Purchase this article with an account.
Anna Olsen, Ananya Goyal, Manuel Ramirez Garcia, Yousuf M. Khalifa, Mark Buckley; The Effect of Proteoglycan Digestion on the Viscoelastic Shear Properties of the Cornea. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6832.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
Proteoglycans (PGs) are key structural components in the cornea and other ocular tissues. While their role in vitreous humor biomechanics has been studied, their role in corneal biomechanics remains largely unexplored. This study aimed to use enzymatic digestion and torsional rheometry to study how PGs affect the viscoelastic shear properties of the cornea. We hypothesized that removal of PGs would reduce the intrinsic shear stiffness (i.e., the storage and loss moduli) of the cornea.
Central porcine corneal buttons 8 mm in diameter were trephinated and subjected to torsional shear rheometry tests at a tare force of 0.17 N. Each button underwent an oscillatory shear strain amplitude (γ=0.01-10% at f=1 Hz) or frequency (f=0.01-2 Hz at γ=0.2%) sweep before and after treatment (n=8/group). Enzymatic digestive treatments consisted of incubating buttons in balanced salt solution (BSS) or trypsin, an enzyme that digests the core proteins of PGs without affecting fibrillar collagen, for 12 hours at 37° C. Storage and loss moduli were assessed for each test. A dimethylmethylene blue (DMMB) assay was performed to measure the PG content of corneal tissue before and after treatment (n=8/group).
According to strain amplitude sweeps, trypsin treatment significantly increased the storage and loss moduli of the cornea in the linear viscoelastic region. In contrast, storage and loss moduli were not affected by BSS treatment (Fig. 1). Similar results were observed for frequency sweeps (data not shown). The DMMB assay showed a significant decrease in PG content in the trypsin-treated group compared to the BSS-treated group (Fig. 2).
Contrary to our hypothesis, removal of stromal PGs caused an increase in the intrinsic shear stiffness (i.e., the shear storage and loss moduli) of the cornea. This could be explained by an increased interaction between the collagen fibrils after PG removal. Specifically, digestion of PGs could lead to the removal of lubricating layers of water between collagen fibrils or lamellae, which increases the cornea’s resistance to shear deformation. This study advances knowledge of structure-function relationships in the cornea and may be relevant to understanding diseases associated with altered corneal PG content.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
This PDF is available to Subscribers Only