Applied make it clear in an independent test group, these formulas were relatively precise in predicting the ICP. The 3.0-T MRI protocols, based on T2WI-FRFSE with fat-suppression sequences, depicted the orbital optic nerve-sheath complex in its full length with a pixel resolution of 0.16 �� 0.16 mm. At the same time, the image-acquisition time (11 seconds per slice) was decreased, thus reducing the risk of potential motion artifacts.For the control, we assessed the interobserver and intraobserver reproducibility and variability to ascertain the quality of the image analyses. In our evaluation, the relatively high ICC (��0.84) and low difference (��0.23 mm) suggested that the standardized region-of-interest evaluation was sufficiently reliable and reproducible.Our study confirmed previous investigations [12-21].

The anatomic basis for our results was the observation of free communication of CSF between the intracranial cavity and the orbital space through the optic nerve canal [10]. The physiological explanation for our results was that the pressure in the orbital subarachnoid space is correlated with the ICP, and that the orbital subarachnoid space can distend, depending on its pressure, because of the principles of elasticity, according to the Poisson effect. Correspondingly, patients with elevated ICP had a wide orbital CSF space, whereas patients with intracranial hypotension showed a shallow orbital CSF space [12-18]. A linear relation between invasive ICP measurements and the optic nerve-sheath diameter was reported in previous studies on patients with traumatic brain injury [20,21].

In these studies, the optic nerve-sheath diameter showed lower correlation coefficients (0.66 �� r �� 0.76) for the associations with lumbar CSF-pressure measurements than did the OSASW in our study (0.83 �� r �� 0.88). Correspondingly, Carfilzomib the retinal nerve fiber-layer thickness as a surrogate for the status of the optic nerve was strongly related to the optic nerve diameter (r = 0.61; P < 0.0001 at 9 mm; and r = 0.75; P < 0.0001 at 15 mm behind the globe), and the optic nerve-sheath diameter (r = 0.57, P = 0.0001 at 9 mm; r = 0.75, P < 0.0001 at 15 mm) in our study, whereas it was not related to the OSASW. It showed that the OSASW, as compared with the optic nerve-sheath diameter, was a better parameter to assess the ICP.Our study confirmed previous investigations on the association of lumbar CSF-P measurements with body mass index and with arterial blood pressure [27-29]. It extends these findings to correlations between arterial blood pressure and body mass index and the OSASW.The results of our study may have clinical implications.