Aim To describe the histological changes in the optic nerve (ON) after experimental segregation of cerebrospinal fluid (CSF).

Methods In seven sheep, a silicone band was placed around one ON to compress the subarachnoid space (SAS) surrounding the nerve, thus blocking the flow of CSF without compressing the ON itself. After 4 or 21 days, both the ligated and untouched ONs were removed and evaluated histologically.

Results All treated ONs showed marked loss of axons, destruction of myelin and swelling of meningoepithelial cells, most pronounced in the proximal ON adjacent to the globe at the location most distant to the ligature. There was no significant difference in histological findings between the ONs that were ligated for 4 days and those with 21 days of ligature.

Conclusion CSF segregation in the ON by blocking the SAS leads within 4 days to severe nerve damage. The increasing severity of these changes with increasing distance from the site of the ligature argues against simple pressure- or microperfusion-dependent effects and supports the hypothesis that interruption of CSF flow in the SAS of the ON can produce damage due to a change of CSF flow and content.