JPH0438404A - Length measuring apparatus - Google Patents

Abstract

PURPOSE:To obtain a distance to an object to be measured by performing calculation based on a distance of a reference interference light path and a periodic wave signal which is obtained by a periodic wave signal forming unit. CONSTITUTION:A ring-like light source projection unit 102 projects illumination light to an eye to be inspected. A ring-like virtual image 121 is formed on a cornea 120 of the eye 103 to be inspected. Reflected light by the cornea 120 is led to a half mirror 114 via an objective lens 104 and a dichroic mirror 115 and split into a first light path 105 and a second light path 106. A laser diode 130 is controlled by a laser driving unit 152. A signal processing circuit 149 has a trigger circuit 153, which is synchronously controlled by the laser driving unit 152. The signal processing circuit 149 has a trigger circuit 153, which is synchronously controlled by the laser driving unit 152. The signal processing circuit 149 samples an interference signal of a photo sensor 142 based on an interference signal of a photo sensor 146 to form a periodic wave signal. An arithmetic circuit 156 calculates a distance to an object to be measured based on a difference in light paths of a reference interference light path and the periodic wave signal.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a length measuring device, and in particular, the corneal apex position is determined using an optical system using the geometrical optics principle, and the fundus position is determined using the physical optics principle. The present invention relates to a length measuring device suitable for measuring the axial length from the fundus of the eye to the vertex of the cornea by using an interference optical system as an optical system that utilizes.

(Prior art) Conventionally, the eye to be examined is irradiated with a light beam from a laser diode LD, a plane wave reflected from the fundus of the eye and a spherical wave reflected from the cornea are interfered with, and the interference signal is used to create a signal between the fundus of the eye and the cornea. A length measuring device, for example, an axial length measuring device, that measures the distance (ocular axial length) of the eye is known.

(Problem to be Solved by the Invention) However, in this conventional length measuring device, when the plane wave reflected from the fundus of the eye and the spherical wave reflected from the cornea are caused to interfere, the alignment of the measuring device with respect to the eye to be examined is difficult. This is a fatal drawback especially when measuring constantly moving eyeballs, which require precision. Also,
If there is even a slight misalignment of the measurement device with respect to the eye being examined, the position of the interference fringes will shift significantly, and the number of interference fringes will rapidly increase in the area that was previously observed, making it difficult to determine whether interference is occurring. Met.

(Means for Solving the Problems) The present invention has been made in view of the above circumstances, and the length measuring device according to claim 1 has a configuration that has a long coherence distance and can change wavelength. a laser light source that emits a laser beam; a measurement interference optical path that causes interference between the laser beam reflected by the object to be measured and the laser beam reflected by the reference surface corresponding to the object to be measured; and a measurement interference optical path having an optical path length longer than the measurement interference optical path. A reference interference optical path is formed in which the laser beam reflected by the reference object and the laser beam reflected by the reference surface corresponding to the reference object interfere with each other, and the laser beam from the laser light source is brought into contact with the measurement interference optical path and the reference interference optical path. a beam splitter that guides the light to the optical path; a first light receiving section that receives the light guided as interference light via the measurement interference optical path; and a first light receiving section that receives the light guided as interference light via the reference interference optical path. a second light receiving section, a laser driving section that changes the emission wavelength of the laser light source, and sampling the output signal of the first light receiving section using the output signal of the second light receiving section as a timing signal to generate a periodic wave signal. A periodic wave signal forming section for forming a periodic wave signal; and a calculation section for calculating a distance to a measurement target based on the optical path length of the reference interference optical path and the period of the periodic wave signal.

The invention according to claim 3 of the present invention includes: a laser light source that emits a laser beam having a long coherence distance and a variable wavelength; a laser beam reflected by the fundus of the eye to be examined; and a laser beam reflected by the fundus-corresponding reference surface. a measurement interference optical path that causes light to interfere with each other; and a reference interference optical path that has a longer optical path length than the measurement interference optical path and causes the laser beam reflected by the reference object to interfere with the laser beam reflected by the reference surface corresponding to the reference object. and a beam splitter that guides the laser light from the laser light source to the measurement interference optical path and the reference interference optical path; and a first light receiver that receives the light guided as interference light via the measurement interference optical path. a second light receiving section that receives the light guided as interference light via the reference interference optical path; a laser driving section that changes the emission wavelength of the laser light source; and an output signal of the second light receiving section. a periodic wave signal forming section that samples the output signal of the first light receiving section using as a timing signal and forms a periodic wave signal; an irradiation optical system that irradiates the cornea of the eye to be examined with a light beam; a light receiving optical system that guides reflected light from the cornea to a third light receiving section; and an output of the third light receiving section. and a corneal position measurement unit that determines the corneal position of the eye to be examined based on the above, and measures the axial length of the eye to be examined.

