WO2000002481A1 - Non-contact tonometer having non-linear pressure increase - Google Patents
Non-contact tonometer having non-linear pressure increase Download PDFInfo
- Publication number
- WO2000002481A1 WO2000002481A1 PCT/US1999/014734 US9914734W WO0002481A1 WO 2000002481 A1 WO2000002481 A1 WO 2000002481A1 US 9914734 W US9914734 W US 9914734W WO 0002481 A1 WO0002481 A1 WO 0002481A1
- Authority
- WO
- WIPO (PCT)
- Prior art keywords
- time
- contact tonometer
- iop
- fluid pulse
- eye
- Prior art date
Links
Classifications
-
- A—HUMAN NECESSITIES
- A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
- A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
- A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
- A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
- A61B3/16—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for measuring intraocular pressure, e.g. tonometers
- A61B3/165—Non-contacting tonometers
Definitions
- the present invention relates generally to the field of non-contact tonometry, and more particularly to a non- contact tonometer having a non-linear pressure ramp during fluid pulse generation for increasing patient comfort.
- an increasing force fluid pulse is discharged through a tube aimed at the eye to deform the cornea from a state of convexity, through an instantaneous state of "applanation" wherein a predetermined area of the cornea is flattened, to a state of concavity; the cornea is then allowed to return to its original convex state under natural forces.
- Opto- electronic means are used to continuously monitor the corneal deformation and thereby determine the moment of applanation.
- the fluid pulse is commonly generated by a piston momentarily driven by a rotary solenoid to rapidly compress air within a plenum chamber, thereby forcing air from a discharge tube in communication with the plenum chamber.
- non-contact tonometers included pressure transducers to measure plenum pressure directly, offering improved accuracy. Although this improvement has obviated the need for the linearly increasing pressure ramp used in older non-contact tonometers, manufacturers continue to rely exclusively on constant current for energizing the drive means to produce a fluid pulse.
- a recognized, but heretofore accepted, drawback of using a constant current source is the system discontinuity related to the abrupt increase in driving current from zero to its constant value, as seen in Fig. 2. Such discontinuity has dictated that a high voltage power supply be used in the instrument to provide the initial rapid rise in current, and has resulted in mechanical oscillations in the fluid pulse system.
- Fig. 1 is a schematic diagram of a PRIOR ART non- contact tonometer, illustrating a fluid pulse system thereof;
- Fig. 2 is a plot of solenoid driving current as a function of time in a PRIOR ART non-contact tonometer;
- Fig. 3 is a plot of plenum pressure as a function of time in a PRIOR ART non-contact tonometer;
- Fig. 4 is a schematic diagram, similar to that of
- Fig. 5 is another schematic diagram of a non-contact tonometer formed in accordance with the present invention
- Fig. 6 is a plot similar to that of Fig. 2, however showing solenoid driving current as a function of time in a non-contact tonometer formed in accordance with the present invention
- Fig. 7 is a plot similar to that of Fig. 3, however additionally showing plenum pressure as a function of time in a non-contact tonometer formed in accordance with the present invention.
- Fig. 8 is a plot of IOP as a function of time for a several groups of trial measurements, wherein the rate of increase of energizing current was different for each group.
- a non-contact tonometer generally designated by the reference numeral 10 is shown schematically as including a fluid compression means 12 arranged in flow communication with a fluid discharge tube 14 aligned in a test position for directing a pulse of air at a patient's eye to cause deformation of cornea C.
- Compression means 12 includes a piston 16 cooperating with a cylinder 18 to define respective first and second plenum chambers 20 and 22.
- a rotary solenoid 24 is provided for automatically driving compression means 12 to generate an air pulse, and includes a moving armature 26 pivotally linked to an end of piston rod 28.
- armature 26 rotates in a clockwise direction, as shown in Fig. 4, to move piston 16 in a generally upward direction to rapidly decrease the volume of the first plenum chamber 20, causing an air pulse to be discharged from fluid discharge tube 14.
- armature 26 rotates in a clockwise direction, as shown in Fig. 4, to move piston 16 in a generally upward direction to rapidly decrease the volume of the first plenum chamber 20, causing an air pulse to be discharged from fluid discharge tube 14.
