JP3118270B2 - Eye axis length measuring device - Google Patents

Eye axis length measuring device

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Publication number
JP3118270B2
JP3118270B2 JP03082657A JP8265791A JP3118270B2 JP 3118270 B2 JP3118270 B2 JP 3118270B2 JP 03082657 A JP03082657 A JP 03082657A JP 8265791 A JP8265791 A JP 8265791A JP 3118270 B2 JP3118270 B2 JP 3118270B2
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Japan
Prior art keywords
light
optical
fundus
corneal
wavelength
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JP03082657A
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JPH04314419A (en
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大友文夫
関根明彦
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株式会社トプコン
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Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of irradiating a coherent light having a single wavelength and a wavelength changeable to an eyeball and causing a reflected light from the fundus to interfere with a fundus corresponding reference light to obtain an interference signal.
An interference signal is obtained by causing the reflected light from the cornea to interfere with the cornea-corresponding reference light, and these two interference signals are mixed while changing the wavelength to form a beat signal, and the axial length is determined based on the beat signal. The present invention relates to an axial length measuring device.

[0002]

2. Description of the Related Art Conventionally, coherent light emitted from a laser diode is radiated to an eye to be examined, and the fundus reflection light and the corneal reflection light interfere with each other to perform photoelectric conversion. An axial length measuring device for measuring the length is known.

[0003]

However, the conventional apparatus for measuring the axial length of the eye uses the coherent light of high intensity because the restriction that the amount of coherent light that can be irradiated on the eye to be examined must not cause retinal damage. Is limited, and because of the low reflectance of the fundus and the cornea, it is not possible to obtain a high intensity of the interference light, and the photoelectric conversion signal based on the interference light is weak.
There is a problem that a sufficient photoelectric conversion signal with a / N ratio cannot be obtained.

In addition, since the fundus is an optically rough surface, its photoelectric conversion signal is unstable, and it is difficult to distinguish it from noise in combination with the weakness of the photoelectric conversion signal. It is difficult to perform accurately.

The present invention has been made in view of the above problems, and has as its object to reduce the intensity of coherent light more than necessary, that is, to reduce reflected light from the fundus and reflected light from the cornea. However, an object of the present invention is to provide an eye axial length measuring device capable of extracting information useful for measuring the axial length .

[0006]

[0007]

According to a first aspect of the present invention, there is provided an eye axial length measuring apparatus, comprising: a measuring optical system having a coherent light source for irradiating an eyeball with a single wavelength and coherent light whose wavelength can be changed; A fundus optics system that irradiates the fundus with coherent light and receives reflected light from the fundus, divided by a beam splitter, and a cornea optics that irradiates the cornea with coherent light and receives the reflected light from the cornea The fundus optical system is provided with a fundus-corresponding reference surface for reflecting a part of the coherent light and forming a fundus-corresponding reflected reference light, and the cornea optical system is provided with a A corneal-corresponding reference surface for partially reflecting and forming a corneal-corresponding reflected reference light is provided, and the fundus optics includes a light receiver that receives interference light based on the fundus-reflected light and the fundus-corresponding reference light. The corneal optical system has a light receiver that receives interference light based on the corneal reflected light and the cornea-corresponding reference light, and further changes an interference signal from each light receiver to the mixer while changing the wavelength of the coherent light. A beat signal is formed by inputting the beat signal, and an arithmetic unit for calculating an axial length based on the frequency of the beat signal is provided. An eye axial length measuring apparatus according to claim 2, wherein the measuring optical system having a coherent light source for irradiating coherent light having a single wavelength and a wavelength that can be changed is a light beam having a polarization component different from that of a beam splitter. It is split and irradiates the fundus with coherent light of one polarization component and irradiates the cornea with an optical system for the fundus that receives reflected light from the fundus and coherent light of another polarization component and reflects light from the cornea. An optical system for the cornea that receives the fundus, the fundus optical system is provided with a fundus-corresponding reference surface for reflecting a part of the coherent light and forming a fundus-corresponding reflected reference light. Is provided with a corneal-corresponding reference surface for reflecting a part of the coherent light and forming a corneal-corresponding reflected reference light, and the measuring optical system includes an interference light based on the fundus reflected light and the fundus-corresponding reference light. It has a light receiver for receiving at the same time the interference light based on the cornea reflected light and the cornea corresponding reference light as well as light, and further outputs a beat signal from the photodetection unit while changing the wavelength of the coherent light, the beat signal And a calculating unit for calculating the axial length based on the frequency of. An eye axial length measuring apparatus according to claim 3 is an illumination optical system having a coherent light source that irradiates coherent light having a single wavelength and a wavelength changeable to the eyeball of the eye to be examined, and receives reflected light from the eye to be examined. Measurement optical system,
Further, the measurement optical system includes a fundus optical system that receives fundus reflected light and a corneal optical system that receives corneal reflected light,
The illumination optical system includes a fundus reference light optical system that guides the fundus-corresponding reference light to the fundus optical system, and a corneal reference light optical system that guides the corneal reflection-compatible reference light to the corneal optical system. Corresponding reference light and a light receiver that receives interference light based on the fundus reflection light, the corneal optical system includes a light receiver that receives interference light based on the corneal correspondence reference light and the corneal reflection light, It is provided with an arithmetic unit for inputting the interference signal from each light receiver to the mixer while changing the wavelength of the coherent light to form a beat signal, and calculating the axial length based on the frequency of the beat signal. Features. According to another aspect of the present invention, the coherent light source is configured to change its wavelength linearly with time. The optical axis length measuring device according to claim 5, wherein the optical system having a coherent light source for irradiating coherent light having a single wavelength and a wavelength changeable is such that the reference optical path difference is formed longer than the axial length. An interference optical system and a measurement optical system for irradiating coherent light toward the subject's eye, the measurement optical system is divided by a beam splitter to irradiate the fundus with coherent light and reflect light from the fundus It comprises a fundus optical system that receives light and a cornea optical system that irradiates the cornea with coherent light and receives light reflected from the cornea.The fundus optical system reflects part of the coherent light. A fundus-corresponding reference surface for forming a fundus-corresponding reflected reference light is provided, and the corneal optical system reflects a part of the coherent light to form a cornea-corresponding reflected reference light. An illumination surface is provided, the fundus optical system has a light receiver that receives interference light based on the fundus reflection light and the fundus reference light, and the cornea optical system has an interference based on the corneal reflection light and the cornea reference light. A light receiver for receiving light, and inputting an interference signal from each light receiver to the mixer while changing the wavelength of the coherent light to form a beat signal; and the reference interference optical system receives the reference interference light. A photodetector that outputs a reference interference signal, and further includes a calculation unit that calculates an axial length based on a ratio between the frequency of the beat signal and the frequency of the reference interference signal. The eye axial length measuring device according to claim 6,
The coherent light source of the measurement optical system is configured to be controlled so that its wavelength does not change linearly with time. The coaxial light source of the measurement optical system according to the eye axial length measurement device according to claim 7,
A mode in which the mode hop interval is wider than the wavelength change width for changing the wavelength is selected.

