JP2005087549A - Non-contact tonometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a non-contact tonometer capable of eliminating the influence of cornea thickness and accurately correcting an intraocular pressure without giving unpleasant feelings to a patient. <P>SOLUTION: The non-contact tonometer is provided with an alignment means for positioning the optical axis of an objective lens barrel facing an eye to be examined to the cornea vertex of the eye to be examined, a projection means for projecting a measurement luminous flux along the optical axis, an air blowing means for which a nozzle is arranged along the optical axis for blowing air to the cornea vertex, a detection means for detecting the air pressure of the air chamber of the air blowing means, a light receiving means for receiving a cornea reflected luminous flux at the time of blowing the air by the air blowing means, a detection means for detecting waveform parameters before and after the cornea prescribed deformation of the light receiving means, an arithmetic means for converting the detected parameters of the detection means to the cornea thickness, and an intraocular pressure correction means for converting an intraocular pressure value from the pressure data of the air detection means and correcting the intraocular pressure value from the result of the arithmetic means. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a non-contact keratometer that calculates intraocular pressure by optical detection when air is blown onto a subject's eye to deform the subject's cornea.

  As a means for measuring the intraocular pressure of the eye to be examined, a Goldman type is known in which a probe is brought into direct contact with the cornea and measured. This is the principle that, when the cornea thickness is 520 μm, the probe pressing force when the contact surface diameter is φ3.06 mm cancels the hardness of the cornea and the surface tension of the tears, thereby obtaining a correct measurement value.

  On the other hand, as a non-contact tonometer, an air spray type tonometer developed by Bernard Grohlman (USP 3,585,849) is represented. In this method, air is blown from a nozzle 11 mm away from the subject's eye cornea, the applanation of the cornea is detected optically, the time to applanation is calibrated with a Goldman-type tonometer, and the intraocular pressure value is calculated. Yes. As for the size of the applanation, an accurate measurement value can be obtained using the principle of the Goldman type.

  However, it is also known that when the corneal thickness varies greatly from a thickness of 520 μm, it affects the intraocular pressure measurement value. In recent years, as typified by LASIK, it has become popular to perform refractive correction by intentionally reducing the corneal thickness. In such an ophthalmology situation, the following technological developments are also being carried out.

  An apparatus for measuring the intraocular pressure by blowing air on the eye to be examined as in Patent Document 1 has a function of measuring the corneal thickness, and an apparatus for correcting the intraocular pressure value based on the result of the corneal thickness measurement is disclosed. Yes. Further, as disclosed in Patent Document 2, a technique for correcting intraocular pressure by regarding the restoration time of the cornea deformed by air blowing as the hardness of the cornea has been disclosed.

JP-T 8-507463 JP 2000-212 JP

  However, in the technique disclosed in Patent Document 1, when the light is projected from the rear of the nozzle axis toward the apex of the cornea, the nozzle blocks the light beam and cannot sufficiently illuminate the cornea. Even if the illumination light is projected from an oblique direction, strong illumination such as strobe light is required to receive the reflected light on the front and back surfaces of the cornea that easily transmits the light flux. This is uncomfortable for the subject. In addition, if the intraocular pressure is measured by air stimulation, the subject's pain will only increase. In addition, the light detector array that receives the illuminated cornea needs to use an expensive CCD sensor to detect a minute change of 0.4 to 0.8 mm.

  The technique of Patent Document 2 is a method for measuring the hardness of the cornea using the principle of a conventional non-contact tonometer. However, the measurement of the time from when the cornea starts to deform until it returns can be performed in addition to the hardness of the cornea. If the intraocular pressure factor and air blowing force are not constant, the parameter does not indicate true hardness.

  In fact, if the intraocular pressure is high, the restoration time is long, and if the intraocular pressure is small, it is short. In addition, when air blowing is changed according to intraocular pressure in order to reduce the air stimulation of the subject, the restoration time is shortened if the air blowing force is reduced, and is increased if the air blowing force is strong.

  Therefore, a small-scale improvement of the conventional non-contact tonometer requires a means for correcting intraocular pressure without causing discomfort to the subject and accurately eliminating the influence of corneal thickness.

