Morphogenesis of rabbit corneal stroma.

Corneas of fetal and young albino rabbits were examined by light and transmission electron microscopy. In addition, DNA and hydroxyproline content were measured in developing stroma. The results were compared with similar data from healing corneas in adult rabbits and from developing corneas of other animal species. In the fetal rabbit, the prospective corneal stroma region contains an unorganized, sparse extracellular matrix until about the 13th day of gestation, when mesenchymal cells and capillaries from the hyaloid vessels move in to form the vascular pupillary membrane, endothelium, and stroma. Stromal growth is due to alteration in the density and morphology of the cell population early in development, along with a sequential thickening and thinning of the whole stroma. These events are similar to those reported in primates, but differ markedly from those reported in avian species. Normal developing cornea and healing adult cornea both involve migration of stomal fibroblasts and deposition of extracellular matrix. Stromal fibroblasts in the rabbit fetus are oriented with their long axis parallel to the corneal surface early in development compared with randomly oriented fibroblasts in the early healing wound of adult rabbit corneas. Although collagen and cell number progressively increase throughout the developmental periods studied, the ratio of cells to collagen is high initially but decreases with development. In contrast, the proportion of cells to collagen in the young scar tissue of adult cornea is low initially, indicating a marked deposition of collagen in comparison to that in the early normal developing stroma. The results suggest that the healing tissue differs from the normal fetal stroma in its coordination of cell population growth with collagen deposition and cellular organization.