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Tomas White, Philip Nigel Lewis, Keith M Meek, Structural Biophysics; Identification of an extensive fibre system in ‘pre-Descemet’s layer’ (PDL) of the cornea using serial block face scanning electron microscopy (SBFSEM). Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):1938.
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Recently, it has been controversially postulated that an additional sixth layer exists in the cornea, between Descemet’s membrane and the posterior stroma, termed ‘PDL.’ The aim of this study was to characterise the ‘PDL’ using serial block face SBF SEM in order to determine if any structural differences are present when compared to the overlying stroma.
Human corneas were fixed in 2% paraformaldehyde and 2.5% glutaraldehyde, en-block stained with multiple staining solutions to intensify backscatter electron (BSE) contrast, including osmium tetroxide, tannic acid, uranyl acetate and lead acetate, prior to dehydration and embedding in CY212 resin. Polymerised blocks were attached to Gatan specimen pins, the block surface polished and transferred to a Zeiss Sigma FEG equipped with a Gatan 3View system. Data sets of up to 1000 images were acquired of the block face surface every 50 nm by automated serial sectioning. 3D reconstructions of selected image sequences were made using Amira 5.6 software.
The 3D models identified long elastic-like fibres running through PDL, both transversely and longitudinally, along the plane of the cornea. These fibres occasionally branched into two, and were more concentrated immediately above Descemet’s membrane and below the last line of keratocytes, in the region of ‘PDL’, compared to more anterior regions of the stroma. Additionally, these fibres appeared to be more abundant in the peripheral cornea when compared to the central region.
SBF SEM has identified an extensive elastic-like fibre system present in the PDL region of the cornea. Although it is not exclusive to this region, the fibres are clearly much more concentrated here when compared to the overlying stroma. The discovery of this fibre system will have an impact on posterior corneal surgery as well as increasing our understanding of corneal biomechanics.
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