Abstract
Background: The pressure in the fluid compartment surrounding the optic nerve (ONSAS) constitutes a counter-pressure to the intraocular pressure at the posterior of the eye. The difference between these two pressures, the so-called trans-lamina cribrosa pressure difference, is believed to contribute to glaucoma pathophysiology. However, the ONSAS pressure is not truly known as it is highly difficult to measure in vivo, and intracranial pressure (ICP) is often used as a surrogate. However, these two pressures are not necessarily the same, especially in the upright posture where the ONSAS decreases in size. Furthermore, the microstructural content of the ONSAS may further alter the pressure communication between ICP and the ONSAS pressure. Studying these factors could reveal new knowledge relevant for
ocular disorders where a pressure imbalance is suspected.
Methods: A mathematical compartment model that coupled the ONSAS to the craniospinal CSF system was applied to predict the ONSAS pressure in both horizontal and upright postures. Effects of a posture-dependent ONSAS size were included, as well as the effects of microstructural content within the ONSAS.
Ocular glymphatics were also studied.
Results: The ONSAS pressure was equal to or slightly lower than ICP in horizontal positions, while a compartmentalization of the ONSAS occurred in upright postures, resulting in higher ONSAS pressures (than the ICP). The resulting pressure difference depended on the distensibility of the optic nerve sheath and the porosity of the ONSAS. Substantial glymphatic flow from the eye to the ONSAS did not
substantially affect the ONSAS pressure.
Conclusions: The ICP and ONSAS pressure need not be the same, as a compartmentalization of the ONSAS may protect the eye from large pressure differences in upright postures. Variations in ONSAS microstructural content and optic nerve sheath distensibility could be factors that contribute to detrimental
ONSAS pressures and an imbalanced trans-lamina cribrosa pressure difference.
ocular disorders where a pressure imbalance is suspected.
Methods: A mathematical compartment model that coupled the ONSAS to the craniospinal CSF system was applied to predict the ONSAS pressure in both horizontal and upright postures. Effects of a posture-dependent ONSAS size were included, as well as the effects of microstructural content within the ONSAS.
Ocular glymphatics were also studied.
Results: The ONSAS pressure was equal to or slightly lower than ICP in horizontal positions, while a compartmentalization of the ONSAS occurred in upright postures, resulting in higher ONSAS pressures (than the ICP). The resulting pressure difference depended on the distensibility of the optic nerve sheath and the porosity of the ONSAS. Substantial glymphatic flow from the eye to the ONSAS did not
substantially affect the ONSAS pressure.
Conclusions: The ICP and ONSAS pressure need not be the same, as a compartmentalization of the ONSAS may protect the eye from large pressure differences in upright postures. Variations in ONSAS microstructural content and optic nerve sheath distensibility could be factors that contribute to detrimental
ONSAS pressures and an imbalanced trans-lamina cribrosa pressure difference.