[0008]

According to the apparatus for measuring the axial length of the eye according to the present invention, interference information including corneal position information can be obtained by causing the corneal reflected light to interfere with the corneal reference light. Further, interference information including fundus position information can be obtained by causing the fundus reflection light and the fundus-corresponding reflection light to interfere with each other. When a beat signal is formed by mixing these pieces of interference information, there is a fixed relationship between the frequency of the beat signal and the axial length in principle.
The axial length can be calculated.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an eye axial length measuring device according to the present invention will be described below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a measuring optical system, and 2 denotes a reference
It is an optical system . The measurement optical system 1 has a beam splitter 3, and the fundus measurement optical system 4
And a corneal measurement optical system 5. Measurement optical system 1
Is provided with a semiconductor laser 6 for emitting coherent light of a single wavelength. The coherent light is converted into a parallel light by the collimator lens 7. The parallel light beam is
The light is guided to the beam splitter 9 via the optical isolator 8. The optical isolator 8 plays a role in preventing reflected light described later from returning to the semiconductor laser 6. by this,
In the semiconductor laser 6, modulation distortion due to return of the reflected light is prevented.

The beam splitter 9 serves to split the parallel light beam and guide one of the split light beams to the reference interference optical system 2. The other split beam is the beam splitter 9
Is transmitted to the beam splitter 3 as measurement light. The beam splitter 3 serves to split the measurement light beam into a measurement light beam for the fundus and a measurement light beam for the cornea. The measurement light beam for the fundus is guided to the fundus measurement optical system 4, and the measurement light beam for the cornea is guided to the cornea measurement optical system 5. I will

The fundus measuring optical system 4 includes a beam splitter 10,
Lens 11, lens 12, aperture 13, mirror 14, movable lens 1
5, beam splitter 16, objective lens 17 facing eyeball E,
It has a fundus-corresponding reference surface 18, a condenser lens 19, and a light receiver 20.
The diaphragm 13 is disposed between the lens 11 and the lens 12.
The aperture 13 serves as a low-pass filter in combination with the Fourier transform action of the lenses 11 and 12, and the configurations of the lenses 11, 12 and the aperture 13 are known.

The fundus measuring light is split by the beam splitter 10, one of which is guided to a fundus-corresponding reference surface 18,
The light is reflected by the fundus-corresponding reference surface 18, returns to the original optical path, passes through the beam splitter 10, and is guided to the light receiver 20 by the condenser lens 19. The other passes through the lens 11, the aperture 13, and the lens 12, is reflected by the mirror 14, and
Then, the light is guided to the beam splitter 16 via the optical axis, is reflected by the beam splitter 16, and is irradiated on the eyeball E via the objective lens 17. The movable lens 15 has the function of correcting the refractive power of the eye to be examined and converging the fundus measurement light to the fundus R.

The light reflected from the fundus R is reflected by an objective lens 17, a beam splitter 16, a movable lens 15, a mirror 14,
2, guided to the aperture 13 and the lens 11. The scattered component contained in the reflected light of the fundus R is the lens 12, aperture 13, lens 11
Is removed when guided to The reflected light of the fundus R is reflected by the beam splitter 10, guided to the light receiver 20, and interferes with the reflected light from the fundus corresponding reference surface 18, and the light receiver 20 photoelectrically converts the interference light and outputs an interference signal. .

