A self-operated non-contact tonometer for measuring the intra-ocular pressure of an eye, projecting light into the eye and measuring the reflected light as affected by mechanical distortion. The cornea is distorted by delivering a pneumatic pulse. The tonometer consists mainly of an electro-optical unit mountable on the head of a user and a control unit. The control unit of the tonometer includes a display and optionally an audio device for instructing the user. The electro-optical unit employs a tubular wave guide, a light detector, and a reflector for deflecting a light beam to the eye and for eliminating a part of the reflected light reaching the detector. The aligning of the tonometer with the head of the user is optionally assisted by a reticle.