# US 11,026,577 B2 · Rebound tonometry method and apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 11,026,577 B2 - Document ID: US11026577B2 - Status: Granted - Kind: B2 - Application number: 16/007,501 - Filed: 2018-06-13 - Published: 2019-12-19 - Granted: 2021-06-08 - Earliest claimed: 2018-06-13 - Assignees: Reichert, Inc. - Applicants: Reichert, Inc. - Inventors: Gabriel N. Martin - Web page: https://patentgrep.com/patent/US11026577B2 ## CPC - A61B 3/16: for measuring intraocular pressure, e.g. tonometers - A61B 3/0025: {characterised by electronic signal processing, e.g. eye models} - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## 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. ## Claims ### Claim 1 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. ### Claim 2 (depends on 1) The ophthalmic instrument according to claim 1, wherein the signal processing logic is further configured to calculate an intra-ocular pressure value based on the measurement signal. ### Claim 3 (depends on 2) The ophthalmic instrument according to claim 2, wherein the signal processing logic is 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 the intra-ocular pressure value is a correlate of the first derivative. ### Claim 4 (depends on 2) The ophthalmic instrument according to claim 2, wherein the signal processing logic is further configured to adjust the intra-ocular pressure value based on the at least one viscoelastic parameter. ### Claim 5 (depends on 1) The ophthalmic instrument according to claim 1, wherein the at least one viscoelastic parameter includes at least one parameter selected from the group of parameters consisting of: a Lost Energy Ratio, a Time Shift, a damping parameter, and an elastic parameter. ### Claim 6 (depends on 1) The ophthalmic instrument according to claim 1, wherein the drive coil is the measurement coil. ### Claim 7 (depends on 1) The ophthalmic instrument according to claim 1, wherein the drive coil and the measurement coil are different conductive coils. ### Claim 8 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. ### Claim 9 (depends on 8) The ophthalmic measurement method according to claim 8, further comprising calculating an intra-ocular pressure value based on the measurement signal. ### Claim 10 (depends on 9) The ophthalmic measurement method according to claim 9, wherein the intra-ocular pressure value is calculated by 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 intra-ocular pressure. ### Claim 11 (depends on 9) The ophthalmic measurement method according to claim 9, further comprising adjusting the intra-ocular pressure value based on the at least one viscoelastic parameter. ### Claim 12 (depends on 8) The ophthalmic instrument according to claim 8, wherein the at least one viscoelastic parameter includes at least one parameter selected from the group of parameters consisting of: a Lost Energy Ratio, a Time Shift, a damping parameter, and an elastic parameter. ### Claim 13 (depends on 8) The ophthalmic measurement method according to claim 8, wherein the measurement signal is detected using a measurement coil through which the probe moves, whereby the moving probe induces a current in the measurement coil. ### Claim 14 (depends on 8) The ophthalmic measurement method according to claim 8, wherein the measurement signal is detected by capturing and analyzing a series of images representing motion of the probe in the forward direction and the reverse direction. ### Claim 15 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. ### Claim 16 (depends on 15) The tonometer according to claim 15, wherein the drive coil is the measurement coil. ### Claim 17 (depends on 15) The tonometer according to claim 15, wherein the drive coil and the measurement coil are different coils. ### Claim 18 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. ### Claim 19 (depends on 18) The ophthalmic measurement method according to claim 18, wherein the measurement signal is detected using a measurement coil through which the probe moves, whereby the moving probe induces a current in the measurement coil. ### Claim 20 (depends on 18) The ophthalmic measurement method according to claim 18, wherein the measurement signal is detected by capturing and analyzing a series of images representing motion of the probe in the forward direction and the reverse direction.