The corneal measuring optical system 5 includes a beam splitter 2
1.A mirror 22, an optical path length compensator 23, a lens 24, an aperture 25, a corneal reference surface 26, a condenser lens 27, and a light receiver 28, which are coaxial with the optical axis of the objective lens 17 by the beam splitter 16. ing. The aperture 25 plays a role of a low-pass filter in combination with the Fourier transform action of the objective lens 17 and the lens 24. The corneal measurement light is guided to the beam splitter 21 and split. One of them is guided to the cornea-corresponding reference surface 26, is reflected by the cornea-corresponding reference surface 26, and returns to the original optical path.
The light passes through the beam splitter 21, is collected by the condenser lens 27, and is guided to the light receiver 28.

The other is a mirror 22, an optical path length compensator 23, a lens
The light passes through the aperture 24, the aperture 25, the beam splitter 16, and the objective lens 17 and is converged on the vertex M of the cornea C. The light reflected by the vertex M of the cornea C returns to the original optical path, and is guided to the beam splitter 21 via the objective lens 17, the beam splitter 16, the stop 25, the optical path length compensator 23, and the mirror 22. The scattered component of the reflected light from the cornea C is removed when passing through the objective lens 17, the diaphragm 25 and the lens 24. The reflected light of the cornea C is reflected by the beam splitter 21, guided to the light receiver 28, and interferes with the reflected light from the reference surface 26 corresponding to the cornea. The light receiver 28 photoelectrically converts the interference light and outputs an interference signal. . The optical path length compensator 23 has an optical path length L from the center of the beam splitter 21 to the vertex M of the cornea.
This is used to eliminate the difference Ls = Lr′−Lc between c and the optical path length Lr ′ from the center of the beam splitter 10 to the corneal vertex M. That is, using this, the optical path length Lr ′ = L
Adjust to be c.

The reference interference system 2 is roughly composed of a beam splitter 29, mirrors 30 and 31, and a light receiver 32. The reference light beam is split by the beam splitter 29, and the split light beams are guided to the mirrors 30 and 31, respectively. , 31 return to the original optical path, are combined by the beam splitter 29, and guided to the light receiver 32. The light receiver 32 receives the interference light, performs photoelectric conversion, and outputs a reference interference signal. Here, assuming that the distance from the beam splitter 29 to the mirror 30 is LK2 and the distance from the beam splitter 29 to the mirror 31 is LK1
The reference optical path difference is Lbase = 2 (LK1-LK2). This reference optical path difference Lbase is set to be sufficiently longer than the eye axis length Leye. The reason will be described later.

The semiconductor laser 6 is heated and cooled by temperature control means such as a Peltier effect device,
The wavelength of the coherent light emitted from is controlled.

Next, the principle of measurement will be described together with the signal processing circuit.

In FIG. 2, reference numeral 33 denotes a synchronization control circuit. The synchronization control circuit 33 outputs the synchronization signal to the clock circuit 34.
And the wavelength control circuit 35. The wavelength control circuit 35 outputs to the drive circuit 36 and the wavelength control means 37.

The intensity I1 of the interference light at the light receiver 20 is
The following formula is theoretically followed.

I1 = 2Ar · Aref1 · cos {2π · 2 (Lr−L1) / λ} (1) The intensity I2 of the interference light at the photodetector 28 theoretically follows the following equation.

I2 = 2Ac · Aref2 · cos {2π
2 (Lc−L2) / λ} (1) ′ where Ar is the amplitude of the light reflected from the fundus R, Ac is the amplitude of the light reflected from the cornea C, and Aref1 is the reference surface 18 corresponding to the fundus.
Aref2 is the amplitude from the reference surface 26 corresponding to the cornea, and λ is the wavelength of the coherent light.

In both (1) and (1) ', the DC component and the initial phase were ignored.

Further, Lr = Lr '+ Leye.

Further, 2π · 2 (Lr−L1) / λ, 2
π · 2 (Lc−L2) / λ indicates the phase difference of the interfering light.

Here, when the wavelength of the coherent light is continuously changed by Δλ, each phase difference is 2π · 2 (Lr-L
1) / (λ + Δλ), 2π · 2 (Lc−L2) / (λ +
Δλ).

Now, assuming that λ≫Δλ, the terms of each phase difference are series-expanded. Each phase difference is 2π · 2 (Lr−L1) Δλ / λ 2 , 2π · 2 (Lc−L2) Δλ / λ 2 . 2) can be expressed as Since the intensities I1 and I2 of the interference light periodically change every 2π phase difference, if the wavelength of the coherent light is changed, the interference signal output from each of the light receivers 20 and 28 also changes periodically. The term (2) means the number of periods of the interference signal.

Here, it is assumed that the wavelength control means changes the wavelength λ of the coherent light linearly with respect to time t, as shown in FIG. Now, the time tm required to modulate the wavelength λ by Δλ is 1 second, and the optical path length L = 1m
Assume that Δλ / λ 2 = 1 for m. Receiver 2
The interference signals of 0, 28, 32 are amplified by amplifiers 38, 39, 40
Are amplified by the DC component removing circuits 41 and 4 respectively.
DC components are removed by 2, 43.

Based on the above assumption, Δλ / λ 2 = 1 with respect to the time tm = 1 second and the optical path length L = 1 mm. Therefore, the frequency f1 of the interference signal corresponding to the intensity I1 of the interference light and the intensity I2 of the interference light Are respectively f1 = 2 (Lr-L1) Hz ... (3) f2 = 2 (Lc-L2) Hz ... (3) '.

