engleski

Correlation between intraocular and intracranial pressure – new approach in investigation

Introduction Studies about the correlation between intraocular pressure (IOP) and intracranial (cerebrospinal fluid - CSF) pressure are contradictory. It seems that different methods for measuring pressures inside the CSF system and the eye, as well as the fact that the measuring instruments were not set to the same reference point, could be the reasons for the contradictory results that exist in literature. In addition, factors involved in regulation of CSF pressure during postural changes are not well defined. Material and Methods To solve mentioned problems, we have developed a new experimental animal (cats) model in which CSF pressure and IOP are measured using an identical invasive method (cannulation), and with the pressure transducers set to the same reference point and positioned at an adequate hydrostatic level. CSF pressure was recorded at three different sites (the lateral ventricle - LV, cortical - CSS and lumbar subarachnoid spaces - LSS), and we correlated the changes in CSF pressure and the changes in IOP during alterations of the body position. In addition, volume and pressure changes in the newly developed artificial CSF model, which by its anatomical dimensions and basic biophysical features imitates the cranio- spinal system in animals, are compared to those obtained on animals in different body positions. Results In horizontal position all measured pressures (IOP, CSF pressure in LV, CSS and LSS) were similar (about 18 cm H2O). After verticalization, a permanent appearance of negative CSF pressure (about -4 cm H2O) inside the cranium (LV, CSS) without changes in the blood and CSF volume was observed, while IOP was slightly decreased (from 18 cm H2O to 14 cm H2O) and CSF pressure in LSS was significantly increased (about 30 cm H2O). CSF pressure gradients change depending on the body position, but those gradients do not enable unidirectional CSF circulation from the hypothetical site of secretion to the site of absorption in any of them. Conclusions Similarity of results between animals and the new artificial CSF model implicates that CSF pressure inside the cranium in an upright position is determined by laws of fluid mechanics but not by changes of CSF and blood volume inside the cranium. It seems that in upright position the normal CSF pressure is subathmospheric. Slight changes in IOP, as well as drastic changes in CSF pressures in certain parts of the CSF system during postural changes imply that IOP and CSF pressure are not correlated, and that we cannot make any conclusions regarding the changes in CSF pressure based on IOP. It seems that pressure gradient between intraocular and intracranial pressure in upright position is much higher than previously supposed.

intraocular pressure ; intracranial pressure

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