- other automatic drive means may be employed to move the piston, for example a linear motor.
- measurement means are provided for detecting corneal applanation and determining IOP.
- the progressive deformation of cornea C is monitored by an opto-electronic system such as that currently found in the XPERT NCT manufactured by Leica Microsystems Inc.
- Fig. 5 illustrates one possible opto- electronic system which includes an emitter 32 for directing an obliquely incident beam of light to cornea C and a photosensitive detector 33 arranged to receive corneally reflected rays.
- Non-contact tonometer 10 of Figs. 4 and 5 differs from the PRIOR ART non-contact tonometer depicted in Fig. 1 with respect to the nature of energizing means 30 supplying current to rotary solenoid 24 (or other automatic drive means) to move piston 16.
- the present invention utilizes a current source which increases the current delivered to solenoid 24 as a function of time, such that the force moving piston 16 increases as a corresponding function of time.
- a current source which increases the current delivered to solenoid 24 as a function of time, such that the force moving piston 16 increases as a corresponding function of time.
- energizing means 30 includes a ramp generator circuit 40 connected to a current generator circuit 42 for supplying current to solenoid 24 under the control of measurement electronics 36.
- Ramp generator circuit 40 supplies a linearly increasing voltage across voltage controlled current generator circuit 42, which in turn supplies linearly increasing current to solenoid 24, as depicted graphically in Fig. 6.
- the piston velocity is expressed as a squared function of time. Based on fluid mechanics of the system, the force delivered to cornea C is approximately proportional to the piston velocity, whereby
- the plenum pressure which is preferably measured by pressure sensor 34 and correlated with IOP, also increases as a squared function of time.
- the crossover point at which the nonlinear pressure ramp crosses a linear pressure ramp of the prior art is chosen to occur at the pressure corresponding to the average population IOP, which is about 15 mmHg, within a time interval of about two milliseconds.
- both a prior art non-contact tonometer and a non-contact tonometer according to the present invention will have delivered an air pulse sufficient to cause corneal applanation in the same period of time; however, the impulse felt by the patient will be significantly less with the instrument of this invention.
- the crossover point may be controlled by suitably selecting the rate of increase a of the driving current.
- Fig. 8 based on Tables I through IV below, shows the effect of varying oc on the shape of the non-linear pressure ramp and the crossover point.
- Tables I-IV each offer a comparison of pressure ramp data for a prior art non-contact tonometer using a constant current source whereby the measured IOP equals 10t, and a new non-contact tonometer using a ramped current source whereby the measured IOP equals K 3y3 o't 2 , with K ⁇ representing a system constant for the particular air pulse mechanism.
- the designations t 1 and t 2 denote time in milliseconds for prior art and new non-contact tonometers, respectively, while Aj and A 2 refer to areas under the prior art and new pressure-time curves, respectively. The crossover point is highlighted in each table.
- Table II is a second comparison of pressure ramp data similar to the comparison presented in Table I, however the value of ⁇ is chosen such that K ⁇ equals 5.00.
- Table III is a third comparison of pressure ramp data similar to the comparisons presented in Tables I and II, but the value of a is chosen so that K ⁇ cr equals 3.33.
- Table IV is a fourth comparison of pressure ramp data similar to the comparisons presented in Tables I through III, however the value of a is chosen such that K 3y3 Q' is equal to 2.50.
- the present invention offers a significant decrease in impulse delivered to the eye for a majority of the population having an IOP near the population average, thereby improving patient comfort during testing. This has the added benefit of reducing the incidence of false readings due to blinking.
- the preferred embodiment of the present invention advantageously eliminates the aforementioned system discontinuity found in the prior art by allowing the driving ,current to increase at a constant rate during air pulse generation.
