Abstract: A tonometer with an improved objective unit containing a fluid discharge tube having a portion thereof extending into a plenum chamber enhances the consistency of repeated regulated air discharges. The consistency is further enhanced by texturizing the inner wall of the discharge tube. Since the discharge tube extends into the plenum chamber, the objective unit can have substantial interchangeability with other tonometers.

Abstract: An electrical circuit for operating upon a slowly varying input signal (on the order of one volt per minute) to provide an output signal representative of the input signal derivative. The circuitry employs at least two feedback loops, one of which is constructed similar to an integrator amplifier. One particularly useful electro-medical application of this apparatus and method lies in the measurement of osmotic fragility of red blood cells, where percentage hemolysis of the blood slowly varies as a function of tonicity of suspension of the medium in which the blood sample is suspended. In this measurement the exact point of maximum slope is important and is provided by the present invention.

Abstract: Apparatus for evaluation a human subject's color vision response including light emmiting diodes providing luminance in the yellow and red and green color spectrums, means for controlling the individual luminescence of the red and green diodes in an inverse relationship and means for displaying the yellow and red-green luminescence for comparative viewing by the human subject.