June 2017
Volume 58, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2017
Increased Posterior Collagen Fibril Spacing is the Main Contributor to the Greater Thickness of the Peripheral Human Cornea
Author Affiliations & Notes
  • Jan P G Bergmanson
    Univ of Houston Coll of Optometry, Houston, Texas, United States
  • Alan Robert Burns
    Univ of Houston Coll of Optometry, Houston, Texas, United States
  • Footnotes
    Commercial Relationships   Jan Bergmanson, None; Alan Burns, None
  • Footnotes
    Support  NIH Grant P30EY007551
Investigative Ophthalmology & Visual Science June 2017, Vol.58, 3910. doi:
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      Jan P G Bergmanson, Alan Robert Burns; Increased Posterior Collagen Fibril Spacing is the Main Contributor to the Greater Thickness of the Peripheral Human Cornea. Invest. Ophthalmol. Vis. Sci. 2017;58(8):3910.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : The human cornea is ~20% thicker peripherally than centrally and previously we determined the difference was not due to an increase in stromal lamellar counts. The purpose of this study was to assess collagen fibril caliber, spacing and density across the human cornea to determine if peripheral lamellar thickening is explained by changes in collagen fibril architecture.

Methods : The cornea from a 70 y.o. African American female (previously used to assess lamellar counts) was fixed in 0.1M sodium cacodylate buffer containing 2.5% glutaraldehyde and further processed for routine electron microscopic examination. Transverse images of collagen fibrils were collected from the anterior stroma (100-150 um posterior to the anterior limiting lamina) and posterior stroma (100-150 um anterior to the posterior limiting lamina). A total of 40 distinct non-overlapping views were imaged (26,000X magnification) from the center and extreme periphery of the cornea. A morphometric counting frame (400 um x 400 um) was used to estimate fibril density. Differences in collagen fibril caliber and spacing were evaluated using a Kolmorogov-Smirnov statistical test.

Results : Collagen fibril caliber was similar across the cornea (range 23.3 to 24.1 nm). Going from central to peripheral cornea, collagen fibril spacing increased but the increased spacing was greater in the posterior compared to the anterior stroma (8% and 5% increase, respectively). Consequently, the reduction in collagen fibril density was greater in the posterior compared to the anterior stroma (22% and 11% decrease, respectively).

Conclusions : Increased posterior collagen fibril spacing is the main contributor to the greater thickness of the peripheral human cornea. Similar changes occurred in the anterior stroma but they were of a smaller magnitude. The increased peripheral corneal thickness is not dependent on a change in collagen fibril caliber or an increase in the number of lamellae (previous study). Hence, while the collagen fibrils remained of a uniform caliber across the cornea, their spacing did not maintain such uniformity. The general applicability of these findings will benefit from further study on additional corneas.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.

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