Morphological characteristics and intercellular connections of corneal keratocytes

PURPOSE: To investigate the morphological characteristics of keratocytes and the interconnection of keratocytes with adjacent keratocytes using the flat preparation method and scanning electron microscopy with a frontal section of the human corneal stroma. METHODS: The thin, corneal collagen lamellae were carefully dissected from the cornea (n=7), which had been stained by the flat preparation method. The remaining tissue was fixed in 3% glutaraldehyde and observed by transmission electron microscopy following the frontal section. RESULTS: The flat preparation revealed the corneal fibroblasts between the lamellae of the collagen fibers and showed that the ramifying cellular processes of the keratocytes were in contact with the cytoplasmic processes or cell bodies of neighboring fibroblasts. Two types of discrete subpopulations of keratocytes were identified: a smaller, cellular type of keratocyte with spindle-shaped nucleus with heterochromatin, and a larger, cellular type with a large indented nucleus with relatively scanty cytoplasm. Collagen fibers ran parallel to each other toward the fenestration of the cytoplasmic wall of the keratocyte. CONCLUSIONS: These flat preparation method results showed that the keratocytes within the corneal stroma are interconnected with the adjacent keratocytes, which indicates the presence of a functional communicating network through the keratocyte circuits within the stroma. A smaller, cellular type of keratocyte with spindle-shaped nucleus was morphologically differentiated from a larger, cellular type with a large, indented nucleus by flat preparation and transmission electron microscopy.