Optic nerve sheath bleeding driven by rapid cerebrospinal fluid pressure amplification

The optic nerve is a collection of dendrite fibres connecting the eye to the brain, surrounded by a sheath which contains a thin layer of cerebrospinal fluid (CSF). This CSF pressure is directly influenced by pressure changes in the brain. Bleeding of the optic nerve sheath is often observed in conjunction with traumatic brain injury. We propose a theoretical model to explain this correlation, examining the flow of CSF along the optic nerve sheath driven by a sudden large pressure perturbation in the brain. The model predicts that this perturbation triggers a propagating pressure wave along the nerve sheath towards the eye, and for sufficiently large perturbations this wave can steepen to form an elastic jump. We show that this pressure wave is reflected back towards the brain by the sclera, resulting in amplification of the CSF pressure of up to five times the perturbation pressure in some cases. We hypothesise that this rapid expansion of the sheath can lead to localised tissue bleeding. Furthermore, we show that this pressure perturbation constricts the blood vessels spanning the sheath, transmitting a pressure wave directly into the retinal circulation in the eye.