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M. C. Herwig, A. M. Mueller, F. G. Holz, K. U. Loeffler; Corneal Development in the Human Fetus. Invest. Ophthalmol. Vis. Sci. 2010;51(13):6308.
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The development of corneal structures in the human has only partially been investigated. E.g. the origin of Bowman’s layer is not completely understood. Data from studies in animals do not allow to unrestrictedly transfer findings to human material because of differences in tissue structure. In this study, we have investigated the corneal development in the human fetal eye using antibodies (Abs) to various collagens.
15 formalin-fixed fetal eyes without any obvious irregularities of the anterior segment were investigated with regard to the development of the cornea. The age of the fetal eyes ranged from 11 to 27 weeks of gestation (WoG). In addition to routine Hematoxylin & Eosin- and Periodic acid Schiff-staining, immunohistochemical labeling with Abs to collagen IV, collagen V, collagen IX and collagen XVII was performed.
With anti-collagen IV, the basement membrane (BM) of both the cornea and conjunctiva was labeled in fetal eyes up to the age of 23 WoG. In fetal eyes older than 23 WoG, the corneal BM did not display a significant staining in contrast to the conjunctival BM. Descemet’s membrane showed marked immunoreactivity in all eyes investigated.With the Ab against collagen V the corneal stroma was intensely stained. In fetal eyes from 16 to 18 WoG the developing Bowman’s layer also displayed a slight staining in contrast to older eyes in which the basement membrane but not Bowman’s layer was labeled. Descemet’s membrane lacked staining with anti-collagen V.The Ab against collagen IX labeled the conjunctival and corneal epithelium and in some eyes also the endothelium albeit very slightly.With anti-collagen XVII the BM of the cornea and conjunctiva was stained in all fetal eyes.
These results indicate a switch of collagen expression for collagen IV and V probably depending on the maturation of the cornea. With regard to collagen IV expression the existence of six subgroups has to be discussed and further investigated. The immunoreactivity of collagen V in Bowman’s layer of fetal eyes in the early 2nd trimester possibly indicates - as has been suggested before - that this structure develops from the corneal stroma. However, it has to be considered that the distinction between staining of Bowman’s layer and the BM is very difficult in such early stages. Further analysis using electron microscopy is required for a more detailed analysis.
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