographies (bottom) for normal subjects (A, B, C), and Fuchs’ patients (D, E, F).