JPH0360263B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a tonometer that utilizes corneal deformation and is used in eye clinics and the like.

[Conventional technology]

Conventionally, this type of device detects a predetermined corneal deformation by detecting the amount of light reflected from the cornea, as known from Japanese Patent Publication No. 54-38437. The device disclosed in the publication projects a beam of light toward the cornea from off the optical axis and detects the amount of light reflected from the cornea using a photoelectric element placed off the optical axis to determine the state of applanation of the cornea. There is.

[Problem that the invention seeks to solve]

However, in the conventional method, corneal deformation was determined by detecting the amount of light reflected from the cornea, which caused measurement errors if the amount of light source changed during measurement.
In order to prevent this, stability of the light source was required.

Furthermore, it has been necessary to strictly adjust and measure the distance in the optical axis direction between the eye to be examined and the device, the so-called working distance.

An object of the present invention is to provide a new tonometer that eliminates the problems of the conventional example described above.

[Means for solving problems]

As a means for solving the above problems, for example, in this embodiment, a light source 9 emits pulsed light to irradiate the cornea, a photoelectric conversion element 12 that receives corneal reflected light, and a control box 1 that determines the intraocular pressure value from frequency displacement.
6, and further includes a fixation light source 14.

[Operation] In such a configuration, the light source 9 emits pulse light to illuminate the cornea, the photoelectric conversion element receives the corneal reflected light, and the control box 16 determines the intraocular pressure value from the frequency shift of the corneal reflected light. Furthermore, before measuring intraocular pressure, the light source 9 and the photoelectric conversion element 12 are used to detect the state of alignment with the subject's eye, and if the alignment is good, the light emitting state of the fixation light source 14 is changed and the subject's eye is examined. Indicates to the person that intraocular pressure measurement is possible.

〔Example〕

FIG. 1 is a diagram showing an embodiment of the present invention, in which air in a compressed air chamber 1 is driven by a solenoid 2, compressed by a piston 3, and blown from a nozzle 4 onto the cornea Ec of the eye E. It's summery. A portion of the compressed air chamber 1 facing the eye E is a flat plate member 5.
is arranged, and the nozzle 4 is attached to this flat member 5. Also, the flat plate member 5 of the compressed air chamber 1
An objective lens 6 is attached to the surface facing the. Behind the objective lens 6 is a half mirror 7.
Further, a lens 8 and a light source 9 are arranged in the direction of reflection. Further, a dichroic mirror 10 that reflects infrared light and transmits visible light is arranged in the transmission direction of the half mirror 7, and a lens 11 and a photoelectric conversion element 12 are arranged on the optical axis in the reflection direction. There is. A lens 13 and a fixation light source 14 are arranged in the transmission direction of the dichroic mirror 10, and the fixation light source 14 is movable by a lever 15 depending on the diopter of the subject. 16 is a control box equipped with a calculation function, and 17 is a measurement switch.

When the subject looks into the nozzle 4 while keeping a certain distance from the objective lens 6, he or she can see the fixation light source 14 blinking. If it is difficult to see clearly, you can use the lever 15 to adjust the position to a position that is easier for you to see. The light source 9 is an infrared light source such as an infrared LED or a semiconductor laser provided substantially on the optical axis of the objective lens 6, and is lit with high frequency pulses, and a narrow light beam is emitted to the lens 8.
, is reflected by a half mirror 7, passes through an objective lens 6 and a nozzle 4, and is projected onto the cornea Ec. The reflected light from the cornea Ec is returned to the nozzle 4 and the objective lens 6.
The light passes through the half mirror 7, is reflected by the dichroic mirror 10, and is guided via the nozzle 11 to the photoelectric conversion element 12 provided substantially on the optical axis of the objective lens 6. When the photoelectric conversion element 12 detects the reflected light of the light source 9 from the cornea Ec, it is determined that the alignment state in the direction perpendicular to the optical axis is good, and the control box 16 switches the fixation light source 14 on.
stops blinking and remains lit, and the subject knows that the alignment in the direction perpendicular to the optical axis has been completed. Note that if the light source 9 and the photoelectric conversion element 12 are substantially conjugate with the cornea, the amount of light received by the photoelectric conversion element 12 is assumed in advance, and the optical axis is adjusted by determining whether the amount of received light reaches the expected value. Directional alignment is also possible. After positioning, when the subject presses the measurement switch 17, the solenoid 2 is activated and the piston 3 is activated.
The compressed air passes through the nozzle 4 and is blown onto the cornea Ec of the eye to be examined. The cornea Ec is deformed by air pressure. The feature of this device is that the deformation of the cornea is determined by, for example, the Doppler effect of high-frequency pulses, and the intraocular pressure value is determined based on the displacement speed. Figure 2 shows its basic principle. A is an output signal of a basic pulse that causes the light source 9 to emit light.
B is an output signal of the photoelectric conversion element 12. Since the cornea is displaced toward the fundus of the eye due to air pressure, the frequency is lower than A due to the Doppler effect. That is, if the frequency of the pulsed light incident on the cornea is F, the frequency of the pulsed light reflected from the cornea is F', the corneal deformation speed is V, and the speed of light is C, then F-F'/F=V/C.

