THE HUMAN OPTIC-NERVE - FASCICULAR ORGANIZATION AND CONNECTIVE-TISSUETYPES ALONG THE EXTRA-FASCICULAR MATRIX

Fibres in the mammalian optic nerve are arranged into fascicles betwee n which there is an extra-fascicular matrix containing connective tiss ue, a feature similar to that found in association with fibres in peri pheral nerves, but not otherwise found in the CNS. The relationship be tween these major features of the nerve architecture are not known. We have addressed this question by examining the fascicular organisation of the optic nerve and the distribution of connective tissue and spec ific collagen types in the human. We have also examined the spatial de velopment of connective tissue in the human nerve to determine when an d from where it originates. Fibres are grouped into fascicles at all l ocations along the nerve, except intracranially, close to the chiasm w here this pattern is lost. Relatively large fascicular numbers are fou nd directly behind the eye and in the region of the optic canal, but d ecline in the mid-orbital segment of the nerve. Connective tissue is p resent in the extra-fascicular matrix throughout the fasciculated segm ent, but in many cases it does not fully encircle fascicles. The propo rtion of matrix occupied by connective tissue is similar along the len gth of the nerve (approximately 60%). Within the matrix, collagen type s I, III, IV, V and VI are present throughout fasciculated regions. St aining for types V and VI appeared relatively weak compared with that for the other types. Although the collagen types in the nerve are simi lar to those at the lamina cribrosa and in peripheral nerves, they did not appear to be differentially distributed as in regions of the PNS. Connective tissue enters the nerve at a number of widespread location s early in development, consistent with the notion that it enters the nerve with the blood supply. It is present within the matrix before it is established at the lamina cribrosa.