April 2011
Volume 52, Issue 14
Free
ARVO Annual Meeting Abstract  |   April 2011
Axial Anisotropy of Corneal Collagen Organization and Biomechanics
Author Affiliations & Notes
  • Moritz Winkler
    Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Orange, California
  • Dongyul Chai
    Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Orange, California
  • Shelsea Kriling
    Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Orange, California
  • Chyong Jy Nien
    Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Orange, California
  • Donald J. Brown
    Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Orange, California
  • James V. Jester
    Ophthalmology, Gavin Herbert Eye Institute, University of California, Irvine, Orange, California
  • Footnotes
    Commercial Relationships  Moritz Winkler, None; Dongyul Chai, None; Shelsea Kriling, None; Chyong Jy Nien, None; Donald J. Brown, None; James V. Jester, None
  • Footnotes
    Support  NIH grants EY07348, EY018665, EY016663, The Discovery Eye Foundation, The Skirball Program in Molecular Ophthalmology, Support grant from Research to Prevent Blindness, Inc
Investigative Ophthalmology & Visual Science April 2011, Vol.52, 4202. doi:
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      Moritz Winkler, Dongyul Chai, Shelsea Kriling, Chyong Jy Nien, Donald J. Brown, James V. Jester; Axial Anisotropy of Corneal Collagen Organization and Biomechanics. Invest. Ophthalmol. Vis. Sci. 2011;52(14):4202.

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Abstract

Purpose: : Visual acuity depends on corneal curvature, which is determined by its mechanical properties. We aim to characterize and quantify the lamellar organization of human corneas in three dimensions using non-linear optical High Resolution Macroscopy (NLO-HRMac), and to correlate these findings with mechanical data obtained by compression testing of corneal flaps, to establish a link between the supramolecular organization and corneal shape.

Methods: : Vibratome sections, 200µm thick, from 5 donor eyes were cut along the vertical meridian from limbus to limbus (arc length: 12mm). Backscattered SHG signals from these sections were collected as a series of overlapping 3-D images, which were concatenated to form a single 8GB+ mosaic (resolution: 0.44µm/px lateral, 2µm/px axial). Lamellar intertwining was quantified by determining branching point density as a function of stromal depth. Lamellae were manually segmented to create 3-D reconstructions using Amira software. Mechanical testing was performed on corneal flaps from 5 additional eyes. Corneas were cut into 3 layers (anterior, mid, posterior) using an Intralase femtosecond surgical laser system and then underwent compression tests to determine the elastic modulus for each layer.

Results: : 3-D reconstructions revealed a complex collagen fiber branching pattern in the anterior cornea with fibers extending from the anterior limiting lamina (ALL), intertwining with deeper fibers and reinserting back to the ALL forming ‘bowspring-like’ structures. Measured branching point density was 4 times higher in the anterior third of the cornea compared to the posterior third and decreased logarithmically with increasing distance from the ALL. Compression testing showed an 8-fold increase in elastic modulus in the anterior stroma.

Conclusions: : The axial gradient in lamellar intertwining appears to be associated with an axial gradient in effective modulus of the cornea suggesting that collagen fiber intertwining and formation of ‘bowstring-like’ structures provide structural support similar to cross-beams in bridges and large-scale structures. We hypothesize that radial and axial structural/mechanical anisotropy may determine the characteristic parabolic shape of the cornea and play a role in astigmatism and other refractive errors.

Keywords: cornea: basic science • cornea: stroma and keratocytes • imaging/image analysis: non-clinical 
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