Abstract: A system for determining an lop of a subject includes a pressurizing device for applying pressure of varying magnitude over an external surface of an eye of the subject; a monitoring device for monitoring internal vasculature of the eye and vasculature on or around the eye; and a processing unit for correlating a first pressure or pressure range with pulsation or collapse of the internal vasculature of the eye and a second pressure or pressure range with pulsation or collapse of the vasculature on or around the eye to thereby derive the IOP of the subject.