Histology of the optic nerve head with special reference to the layer-specific distribution of composite fibers at and near the lamina cribrosa: An immunohistochemical study using specimens from elderly donated cadavers.

Background: This study aimed to demonstrate the composite fibers of the lamina cribrosa (LC) and their layer-specific distributions. The elastic fiber-rich septa, showing a cribriform arrangement in the optic nerve, may continue into the LC.

Methods: Orbital content, including the long course of the optic nerve, was obtained from 25 elderly cadavers. Sagittal and cross-sections were prepared from each specimen. In addition to elastica Masson staining, immunohistochemistry was performed for elastin, glial fibrillary acidic protein (GFAP), S100 protein (S100), and CD68 in microglia.

Results: The LC beam usually had fewer elastic fibers than the septa, but an elastic fiber-rich zone was observed along the scleral flange. GFAP-positive fibers were rich in the prelaminar area, whereas S100-positive fibers were rich in all layers of the LC. Double-positive (GFAP+/S100+) fibers were present in the prelaminar area. In contrast, S100-single positive fibers were evident in the LC and retrolaminar areas and were likely to insert into a sclera-choroid border area. The density of macrophages and microglia was not different between the septa and LC. Individual variations were observed in the distribution and density of the nerve-associated fibrous tissues.

Conclusion: The LC beam was quite different from the septa in the composite fibers and architecture. Transverse fibers, dominant in the LC beam, corresponded to fibrous processes of astrocytes and other nerve-associated fibrous tissues. Many of these nerve elements suggest low mechanical properties of the LC.