When the output signals A and B are added, the output signal has a waveform as shown in C, and when the high frequency component is removed and the waveform is shaped, a frequency signal of the difference between A and B appears as shown in D. This frequency displacement F-
It is clear from the above equation that the corneal deformation speed V can be determined from F'.

Here, it is known that the intraocular pressure of the subject's eye can be determined by changing the pressure value over time so that a predetermined pressure distribution is achieved, applying air pressure to the cornea, and determining the time required to reach a certain degree of corneal deformation.

Therefore, the intraocular pressure of the subject's eye can be calculated by integrating the corneal deformation speed V over time to determine the amount of deformation, and from the time T at which a constant amount of deformation Xo is achieved. Specifically, the constant deformation amount Xo
=∫ ^T _p Vdt, and as a means of confirming that the deformation has occurred by a certain amount of deformation Xo, for example, JP-A-58-
A corneal topography measuring device as known from Japanese Patent No. 50937 is used. It has also been proposed that when constant air pressure is applied to the cornea in a pulsed manner, the intraocular pressure of the eye to be examined can be determined from the amount of deformation.

Therefore, integrating the corneal deformation speed V over time,
The intraocular pressure of the subject's eye can be calculated from the amount of deformation X when the amount of deformation is determined and integrated over time for a predetermined period of time. Specifically, the amount of deformation X=∫ ^To _p Vdt (where To is the time at which the corneal deformation is considered to be stable). Furthermore, the intraocular pressure in the eye to be examined may be calculated from the time when the corneal deformation speed V reaches its extreme value.

That is, when an air pulse is applied to the cornea, the cornea generally deforms and restores itself in time S due to the intraocular pressure. Accordingly, the waveform shown in FIG. 2D draws a waveform whose frequency changes in accordance with changes in the deformation speed, as shown in FIG. 3D'. The time interval between two peaks of the demodulated waveform D' corresponds to the intraocular pressure. That is, if the intraocular pressure is high, the time interval becomes short, and if the intraocular pressure is low, the time interval becomes long.

Now, in the present invention, since the corneal deformation detection system determines the speed change of corneal deformation, high accuracy is not required for adjusting the working distance between the corneal deformation detection system and the eye to be examined. Here, if the corneal deformation pressure system is incorporated into the device main body together with the corneal deformation detection system and moves together with both in the optical axis direction, the corneal deformation detection system still correctly detects corneal deformation, but the corneal deformation pressure system Since the system changes the distance in the optical axis direction to the eye to be examined and the pressure acting on the cornea changes, a predetermined pressure is not applied to the cornea, making it impossible to accurately measure intraocular pressure.
Therefore, a change in the distance from the nozzle 4 to the eye to be examined in the optical axis direction is corrected using an arbitrary correction means. Note that since the measured value of intraocular pressure generally changes due to changes in atmospheric pressure, it is desirable to also correct the amount of change corresponding to this atmospheric pressure.

[Modified example]

In the above embodiment, the light source emits pulsed light, but a shutter (mechanical shutter, liquid crystal shutter, etc.) may be provided in the optical path and the pulsed light may be extracted by the shutter. Further, although the cornea was deformed by air flow in the above embodiment, ultrasonic waves may be used instead. In this case, the ultrasound waves are preferably focused on the cornea.
Furthermore, in the above embodiment, the Doppler effect was used to detect the frequency change to determine the corneal deformation speed.
It is clear that wavelength changes may be detected instead.

That is, if the wavelength of light incident on the cornea is λ, the wavelength of light reflected from the cornea is λ', the corneal deformation speed is V, and the speed of light is C, then λ (1/λ-1/λ') = V/
becomes C′. In this case, the light incident at an angle may be continuous light rather than pulsed light. And it is clear that infrared light is preferred.

Further, in the above embodiment, an apparatus is shown in which the subject measures the tonometer by himself/herself, but a non-contact tonometer can also be constructed which requires an examiner by providing an observation means.

In the above embodiment, the fixation target is used as a light source, but a so-called starburst or a chart such as a landscape may also be used.

Furthermore, although the fixation target is movable, the diopter may be adjusted by making the lens system movable.

