Pressure measuring method and apparatus with digital readout

• US 3,992,926 A
• Filed: 07/28/1975
• Issued: 11/23/1976
• Est. Priority Date: 07/28/1975
• Status: Expired due to Term

• Current Assignee: Professional Technologies Incorporated
• Original Assignee: Ber-Tek Incorporated
• Inventors: Berryhill, Robert C.
• Primary Examiner(s): Gill, James J.
• Assistant Examiner(s): Ciarlante, Anthony V.
• Application Number:
  US05/599,925
• Time in Patent Office: 484 Days
• Field of Search: 73/80, 73/81
• US Class Current: 600/405
• CPC Class Codes: A61B 3/16 for measuring intraocular pressure, e.g. tonometers
• CPC Class Codes: G01L 1/005 by electrical means and not provided for in G01L1/06 - G01L1/22

Abstract

A pressure-measuring apparatus and method is described for providing a digital readout of the intra-ocular pressure of an eye. The apparatus comprises a transducer for applanating the cornea of an eye and providing a variable output proportional to pressure as the transducer is applied to the cornea. Electronic means responsive to a change in the output of the transducer is coupled to the transducer for providing a digital readout of the pressure sensed by the transducer when there is a change in the slope of the output of the transducer and the change in the slope has a predetermined polarity and exceeds a predetermined rate. Means are also provided for simultaneously displaying at least four digital readouts of pressure corresponding to four successive pressure measurements. The multiple readouts permit an operator to use the lowest of the four readouts as an accurate measure of intra-ocular pressure when the measurements are taken from a given eye.

Claims

1. A pressure measuring apparatus comprising:

means responsive to a variable pressure for providing an output signal proportional to said pressure; and

means responsive to a predetermined change in said output signal for indicating the magnitude of said pressure at the time of said predetermined change, said indicating means comprising;

means responsive to said output signal for outputting a first and a second signal proportional, respectively, to the first and second derivatives of said output signal;

means responsive to said first and said second signals for providing a digital output corresponding to the output of said pressure-responsive means when said first derivative has a predetermined polarity and said second derivative exceeds a predetermined magnitude;

means for storing said digital output; and

means coupled to said storing means for visually displaying the magnitude of said digital output.

2. An apparatus according to claim 1 wherein said means for providing said digital output comprises an analog-to-digital converter.

3. An apparatus according to claim 1 wherein said storing means comprises a plurality of digital registers and said displaying means comprises separate displaying means coupled to each of said digital registers for displaying the contents of each of said digital registers and further comprising means for storing separate digital outputs corresponding to the output of said pressure-responsive means in each of said plurality of digital registers for each of an equivalent number of time in a given sequence that said first derivative has a predetermined polarity and said second derivative exceeds a predetermined magnitude.

4. A method of measuring the internal pressure of an enclosed member having a flexible wall comprising the steps of:

causing a movable piston disposed between fixed surfaces to bear against said wall;

generating a signal proportional to the distance said piston moves relative to said fixed surfaces;

detecting a change in the slope of said signal as said piston and surfaces are brought to bear against said wall; and

automatically measuring the magnitude of said signal when said change in the slope of said signal exceeds a predetermined rate, said steps of detecting a change in the slope of said signal and measuring the magnitude of said signal comprising the steps of;

differentiating said signal for generating a first and a second differential signal;

comparing said first and said second differential signal with a first and a second reference signal, respectively; and

generating a control signal for controlling an analog-to-digital conversion circuit to provide said measurement of the magnitude of said signal when there is a predetermined relationship between said first and said second differential signal and said first and said second reference signal, respectively.

5. A method according to claim 4 wherein said step of measuring the magnitude of said signal further comprises the step of automatically routing the output of said analog-to-digital display circuits to simultaneously display the results of a corresponding number of pressure measurements.

6. A method according to claim 4 wherein said step of generating a signal proportional to the distance said piston moves relative to said fixed surfaces comprises the step of changing the capacitance of a variable capacitor in proportion to the distance said piston moves relative to said fixed surfaces.