6:5. The inventors also proposed formulae that relate ICP to the intensity or phase of the measured OAE signal, and described how the other physiological signals or behaviors that are known to affect ICP such as small oscillations of ICP with each heartbeat, respiration, or posture changes, can be used to confirm the validity of the obtained measurements (e.g. the absence of modulation of the measured OAE phase with respiration may indicate occlusion of the cochlear aqueduct, in which case OAE cannot provide any information about ICP). There is little data up to date about the clinical utility or accuracy of otoacoustic emission as a measure of ICP. A pilot study of Frank and colleagues that evaluated different modalities of OAE in 12 healthy volunteers and 5 patients with implanted ventricular catheters for direct ICP monitoring revealed that increased ICP or conditions known to increase ICP (e.g. posture changes, abdomen compression, coughing) were associated with notable decreases (between -2.1 and -7.9SPL) in intensity of the evoked OAE. All results were however reported only as group averages, and no attempt was made to derive a quantitative one-to-one relation between the OAE intensity and ICP. This method as all other correlation-based approaches cannot be used for absolute ICP value measurement because of the impossibility of individual calibration. Ocular measurements Eye provides another possible window into the pressure changes in the intracranial compartment thanks to the fact that the space between the optic nerve and its sheath is a continuation of the subarachnoid space, and is consequently filled with cerebrospinal fluid whose pressure is equal to intracranial pressure. Intracranial hypertension will thus manifest in an increased diameter of the optic nerve sheath and will impede the blood flow through the central retinal vein that courses within the sheath, along and in part inside of the optical nerve. The impediment of venous return causes visible changes in the eye fundus (venous engorgement, and papilledema, i.e. swelling and elevation of the optic nerve disc) that can be observed with an ophthalmoscope and have therefore been used by clinicians for more than a century as signs of increased ICP. Quantitative assessment of ICP can be made noninvasively in two different ways: by measuring changes in diameter of the optic nerve sheath with an appropriate technique (ultrasound or MRI), or by using ophthalmodynamometry to determine the pressure in the central retinal vein, which is normally slightly higher