  The present invention has been made in view of the above problems, and the object of the present invention is a non-contact tonometer capable of correcting intraocular pressure without causing discomfort to the subject and accurately eliminating the influence of corneal thickness. Is to provide.

  In order to achieve the above object, the present invention provides an alignment means for aligning the apex of the eye cornea with the optical axis of the objective tube facing the eye to be examined, a projecting means for projecting a measurement light beam along the optical axis, An air spraying means for disposing air along the optical axis and blowing air toward the apex of the cornea, a detecting means for detecting the air pressure of the air chamber of the air spraying means, and the air of the air spraying means A light receiving means for receiving a corneal reflected light beam at the time of spraying, a detecting means for detecting a waveform parameter before and after a predetermined corneal deformation of the light receiving means, a computing means for converting a detection parameter of the detecting means into a corneal thickness, The non-contact tonometer is configured to include an intraocular pressure correction unit that converts the pressure data of the air detection unit into an intraocular pressure value and corrects the intraocular pressure value from the result of the calculation unit.

  According to the present invention, it is possible to correct an intraocular pressure value and perform accurate intraocular pressure measurement even in an eye to be examined in which the cornea has been excised after refractive surgery, which has recently become popular. In the present invention, it is possible to obtain an intraocular pressure value that eliminates the influence of the corneal thickness on the intraocular pressure value by small-scale improvements while taking advantage of the principle of the conventional tonometer, and subject to strong stimulation such as strobe light. Optometry can be performed quickly without giving to the patient.

  The present invention will be described in detail based on the illustrated embodiment.

  FIG. 1 is an external view of a non-contact tonometer of the present invention.

  The surface operated by the examiner is a display device 1 (liquid crystal monitor or CRT monitor) for selecting the display of measured values, eye images, etc. and setting of various devices, and for operating the display screen, and roughing the measurement unit. A trackball 2 and a roller 3 for aligning with the eye to be examined, a printer printing switch 4 and a measurement start switch 5 are arranged. When operated by the examiner, the measurement unit 7 can move in the vertical and horizontal directions and the front-rear direction with respect to the main body fixing side 6, and the intraocular pressure can be measured by aligning with the subject eye. On the side opposite to the surface operated by the examiner, a chin rest 8 on which the subject's face is placed is arranged, and the chin rest 8 is moved up and down by the chin rest vertical movement switch 9 on the side operated by the examiner. Can do.

  As shown in FIG. 2, a nozzle 12 is disposed on the central axis of the plane-parallel glass 10 and the objective lens 11 so as to face the eye E, and an air chamber 13, an observation window 14, and a dichroic are on the opposite side of the eye E. The mirror 15, the prism diaphragm 16, the imaging lens 17, and the image sensor 18 are arranged in this order. This is the light receiving optical path and the alignment detecting optical path of the observation optical system of the eye to be examined. The air in the air chamber 13 is compressed by a piston 20 that is pushed up by the drive of a solenoid 19, and pulsed air is ejected to the eye E through the nozzle 12.

  In the reflection direction of the dichroic mirror 15, a relay lens 21, a half mirror 22, an aperture 23, and a light receiving element 24 are disposed, which is a deformation detection light receiving optical path. Here, the position of the aperture 23 is arranged at a position where a cornea reflection image of a measurement light source, which will be described later, is conjugated at the time of predetermined deformation. A half mirror 25, a projection lens 26, and a measurement light source 27 are arranged in the reflection direction of the half mirror 22, and a fixation LED 28 that can be fixed by the subject is arranged in the reflection direction of the half mirror 25.

  The measurement light source 27 uses a near-infrared LED that is used for both measurement and alignment with the eye to be measured in intraocular pressure measurement. The light beam of the measurement light source 27 projected onto the eye to be examined is converted into parallel light by the projection lens 25, and half It is bent by the mirror 25, imaged once in the nozzle 12 by the relay lens 21, and irradiated to the cornea of the eye E to be examined.

  The reflected light beam of the measurement light source 27 at the cornea passes through the parallel flat glass 10 and the objective lens 11 outside the nozzle 12. In the reflection direction of the dichroic mirror 15, a deformation detection light receiving optical system when the cornea of the eye E to be examined is deformed in the visual axis direction by the air emitted in a pulse shape is arranged.

