IntroductionThe orbital subarachnoid space surrounding the optic nerve is continuous with the circulation system for cerebrospinal fluid (CSF) and can be visualized by using magnetic resonance imaging (MRI). We hypothesized that the orbital subarachnoid space width (OSASW) is correlated with and can serve as a surrogate for intracranial pressure (ICP). Our aim was to develop a method for a noninvasive measurement of the intracranial CSF-pressure (CSF-P) based on MRI-assisted OSASW.MethodsThe prospective observational comparative study included neurology patients who underwent lumbar CSF-P measurement and 3.0-Tesla orbital magnetic resonance imaging (MRI) for other clinical reasons. The width of the orbital subarachnoid space (OSASW) around the optic nerve was measured with MRI at 3, 9, and 15 mm behind the globe. The study population was randomly divided into a training group and a test group. After adjusting for body mass index (BMI) and mean arterial blood pressure (MABP), algorithms for the associations between CSF-P and OSASW were calculated in the training group. The algorithms were subsequently verified in the test group. Main outcome measures were the width of the orbital subarachnoid space (OSASW) and the lumbar cerebrospinal fluid pressure (CSF-P).ResultsSeventy-two patients were included in the study. In the training group, the algorithms for the associations between CSF-P and OSASW were as follows: (a) CSF-P = 9.31 × OSASW (at 3 mm) + 0.48 × BMI + 0.14 × MABP-19.94; (b) CSF-P = 16.95 × OSASW (at 9 mm) + 0.39 × BMI + 0.14 × MABP-20.90; and (c) CSF-P = 17.54 × OSASW (at 15 mm) + 0.47 × BMI + 0.13 × MABP-21.52. Applying these algorithms in the independent test group, the measured lumbar CSF-P (13.6 ± 5.1 mm Hg) did not differ significantly from the calculated MRI-derived CSF-P (OSASW at 3 mm: 12.7 ± 4.2 mm Hg (P = 0.07); at 9 mm: 13.4 ± 5.1 mm Hg (P = 0.35); and at 15 mm: 14.0 ± 4.9 mm Hg (P = 0.87)). Intraclass correlation coefficients (ICCs) were higher for the CSF-P assessment based on OSASW at 9 mm and at 15 mm behind the globe (all ICCs, 0.87) than for OSASW measurements at 3 mm (ICC, 0.80).ConclusionsIn patients with normal, moderately decreased or elevated ICP, MRI-assisted measurement of the OSASW appears to be useful for the noninvasive quantitative estimation of ICP, if BMI and MABP as contributing parameters are taken into account.Trial registrationClinical trial registered with the Chinese Clinical Trial Registry: ChiCTR-OCC-11001271

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ABSTRACT.Purpose: To assess whether a Valsalva manoeuver influences intra-ocular pressure (IOP), cerebrospinal fluid pressure (CSF-P) and, by a change in the trans-laminar cribrosa pressure difference, optic nerve head morphology. Methods: In the first part of the study, 20 neurological patients (study group 'A') underwent measurement of IOP and lumbar CSF-P measurement in a lying position before and during a Valsalva manoeuver. In the second study part, 20 healthy subjects (study group 'B') underwent ocular tonometry and confocal scanning laser tomography of the optic nerve head before and during a Valsalva manoeuver. Results: During the Valsalva manoeuver in study group 'A', the increase in CSF-P by 10.5 AE 2.7 mmHg was significantly (p < 0.001) higher than the increase in IOP by 1.9 AE 2.4 mmHg. The change in CSF-P was not significantly (p = 0.61) correlated with the change in IOP. During the Valsalva manoeuver in study group 'B', IOP increased by 4.5 AE 4.2 mmHg and optic cup volume (p < 0.001), cup/disc area ratio (p = 0.02), cup/disc diameter ratio (p = 0.03) and maximum optic cup depth (p = 0.01) significantly decreased, while neuroretinal rim volume (p = 0.005) and mean retinal nerve fibre layer thickness (p = 0.02) significantly increased. Conclusions: The Valsalva manoeuver-associated short-term increase in CSF-P was significantly larger than a simultaneous short-term increase in IOP. It led to a Valsalva manoeuver-associated decrease or reversal of the trans-laminar cribrosa pressure difference, which was associated with a change in the threedimensional optic nerve head morphology: optic cup-related parameters decreased and neuroretinal rim-related parameters enlarged. These findings may be of interest for the pathogenesis of glaucomatous optic neuropathy.