Increased intracranial pressure (ICP) is one of the major causes of secondary brain ischemia that accompanies a variety of pathological conditions, most notably traumatic brain injury (TBI), strokes, and intracranial hemorrhages. It can cause complications such as vision impairment due to intracranial pressure (VIIP), permanent neurological problems, reversible neurological problems, seizures, stroke, and death. However, aside from a few Level I trauma centers, ICP monitoring is rarely a part of the clinical management of patients with these conditions. The infrequency of ICP can be attributed to the invasive nature of the standard monitoring methods (which require insertion of an ICP sensor into the brain ventricle or parenchymal tissue). Additional risks presented to patients can include high costs associated with an ICP sensor's implantation procedure, and the limited access to trained personnel, e.g. a neurosurgeon. Alternative, non-invasive measurement of intracranial pressure, non-invasive methods for estimating ICP have, as a result, been sought. Correlation-based approaches Many approaches to non-invasive ICP estimation are based on the idea that something in the human head's anatomical structure or in the intracranial and extracranial physiology correlates with ICP. "Correlation-based" approaches can reflect factors associated with ICP only with limited accuracy (expressed by systematic error) and precision (expressed by the standard deviation of random error). Measuring absolute ICP value is limited by the need for individual patient-specific calibration. Absolute ICP values in mmHg or other units are needed to determine the correct patient treatment. The only accurate, precise, and patient-specific, calibration-free, non-invasive, absolute ICP value measurement method relies not on the correlation, but on direct ICP and extracranial pressure comparison principle. Two depth transorbital doppler (TDTD) An innovative method using a two-depth transorbital doppler (TDTD) of intracranial pressure quantitative absolute (ICP) value measurement relies on the same fundamental principle that is used to measure blood pressure with a sphygmomanometer. A sphygmomanometer works using a pressure balance principle - an air-filled pressure cuff wrapped around the arm compresses the brachial artery to a point where blood can no longer flow. Externally applied pressure is equal to systolic blood pressure in this case. The examiner slowly releases the air from the cuff and uses a stethoscope to listen for the return of blood flow. At the pressure balance point, where the pressure in the cuff equals systolic artery pressure, a ‘whooshing’ noise can be heard as blood flows through the artery again. Pressure balance based a non-invasive blood pressure