Differential pressure applanation tonometer
First Claim
1. An applanation tonometer, comprising:
- first and second probes for contacting the surface of an eye, the probes being arranged coaxially in a housing and being movable longitudinally with respect to one another and with respect to the housing; and
a first sensor circuit coupled to the first and second probes and operative to sense longitudinal movement of the first probe relative to the second probe and generate a first signal in response to the relative movement,the first signal being related to the intraocular pressure of the eye.
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Accused Products
Abstract
An applanation tonometer for sensing the intraocular pressure of the eye. The tonometer includes coaxial inner and outer probes which are placed in contact with the eye. The difference in longitudinal forces applied by the eye to the inner and outer probes is measured and the intraocular pressure is determined therefrom. The total pressure applied to the eye by the tonometer is not measured as only the differential pressure on the two probes is needed. The tonometer may include a feedback mechanism to oppose relative longitudinal movement between the probes, thus improving the linearity, accuracy and stability of the instrument. The differential-pressure sensing circuitry includes a sample-and-hold circuit for receiving the measured result and supplying it to an indicating meter. The circuitry also includes compensating means for compensating for the force effects of gravity on the masses of the device. Finally, a level sensing circuit is used to indicate that a complete measurement has been made when a predetermined force has been applied to the eye by the outer probe.
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Citations
14 Claims
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1. An applanation tonometer, comprising:
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first and second probes for contacting the surface of an eye, the probes being arranged coaxially in a housing and being movable longitudinally with respect to one another and with respect to the housing; and a first sensor circuit coupled to the first and second probes and operative to sense longitudinal movement of the first probe relative to the second probe and generate a first signal in response to the relative movement, the first signal being related to the intraocular pressure of the eye. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. An application tonometer, comprising:
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inner and outer probes for contacting the surface of an eye, the probes being arranged coaxially in a housing; first sensing circuit means for sensing a difference in longitudinal forces applied to the inner and outer probes when the probes are placed in contact with the eye and for generating a signal proportional to the difference; feedback means for receiving the signal and for applying an opposing longitudinal force to oppose movement of the inner probe relative to the outer probe, the magnitude of the opposing longitudinal force being proportional to the magnitude of the signal, and the magnitude of the signal being proportional to the intraocular pressure of the eye. - View Dependent Claims (10, 11, 12, 13)
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14. A differential applanation tonometer, comprising:
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an outer cylindrical probe adapted at a first end to contact the surface of an eye and having, at a second end, a first flange about its outer circumference; an inner rod-like probe coaxial with and positioned within the outer probe, the inner probe being adapted at a first end to contact the surface of an eye, the first ends of the inner and outer probes lying substantially in a plan perpendicular to their longitudinal axes; a cylindrical spool connected to a second end of the inner probe and being spaced longitudinally from the first flange, the spool having an outer diameter substantially equal to the outer diameter of the first flange; an electrical winding about the outer circumference of the spool; a magnet for location adjacent the spool; a generally cylindrical housing for receiving the inner and outer probes, the spool and the magnet, the probes and spool being slidable longitudinally within the housing; a second flange positioned about the circumference of the housing and spaced longitudinally from the first flange on the outer probe; an outer probe capacitance formed between the first and second flanges; an inner probe capacitance formed between the first flange and one end of the spool; a first sensing circuit connected to the inner probe capacitance and operative to sense variations in the inner probe capacitance; a second sensing circuit connected to the outer probe capacitance and operative to sense variations in the outer probe capacitance; a compensator connected to the first and second sensing circuits and operative to compensate for gravity force effects on the outer and inner probes; a level sensor operative to sense a predetermined level of force differential between the outer probe and the housing and responsive to generate a signal; the electrical winding adapted to receive a signal from the first sensing circuit and operative to co-act with the magnet to apply a longitudinal force to the inner probe to oppose longitudinal movement by the inner probe to the outer probe.
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Specification