Quantification of Collagen Ultrastructure after Penetrating Keratoplasty – Implications for Corneal Biomechanics

Abstract

PurposeTo quantify long-term changes in stromal collagen ultrastructure following penetrating keratoplasty (PK), and evaluate their possible implications for corneal biomechanics.MethodsA pair of 16 mm post-mortem corneo-scleral buttons was obtained from a patient receiving bilateral penetrating keratoplasty 12 (left)/28 (right) years previously. Small-angle x-ray scattering quantified collagen fibril spacing, diameter and spatial order at 0.5 mm or 0.25 mm intervals along linear scans across the graft margin. Corresponding control data was collected from two corneo-scleral buttons with no history of refractive surgery. Wide-angle x-ray scattering quantified collagen fibril orientation at 0.25 mm (horizontal)×0.25 mm (vertical) intervals across both PK specimens. Quantification of orientation changes in the graft margin were verified by equivalent analysis of data from a 13 year post-operative right PK specimen obtained from a second patient in a previous study, and comparison made with new and published data from normal corneas.ResultsMarked changes to normal fibril alignment, in favour of tangentially oriented collagen, were observed around the entire graft margin in all PK specimens. The total number of meridional fibrils in the wound margin was observed to decrease by up to 40%, with the number of tangentially oriented fibrils increasing by up to 46%. As a result, in some locations the number of fibrils aligned parallel to the wound outnumbered those spanning it by up to five times. Localised increases in fibril spacing and diameter, with an accompanying reduction in matrix order, were also evident.ConclusionsAbnormal collagen fibril size and spatial order within the PK graft margin are indicative of incomplete stromal wound remodelling and the long term persistence of fibrotic scar tissue. Lasting changes in collagen fibril orientation in and around PK wounds may alter corneal biomechanics and compromise the integrity of the graft-host interface in the long term.

Identifying the Palisades of Vogt in Human Ex Vivo Tissue

“…Structural collagen in the human eye provides stability to the cornea, maintains intra-ocular pressure, and affects the degree of corneal astigmatism present 20, 21 . The preferential alignment of corneal collagen and variations in regional density and thickness has been shown to have physiological importance in stability and function, and maintaining alignment during transplantation may facilitate graft healing, survival or post-surgical refraction 19,20,22–24 . A technical drawback to testing this hypothesis has been that Eye Banks would need to mark the orientation of every cornea prior to removal from the globe, not only those corneas destined for corneal transplants.…”

Fibrogenesis and epithelial coating of skin wounds in rats treated with angico extract (Anadenanthera colubrina var. cebil)

“…It should be noted that the stage of remodeling of the extracellular matrix is the period of consolidation, enhancing wound. The deposition, clustering and collagen remodeling are responsible for increased tensile strength and decreased scar size 10,11 .…”

Interfibrillar packing of bovine cornea by table-top and synchrotron scanning SAXS microscopy

“…In particular, both small-and wide-angle X-ray scattering (SAXS and WAXS) allow the collection of structural quantitative data from the entire cornea and across its full thickness. The SAXS signal from axially aligned fibrils in each lamella can provide a quantitative evaluation of the diameter (') and the lateral interfibrillar spacing (L), along the equatorial direction, and of the D periodicity along the fibril axis, which coincides with the meridional direction (Boote et al, 2013;Meek & Fullwood, 2001). The presence of the equatorial contribution in SAXS patterns of cornea is due to the uniform diameter of the collagen fibrils in cornea and to a short-range order in their lateral arrangement.…”

“…The WAXS signal, produced by the intrafibrillar structure of the collagen, allows the evaluation of the orientation and distribution of the collagen molecules and the intermolecular spacing (Boote et al, 2011(Boote et al, , 2013.…”