An X-Ray Scattering Study into the Structural Basis of Corneal Refractive Function in an Avian Model

Abstract

Avian vision diseases in which eye growth is compromised are helping to define what governs corneal shape and ultrastructural organization. The highly specific collagen architecture of the main corneal layer, the stroma, is believed to be important for the maintenance of corneal curvature and hence visual quality. Blindness enlarged globe (beg) is a recessively inherited condition of chickens characterized by retinal dystrophy and blindness at hatch, with secondary globe enlargement and loss of corneal curvature by 3-4 months. Here we define corneal ultrastructural changes as the beg eye develops posthatch, using wide-angle x-ray scattering to map collagen fibril orientation across affected corneas at three posthatch time points. The results disclosed alterations in the bulk alignment of corneal collagen in beg chicks compared with age-matched controls. These changes accompanied the eye globe enlargement and corneal flattening observed in affected birds, and were manifested as a progressive loss of circumferential collagen alignment in the peripheral cornea and limbus in birds older than 1 month. Progressive remodeling of peripheral stromal collagen in beg birds posthatch may relate to the morphometric changes exhibited by the disease, likely as an extension of myopia-like scleral remodeling triggered by deprivation of a retinal image.

The chick eye in vision research: An excellent model for the study of ocular disease

“…This was different from rge mutants who do show significant ultrastructural changes at one month post-hatch even though they are just beginning to lose their vision at that time (Boote et al, 2009). In terms of the actual collagen fibril orientation, Morgan et al (2013) observed similar findings to the Boote et al (2009) rge study: beg mutants had orthogonal patterns in the central cornea similar to controls; however, the annular pattern present in the peripheral cornea of controls was disrupted in beg mutants. This disarray of the peripheral cornea was progressive out to nine months of age, the latest time point studied.…”

“…Similar to the rge mutant, the blindness enlarged globe ( beg ) mutant is characterized by a developmental retinal dystrophy followed by subsequent globe enlargement; however, one key difference is that beg mutants are blind at hatch (Morgan et al, 2013). Retinal changes in beg mutants include the development of intracellular spaces, loss of photoreceptors, and clumping of the retinal pigment epithelium.…”

“…Retinal changes in beg mutants include the development of intracellular spaces, loss of photoreceptors, and clumping of the retinal pigment epithelium. Morgan et al (2013) examined the corneal structure of beg mutants in analogous fashion to the Boote et al (2009) investigation of rge mutant corneas (described in section 4.8). They found no significant difference between control and beg corneas at one month post-hatch, despite the fact that these birds are blind at hatch.…”

Age Distribution and Associated Factors of Cornea Biochemical Parameter Stress-Strain Index in Chinese Healthy Population

“…SSI was found to be negatively correlated with axial length, which indicated that the corneal material stiffness decreased when axial length increasing. Previous studies indicated that the cornea and sclera were mainly composed of the same types of collagen 24 .In addition, when the collagen bers of the sclera became longer and were damaged in myopia progression, the overall arrangement of collagen bers of corneal stroma also restructured [25][26][27] .In infant monkeys and chicks, corneal astigmatism changes were also associated with induced eye growth 28,29 . Chang's study pointed out that the axial elongation led to corneal attening and thickness reduction 30 , suggesting that the increase of axial length may affect the biomechanics of the cornea and previous studies have proved this.…”

From nano to macro: Studying the hierarchical structure of the corneal extracellular matrix

“…A similar trend was also observed in a WAXS study of mouse postnatal corneal development (Sheppard et al, 2010), in which circumferentially aligned limbal collagen was shown to be progressively reinforced between postnatal days 10 and 28. The application of WAXS in some animal disease models has also shed some light on the structural basis of biomechanical homeostasis in the healthy eye, with studies in chicks (Boote et al, 2008; Morgan et al, 2013) and mice (Quantock et al, 2003b), pointing to the importance of a preferential circumferential alignment of a population of collagen fibrils at the limbus.…”