Mapping Collagen Orientation Changes In The Corneas Of Blindness Enlarged Globe (beg) Chicken Mutants

Abstract

Purpose: : The precise relationship between corneal shape and the organization of stress-bearing collagen in the stroma remains to be clarified. The aim of the current study was to define potential changes in collagen organisation in the blindness enlarged globe (beg) phenotype, an inherited autosomal recessive condition in chickens. The beg phenotype is characterised by retinal dystrophy and blindness at hatch, with secondary globe-enlargement and loss of corneal curvature by age 3-4 months.

Methods: : Wide-angle x-ray scattering (WAXS) data were collected from four homozygous beg chick corneas at 1, 3 and 9 months post-hatch, using station I02 at the Diamond Light Source synchrotron facility (Didcot, UK). Maps showing the orientation of corneal collagen and its relative mass distribution at 1, 3 and 9 months post-hatch were quantified from WAXS patterns collected at 0.5 mm intervals across each specimen. Correlation analysis was performed on the fibril orientation distribution functions in order to detect differences in collagen alignment in beg mutants compared to previously characterised age-matched controls.

Results: : WAXS results disclosed alterations in the bulk alignment of collagen lamellae in the beg chick cornea, compared to age-matched controls. These changes accompanied eye globe enlargement and corneal flattening in affected birds, and were manifest as a progressive loss of circumferential collagen alignment in the peripheral cornea and limbus in birds older than 1 month.

Conclusions: : Our data supports the hypothesis that the limbal fibril annulus is important in corneal shape preservation. We propose that corneal flattening in beg chickens is related to biomechanical changes brought about by an alteration in collagen arrangement at the corneal periphery. The beg chicken is a valuable animal model for investigating how pathological changes in collagen fibril arrangement impact on tissue form and function.

Keywords: cornea: basic science • cornea: stroma and keratocytes • degenerations/dystrophies