Here, the optical path length Lr is generally Lr = Lc
+ Leye + Ls, the frequency f1 of the interference signal of the photodetector 20 is f1 = 2 (Lc + Leye + Ls-L1) Here, the optical path length compensator 23 is adjusted so that Ls = 0, and L1 = L2. When the measuring optical system 1 is configured as follows, the following equation is obtained: f1 = 2 (Lc + Leye−L1) (1) f2 = 2 (Lc−L1) (4) ′

Here, assuming that Lc−L1≫Leye,
The frequencies f1 and f2 are close to each other. When the amplitudes of the interference signals are adjusted by the gain adjustment circuits 44 and 45 and the interference signals are mixed by the mixer 46, a beat is generated.
The gain adjustment circuits 44 and 45 are used for adjusting the contrast of the beat signal.

The beat frequency fb is given by fb = f1-f
2 = 2Leye.

The composite frequency f0 is f0 = (f1 + f2) / 2 = 2Lc-2L1 + Leye.

Therefore, the beat signal S is represented by the following equation: φ1 and φ2 are initial phases of the respective light receivers 20 and 28. The waveform of the beat signal S is shown in (2) of FIG. Therefore, the beat signal S is detected by the detection circuit 47 and the beat frequency fb
Is obtained, from the formula of fb = 2Leye, the axial length Ley is obtained.
e can be obtained. The detected waveform is shown in FIG.
Is shown in If Ls does not become completely zero due to the optical path length compensating plate 23, fb = 2Leye + 2Ls, so Ls is subtracted from the measured value to make correction.

Actually, the wavelength λ is equal to the wavelength λ + Δ
If it takes tm to change to λ, then f1 = {2 (Lc + Leye−L1) · (Δλ / λ 2 )} / tm (5) f2 = {2 (Lc−L1) · (Δλ / λ 2 )} / tm (5) ′.

When the beat frequency is obtained using the equations (5) and (5) ′, the following equation is obtained: fb = f1−f2 = (2Leye · Δλ / λ 2 ) / tm (6)

Therefore, the beat frequency fb and Δλ / (λ 2
Tm), 2Leye can be calculated. The detected waveform is stored in the waveform memory 49 via the A / D converter 48. FIG. 3D shows the waveform stored in the waveform memory 49. The A / D converter 48 receives a conversion timing signal from the clock circuit 34.

Here, since it is difficult to directly determine the wavelength λ and the variation Δλ, the frequency fb is not directly related to Leye but to the frequency of the reference interference signal obtained by the reference interference optical system 2.

Now, when the wavelength λ is changed to λ + Δλ,
The phase difference change amount Δδbase of the reference interference optical system 2 is Δδbase = (2π · 2LbaseΔλ / λ2) / t
m.

After the DC component is removed from the reference interference signal (see (5) in FIG. 3), the reference interference signal is stored in the waveform memory 50 via the A / D converter 49 '. A timing signal is input from the clock circuit 34 to the A / D converter 49 '. The waveform stored in the waveform memory 50 is shown in FIG.

Assuming that λ and Δλ are unknown and a reference interference signal of frequency fbase is obtained from the photodetector 32, fbase = (2Lbase · Δλ / λ 2 ) / tm ...
(7)

Accordingly, the frequencies f1 and f2 are given by the following equation (7): f1 = fbase · 2 (Lc + Leye−L1) / 2Lbase f2 = fbase · 2 (Lc−L1) / 2Lbase

Accordingly, the beat frequency fb of the interference signal is given by fb = fbase ・ 2Leye / 2Lbase (8)

Therefore, by measuring the beat frequency fb of the interference signal, the eye axis length Leye can be calculated from the following equation (9) obtained by modifying the equation (8).

Leye = (Lbase · fb) / fbase (9) The beat frequency fb and the reference frequency fbase are obtained by the procedure described below.

In the wavelength change section tm, the interference signal and the reference interference signal are stored in the waveform memories 49 and 50. Assuming that the clock timing frequency of the waveform data to be stored in the waveform memories 49 and 50 is fad, the number of data in the wavelength change section tm is N = fad · tm.

Therefore, when the number of data constituting one cycle of the reference interference signal is calculated, the reference interference signal frequency fbase
Is obtained as fbase = fad / ns (9) ′, where ns is the number of data constituting one cycle.

Therefore, the reference interference signal and the beat signal are simultaneously obtained while taking the timing with the clock signal. If the above calculation is performed on the beat frequency, even if the frequency fad of the clock signal is an unknown value, the equation (9) is obtained. Fb / f
base can be determined.

Fb / fbase = nbs / ns (nbs
Is the number of periods within one wavelength modulation section of the beat signal). here,
Assuming that the total number of data within one wavelength change section tm is N, ns is determined by the number of cycles nbase of the reference interference signal included in one wavelength modulation section tm.

That is, N (the total number of data within one wavelength modulation section of the reference interference signal), ns (the number of data constituting one cycle of the reference interference signal), and nbase (the number of cycles within one wavelength modulation section of the reference interference signal) ), The relational expression of N = ns · nbase holds.

On the other hand, N is also the total number of data of the interference beat signal. Now, if nb is the number of data in one cycle of the beat signal, the relational expression of N = nb · nbs holds.

Therefore, nbs / ns = nbase / nb, and fb / fbase = nbase / nb can be written.

The arithmetic circuit 51 performs an arithmetic operation by using any one of these relational expressions to calculate the axial length.

