1. A method for measuring the intracranial pressure (ICP) in a subject, the method comprising: with a first sensor, detecting whether spontaneous retinal venous pulsations (SRVPs) are occurring in an eye of the subject as the orientation of the head of the subject changes; with a second sensor attached to a table, bed or chair on which the subject is sitting or lying, measuring the orientation of the head of the subject at which SRVPs start to occur and stop occurring, the measured orientation of the head of the subject being an angle of rotation of the head about an axis that is perpendicular to a sagittal plane through the head or body of the subject; and with a control unit, using the measured orientation of the head of the subject at which SRVPs start to occur or stop occurring to determine the ICP in the subject by determining a pressure difference between an intraocular pressure (IOP) in the eye of the subject and the ICP at a predetermined orientation using the measured orientation.