April 2014
Volume 55, Issue 13
Free
ARVO Annual Meeting Abstract  |   April 2014
Atomic Force Microscopy Determination of Young’s Modulus of Bovine Extra-ocular Tendon Fiber Bundles
Author Affiliations & Notes
  • Lawrence Hyun Yoo
    Ophthalmology, Jules Stein Eye Inst UCLA, Los Angeles, CA
  • Andrew Shin
    Ophthalmology, Jules Stein Eye Inst UCLA, Los Angeles, CA
  • Joseph L Demer
    Ophthalmology, Jules Stein Eye Inst UCLA, Los Angeles, CA
Investigative Ophthalmology & Visual Science April 2014, Vol.55, 2558. doi:
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    • Get Citation

      Lawrence Hyun Yoo, Andrew Shin, Joseph L Demer; Atomic Force Microscopy Determination of Young’s Modulus of Bovine Extra-ocular Tendon Fiber Bundles. Invest. Ophthalmol. Vis. Sci. 2014;55(13):2558.

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Abstract

Purpose: Extra-ocular tendons (EOTs), composed of parallel bundles of small fibers, transmit oculorotary force of the muscles to the eyeball to generate dynamic eye movements and align the eyes. Young’s modulus represents a standard measure of elasticity per unit area. The current investigation aims to determine the transverse Young’s modulus of EOT fiber bundles by nano-indentating them using the cantilever tip of an atomic force microscope (AFM).

Methods: Bovine EOT fiber bundles were isolated under a dissecting light microscope from fresh tendons maintained under optimal physiologic temperature and humidity control. Bundles were then indented transversely to their long dimensions to a depth of 100 nm using the inverted pyramid-shaped tip of an AFM (Veeco Digital Instruments, NY). Ten indentations were conducted for each of 3 different locations of 10 different specimens from each of the 6 anatomical EOTs, comprising a total of 1,800 indentations. Young’s modulus for each EOT was determined using a Hertzian contact model.

Results: Mean Young’s moduli for fiber bundles were similar for all of the 6 anatomical EOTs: lateral rectus 60.1 ± 2.7 (±SD) MPa, inferior rectus 59.7 ± 5.3 MPa, medial rectus 56.9 ±1.9 MPa, superior rectus 59.7 ±2.6 MPa, inferior oblique 57.7± 1.4 MPa, and superior oblique 59.2± 2.0. Variation in Young’s moduli among the six EOTs was not statistically significant (P > 0.25). Mean Young’s modulus for EOT was 20 times smaller than that of tibial anterior tendon at 1.2 GPa, indicating lesser stiffness.

Conclusions: Young’s modulus of bovine EOT fibers is highly uniform among the 6 anatomic extraocular muscles, suggesting that each EOT is assembled from the same biomechanical elements. The transverse Young’s modulus for EOT fibers could reasonably be assigned to be 60 MPa in finite element analysis (FEA) of the ocular motor system. The experimental measurement of Young’s modulus and the uniformity in measurements would be useful for accurate FEA of orbital mechanics and would simplify simulations.

Keywords: 522 eye movements • 722 strabismus • 521 extraocular muscles: structure  
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