Tonometer

A tonometer (10), for determining intraocular pressure, has a body, which can be a transparent, substantially tubular body (12). A plunger (28) is located within the body and a coil spring (36) acts between the body and the plunger. A marker (24) member is frictionally retained within the body and is displaced relative to an external scale (20) on the body. In use, the tonometer is brought up against the eyelid (50) 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. The device may include a return member (49) for returning the marker member to a zero or rest position.