According to this measurement, since the beat frequency fb depends on the eye axis length Leye, the sensitivity to the misalignment and the movement of the eyeball, particularly the movement of the head of the subject can be reduced.

That is, Lr, Lc
Are changed by ΔL, the signal frequencies f1 and f2 in the wavelength modulation section change.

F1 = {2 (Lr + ΔL−L1) Δλ / λ 2 } / tm f2 = {2 (Lc + ΔL−L2) Δλ / λ 2 } / tm Accordingly, the composite frequency f0 also changes.

F0 = {(2Lc−2L1 + Lceye + ΔI) Δλ / λ 2 } / tm However, since f1 and f2 simultaneously change by the same amount, the beat frequency fb is constant.

Therefore, it is only necessary to configure a circuit capable of sufficiently separating the frequency values of f0 and fb and measuring the beat frequency with a margin for the fluctuation of the composite frequency f0.

As is apparent from the equation (1), the amplitude of the interference light is determined by the product of the amplitude of the measurement light and the reference light. Therefore, the signal amplitude of the interference light can be increased by increasing the amplitude of the reference light.

The above is an embodiment in which the wavelength of the coherent light of the semiconductor laser 6 for explaining the principle is changed linearly with time.

Next, since it is difficult to change the wavelength of the coherent light linearly with time, a more preferred embodiment will be described below.

In this embodiment, the semiconductor laser 6 is pulse-driven, and the wavelength of the coherent light is changed nonlinearly with time.

In FIG. 4, reference numeral 52 denotes a clock circuit. The clock circuit 52 is controlled by the synchronization control circuit 33. The drive circuit 36 is controlled by the clock control circuit 52, outputs a rectangular pulse current (see (1) in FIG. 5), and drives the semiconductor laser 6. When the semiconductor laser 6 receives a rectangular signal and is turned on, oscillation starts and the chip temperature T rises as shown in (2) of FIG. When the chip temperature of the semiconductor laser 6 changes, the oscillation wavelength changes. The relationship between the temperature and the wavelength has a one-to-one correspondence at positions other than the mode hop position. The fluctuation of the oscillation output is very small compared to the change of the wavelength and can be ignored.

This temperature change is abrupt immediately after the start of oscillation and gradually converges. After a certain time, the semiconductor laser 6
Is turned off to return the temperature to the original state, and the irradiation of the coherent light is stopped. The width of the rectangular pulse is determined in consideration of the wavelength change width Δλ. For example, when the semiconductor laser 6 is pulse-driven at about 1 KHz, the main characteristic portion of the wavelength change with respect to the temperature change can be used, and the reproducibility is high.

A semiconductor laser 6 having a mode hop interval wider than the wavelength change width is used, and a reference temperature of the semiconductor laser 6 is set to a temperature control circuit 53 shown in FIG. 4 so that a mode hop does not occur in the wavelength modulation section. To control.

The wavelength change corresponds to the temperature change. Similarly, the wavelength change is not linear but changes greatly at the beginning, and the amount of change gradually decreases. Therefore, the frequency fba of the reference interference signal
se, interference signal frequencies f1, f2, beat frequency fb
Changes similarly. The beat signal S changes as shown in (3) of FIG.

Therefore, when the interference signal and the mixed signal are A / D-converted by using a trigger circuit having a constant frequency, the data is initially recorded as data whose frequency is high and whose frequency temporarily decreases.

Now, according to equation (8), there is a relationship of fb = fbase.Leye / Lbase.

This equation means that fb is a multiple of fbase if Leye and Lbase are constant within one wavelength change section tm.

Therefore, the reference interference signal of frequency fbase (see the waveform of (6) in FIG. 5) is sliced by a predetermined threshold value V of the trigger circuit 53 to generate a trigger signal shown in (7) of FIG. . This trigger signal is used as a conversion timing signal of the A / D converter 54. The trigger signal is input to the analog switch driving circuit 56 via the frequency divider 55. The analog switch driving circuit 56 is used for switching a cutoff frequency of a variable frequency low-pass filter 58 described later.

The variable frequency low-pass filter 58 forms a detection circuit 47 together with the square circuit 57. The frequency variable low-pass filter 58 is configured such that the beat frequency fb may be higher than the composite frequency f0 at the beginning and end of one wavelength change section tm, and the initial beat of one wavelength change section tm can pass. If at the end, the frequency f
This is because the mixed signal of 0 itself is transmitted, and detection cannot be performed reliably.

The cut-off frequency of the frequency variable filter 58 is changed in synchronization with the frequency change. As shown in FIG. 6, the frequency variable filter 58 is connected in parallel to a series body of resistors R1, R2,..., R6 having different resistance values and resistors R1, R2,. , R2,..., R6 are short-circuited, and a capacitor C is provided. The analog switch driving circuit 56 has a function of turning on and off the analog switches S1, S2,..., S6. Now, let the ratio of the resistance values R1 to R6 be 1, 2, 4, 8,
If it is set to 16 or 32 and has a 6-bit configuration, the cutoff frequency is fcut = constant × (1 / CR) where C
Is determined by the capacitance of the capacitor, and R is determined by the combined resistance value.

Therefore, the cutoff frequency is set to a high frequency initially, and as the frequency of the reference interference signal decreases,
Decrease cutoff frequency.

