Morphological studies of the optic canal.

Background: In some cases of closed head injuries after minor blunt trauma, an amaurosis can occur. Our knowledge concerning the pathophysiological mechanisms of traumatic optic neuropathy is limited. The aim of this study is to analyze the morphology of the optic canal in order to understand the effect of mechanical forces in the optic canal and the consecutive injuries.

Methods: Forty-one optic canals from body donors were analyzed by light microscopic, polarization microscopic, immunohistochemical and scanning electron microscopic techniques.

Results: In the optic canal, collagen fibrils of the dural sheath are organized in a scissor-like pattern. Within this collagen network multiple vessels are integrated. The main component of the extracellular matrix is collagen type I. The dural sheath and pial sheath are connected by collagen bundles. Parallel to these bundles, small vessels form anastomoses between the dural and pial vessel systems. In the arachnoidea, no blood vessels can be detected by immunohistochemical techniques.

Conclusions: Based on morphological findings, the following pathophysiological mechanisms can be discussed in cases of blunt closed head injury with consecutive amaurosis: 1. Squeezing and rupture of nutritive vessels by transduction of shearing forces via the scissor-like collagen network. 2. Atrophy by pressure of the optic nerve after injury to the microvasculature followed by formation of microhematomas and reactive edema. 3. Direct injury of axons of the optic nerve by shearing forces within the optic canal. These mechanisms should be studied further in the future.