June 2013
Volume 54, Issue 15
Free
ARVO Annual Meeting Abstract  |   June 2013
Regional Variation of Biomechanical Properties of Intact Eye Globes
Author Affiliations & Notes
  • Ahmed Elsheikh
    Engineering, University of Liverpool, Liverpool, United Kingdom
    National Institute for Health Research Biomedical Research Centre at Moorfields Eye Hospital NHS Foundation Trust and UCL Institute of Ophthalmology, London, United Kingdom
  • Charles Whitford
    Engineering, University of Liverpool, Liverpool, United Kingdom
  • Akram Joda
    Engineering, University of Liverpool, Liverpool, United Kingdom
  • Ahmed Abass
    Engineering, University of Liverpool, Liverpool, United Kingdom
  • Fangjun Bao
    Eye Hospital, Wenzhou Medical College, Wenzhou, China
  • Paolo Rama
    Ophthalmology Department, San Raffaelle Scientific Institute, Milan, Italy
  • Footnotes
    Commercial Relationships Ahmed Elsheikh, None; Charles Whitford, None; Akram Joda, None; Ahmed Abass, None; Fangjun Bao, None; Paolo Rama, None
  • Footnotes
    Support None
Investigative Ophthalmology & Visual Science June 2013, Vol.54, 1631. doi:
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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)

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Abstract
 
Purpose
 

To determine the regional variation in biomechanical properties across the whole surface of the cornea and sclera of human and porcine eyes

 
Methods
 

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.

 
Results
 

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).

 
Conclusions
 

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.

 
 
Fig 1 Numerical model used to determine material properties of a porcine eye
 
Fig 1 Numerical model used to determine material properties of a porcine eye
 
 
Fig 2 Average regional variation of tangent modulus over the cornea and sclera
 
Fig 2 Average regional variation of tangent modulus over the cornea and sclera
 
Keywords: 480 cornea: basic science • 708 sclera  
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