When only the resistance value corresponding to 1 is turned off, f
The maximum set value of cut can be set to “1”, and all analog switches can be turned off from “1” to change to 1/63, and as shown in FIG.
, The cutoff frequency can be changed as shown in FIG.

The signal passing through the detection circuit 47 (see the waveform (4) in FIG. 5) is input to the A / D converter 54.
The A / D converter 54 takes in data using the trigger signal shown in (7) of FIG. 5 as a timing signal. The generation interval of the trigger signal changes with the frequency change as shown in (7) of FIG. A / D conversion by the A / D converter 54
Since the frequency of the beat signal to be D-converted also changes in the same manner as the frequency of the reference interference signal, and the ratio is constant, the waveform stored in the waveform memory 49 through the A / D converter 54 is apparently equal. It becomes a periodic signal. Therefore, the waveform shown in FIG. 5 (5) is stored in the memory 49. When the number of data in one cycle of the obtained signal is measured, fb
case / fb.

Therefore, fb = fbase · Leye / L
From the expression of base, it is obtained as follows: Leye = Lbase / (the number of data in one cycle).

In the above embodiments, it has been discussed that the corneal reflected light passes only through the corneal measuring optical system 5 and the fundus reflected light goes back only through the fundus measuring optical system 4. However, there is a possibility that reflected light as shown below is mixed. One is that a part of the fundus reflected light by the fundus measuring optical system 4 is reflected by the cornea, and the reflected light near the optical axis is reflected by the cornea measuring optical system 5.
And reaches the light receiver 28 (hereinafter, this reflected light is denoted by a symbol R1).
). Further, a part of the corneal illumination light by the corneal measurement optical system 5 reaches the fundus and is reflected there, and is reflected there.
To reach the light receiver 19 (hereinafter, this reflected light is denoted by the symbol R
2). Further, a part of the fundus reflection light and the corneal reflection light return to the corneal measurement optical system 5 and the fundus measurement optical system 4 to reach the light receiver 28 and the light receiver 19, respectively (the reflected light returning to the light receiver 28 is referred to as R3, and the reflected light returning to the light receiver 19 is represented by R4). Of these, the combination of R1 and R3 and the combination of R2 and R4 overlap the regular reflected light and cause interference. At this time, if the phases of the corneal illumination light and the fundus illumination light can be matched at the apex of the cornea, the light receiver 28 has no phase difference between R1 and the regular corneal reflected light R5, and R3
And the regular corneal reflected light R5 has a phase difference of 2 Leye, while the light receiver 19 has R2 and the regular fundus reflected light R6.
Has no phase difference, and the phase difference between the regular fundus reflection light R6 and R4 is 2Leye. That is, the phase difference of the combination of the reflected light can be made only depending on the axial length of the eye, and when the signal is beaten, the signal becomes the beat signal of the frequency fb and after the equations (4) and (4) ′. The synthesized frequency f shown
It can be limited to a combination of a signal of 0 and a noise signal having the same frequency fb as the beat signal frequency (excluding electrical noise).

Therefore, the signal after detection is composed of signal components having the same period although the noise signal is slightly modulated. Therefore, when reflected light noise is mixed, the optical path length Lr0 from the beam splitter 3 to the beam splitter 10 and the optical path length Lc0 from the beam splitter 3 to the beam splitter 21 are made the same, and Lr '=
The optical system is configured so that Lc and L1 = L2. In this way, the axial length can be obtained by the same processing as when there is no noise.

Although the embodiment has been described above, the present invention is not limited to this, but includes the following.

(1) A polarizing beam splitter is used as the beam splitter 16, and a light beam incident on the beam splitter 4 is set to P-polarized light. Further, a λ / 2 plate is inserted into the optical path of the fundus optical system 4 immediately after the beam splitter 3 to make the polarization plane 90 °.
When rotated, the measurement light traveling toward the optical path of the cornea optical system 5 becomes P-polarized light, and the measurement light traveling toward the optical path of the fundus optical system 4 becomes S-polarized light. With such a configuration, the corneal reflection and the fundus reflection tend to preserve polarized light, so that the light amount loss due to the beam splitter 16 can be reduced. Furthermore, since the P-polarized light and the S-polarized light do not interfere with each other, even if the light reflected by the cornea and the light reflected by the fundus may enter each other's optical path, interference does not occur and optical noise is reduced. The optical path difference between Lr 'and Lc does not need to be completely zero, and can be corrected by further subtracting the optical path difference Ls from the measured value.

(2) When the polarized light is used as described above, the luminous fluxes incident on the light receivers 20 and 28 are relayed to one light receiver at the same time as P-polarized light (for the cornea) and S-polarized light (for the fundus). ). Since the P-polarized light and the S-polarized light do not interfere with each other, when the wavelength of the coherent light is changed, interference fringes based on the corneal reflected light and the corneal reference light,
Interference fringes based on the fundus reflection light and the fundus reference light independently change in intensity, and the sum of the intensity of the interference fringes is photoelectrically converted to output a beat signal.

