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F. Schroedl, A. Brehmer, W. L. Neuhuber, H. A. Reitsamer, D. L. Nickla; The Choroidal-Scleral Interface in Young and Adult Chickens: An Ultrastructural Study. Invest. Ophthalmol. Vis. Sci. 2010;51(13):3688.
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© ARVO (1962-2015); The Authors (2016-present)
In chicks, changes in choroidal thickness are associated with changes in eye growth, but the mechanisms whereby these changes might influence ocular growth are unknown. Three possibilities are that choroidal thickness changes (1) result in changes in signal molecules, (2) provide a mechanical stimulus operating on the sclera, or (3) alter the diffusional efficacy. The aim of this study was to investigate the ultrastructural properties of the choroidal-scleral interface in young, fast growing eyes, and older, slow-growing eyes to elucidate the potential mechanism.
Eyes from young chickens (2 weeks of age) and adults (1.5 years of age) were dissected out. Cross sections through all layers of the posterior globe were prepared and fixed for standard transmission electron microscopy.
In older chickens, the choroidal extracellular matrix is densely packed at the interface, while in younger birds it is much looser. A clear border of 1-2 layers of fibroblast-like cells was present at the choroidal-scleral interface at both ages; these cells did not have a basement membrane, nor were there membrane specializations facing the sclera. The concentration of ribosomes was more pronounced in the cells of younger animals. Mechanical adhesion of these cells to scleral tissue is achieved by bolt-like protrusions (approximately 100 nm in length) of the choroidal fibroblasts into the scleral extracellular matrix, at both ages. Furthermore, off-shoots of scleral collagen fibrils cut under the fibroblast layer.
We did not find any evidence of mechanosensory structures in the interface between the choroid and sclera, weakening the hypothesis for a choroidally-mediated mechanical mechanism in ocular growth regulation, although not precluding it. The looser arrangement of the suprachoroidal matrix in younger chickens may indicate a lesser diffusion barrier between the layers. The greater number of ribosomes indicate higher protein turnover. Both these factors might influence the relative growth rates of fast-growing young eyes versus slower-growing older eyes.
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