Hand held tonometer including optical procimity indicator

摘要

A puff tonometer includes two light sources located at diametrically opposite points, preferably equidistant from the optical axis of the objective lens assembly of the tonometer. The sources are arranged to direct light forwardly of the tonometer such that, in use, and when positioned close to a patient's eye under test, light from the two sources, after reflection by the anterior corneal surface of the eye under test, will be imaged by the objective lens assembly of the tonometer, to appear as two small areas of light in the field of view. The spacing and position of the two supplementary light sources relative to the objective lens assembly are selected so that as the tonometer is moved towards an eye under test and begins to approach the distance from the eye at which the tonometer will automatically discharge a puff of air towards the eye, the light reflected by the corneal surface will appear as two closely spaced spots of light which, with continued movement of the unit towards the eye, will begin to move away from each other, and will be replaced by two segments of light reflected from the corneal surface of the eye, which reflected light also becomes focused onto an array of photoelectric detectors as the unit approaches the critical firing distance from the eye. The light from the two supplementary light sources is coloured and is distinct from the light used to form the two segments and when in focus trigger the air discharge. If the latter light is red, the light from each of the two supplementary light sources may be green or blue for example. When equidistant the position of the two spots of light relative to the centre of the field of view readily indicates to the user whether the unit is centered on the eye. A resilently deformable extension may be fitted to the tonometer nozzle whose natural length is greater than the critical distance of the front of the nozzle from the eye at which an air pulse is released, and which can be pushed against the patient's face and thereby reduced in length until the critical distance is reached.