Cornea-Corneal Stroma

The sclera consists of a weave of tough undulating collagen fibers, which provide controlled plasticity and tensibility. In contrast, the collagen fibers of the corneal stroma ( substantia propria corneae ) are stretched. The about 50 0- μm thick corneal stroma is considered a modified connective tissue, which ascertains stability and translucency. Its fibrils contain collagen types I, III, V and VII and form parallel bundles with a cross-striation periodicity of 21 or 6 4 nm. The fibers form lamellae, which are layered parallel over the corneal surface. Lamellae are between 1 and 6 μm thick . There are therefore variable numbers of fibrils in each stack of lamellae. There are up to 250 lamellae. The direction of adjacent fibrils may be offset by an angle. However, the fibrils in each lamella are strictly parallel and stacked in equal distance. The basic substance pre dominantly consists of glycosaminoglycans.  It f ills the spaces between and inside the lamellae (interfibrillar substance). Fibrocytes (keratinocytes) and their branched cytoplasmic processes are embedded in the basic substance. Sporadically, macrophages are found. This figure shows a Vibratome section through the substantia propria corneae with its lamellar structure.

Scanning electron microscopy; magnification: × 700

References

Kuehnel, W.(2003). Color Atlas of Cytology, Histology, and Microscopic Anatomy. 4^th edition . Institute of Anatomy Universitätzu Luebeck Luebeck, Germany . Thieme Stuttgart · New York .