  The cornea-reflected light beam transmitted through the half mirror 22 is designed to form a cornea-reflected image having substantially the same size as that of the aperture 23 when the relay lens 21 is deformed, and the received light beam is photoelectrically converted by the light-receiving element 24 to be electrically converted. Converted to a signal. The outer diameter of the plane parallel glass 10 is supported by the objective lens barrel 29, and illumination light sources 30a and 30b for illuminating the eye to be examined are arranged on the outside thereof.

  A pressure sensor 31 for monitoring the pressure in the air chamber 13 when the piston 20 is pushed up by the solenoid 19 is disposed.

  With such an optical configuration, alignment with the eye to be examined is as disclosed in Japanese Patent Laid-Open No. 9-84760, and detailed description thereof is omitted.

  Since the configuration of the apparatus other than the measurement unit 7 for measuring intraocular pressure is not a part directly related to the present invention, it will be briefly described. The measuring unit 7 can move within a range of 90 mm in the left-right direction, 40 mm in the front-rear direction of the eye to be examined, and 30 mm in the up-down direction with respect to the body fixing side 6. The movement of the measuring unit 7 may be a type in which the measuring unit is mounted on a movable base and is moved in the same manner by operating a joystick, as in the case of driving by electric control as in JP-A-8-126611.

  Next, the electrical system of the entire apparatus when the positioning of the measurement unit 7 is performed by electrical control will be described.

  FIG. 3 is an electric block diagram of the entire system of the tonometer. To print a measurement board 5, a switch board 40 on which a printer printing switch 4 and the like are arranged, a trackball 2 for roughly aligning the measurement unit with the eye to be examined, a rotary encoder built in the roller 3, and a measurement result Printer 41 is connected to the MPU 42 port.

  The MPU 42 includes a PROM 42a for storing a program for controlling the system for controlling the entire system, an arithmetic processing unit 42b for calculating data obtained from various devices (light receiving elements, imaging elements, etc.), and a function for correcting intraocular pressure. It includes a parameter POM 42c storing data, an I / O 42d for controlling data input / output, and the like.

  The video signal of the anterior segment image of the eye to be examined photographed by the image sensor 18 is converted into digital data by the A / D converter 43 and stored in the image memory 44. The MPU 42 extracts a cornea reflection image of the eye to be examined based on the image stored in the image memory 44 and performs alignment detection. The video signal of the anterior segment image captured by the image sensor 18 is combined with the signal from the character generating device 45, and the anterior segment image, measurement values, and the like are displayed on the display device 1.

  The signal received by the light receiving element 18 and the pressure signal detected by the pressure sensor 31 in the air chamber 13 are amplified, converted into digital data by the A / D converter 46, and sequentially stored in the memory 47. When the MPU 42 detects the peak value of the light reception signal from the A / D converted PD element 24, the MPU 42 reads the data of the A / D converted pressure sensor 31 and stores it in the memory 47. All of the light reception signal and pressure signal data are stored in the memory 47.

  The up / down motor 48, the front / rear motor 49, the left / right motor 50, and the chin rest driving motor 51 are connected to motor drivers 52, 53, 54, and 55, respectively, and driven by commands from the MPU 42. The solenoid 19 is connected via a drive circuit 56 and is driven and controlled based on a command from the MPU 42. The measurement light source 27 and the illumination light sources 30a and 30b that illuminate the eye to be inspected are connected to the D / A converter 57 and can change the amount of light according to a command from the MPU 42.

  When a corneal reflection image is extracted by the detection of the image sensor 18, a deviation amount with respect to an appropriate position is calculated, and realignment is performed by the deviation. When the objective tube 29 is aligned at an appropriate position with respect to the cornea by auto alignment control, the MPU 42 automatically blows pulsed air toward the eye to be examined.

  FIGS. 4A to 4E are diagrams showing the state of the cornea E in which the air hits the cornea and the state of the light beam L of the light beam of the measurement light source 27, and photoelectric conversion by the light receiving element 24 in a minute time state. It is the graph which showed the output state of the electric signal. The horizontal axis represents time T, and the vertical axis represents the magnitude of output. The total phenomenon is about 15 msec to 20 msec.

