Rebound tonometry method and apparatus
AssigneeReichert, Inc.
InventorGabriel N. Martin
Life of this patent
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Abstract
Viscoelastic properties of the cornea are derived from an ophthalmic measurement signal representing velocity as a function of time of a contact probe rebounded by the eye. The viscoelastic properties include a “Lost Energy Ratio” (LER), a “Time Shift” (TS), a damping parameter (σ), and an elastic parameter (η). An improved method for determining intra-ocular pressure from the measurement signal is also disclosed, wherein a first derivative of the measurement signal at a moment in time when velocity of the probe is zero due to contact of the probe with the cornea is calculated and correlated to an intra-ocular pressure value.
Claims20
An ophthalmic instrument comprising:
- a probe;
- a conductive drive coil in which the probe is received;
- a controller configured to momentarily energize the drive coil to propel the probe in a forward direction toward an eye of test subject, wherein the probe contacts a cornea of the eye and is rebounded from the cornea in a reverse direction opposite the forward direction;
- a conductive measurement coil through which the probe moves;
- wherein the controller is further configured to measure a current induced in the measurement coil by the moving probe and provide a measurement signal representing velocity of the probe as a function of time, and wherein the drive coil is energized such that a magnitude of the velocity of the probe is not kept constant after the probe is rebounded from the cornea;
- and
- signal processing logic configured to calculate at least one viscoelastic parameter of the cornea based on the measurement signal.
An ophthalmic measurement method comprising:
- propelling a probe in a forward direction toward an eye of a test subject, wherein the probe contacts a cornea of the eye and is rebounded from the cornea in a reverse direction opposite the forward direction;
- detecting a measurement signal representing velocity of the probe as a function of time, wherein the probe is propelled such that a magnitude of the velocity of the probe is not kept constant after the probe is rebounded from the cornea;
- and
- calculating at least one viscoelastic parameter of the eye cornea based on the measurement signal.
A tonometer comprising:
- a probe;
- a conductive drive coil in which the probe is received;
- a controller configured to momentarily energize the coil to propel the probe toward a cornea of an eye of a test subject;
- a conductive measurement coil through which the probe moves;
- wherein the controller is further configured to measure a current induced in the measurement coil by the moving probe and provide a measurement signal representing velocity of the probe as a function of time, and wherein the drive coil is energized such that a magnitude of the velocity of the probe is not kept constant after the probe is rebounded from the cornea;
- and
- signal processing logic configured to calculate a first derivative of the measurement signal at a moment in time when velocity of the probe is zero due to contact of the probe with the cornea and correlate the first derivative to an intra-ocular pressure value.
A tonometry method comprising:
- propelling a probe toward a cornea of an eye of a test subject such that a magnitude of the velocity of the probe is not kept constant after the probe is rebounded from the cornea;
- detecting a measurement signal representing velocity of the probe as a function of time;
- and
- calculating a first derivative of the measurement signal at a moment in time when velocity of the probe is zero due to contact of the probe with the cornea;
- and
- correlating the first derivative to an intra-ocular pressure value.
Dependencies are inferred from the claim text.