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S. Hayes, C. S. Kamma-Lorger, C. Boote, S. Redrobe, A. J. Quantock, K. M. Meek; A Comparative Study of Collagen Organisation in the Corneas of Mammals and Fish. Invest. Ophthalmol. Vis. Sci. 2009;50(13):4529.
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© ARVO (1962-2015); The Authors (2016-present)
The strength and transparency of the cornea is governed to a large extent by the size and organization of fibrillar collagen within the stroma. Although much is known about the arrangement of collagen in the human cornea, little is known about the precise orientation, size and spacing of collagen fibrils in the corneas of other mammals and fish.
Low-angle x-ray scattering patterns were gathered at 1mm intervals across the centre of paired excised corneas obtained from mammals (marmoset, deer, guinea pig, capybara and rabbit) and fish (hake). From these data the average (± s.d.) size of the collagen fibrils and the spacing between them at their respective points in the tissue was calculated. In addition, high-angle x-ray scattering patterns were recorded at 1mm intervals over a range of paired fish corneas (hake, salmon and mackerel). These data were analysed to produce quantitative information regarding the predominant orientation of fibrillar collagen throughout the respective corneas.
The collagen fibrils in the hake cornea were much narrower on average than those seen in the mammalian cornea (25nm ± 2.9 and 35.5nm ± 1.04 respectively). Although the average diameter of fibrils and the spacing between them varied among terrestrial animals, the values remained constant across each cornea and increased at the limbus. However, in the fish, the diameter of the fibrils remained consistently low in the peripheral cornea (24.5nm ± 1.3) but increased sharply in the central cornea (29.6nm ± 2.7). Left/right symmetry of preferred collagen orientation was observed in all fish corneas, however, as seen in our previously published study of mammalian cornea, the predominant orientation(s) of collagen differed greatly between species. In salmon, collagen is predominantly aligned tangentially to the edge if the cornea, whereas a radial preferred orientation of collagen occurs in the mackerel cornea and an alignment of collagen in the superior-inferior direction predominantes in the hake cornea.
Variations in the structural parameters of stromal collagen in the cornea of mammals and fish are likely to be due to environmental differences (land dwelling versus water), which impact on the optical and mechanical requirements of the tissue. For example in fish, the presence of narrow fibrils in the peripheral cornea increases light transmission particularly at lower wavelengths and this may improve peripheral vision in a predatory aquatic environment.
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