Abstract
Purpose: :
The collagen architecture of the posterior sclera is likely to be important in glaucoma, since it plays a major role in determining the mechanical environment of the optic nerve head. However, despite its potential clinical value; direct, quantitative information on human posterior scleral fibre arrangement is presently lacking in the literature. Here we address this knowledge shortfall through the first application of X-ray scattering to normal and glaucomatous human scleras.
Methods: :
Wide-angle X-ray scattering, using a high intensity synchrotron source (Diamond Light Source, Harwell, UK), was used to map the preferential orientation and relative distribution of fibrous collagen at 0.5mm intervals across ~15mm diameter circular specimens of sclera circumscribing the optic nerve head. 3 glaucoma and 2 normal specimens were examined. The results are considered in relation to the sclera’s physiological behaviour, simulated experimentally via newly developed inflation methods.
Results: :
X-ray scattering indicated that the collagen architecture of the posterior human sclera is highly complex, anisotropic and regionally variable. At any given point, scleral collagen fibre anisotropy (as an average through the tissue thickness) could be represented in terms of 1 or 2 preferred fibre orientations with associated Gaussian-type distribution about each. The data suggests that the peripapillary sclera is dominated by a pseudo-annulus of collagen ringing the optic nerve head, in-line with microscopic observations, and that collagen around the nerve is typically 3-6 times more highly aligned than in more distal scleral regions. One glaucoma specimen exhibited significantly increased deposition of uni-axially aligned collagen both within and outside the peripapillary region, relative to the other specimens studied.
Conclusions: :
Wide-angle X-ray scattering is an effective method for gaining depth-averaged, quantitative information on collagen architecture in the posterior sclera. The data would be appropriate for inclusion in finite-element simulations with which to model scleral behaviour under IOP and its possible alteration in glaucoma.
Keywords: sclera • extracellular matrix • optic nerve