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C R. Ethier, Benedicte Bertin, John G. Flanagan, Michael Girard; Preliminary Small-Angle Light Scattering (SALS) Investigation of Lamina Cribrosa (LC) Structure in Human Eyes. Invest. Ophthalmol. Vis. Sci. 2012;53(14):3183.
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SALS is a non-invasive technique that can measure collagen and elastin fiber orientation, which is a key determinant of tissue biomechanics. Here we determined whether SALS, previously used to interrogate scleral collagen fibre orientation, could be extended to measure collagen/elastin fibre orientation in human optic nerve heads (ONHs).
SALS measurements on human eyes require preparatory steps, including freezing (for cryosectioning), fixation and/or glycerol clearing. These steps were optimised in our previous work on porcine and rat eyes to minimise any artefactual changes in microstructure. An ostensibly normal enucleated, fixed human donor eye, used in a previous study (EER, 90:227, 2010), was then dissected to produce several 5 by 7 mm scleral patches, one of which contained the ONH. These patches were cryosectioned in the plane of the sclera (180 um thickness, determined as optimal) to produce a series of "slabs" of sufficient transparency to allows SALS measurements to be taken on an x-y grid of points with 100 um spacing. At each measurement location the preferred fiber orientation and the degree of alignment of such fibers were computed.
The preferred fibre orientation (black lines) and degree of alignment (color, where 0 = random distribution and 1 = perfect alignment) are shown in one tissue slab (T = temporal; N = nasal; I = inferior; S = superior). The LC (blue disc) showed connective tissue fibres generally running radially outwards towards the peripheral lamina, where they merged with circumferential fibres in the peripapillary sclera (red ring). This radial-to-circumferential transition was surprisingly abrupt. In other tissue slabs that did not contain the ONH, the degree of alignment consistently decreased with distance from the ONH (data not shown).
SALS measurements of tissue architecture within the LC are feasible in post mortem human eyes, with a 3D representation achievable by assembly of data from sections through the LC. This relatively rapid technique has the potential to quantify LC connective tissue changes (e.g. secondary to ocular hypertension) and drive biomechanical modelling of the normal and glaucomatous ONH.
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