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Ning-Jiun Jan, Jonathan L Grimm, Bo Wang, Kira L Lathrop, Huong Tran, Gadi Wollstein, Larry Kagemann, Hiroshi Ishikawa, Joel S Schuman, Ian A Sigal; Collagen Crimp Period in the Corneoscleral Shell. Invest. Ophthalmol. Vis. Sci. 2014;55(13):3715.
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The mechanical properties of the corneo-scleral shell are central to the physiology and pathophysiology of the eye. These properties are largely determined by the architecture of their constitutive collagen fibers, and in particular the collagen fiber crimp period. Our goal was to measure the distribution of collagen fiber crimp period of the corneo-scleral shell from the apex of the cornea to the optic nerve head (ONH).
A sheep eye (<2 yo) was obtained from a local slaughterhouse and fixed overnight in formalin (10%) within 24 hours of death. Following fixation, the eye was cryosectioned axially (35 µm). Five consecutive sections were selected for analysis, starting with the one passing through the central cornea and ONH and progressing superiorly into the peripapillary sclera (PPS). Sections were imaged using light microscopy (Olympus BX60, 12bit gray-scale, 10x, NA 0.30, 0.73µm/pixel). The crimp period (averaged over 3 consecutive periods) was manually measured in 17 regions (Fig1) with at least 20 measurements per region. A matrix of two-sample t-tests were done to see which regions were significantly different from one another (P<0.001) (Fig2B).
Collagen crimp period varied substantially over the globe (Figure 2A), being smallest in the cornea (mean±SD) 17±5.3µm and PPS 23±9.3µm regions, and increasing with distance from these two areas. Within the cornea, the nasal cornea crimp period was significantly different from the central and temporal cornea and within the PPS, the temporal PPS was significantly different from the superior PPS (Fig2B).
There were substantial and significant differences in collagen crimp period across the corneoscleral shell. Collagen fiber crimp period was lowest at the poles and twice as large near the equator. The biomechanical consequences and role of these variations are still unclear and should be further investigated.
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