(Function) According to the length measuring device according to claim 1 of the present invention, if calculation is performed based on the distance of the reference interference optical path and the periodic wave signal obtained by the periodic wave signal forming section, the distance to the object to be measured can be calculated. You can find the distance.

According to the length measuring device according to claim 3 of the present invention, the corneal apex position is measured using the irradiation optical system and the light receiving optical system that utilize the principle of geometric optics, and the position of the fundus of the eye is measured using the principle of physical optics. The axial length of the eye is determined using an interference optical system.

(Example 1) FIG. 1 shows an example of a corneal distance measuring system in which a ring image is projected onto the cornea to determine the corneal apex position.

In FIG. 1, 100 is a corneal distance measurement system, 101 is an interference optical system, 102 is a ring-shaped light source projection unit as an irradiation optical system that irradiates the cornea of the eye to be examined, 103 is the eye to be examined;
04 is an objective lens. The corneal distance measuring system 100 is a first
It has an optical path 105 and a second optical path 106. 1st optical path 1
05 is a two-dimensional image sensor 107 as a third light receiving section
, imaging lens 108, half mirror 109, aperture 110
, lens 111, total reflection mirror 112) lens 11
3. Half mirror 114, dichroic mirror 115
, and an objective lens 104. The second optical path 106 includes a lens 117, total reflection mirrors 116, 118 .
119 and an aperture 124.

The ring-shaped light source projection unit 102 consists of a ring-shaped light source and a pattern plate (not shown), and here projects illumination light such that the meridional cross-section rays are parallel to the subject's eye. Radiant illumination light may also be projected. When this illumination light is irradiated toward the eye 103 to be examined, a ring-shaped virtual image 121 is formed on the cornea 120 of the eye 103 to be examined. Here, the wavelength of the illumination light from the ring-shaped light source projection unit 102 is 900 nm to 11000 nm. The dichroic ink mirror 115 transmits the illumination light and reflects the laser light, which will be described later.

The light reflected by the cornea 120 is guided to the half mirror 114 via the objective lens 104 and the dichroic ink mirror 115, and is branched into a first optical path 105 and a second optical path 106. The reflected light guided to the first optical path 105 is once imaged as a ring-shaped aerial image 122 based on the lens 113, and further includes a total reflection mirror 112), a lens 111, an aperture 110,
A ring image i2 is sent to the two-dimensional image sensor 107 via the half mirror 109 and the imaging lens 108 (see Figure 2).
imaged as. Note that the imaging magnification of this ring image 12 is assumed to be 0.5 times here. The reflected light guided to the second optical path 106 is reflected by a total reflection mirror 119, and is once formed into an aerial image 123 based on the objective lens 104.
16, aperture 124, half mirror 109, imaging lens 1
08, the ring image 11 is formed on the two-dimensional image sensor 107. Note that the imaging magnification of this ring image 11 is set larger than that of the ring image 12.

The aperture 110 serves as a second aperture, and is relayed to the rear focal position of the objective lens 104 by the lens 111 and lens 113, and a conjugate image 125 is formed at the rear focal position of the objective lens 104, and the first optical path 105 The optical system of is physically telecentric. The aperture 124 is
It plays the role of a first aperture, and is relayed to the front of the eye 103 to be examined (in front of the objective lens 104) by the lens 117. Here, a conjugate image (real image) 126 is formed at a location 25 mm to 50 mm in front of the eye to be examined. Ru.

Here, the relationship between the objective lens 104 and the aperture 110, 124 will be explained with reference to FIGS. 3 and 4, which schematically show the relationship. Now, the optical axis O where the conjugate image 126 of the aperture 124 is formed
The above position is defined as the origin G, and a reference position Y is determined at a distance L1 from the origin G in the optical axis direction. This reference position Y is determined to such an extent that the ring images L+, i2 are not out of focus. Then, an object having a height h (corresponding to the radius of the ring image i) is placed at this reference position Y. At this time, the observation surface 127 (two-dimensional image sensor 1
The image height formed at the position 07) is yl, and the first optical path 105
Let the image height formed on the observation surface 127 be y2.

Next, this known object is moved by a distance Xs, and the image height at this time is set to Yl'y2'. Also, the distance from the observation surface 127 to the point Z is L+', and the distance from the reference position Y to the point Z' is L2) From the aperture 110 to the observation surface 12
Let the distance to 7 be L2', and further, let the angular magnification be β1
, β2.

