Increased Intracranial Pressure Damages Optic Nerve Structural Support

Quantitative ultrasound image assessment of the optic nerve subarachnoid space during 90-day head-down tilt bed rest

“…As a result, any increase in pressure would stretch the trabeculae and open up a reserve space 51 . The increased porosity of trabecular fibers immediately after an ICP increase (leading to ONS dilation) remains 30 days post-procedure, even though the size of the ONSD returns to near-normal levels 20 . Moreover, the optic nerve sheath may possess exceptional elasticity properties, allowing considerable distension 34 .…”

“…Such a multichambered tubular system is sparse anteriorly and denser posteriorly, ending blindly in the brain, with considerable structural variations based on the location along the optic nerve 33 . The stretching force of ONSP applies pressure across the surface in a uniform direction, while shearing forces caused by the pressure wave of fluid can apply pressure in disparate directions that lead to the “fraying” of the fibers at breakpoints, resulting in increased porosity 20 . Furthermore, second harmonic generation microscopy has revealed the helical and axial orientation of the ONS collagen fibers.…”

“…Also, there were challenges in assessing ONSD measurement quality without a sample image, potential issues like researcher experiences or blinding during measurements, and the distinction between the inclusion of the dura in ONSD measurement and the measurement at the interface between the SAS and dura 19 . Furthermore, the collagen fibers of the ONS were primarily oriented axially and helically but with inhomogeneity 9 , and the CSF shear stress distribution across the optic nerve sheath wall may also show inhomogeneity 20 . Our previous neurological study has demonstrated the correlation coefficient between the ICP and ONSSA was the highest compared with that of the ICP and ONSD or optic nerve subarachnoid space width (ONSSW) at 3 mm point using non-portable ultrasonography 21 .…”