The influence of hydration on different mechanical moduli of the cornea
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To determine the interrelation of different elastic moduli of the cornea and to investigate their dependency on corneal hydration.
Rabbit eyes were divided into four groups. Corneas were excised and mounted into a Barron artificial anterior chamber. Various corneal hydration steady states were achieved with different dextran T-500 concentrations in the anterior chamber, as well as on the corneal anterior surface. The treatment-solutions of each group contained either 5, 10, 15, or 20% w/w dextran. Ultrasound pachymetry was used to measure central corneal thickness. Brillouin microscopy of the central cornea determined the longitudinal bulk modulus by means of Brillouin frequency shift. Subsequently, a 5-mm-wide central strip was taken for extensiometry to measure the tangential elastic modulus.
The longitudinal bulk modulus was 1.2-times higher in corneas dehydrated with 20% dextran compared to those hydrated with 5% dextran. In contrast, the tangential elastic modulus increased by 4.4 times. The obtained longitudinal bulk moduli were two orders of magnitude bigger than the tangential elastic moduli. Regression analysis of longitudinal bulk modulus and tangential elastic modulus revealed a quadratic relation. The bulk modulus seemed to be independent of tension, whereas the elastic modulus was tension-dependent. Greater corneal hydration led to significantly thicker pachymetry.
Corneal biomechanics are highly dependent on the level of corneal hydration. Surprisingly, tangential elastic moduli were more sensitive to hydration changes than longitudinal bulk moduli. A quadratic relation was found between both moduli.
KeywordsCornea Biomechanics Hydration Brillouin Stress strain Extensiometry Tangential elastic modulus Longitudinal elastic modulus
The authors thank Irene E. Kochevar, PhD; Marleen Engler, BSc; and Eric Beck, BSc for their support.
T. G. Seiler was supported by an unrestricted grant from the Swiss National Science Foundation. The sponsor had no role in the design or conduct of this research.
Compliance with ethical standards
Conflict of interest
S.H. Yun is a co-founder of Intelon Inc., Boston, MA. T. Seiler and P. Shao are scientific consultants of Intelon Inc. T.G. Seiler and B.E. Frueh certify that they have no affiliations with or involvement in any organization or entity with any financial interest (such as honoraria; educational grants; participation in speakers’ bureaus; membership, employment, consultancies, stock ownership, or other equity interest; and expert testimony or patent-licensing arrangements), or non-financial interest (such as personal or professional relationships, affiliations, knowledge, or beliefs) in the subject matter or materials discussed in this manuscript.
All applicable international, national, and institutional guidelines for the care and use of animals were followed.
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