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Exp Eye Res. 2017 Jun;159:40-48. doi: 10.1016/j.exer.2017.03.002. Epub 2017 Mar 14.

Elastic microfibril distribution in the cornea: Differences between normal and keratoconic stroma.

Author information

1
Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff CF24 4HQ, UK.
2
Department of Ophthalmology, Kyoto Prefectural University, Kyoto, Japan; Department of Frontier Medical Science and Technology for Ophthalmology, Kyoto Prefectural University, Kyoto, Japan.
3
Department of Ophthalmology, Kyoto Prefectural University, Kyoto, Japan.
4
Department of Frontier Medical Science and Technology for Ophthalmology, Kyoto Prefectural University, Kyoto, Japan.
5
Structural Biophysics Research Group, School of Optometry and Vision Sciences, Cardiff University, Maindy Road, Cardiff CF24 4HQ, UK. Electronic address: meekkm@cardiff.ac.uk.

Abstract

The optical and biomechanical properties of the cornea are largely governed by the collagen-rich stroma, a layer that represents approximately 90% of the total thickness. Within the stroma, the specific arrangement of superimposed lamellae provides the tissue with tensile strength, whilst the spatial arrangement of individual collagen fibrils within the lamellae confers transparency. In keratoconus, this precise stromal arrangement is lost, resulting in ectasia and visual impairment. In the normal cornea, we previously characterised the three-dimensional arrangement of an elastic fiber network spanning the posterior stroma from limbus-to-limbus. In the peripheral cornea/limbus there are elastin-containing sheets or broad fibers, most of which become microfibril bundles (MBs) with little or no elastin component when reaching the central cornea. The purpose of the current study was to compare this network with the elastic fiber distribution in post-surgical keratoconic corneal buttons, using serial block face scanning electron microscopy and transmission electron microscopy. We have demonstrated that the MB distribution is very different in keratoconus. MBs are absent from a region of stroma anterior to Descemet's membrane, an area that is densely populated in normal cornea, whilst being concentrated below the epithelium, an area in which they are absent in normal cornea. We contend that these latter microfibrils are produced as a biomechanical response to provide additional strength to the anterior stroma in order to prevent tissue rupture at the apex of the cone. A lack of MBs anterior to Descemet's membrane in keratoconus would alter the biomechanical properties of the tissue, potentially contributing to the pathogenesis of the disease.

KEYWORDS:

Cornea; Elastic fibers; Fibrillin; Keratoconus; Microfibrils

PMID:
28315339
PMCID:
PMC5451143
DOI:
10.1016/j.exer.2017.03.002
[Indexed for MEDLINE]
Free PMC Article

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