Purchase this article with an account.
Steven J. Petsche, Peter M. Pinsky, Dimitri Chernyak, Jaime R. Martiz; Direct Measurement of Depth-Dependent Transverse Shear Properties of the Corneal Stroma. Invest. Ophthalmol. Vis. Sci. 2011;52(14):5189.
Download citation file:
© ARVO (1962-2015); The Authors (2016-present)
The aim of this study is to characterize the transverse shear stiffness of the corneal stroma through the depth by mechanical testing. Cross sections of the cornea viewed under polarized light suggest the lamellar sheets of collagen are markedly interwoven in the anterior third region and are relatively less interwoven in the central and posterior regions. As a result of this microstructural variation through the depth, we hypothesize that the transverse shear stiffness, which is directly attributable to the composition and organization of the extracellular matrix, will be greatest in the anterior third. Accurate shear stiffness properties are essential for biomechanical modeling of corneal tissue; scant data has existed heretofore.
A torsional rheometer was used to measure the transverse shear properties of 6 mm diameter buttons of human cadaver corneas. Pairs of corneas from the same donor were tested. One cornea from each pair was dissected into thirds through the thickness with a femtosecond laser (iFS from Abbott Medical Optics) and each stromal third was tested individually to compare properties at different depths. The other cornea from each pair was tested with the full stroma left intact. The dynamic modulus from a 1% shear strain oscillatory test was measured at various levels of axial compression for each sample. Tests were performed in an Optisol bath heated to 37ºC.
Viscoelastic and compression properties were recorded for the sixteen samples. Transverse dynamic shear moduli ranged from 1 to 25 kPa and were strongly positively correlated with axial compression. Therefore, the degree of axial compression was used as a covariate in an analysis of covariance on the log transformed shear modulus data with the third type (anterior, central, posterior, or intact) as the categorical predictor.
The shear moduli of anterior corneal thirds were significantly higher than the moduli in the central and posterior thirds as hypothesized. For the central/posterior regions, typical shear moduli lie in a range of 1 to 6 kPa. This stiffness, which is three orders lower than the tensile stiffness, reflects the gel-like properties of the stromal matrix fluid and emphasizes the need for improved biomechanical models.
This PDF is available to Subscribers Only