Abstract
Purpose :
The biomechanical properties of ocular tissues play a role in the development of glaucoma. For example, it has been shown that the stiffness of the sclera and the trabecular meshwork (TM) increases in glaucoma (Liu et al. 2018, Last et al. 2011). Additionally, in human eye tissue, low flow (LF) regions within the TM were found to be stiffer than high flow (HF) regions in normal and elevated intraocular pressure conditions (Vranka et al. 2017). However, measuring tissue stiffness in smaller animal models of glaucoma remains challenging. Given the importance of tissue stiffness in glaucoma, our objective was to investigate the stiffness of the TM, sclera, and cornea using atomic force microscopy (AFM).
Methods :
Eyes from female Brown Norway rats (5-6 months; n = 14) were enucleated and prepared for AFM stiffness measurements. In brief, for one eye per animal, 2-4 sagittal cryosections (10 µm thick) of the anterior segment were placed on a glass slide, and the stiffnesses of the TM, cornea, and sclera were measured via force maps using AFM. The resulting force-displacement curves were analyzed using the Hertz model to calculate the Young’s modulus. The Young’s moduli were then pooled, log-transformed, and fit to a normal distribution to obtain a single stiffness value for each tissue region (Wong et al. 2023).
The contralateral eyes of six animals were bead perfused (100nm fluorescent beads, 1.22x109 beads/mL) at a constant flow rate (835 nL/min) to identify LF and HF TM regions. We then assessed the stiffness of the TM in each flow region. An ANOVA with an appropriate post-hoc test was used to detect differences in the stiffness values between the TM, cornea, and sclera, and an unpaired two-sample t-test was used to directly compare the stiffness of the LF and HF regions.
Results :
We observed significant differences between the stiffness of each tissue region. The stiffness of the sclera was 494% and 403% higher than the cornea (p<0.001) and TM (p<0.001), respectively. However, we found no significant differences between the cornea and TM (p=0.42). Additionally, we found no significant differences in the stiffness between the LF and HF regions of the TM (p=0.86).
Conclusions :
These results serve as reference measurements for future experiments of diseased animal models, and we plan to expand on this study by correlating TM stiffness values with outflow facility in different age groups of rats.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.