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Ahmed Elsheikh, Charles Whitford, Akram Joda, Ahmed Abass, Fangjun Bao, Paolo Rama; Regional Variation of Biomechanical Properties of Intact Eye Globes. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1631.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the regional variation in biomechanical properties across the whole surface of the cornea and sclera of human and porcine eyes
Four human eyes and eight porcine eyes were tested using a new inflation test method to determine the regional variation of their stress-strain behavior. New techniques have been developed to allow the testing of intact eye globes, prevent degradation and swelling, remove internal components, and simulate the eye's support by the surrounding soft tissue. The specimens were covered with a fine-particle speckle pattern and the behavior monitored using spatially oriented cameras. Finite element models that closely represent eye topography were constructed (Fig 1) and the deformation across eye surface used to determine regional variation of corneal and scleral stiffness within an inverse modeling procedure.
The results revealed consistent stiffness variation trends in both human and porcine eyes. The stiffness (measured using tangent modulus) was highest in the limbal region and reduced gradually across scleral surface until the posterior pole region and the area surrounding the optic nerve, where the lowest stiffness was recorded, Fig 2 (P<0.05 in porcine eyes, no statistical analysis was possible in human eyes due to the small number tested). Within the cornea, the stiffness in the central 6mm diameter region was higher than the surrounding peripheral region (by 32±12%, P<0.05).
Testing intact eye globes allowed reliable comparisons between the behavior within the cornea and sclera. It also enabled quantifying the behavior of the anterior sclera, which acted as the clamped area in earlier tests on corneal buttons and scleral spheres. The tests revealed gradual stiffness reductions from the limbus to the posterior pole and from central to peripheral cornea. The results can help improve the accuracy of predictive modeling of ocular biomechanical performance and ocular response to surgical procedures. Future ocular biomechanics testing is expected to concentrate on whole eye globes due to the superiority and reliability of the results obtained in spite of the much more demanding and time consuming testing procedure compared to testing corneas and scleras separately.
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