(3) In the embodiment described above, light is condensed on the vertex M of the cornea and reflected light from the vertex M is used. However, when the surface of the cornea is viewed as a spherical surface, the reflected light from the cornea is restricted. There may be other points through 25. For example, it is the center of curvature of the corneal surface. That is, when the light is collected toward the center of curvature of the spherical surface, the reflected light travels in the same optical path as it is, so that the corneal reflected light can pass through the diaphragm 25 and interfere with the reference light. This means that the axial length can be measured at two positions with the same device. Further, in the case of the first embodiment, when the virtual image created by the fundus illumination light reflected on the corneal surface coincides with a position conjugate with the stop 25, the reflected light passes through the stop 25 and reaches the light receiver 28. I do. in this case,
If the optical system is configured as described at the end of the first embodiment, it is possible to measure the axial length even using the reflected light.

(4) In each of the embodiments described so far, the same optical system is used when irradiating the eye fundus or cornea with coherent light and receiving light reflected from the eye fundus or cornea. Had the configuration used for However, it is not always necessary to configure in this way, and the illumination optical system and the light receiving optical system may be separated. FIG. 9 shows an example of this optical system. The illustration of the reference interference optical system 2 is omitted.

In the optical system shown in FIG.
Is used in common for the fundus and the cornea. Here, refractive power correction lenses 83 and 84 are provided, and the coherent light is illuminated as a light flux that corrects the refractive power of the eye to be examined and converges on the fundus. A part of this is reflected as divergent light on the corneal surface, and the rest reaches the fundus to generate reflected light. Of these reflected lights, the portion that has passed through the light beam separating member 85 enters the reflected light receiving system, and is divided into a fundus light receiving system 4 and a cornea light receiving system 5. Then, the reference light is guided to both the light receiving system for the fundus and the light receiving system for the cornea from the middle of the illumination optical system, interferes with the fundus and the cornea, respectively, is received by the light receiving devices 20 and 28, and the output of the light receiving device is mixed to beat. All you have to do is get a signal. However, since the optical path difference and the like of the optical system are different from those in the previous embodiments, the calculation formula needs to be modified. The phase difference of the interference light received by the light receiver 20 is 2π (Li + 2Leye + Lr′−L1) / λ, whereas the phase difference of the interference light received by the light receiver 28 is 2π (Lj + Li + Lc−L2) / λ. Li is the optical path length from the center of the beam splitter 82 to the cornea, Lr 'is the optical path length from the cornea to the beam splitter 10, Lj is the optical path length from the beam splitter 81 to the beam splitter 82, and L1 and L2 are fundus reference light, respectively. The optical path lengths of the optical path 90 and the reference optical path 100 corresponding to the cornea are shown.

Here, if the optical system is configured such that Lr '= Lc and L1 = L2-Lj according to the same concept as before, the difference is 2Le.
y is required.

Note also that the reflections on the corneal surface appear to emerge from points that are neither at the corneal apex nor at the center of the corneal curvature. That is, when the stop 25 and the virtual image formed by the corneal reflected light have a conjugate relationship, the reflected light passes through the stop 25. However, in this case, since there is only one illumination light, R1 and R2 do not exist in the reflected light that becomes noise as described above.
It can be measured in the same manner as in the first embodiment.

[0088]

As described above, according to the present invention, since the signal amplitude is increased by the reference laser beam, the amount of light applied to the eye to be examined is reduced, that is, the reflected light from the fundus, Even if the light reflected from the cornea is weak, a signal having a high S / N ratio can be obtained, and accurate measurement of the axial length of the eye can be easily performed.

[Brief description of the drawings]

FIG. 1 is an optical arrangement diagram showing an embodiment of an eye axial length measuring apparatus according to the present invention.

2 is a signal processing circuit diagram for obtaining an axial length using the optical system shown in FIG. 1;

FIG. 3 is an explanatory diagram of a signal waveform of the signal processing circuit shown in FIG. 2;

FIG. 4 is a diagram showing another embodiment of the signal processing circuit.

FIG. 5 is an explanatory diagram of a signal waveform of the signal processing circuit of FIG. 4;

FIG. 6 is an explanatory diagram of a frequency low-pass filter.

FIG. 7 is a timing chart for explaining the operation of the frequency divider.

FIG. 8 is a graph showing a change in cutoff frequency.

FIG. 9 is an optical diagram showing a modification.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Measurement optical system 2 Reference interference optical system 3 Beam splitter 4 Fundus optics 5 Corneal optics 6 Semiconductor laser 9 Beam splitter 18 Fundus reference surface 26 Cornea reference surface 20, 28, 32 Photoreceiver 51 Arithmetic circuit 81 82 Reference light beam splitter 85 Illumination light reflected light splitting beam splitter 90 Fundus reference light path 100 Cornea reference light path 86, 101 Reflection mirror

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. 7 , DB name) A61B 3/10

Claims (7)

