A sterile, electronic component of an ambulatory ocular volume recording system which is in the form of a contact lens containing a sensor designed to measure and transmit variations in ocular volume (i.e., circumferential changes at the corneoscleral area), to indicate patterns of intraocular pressure (IOP) fluctuation. It is worn during daily activities and sleep (e.g., by patients at risk of glaucoma progression). It is powered by and wirelessly communicates with a patient-worn transceiver which is connected to a recorder. Recorded data is displayed and analysed by an off-the-shelf computing device (e.g., laptop) using dedicated software. This is a single-use device.