  First, a state before the corneal deformation in a), the light beam of the measurement light source 27 imaged in the nozzle 12 is irradiated to the cornea with the outer side being limited at the outlet of the nozzle 12 and separated from the apex of the cornea. The light beam reflected by the surface does not return into the parallel flat glass 10.

  Further, since the light flux returning to the plane parallel glass 10 is not an optical arrangement that can form an image in the aperture 23 by the relay lens 21, most of the light is shielded by the aperture 23. In b) where the cornea begins to deform due to air pressure from the vicinity of the corneal apex due to air blowing, the corneal reflected light beam away from the apex of the cornea also returns into the parallel flat glass 10, so that the amount of light received by the light receiving element 24 increases. The signal is high. In the predetermined deformed state, the amount of received light is maximized and the signal has a peak.

  Furthermore, in c) where the cornea is deformed by air pressure, the apex of the cornea is deformed flat or concave. In this case, when the light beam irradiated from the inside of the spherical corneal nozzle is reflected by the cornea, most of the light returns to the inside of the nozzle or is reflected by the end face of the nozzle so that it is not received by the light receiving element 24. And the output of electrical signals also decreases. When the blowing of air is stopped together with the detection of the deformation of the cornea, the cornea tries to return to the original state by the intraocular pressure and the restoring force.

  In d), since the cornea is restored to the predetermined deformed state again, the light quantity of the light receiving element 24 increases and the signal becomes high. In e), which is completely restored, similarly to a), the reflected light beam away from the corneal apex and the aperture 23 are shielded, and the received light amount is low and the signal level is also low.

  The waveform obtained by monitoring the corneal deformation state with a light reception signal varies depending on intraocular pressure, aerodynamic force, alignment, and corneal thickness. In the case of intraocular pressure, the position Tp1 in the time axis direction that peaks at the initial deformation is delayed if the intraocular pressure is high, and is fast if the intraocular pressure is low. Further, it is known that when the intraocular pressure is high, the interval between the peak positions Tp2 and TP1 at the time of restoration becomes short, and when the intraocular pressure is low, the interval becomes long.

  In addition, the aerodynamic force has a balance with the intraocular pressure. However, if the aerodynamic force is changed at the same intraocular pressure, the initial deformation peak occurs early when the aerodynamic force is large, and Tp1 is accelerated. Tp1 is delayed. Further, it is known that the interval ΔT12 between Tp1 and Tp2 becomes longer when the aerodynamic force is large, and the interval ΔT12 becomes shorter when the aerodynamic force is small.

  Further, regarding the alignment, when the positional relationship between the cornea and the intraocular pressure measurement unit deviates from the appropriate position, for example, when the vertical and horizontal directions are shifted by about 0.8 mm and the front and rear direction by about 2 mm, the aerodynamic force strikes the cornea unevenly, Since the deformation state is disturbed and the corneal reflected light flux is also disturbed, the amount of light received by the light receiving element 24 becomes unstable, and the electric signal is disturbed, making measurement impossible.

  On the other hand, the influence of corneal thickness is considered to be as follows.

  FIG. 5 is a graph showing the relationship between the signal waveform of the light receiving element 24, the corneal thickness, and the half-value width W of the initial peak waveform of the signal waveform. This graph shows the parameters when the cornea thickness is changed by stopping the air blowing operation at a predetermined time of corneal deformation in the atmospheric pressure state when the corneal curvature radius and the corneal reflectance are made constant with a cornea-like material. It is the regression curve which approximated the value of W with the polynomial. It approximates to a clean quadratic function. Therefore, when the corneal curvature radius is constant and the corneal reflectance is constant, the half-value width W increases in a quadratic function when the corneal thickness increases at a constant rate, and a half of the initial deformation peak waveform is obtained as shown in FIG. If the value width W is detected, the corneal thickness can be calculated using the inverse function of this regression equation.

  The actual intraocular pressure correction using such a method is as follows.

