3D collagen orientation study in human cornea using x-ray diffraction and femtosecond laser technology

No author has a financial or proprietary interest in any material or method mentioned. Abstract Aim: To study the distribution and predominant orientations of Type 1 collage n at different depths throughout the entire thickness of the human cornea. This information will form the basis of a full three-dimensional reconstruction of corneal lamellae prefe rred orientations. Methods: Femtosecond laser technology was used to cut five human corneas into separate layers with predetermined thicknesses, and wide-angle x-ray diffraction was used to study the gross collagen fibril orientation and distribution withi n each layer at 0.5mm intervals. Results: The middle and posterior parts of the human cornea demonstrated a preferential orthogonal arrangement of collagen fibrils, directed along the superior-inferior and nasal-temporal meridians with an increase in the number of lamellae towards the periphery. However, the anterior cornea (33% of total corneal thickness) showed no systematic preferred lamella orientations. Conclusion: In the posterior two-thirds of the human cornea, collagen lies predominantly in the vertical and horizontal meridians (directed towards the four major rectus muscles), whereas collagen in the anterior third of the cornea lies more equally in all directions. The predominantly orthogonal arrangement of collagen in the mid-and posterior stroma may help to reinforce the cornea by a factor of up to 21% in each direction, allowing it to withstand the pull of the extraocular muscles, whereas the more isotropic arrangement in the anterior 2 cornea is believed to play an important role in the biomechanics of the cornea by supporting the anterior corneal curvature.