The study on the structure of the intracanal portion of the optic nerve
Shikishima, K.; Ohki, K.; Tsuneoka, H.
Nippon Ganka Gakkai Zasshi 90(9): 1187-1195
1986
ISSN/ISBN: 0029-0203 PMID: 3799392 Document Number: 276549
At blunt frontal head trauma the intracanalicular portion of the optic nerve is thought to be predominantly damaged. Ultrastructure of this portion has not been fully defined yet because this tissue is not fixed in good conditions by means of the ordinary fixation due to anatomical peculiarities. Our original method of fixation and a preparation lead it possible to observe the well fixated ultrastructure of its portion. Twenty adult Macaca monkeys were used in this experiment. Cannulas were inserted into the bilateral common carotid arteries under the pentobarbital anesthesia. 10% neutral buffered formalin and the dilute Karnovsky's fixative were perfused for light and electron microscopic studies, respectively. The skull was open and the brain and the roof of the orbit was removed within 15 min. The optic nerve was carefully prepared from the surrounding bone under the stereoscopic microscopy. Fixation was continued overnight and the specimen were embedded as usual. As a result, the structural differences of the intracanalicular portion of the monkey optic nerve were summarized as follows: The dura mater was surrounded by periosteum and connected tightly to the bony optic canal. Furthermore, the dura mater was thick and consisted of abundant collagen fibers and poor elastic fibers. The arachnoid trabeculae were well developed. The septum derived from pia mater was thick and runned irregularly. Moreover many glial cells were observed in it. The nerve fibers were bending due to abundant septa and glial cells. The present findings demonstrated that the intracanalicular optic nerve is fixed firmly to the surrounding tissues. This structural peculiarity can be one of the factors to cause the intracanalicular optic nerve damage at frontal head trauma.