Changes in Collagen Orientation and Distribution in Keratoconus Corneas
Keith M. Meek,1 Stephen J. Tuft,2 Yifei Huang,3 Paulvinder S. Gill,1 Sally Hayes,1 Richard H. Newton,1 and Anthony J. Bron4

1From the School of Optometry and Vision Sciences, Cardiff University, Cardiff, United Kingdom; 2Moorfields Eye Hospital, London, United Kingdom; the 3Department of Ophthalmology, Great Wall Hospital of PLA, Beijing, Peoples Republic of China; and the 4Nuffield Department of Ophthalmology, University of Oxford, Oxford, United Kingdom.

PURPOSE. To map the collagen orientation and relative distribution of collagen fibrillar mass in keratoconus corneal buttons.

METHODS. Structural analysis was performed by obtaining synchrotron x-ray scattering patterns across the samples at 0.25-mm intervals. The patterns were analyzed to produce two-dimensional maps of the orientation of the lamellae and of the distribution of total and preferentially aligned lamellae.

RESULTS. Compared with normal corneas, in keratoconus the gross organization of the stromal lamellae was dramatically changed, and the collagen fibrillar mass was unevenly distributed, particularly around the presumed apex of the cone.

CONCLUSIONS. The development of keratoconus involves a high degree of inter- and probably intralamellar displacement and slippage that leads to thinning of the central cornea and associated changes in corneal curvature. This slippage may be promoted by a loss of cohesive forces and mechanical failure in regions where lamellae bifurcate.