Further, the light emitting state before the alignment adjustment of the fixation target may be a lighting state, and the light emitting state after the alignment adjustment may be a blinking state.

〔effect〕

As described above, according to the present invention, even if the light intensity of the measurement light source changes over time, the measurement accuracy is not affected. Also, the allowable range of working distance can be widened.

Furthermore, when positioning is achieved, if the light emitting state of the fixation light source is changed to indicate to the subject that intraocular pressure measurement is possible, measurement can be performed by the subject alone without the need for an examiner. Become.

[Brief explanation of drawings]

Fig. 1 is a diagram showing an embodiment of the present invention, Fig. 2 is a waveform diagram showing the basic signal of measurement, and Fig. 3 is a diagram showing frequency changes when the cornea is restored by applying pulsed air pressure. Inside, 1 is a compressed air chamber, 2 is a solenoid, 3 is a piston, 4 is a nozzle, 5 is a flat member, 6 is an objective lens, 7 is a half mirror, 8 is a lens, 9 is an infrared light source, 10 is a dichroic Mirror, 11 is a lens, 12 is a photoelectric conversion element, 13 is a lens, 1
4 is a light source for fixation, 15 is a fixation movement means, 16 is a control box, 17 is a measurement switch, E is the eye to be examined, Ec is the cornea of the eye to be examined, A is the blinking clock waveform of the light source 9, and B is a photoelectric conversion element. 12, C is the summed waveform of waveform A and waveform B, D is the shaped waveform of C, and D' is the waveform when pulsed air pressure is applied.

Claims (1)

[Scope of Claims] 1. A tonometer that measures intraocular pressure by applying pressure to the cornea of the eye to be examined and deforming the cornea,
A tonometer characterized by having a detection system that detects changes in the speed of corneal deformation, and a calculation system that calculates an intraocular pressure value from the changes in speed detected by the detection system. 2. A patent claim in which the detection system includes a projection system that projects pulsed light onto the cornea, a light receiving system that receives reflected light reflected by the cornea, and means for detecting frequency displacement of the reflected light received by the light receiving system. The tonometer according to item 1. 3. The detection system includes a projection system that projects light of a predetermined wavelength onto the cornea, a light receiving system that receives reflected light reflected by the cornea, and means for detecting a change in wavelength of the reflected light received by the light receiving system. The tonometer according to claim 1. 4. The tonometer according to claim 2 or 3, wherein the optical axes of the projection system and the light receiving system are coaxial with the direction in which the pressure is applied. 5. The tonometer according to claim 1, wherein the calculation system includes means for time-integrating the deformation speed detected by the detection system, and means for measuring the time at which the time-integrated value reaches a predetermined amount. 6. The eye according to claim 1, wherein the calculation system includes means for time-integrating the deformation speed detected by the detection system, and means for measuring the time-integrated value (deformation amount) after a predetermined period of time has elapsed. Pressure gauge. 7. The tonometer according to claim 1, wherein the calculation system includes means for measuring the time when the deformation speed detected by the detection system reaches an extreme value. 8. The tonometer according to claim 1, wherein the pressure is a pressure due to air flow. 9. The tonometer according to claim 1, wherein the pressure is a pressure generated by ultrasonic waves. 10 Claim 1, wherein the pressure acts on the cornea with a predetermined pressure distribution whose pressure value changes with time.
Tonometer described in section. 11. The tonometer according to claim 1, wherein the pressure acts on the cornea in pulses of a predetermined pressure value. 12. The tonometer according to claim 2 or 3, wherein the corneal projection light is infrared light. 13. The tonometer according to claim 1, wherein the light source of the projection system and the light-receiving element of the light-receiving system operate before measuring intraocular pressure to detect the state of alignment with the eye to be examined before measuring intraocular pressure. 14. The tonometer according to claim 1, wherein the light source and the light receiving element are provided substantially conjugate to the cornea of the eye to be examined. 15. The tonometer according to claim 13 or 14, which displays to the subject that when the output of the light receiving element reaches a predetermined value, the alignment state with the subject's eye is good. 16 A tonometer that measures intraocular pressure by applying pressure to the cornea of the eye to be examined to deform the cornea, includes a detection system that detects changes in the speed of corneal deformation, and an intraocular pressure value based on the changes in speed detected by the detection system. a fixation system that fixates the eye to be examined; a positioning system that aligns the eye with the eye to be examined; and a fixation light source of the fixation system when the positioning system is aligned. A tonometer characterized by having means for changing the light emitting state of the tonometer. 17. The tonometer according to claim 16, wherein the fixation light source is changed between a blinking state and a lit state. 18. The tonometer according to claim 16, wherein at least a portion of the fixation system is movable in the optical axis direction depending on the diopter of the eye to be examined.