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- Life Sciences & Earth Sciences (AREA)
- Health & Medical Sciences (AREA)
- Medical Informatics (AREA)
- Biophysics (AREA)
- Ophthalmology & Optometry (AREA)
- Engineering & Computer Science (AREA)
- Biomedical Technology (AREA)
- Heart & Thoracic Surgery (AREA)
- Physics & Mathematics (AREA)
- Molecular Biology (AREA)
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- Animal Behavior & Ethology (AREA)
- General Health & Medical Sciences (AREA)
- Public Health (AREA)
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- Eye Examination Apparatus (AREA)
Abstract
Description
Claims
Priority Applications (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
EP99930818A EP1109485A1 (en) | 1998-07-13 | 1999-06-29 | Non-contact tonometer having non-linear pressure increase |
CA002335084A CA2335084A1 (en) | 1998-07-13 | 1999-06-29 | Non-contact tonometer having non-linear pressure increase |
JP2000558749A JP2002520078A (en) | 1998-07-13 | 1999-06-29 | Non-contact tonometer for generating non-linear ramp function pressure. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US09/114,698 US6159148A (en) | 1998-07-13 | 1998-07-13 | Non-contact tonometer having non-linear pressure ramp |
US09/114,698 | 1998-07-13 |
Publications (1)
Publication Number | Publication Date |
---|---|
WO2000002481A1 true WO2000002481A1 (en) | 2000-01-20 |
Family
ID=22356876
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
PCT/US1999/014734 WO2000002481A1 (en) | 1998-07-13 | 1999-06-29 | Non-contact tonometer having non-linear pressure increase |
Country Status (4)
Country | Link |
---|---|
EP (1) | EP1109485A1 (en) |
JP (1) | JP2002520078A (en) |
CA (1) | CA2335084A1 (en) |
WO (1) | WO2000002481A1 (en) |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
WO2006066876A1 (en) | 2004-12-20 | 2006-06-29 | Mechatronic Ag | Mobile tonometer for carrying out contactless automatic tonometry |
EP2092877A1 (en) * | 2002-07-01 | 2009-08-26 | Reichert, Inc. | Method for eliminating error in tonometric measurements |
CN104523223A (en) * | 2014-12-23 | 2015-04-22 | 苏州联科盛世科技有限公司 | Portable intraocular pressure detector and intraocular pressure detection method |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
CN112354210A (en) * | 2020-09-24 | 2021-02-12 | 清华大学 | Air pulse generating device of nuclear pulse extraction column |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4996990A (en) * | 1987-08-12 | 1991-03-05 | Tokyo Kogaku Kikai Kabushiki Kaisha | Air-puff tonometer |
US5279300A (en) | 1991-01-30 | 1994-01-18 | Nidek Co., Ltd. | Noncontact type tonometer |
US5779633A (en) | 1996-06-10 | 1998-07-14 | Leica Inc. | Tonometer air pulse generator |
-
1999
- 1999-06-29 JP JP2000558749A patent/JP2002520078A/en active Pending
- 1999-06-29 EP EP99930818A patent/EP1109485A1/en not_active Withdrawn
- 1999-06-29 WO PCT/US1999/014734 patent/WO2000002481A1/en not_active Application Discontinuation
- 1999-06-29 CA CA002335084A patent/CA2335084A1/en not_active Abandoned
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4996990A (en) * | 1987-08-12 | 1991-03-05 | Tokyo Kogaku Kikai Kabushiki Kaisha | Air-puff tonometer |
US5279300A (en) | 1991-01-30 | 1994-01-18 | Nidek Co., Ltd. | Noncontact type tonometer |
US5779633A (en) | 1996-06-10 | 1998-07-14 | Leica Inc. | Tonometer air pulse generator |
Cited By (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP2092877A1 (en) * | 2002-07-01 | 2009-08-26 | Reichert, Inc. | Method for eliminating error in tonometric measurements |
WO2006066876A1 (en) | 2004-12-20 | 2006-06-29 | Mechatronic Ag | Mobile tonometer for carrying out contactless automatic tonometry |
CN104523223A (en) * | 2014-12-23 | 2015-04-22 | 苏州联科盛世科技有限公司 | Portable intraocular pressure detector and intraocular pressure detection method |
Also Published As
Publication number | Publication date |
---|---|
CA2335084A1 (en) | 2000-01-20 |
EP1109485A1 (en) | 2001-06-27 |
JP2002520078A (en) | 2002-07-09 |
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