Abstract
PurposeThe collagen structure of the human peripapillary sclera plays a significant role in determining optic nerve head (ONH) biomechanics, and is therefore of interest in the study of glaucoma. The aim of the current work was to map the anisotropic collagen structure of the normal human peripapillary sclera as a function of tissue depth.MethodsWide-angle x-ray scattering was used to quantify collagen fibril orientation at 0.5mm intervals across six 150μm-thick serial sections through the peripapillary sclera of eight normal European-derived human eyes. Two structural parameters were measured: 1) the relative number of fibrils preferentially aligned at a given angle within the tissue plane, 2) the degree of collagen alignment (anisotropy).ResultsThe inner-most one-third of the peripapillary scleral stroma (nearest to the choroid) was characterised by collagen fibrils either randomly arranged or preferentially aligned radially with respect to the ONH. In contrast, the outer two-thirds of the tissue was dominated by a circumferential arrangement of collagen encircling the ONH. In all tissue regions the degree of collagen anisotropy peaked in the mid-stroma and progressively decreased towards the tissue surfaces, with the largest depth variations occurring in the inferior-nasal quadrant, and the smallest occurring in the superior-nasal quadrant.ConclusionsSignificant, region-specific variations in collagen structure are present in the human peripapillary sclera as a function of depth. In normal eyes, the circumferential collagen fibril architecture is most prominent in the outer two-thirds of the stroma, possibly as a mechanical adaption to more effectively support the lamina cribrosa at the level of its insertion into the scleral canal wall.
Highlights
The sclera is the white, fibrous tissue that forms 85% of the ocular tunic in humans[1]
In all tissue regions the degree of collagen anisotropy peaked in the mid-stroma and progressively decreased towards the tissue surfaces, with the largest depth variations occurring in the inferior-nasal quadrant, and the smallest occurring in the superior-nasal quadrant
Significant, region-specific variations in collagen structure are present in the human peripapillary sclera as a function of depth
Summary
The sclera is the white, fibrous tissue that forms 85% of the ocular tunic in humans[1]. The material properties of the sclera are paramount to its function as the eye's main load bearing tissue. The orientation of the collagen fibrils in sclera is highly dependent on region and appears mechanically adapted to withstand wall tension derived from the intraocular pressure (IOP) and pull of the extraocular muscles[4, 5]. The peripapillary sclera bordering the optic nerve head (ONH) is dominated by circumferentially oriented collagen[4,5,6,7,8] and elastin[9, 10] which has been suggested to serve a neuroprotective function by limiting scleral canal expansion under fluctuating IOP[11,12,13]. Detailed quantitative information on peripapillary scleral collagen architecture will benefit efforts to understand and model the tissue’s physiological load-bearing behaviour and its potential clinical implications, in particular for glaucoma
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