Fig. 2

Distances relating the hydrostatic reference points for the CSF compartments. The auditory meatus (AM) corresponds to the reference point for the cranial CSF compartment \((c)\), the venous hydrostatic indifference point (HIP) is the reference for the spinal compartment \((s)\), and the lamina cribrosa \((LC)\) is the reference point for ONSAS. Here the tilt-angle is: \(\alpha =45^\circ\). The height from (\(s\)) to \((LC)\) becomes: \({h}_{s-lc} = {l}_{s-am}\mathrm{sin}\left(\alpha \right)+\left({l}_{AP}\mathrm{cos}\alpha +{l}_{SI}\mathrm{sin}\alpha \right).\)