  The MPU 42 carries out arithmetic processing to detect the position of the corneal reflection image from the video signal of the image sensor 18 and determines whether or not it has entered a predetermined position. When the proper position is determined, the solenoid 19 is driven via the drive circuit 56. Air is ejected from the nozzle 12 as the piston 20 moves.

  The corneal deformation phenomenon as described above occurs, and the MPU 42 continues to monitor the phenomenon state with digital data obtained by AD conversion from electrical signals from the light receiving element 24 and the pressure sensor 31 sequentially. When reaching a predetermined level before the first peak of the data of the light receiving element 24, the MPU 42 performs control to stop the solenoid 19 via the drive circuit 56. This is in order not to give excess air to the eye to be examined.

  However, the piston 20 further moves due to the inertial force and then stops. FIG. 7 is a graph showing the data obtained by such a series of phenomena. The intraocular pressure value is calculated from the pressure data P when the first peak (predetermined deformation state) is reached by calling a function for converting into an intraocular pressure value in advance from the parameter POM42C. At the same time, as described above, the half-value width W of the first deformation peak waveform is detected, and this time, a function for calculating the corneal thickness is called from the parameter POM42C.

  Further, the calculation of the intraocular pressure correction value from the calculated corneal thickness is obtained by calling a conversion formula for obtaining the intraocular pressure correction value from the corneal thickness obtained from the clinical experiment from the parameter POM42C. The calculated intraocular pressure value, corneal thickness value, and intraocular pressure correction value can be displayed on a display device or printed on a printer.

  In addition, transfer to other information processing devices via a network driver (not shown) is also possible. With regard to display and printing, it is possible to select only the corrected intraocular pressure value by changing the setting conditions, or to write or select the intraocular pressure value and corneal thickness before correction.

  The intraocular pressure correction based on the above-described corneal thickness has been described by a simple method, but actually, a more accurate regression equation can be obtained by collecting and verifying a large amount of data in a clinical experiment. In actual measurement, the corneal curvature varies depending on the eye to be examined, but the measurement light beam irradiated from within the nozzle 12 is partly near the apex of the entire cornea, so the influence of the curvature radius of the cornea is small. However, if the accuracy is further increased, the corneal thickness may be calculated from a plurality of regression equations with different corneal curvature radius conditions.

  Next, the present invention for measuring the corneal curvature radius will be described.

  FIG. 8 shows a state seen from the subject side. A kerato light source is disposed around the objective lens barrel 29, and a projection projection light source 60 for measuring the corneal curvature radius is provided on the cornea. The light source may be a ring shape as shown in FIG. 8A, or a light source that reflects the four bright spots 60a, 60b, 60c, and 60d on the cornea as shown in FIG. 8B. As shown in FIG. 9 (partial view of FIG. 2), the light-receiving side optical path of the observation light is such that when measuring the corneal curvature radius, the prism diaphragm 16 is discharged from the optical path, and the kerato diaphragm 61 is arranged concentrically with the optical axis. .

  The kerato diaphragm 61 is disposed at a position where the height of the kerato light source image does not change even when the position is shifted in the working distance direction. The wavelength of the kerato light source is the same as the wavelength of the measurement light source 27. After the alignment is completed, the measurement light source 27 is turned off, the above-described diaphragm is replaced, and a corneal reflection image of the kerato light source is captured by the image sensor 18. It is like that.

  FIG. 10 is a partial change of the electrical block diagram. The photographed kerato light source image uses the same circuit for alignment bright spot extraction. If it is a ring light source, the ring image is elliptically approximated to obtain the corneal curvature radius. Even with four light sources, an ellipse approximation is performed from the position of the bright spot to obtain the corneal curvature radius.

  The corneal curvature radius may be measured either before or after measuring the intraocular pressure after completion of alignment. The measured corneal curvature radius is calculated by calling a conversion formula for correcting intraocular pressure from the corneal thickness corresponding to the value from the parameter ROM 42c.

  As described above, a correction value with higher accuracy can be obtained by correcting the intraocular pressure value from the corneal thickness based on the corneal curvature radius.

