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Erin Dooley, Steven Gardner, Sally Hayes, Jonathan Harris, Kim Nielsen, Jesper Hjortdal, Thomas Sorensen, Nicholas Terrill, Craig Boote, Keith Meek; Evaluation of Limbal Ultrastructure in Twelve Year and Twenty-eight Year Post-operative Keratoconic Corneas. Invest. Ophthalmol. Vis. Sci. 2013;54(15):3133.
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To use X-ray scattering techniques to analyse peripheral corneal and limbal, tissue from a patient with advanced keratoconous who underwent bilateral penetrating keratoplasty twelve and twenty-eight years prior.
Peripheral cornea/limbal tissue of the enucleated corneas was evaluated using small and wide angle X-ray scattering techniques at synchrotron stations I22 and I02 Diamond Light Source, Didcot, UK. The corneas were wrapped in clingfilm to prevent dehydration and placed in a purpose built Perspex and Mylar chamber during x-ray exposure. The corneas were sampled at 0.5 mm intervals in a 29 x 29 mm grid (small angle) and at 0.25 mm intervals in a 60 x 67 and 60 x 63 grids (wide angle). Normal human corneas were also scanned in the same manner as controls. Wide-angle patterns were used to quantify collagen orientation and small-angle patterns to measure fibril diameter and spacing.
In both KC corneas, small angle analysis demonstrated a disordered ring of collagen fibril spacing in the peripheral cornea/limbus where an additional equatorial peak was evident consistently at ~80 and ~120 nm. This double peak, which indicates two populations of fibrils each with a different interfibril spacing, was observed only slightly in the corresponding limbal region of the normal tissue ~5mm from centre. In addition, both corneas demonstrated regions of peripheral corneal opacity which appeared to correspond with additional high scatter peaks ~140 nm. Wide angle analysis of the KC peripheral tissue demonstrated unique concentric rings of preferential collagen orientation which were not observed in the normal corneas.
There were clear and evident changes in the corneal ultrastructure in both keratoconus specimens. The causes of the changes are unknown and it is not possible to conclude if they are a result of keratoconus pathology or have occurred during the period following corneal implant. However, this is the first demonstration of structural changes in the periphery and limbus of the keratoconus cornea.
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