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Jan Bergmanson, Alan Burns, Maria Walker; Anatomical explanation for the central-peripheral thickness difference in human corneas. Invest. Ophthalmol. Vis. Sci. 2019;60(9):4652.
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© ARVO (1962-2015); The Authors (2016-present)
The human cornea is thinner in the center when compared to the periphery. Despite this thickness variation, we reported similar ultrastructural lamellar counts (~250) for the stroma. However, the peripheral posterior lamellae were thicker when compared to those in the central posterior stroma. The purpose of this study was to determine if differences in collagen fibril size or spacing explain the corneal thickness variation.
Three female (52-70 y.o.) human eyes obtained from the eye bank were fixed (2.5% glutaraldehyde in 0.1M sodium cacodylate buffer) and the corneas removed and processed through resin. Transverse sections (100 nm thin) were taken from the central and peripheral cornea and images of the anterior, mid- and posterior stroma were made using a Tecnai 12 transmission electron microscope. A systematic uniform random sampling strategy was employed to evaluate collagen fibril caliber, center-center spacing and density. Statistical comparisons were assessed using t-tests.
Each cornea showed some variation in collagen fibril diameter throughout, although centrally collagen fibril diameters were smaller - range 23-26 µm - than those in the periphery - range 24 to 36 µm - (p=0.006). Likewise, center-to-center distance between fibrils was greater (p=0.05) in the peripheral cornea compared to the central cornea (50.6 ± 3.1 and 44.5 ± 2.3, respectively) while the inter-fibrillar spacing remained similar (~19 µm). Collagen fibril density was greater centrally (~20%, p<0.05).
Collectively, the data suggest the inter-fibrillar space, fundamental to corneal transparency, is relatively conserved throughout the cornea. The larger size of the peripheral stromal fibrils, with conserved inter-fibrillar space, accounts for the thicker peripheral cornea and decreased fibril density when compared to the center.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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