  Further, in order to make the corneal reflectance constant, in addition to detecting the half-value width of the peak of the deformed waveform, the imaging sensor 18 measures the corneal reflected light with respect to the irradiation of the predetermined light quantity of the alignment light detection means 27 in the present invention. The half width W may be obtained by detecting at the previous appropriate alignment, detecting the reflectance corresponding to each cornea, and subtracting it from the deformed waveform data by the amount corresponding to the level.

  Further, it is further preferable to perform feedback control of the light amount of the measurement light source 27 in accordance with the corneal reflection level detected by the image sensor 18 so that the corneal reflection light before the measurement is constant even when the eye to be examined is different.

  Further, the half width of the deformation waveform described above corresponds to the corneal deformation change amount before and after the predetermined deformation. Therefore, in addition to the half width, as shown in FIG. 11a, the interval ΔWp between the time axis point TW1 and the peak position Tp1 at a predetermined ratio with respect to the peak value V1 may be used as a parameter.

  Alternatively, as shown in FIG. 11b, the waveform tangent slope θw may be determined at a predetermined level relative to the peak value.

  The present invention can be applied to a non-contact keratometer that calculates an intraocular pressure by optical detection when air is blown onto a subject's eye to deform the subject's cornea.

It is an external view of a non-contact tonometer. It is an optical layout of a non-contact tonometer. It is an electrical block diagram of the whole system of this invention. It is explanatory drawing of a cornea deformation state. It is a relational expression of parameters. It is a cornea deformation detection waveform diagram. It is a wave form diagram in intraocular pressure measurement. It is a kerato light source arrangement drawing. It is an optical layout at the time of a corneal curvature radius measurement. It is electric block explanatory drawing at the time of a corneal curvature radius measurement. It is explanatory drawing of a waveform detection.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display apparatus 6 Main body fixed side 7 Measuring part 12 Nozzle 18 Image pick-up element 24 Light receiving element 27 Measuring light source 31 Pressure sensor 42 MPU
60 Keratoling

Claims (8)

Alignment means for aligning with the optical axis of the objective tube facing the eye to be examined at the apex of the eye cornea, projection means for projecting the measurement light beam along the optical axis, and a nozzle along the optical axis, Air blowing means for blowing air toward the apex of the cornea, detection means for detecting the air pressure of the air chamber of the air blowing means, and light reception for receiving a corneal reflected light beam when air is blown by the air blowing means Means for detecting waveform parameters before and after the predetermined deformation of the cornea of the light receiving means, computing means for converting the detection parameter of the detecting means into corneal thickness, and pressure data of the air detecting means from the pressure data to the intraocular pressure value A non-contact tonometer having an intraocular pressure correcting means for converting and correcting an intraocular pressure value from the result of the calculating means.   The non-contact tonometer according to claim 1, wherein the detecting means for detecting the waveform parameter is a width of a peak waveform at the initial stage of corneal deformation.   2. The non-contact tonometer according to claim 1, wherein the detecting means for detecting the waveform parameter is an inclination of a peak waveform at the initial stage of corneal deformation.   An optical image of a ring shape or at least three bright spots on the cornea of the eye to be examined, a light beam projecting unit disposed symmetrically with the optical axis, a two-dimensional light receiving unit that receives the entire cornea-reflected light beam of the projecting unit in a two-dimensional plane, 2. The non-contact tonometer according to claim 1, further comprising a calculation unit that calculates a corneal curvature radius from an output of the two-dimensional light receiving unit and a correction unit that corrects the parameter of the corneal thickness from the result of the calculation unit. .   The calculation means for calculating the signal data of the detection means for detecting the waveform parameter using the data of the detection signal at the time of alignment of the alignment means, and performing the calculation for converting into the corneal thickness. The non-contact tonometer according to 1.   The control means for controlling the light quantity of the measurement light source using the data of the detection signal at the time of alignment of the alignment means, and the light receiving means for receiving the cornea reflection image of the controlled light quantity. The non-contact tonometer described.   The non-contact tonometer according to claim 1, wherein the result of the intraocular pressure correction means is displayed as an intraocular pressure value before and after correction.   The non-contact tonometer according to claim 1, wherein the result of correction means for correcting the parameter of corneal thickness is displayed as corneal thickness.

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