Abstract: A tonometer, for determining intraocular pressure, has a body, which can be a transparent, substantially tubular body. A plunger is located within the body and a coil spring acts between the body and the plunger. A marker member is frictionally retained within the body and is displaced relative to an external scale on the body. In use, the tonometer is brought up against the eyelid of a closed eye and the body displaced relative to the head of the plunger, until the pressure is sufficient to create a pressure phosphene. The device is then removed and the displacement of the marker member, indicative of the applied pressure is read. This reading corresponds to the intraocular pressure.