Optic Nerve Subarachnoid Space Research Articles

Ultrastructure of the orbital pathway for cerebrospinal fluid drainage in rabbits.

An increasing number of physiological and morphological studies indicate that cerebrospinal fluid (CSF) drains via nonarachnoidal pathways in several mammalian species. Ultrastructural tracer studies were undertaken to examine the orbital route for CSF absorption in the rabbit. At the termination of the optic nerve subarachnoid space, an area of connective tissue containing numerous small tortuous channels is present. Ferritin (molecular weight 400,000) infused into the ventricles at normal and increased intraventricular pressure was present in these channels by 15 minutes postinfusion, and subsequently reached the intraorbital connective tissue. Elevating the intraventricular pressure did not noticeably alter the morphological appearance of this region or change the gross distribution pattern of the ferritin. Ferritin did not penetrate the scleral barrier to reach the choriocapillaris, nor did it breach the arachnoid barrier layer proximal to the transitional zone at the optic subarachnoid space to reach the dura mater. These results are very similar to those described for the hamster orbital region and the rabbit cribriform region. These experiments support the concept that macromolecules exit the subarachnoid space at the termination of the optic nerve via open channels, and that no significant barrier to drainage of macromolecules in CSF is present at this location.

Intraorbital cerebrospinal fluid outflow and the posterior uveal compartment of the hamster eye.

An ultrastructural and tracer study was undertaken to determine normal outflow pathways of cerebrospinal fluid (CSF) at the terminal subarachnoid space (SAS) of the optic nerve. In the morphological studies, the optic nerve dura and arachnoid were found to be continuous with the sclera of the eye beyond the optic nerve SAS. The pia mater is continuous with the inner sclera and the lamina fusca of the eye. Montages and serial sections demonstrated that the distal SAS is divided into numerous tortuous channels to form an "arachnoidal trabecular meshwork". Spaces of this meshwork continue into "microcanals" which bypass the outer arachnoid barrier layers of the optic nerve meninges to reach the sclera and posterior intraorbital connective tissue. Ferritin infused into the cisterna magna entered the optic nerve SAS within 1 min and reached arachnoidal trabecular meshwork channels and the microcanals within 8 min. It then passed into intraorbital connective tissue spaces at the posterior pole of the eye. Ferritin appeared to be blocked by the lamina fusca and a newly discovered "posterior compact zone" which together prevented its entrance into the choroidal interstitium. These observations suggest that a "subarachnoidal-scleral-orbital outflow pathway" provides a route for CSF drainage from the optic nerve SAS to intraorbital connective tissue. The previously described "posterior uveal compartment" in the hamster eye (Kelly et al. 1983) appears to be relatively isolated from this subarachnoidal-scleral-orbital CSF outflow.

Removal of horseradish peroxidase and fluorescein-labelled dextran from CSF spaces of rabbit optic nerve. A light and electron microscope study

Horseradish peroxidase (HRP) and fluorescein-labelled 150 000 mol. wt. dextran (FD) were introduced into the CSF spaces of rabbits by means of intraventricular infusions over approximately 3 hr. By light (LM) and electron (EM) microscopy HRP reaction product was found to have been taken up from the subarachnoid space of optic nerve into cells of the arachnoid around the optic nerve. HRP was also observed inter- and intracellularly in the optic nerve dura and in deep cervical lymph nodes. Fluorescence, associated with FD's was observed in the optic nerves most densely in the nerve sheaths particularly around blood vessels. Arachnoid cells of the optic nerves contained FD's in discrete locations. It is inferred that HRP and FD are carried by CSF currents into the subarachnoid spaces of optic nerves. Tracers are then taken up by the arachnoid and subsequently pass into the deep cervical lymph nodes.