Structural and ultrastructural changes in the developmental process of premature infants' and children's corneas.

Seven corneas ranging in age from 20 weeks of gestation to 6 months after birth were studied and changes observed in five layers. The epithelium thickens through the addition of new cellular layers and the enlargement of cells. The way junctional complexes develop with age is described. The way the collagen fibrils in Bowman's layer is arranged changes over time. The layer arrangement and orientation of the stroma's collagen fibrils are described at different stages of development. The keratocytes progressively flatten out and gather together. The thickness of Descemet's membrane increases from 0.6 m at 20 weeks of gestation to 4 m at 6 months. During the prenatal period, the banded layer appears with cross-linking bridges. The nonbanded layer appears after birth. Several changes were found in the endothelium: flattening out of the initially cube-shaped cells and changes in the intercellular junctions that can be seen from 20 weeks of fetal life. At 20 and 25 weeks of gestation, two layers of cells were observed in the corneal midperiphery. The adult structure of the cornea was reached at about 6 months after birth.