    (57) [Claims]
  1. A measuring optical system having a coherent light source for irradiating an eyeball with coherent light of a single wavelength and of which wavelength can be changed is divided by a beam splitter to irradiate the fundus with coherent light, and The retinal optical system includes a retinal optical system that receives reflected light from the fundus and a corneal optical system that irradiates the cornea with coherent light and receives the reflected light from the cornea. A fundus-corresponding reference surface for reflecting a portion and forming a fundus-corresponding reflected reference light; a cornea for reflecting a part of the coherent light in the cornea optical system to form a cornea-corresponding reflected reference light; A corresponding reference surface is provided, the fundus optics has a light receiver for receiving interference light based on the fundus oculi reflected light and the fundus occupancy reference light, and the corneal optics includes a corneal reflected light and a corneal corresponding reference light. A light receiver for receiving the interference light, and further, while changing the wavelength of the coherent light, the interference signal from each light receiver is input to the mixer to form a beat signal, and an eye is formed based on the frequency of the beat signal. An eye axial length measuring device comprising an arithmetic unit for calculating an axial length.
  2. 2. A measuring optical system having a coherent light source for irradiating a coherent light having a single wavelength and a variable wavelength is divided into light beams having different polarization components by a beam splitter as a boundary. A retinal optical system that irradiates coherent light of a polarized light component and receives reflected light from the fundus, and a corneal optical system that irradiates the cornea with coherent light of another polarized light component and receives reflected light from the cornea The fundus optical system is provided with a fundus-corresponding reference surface for reflecting a part of the coherent light and forming a fundus-corresponding reflected reference light, and the cornea optical system is provided with a part of the coherent light. And a cornea-corresponding reference surface for forming a cornea-corresponding reflected reference light is provided. The measuring optical system receives interference light based on the fundus-reflected light and the fundus-corresponding reference light, Has a light receiver also receiving simultaneously an interference light based on the light and the cornea corresponding reference beam, and further outputs a beat signal from the photodetection unit while changing the wavelength of the coherent light, the eye based on the frequency of the beat signal An eye axial length measuring device comprising an arithmetic unit for calculating an axial length.
  3. 3. An illumination optical system having a coherent light source for irradiating a coherent light beam having a single wavelength and a wavelength changeable to an eye of an eye to be inspected, and a measurement optical system for receiving reflected light from the eye to be inspected. The measurement optical system further includes a fundus optical system that receives fundus reflected light and a corneal optical system that receives corneal reflected light, and the illumination optical system guides the fundus corresponding reference light to the fundus optical system. An optical optical system and a corneal reference light optical system for guiding a corneal reflection corresponding reference light to the corneal optical system, wherein the fundus optical system receives an interference light based on the fundus corresponding reference light and the fundus reflection light. Device, the corneal optical system includes a light receiver that receives interference light based on the corneal reference light and the corneal reflected light, and further changes the interference signal from each light receiver while changing the wavelength of the coherent light. Enter into the mixer and bee Forming a signal, the peripheral of the beat signal
    An axial length measuring apparatus, comprising: an arithmetic unit for calculating an axial length based on a wave number .
  4. Wherein said coherent light source, ocular axial length according to any one of claims 1 to 3, characterized in that it is configured to vary linearly with its wavelength against time measuring device.
  5. 5. An optical system having a coherent light source for irradiating coherent light having a single wavelength and a wavelength change, comprising: a reference interference optical system in which a reference optical path difference is formed longer than an axial length; A measurement optical system for irradiating coherent light toward the fundus, wherein the measurement optical system is divided by a beam splitter to irradiate the fundus with coherent light and receive reflected light from the fundus, and the fundus optical system And a cornea optical system that irradiates the cornea with coherent light and receives reflected light from the cornea.The fundus optical system reflects a part of the coherent light to form a fundus-corresponding reflected reference light. A corneal-corresponding reference surface for reflecting a part of the coherent light and forming a corneal-corresponding reflected reference light in the corneal optical system; The optical system has a light receiver that receives interference light based on the fundus reflection light and the fundus reference light, and the corneal optical system includes a light receiver that receives interference light based on the corneal reflection light and the corneal reference light. A beat signal is formed by inputting an interference signal from each light receiver to the mixer while changing the wavelength of the coherent light, and the reference interference optical system receives the reference interference light and outputs a reference interference signal An optical axis length measuring apparatus, further comprising: a light receiving device for calculating an axial length based on a ratio of a frequency of the beat signal to a frequency of the reference interference signal.
  6. Coherent light source wherein the measuring optical system, <br/> claim 5, characterized in that it is configured to be controlled so as not to change linearly with respect to the wavelength time Eye length measurement device.
  7. Coherent light source according to claim 7, wherein said measuring optical system, according to claim 1 請, characterized in that selected ones wide mode hopping interval than the wavelength change width for changing the wavelength
    The eye axial length measuring device according to any one of claims 6 to 13 .
JP03082657A 1991-04-15 1991-04-15 Eye axis length measuring device Expired - Fee Related JP3118270B2 (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
JP03082657A JP3118270B2 (en) 1991-04-15 1991-04-15 Eye axis length measuring device

Applications Claiming Priority (4)

Application Number Priority Date Filing Date Title
JP03082657A JP3118270B2 (en) 1991-04-15 1991-04-15 Eye axis length measuring device
EP19920401042 EP0509903B1 (en) 1991-04-15 1992-04-14 Process and apparatus for measuring axial eye length
DE1992613806 DE69213806T2 (en) 1991-04-15 1992-04-14 Method and device for determining the axial length of the eye
US07/868,565 US5347327A (en) 1991-04-15 1992-04-15 Process and apparatus for measuring axial eye length

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JPH04314419A JPH04314419A (en) 1992-11-05
JP3118270B2 true JP3118270B2 (en) 2000-12-18

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JP5249073B2 (en) * 2009-02-12 2013-07-31 株式会社ニデック Optical interference type distance measuring device
EP3097382A2 (en) * 2014-01-21 2016-11-30 Santec Corporation Optical coherence tomography system with multiple sample paths
JP6306374B2 (en) * 2014-03-04 2018-04-04 株式会社トーメーコーポレーション Wavelength swept light source device and measuring device

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