Then, the following formula is obtained.

h / L 1= y +・β+ / L + '
■h / (L + 10Xs)
= (V 1 ・β+)/L+' ■h/L
2= Y 2/ (β2・L2') ■
h/ (L2+X@)-'-y2'/(β2・L2
′) In formula ■■, formula ■, angular magnification β1, distance L1, Ll
Assuming that is a constant, and setting K1=(β1·L+)/L+ K 2 =β1/L1, equations (1) and (2) can be transformed into the following equations.

h=ni+-yl ■h
= K +・y1′ 2・y1′ ・Xll
■Also, in formulas ■ and formulas, angular magnification β2) distance L
2) Assuming that L2' is a constant and setting K3=L2/ (L2' ・β2) K4=1/ (L2' ・β2), the equations (1) and (2) are transformed into the following equations.

h = K3・y2
■h = K 3°y2'+ to 4°y2' °X@
■Here, the constant is 1, Ka, Ka, K4 are
It can be determined by actually measuring the object height h1 and the image height y.

That is, by transforming the equation (2), 0, the following equation can be obtained.

K + = h / y +
■2=(h/y+)・(yl-y+'
)/(y+'・X[ri[phase]K3=h/y
2 ■K a =
(h/y2)・(y2-y2')/(y2
' ・XII) @Therefore, by actually measuring the object height and the image height of a known object, we can set the constants to 1, Ka, and K.
a, K4 is found.

Next, a description will be given of measurement when the image height h and the distance X from the reference position Y are unknown.

In this case, distance X is used instead of distance X2 in equations (1) and (2). Also, y, r y2' is y2) y2
Replace with

Then, the following formula is obtained.

h = K +・y H+ K 2・yl・X
■h, = K3・y2+K a・y2・
X ■The above simultaneous equations, distance X1
Solving for the object height is X − (K 3・y2−K ,・yl)/(Ka・yl
− to 4・y2) ■ h=to 1・y1+ to 2・yl・X = (Ka・Ka−Kl・Kj)yl・y2 / (Ka
・yl Ka・y2)■ Therefore, by measuring the image height yI, 3'2, it is possible to measure the distance from the reference position Y to the object.

Next, the measurement of the corneal curvature radius R and its apex position will be explained with reference to FIG. 5.

In FIG. 5, the radius of the ring image i (the major axis or minor axis of the ellipse when approximated to an ellipse) is the object height. At this time,
The object height is determined by the meridional ray. Assuming that the diameter of the ring image is approximately 3 mm, the angle φ is 20
'', and the paraxial calculation formula described below cannot be used.

b”(R-sinφ)/2 Therefore, the distance L2 should be set sufficiently large so that the angle φ is always constant, and the height measured in the second optical path 106 passing through the aperture 124 should be used as the object height. For example, the following formula based on the reflection law can be used.

h=R-sin(φ/2) If the above formula is modified, R=h/5in(φ/2) [Phase] As long as the angle between the rays passing through the aperture 110 and the rays passing through the aperture 124 does not become large. If the distance L1 is set, it is thought that there will be no large error even if the object height obtained by the 0 formula is used in the above [phase] formula, so the position of the corneal vertex 120P is set as the distance PM from the reference position Y, Px=X −
(R-h/lanφ) ■This formula 0 for calculating the corneal apex position assumes that the ring image is on the optical axis of the spherical surface, so it is affected by spherical aberration, but the amount is not so large. This is unlikely, and it is possible to correct it based on experimental values. In FIG. 5, ○' is the center of corneal curvature, AI is the normal line, A2 is the spherical optical axis when the cornea 120 is regarded as a spherical surface, and A3 is the incident light ray on the cornea 120.

Next, the interference optical system will be explained with reference to FIGS. 1 and 6.

The interference optical system 101 includes a laser diode 130 as a laser light source, a collimating lens 131, a beam splitter 132) lens 133, a pinhole plate 134, a beam splitter 135, a collimating lens 136, a focusing lens 137, a collimating lens 138, and a reference mirror 1.
39, pinhole plate 140, lens 141, photodiode 142) beam splitter 143, reference mirror 14
4, a reference mirror 145 and a photodiode 146. The laser diode 130 has a long coherence length and is capable of changing wavelength (for example, a single mode diode). The laser light emitted from the laser diode 130 is made into a parallel beam by a collimating lens 131 and guided to a beam splitter 132.

The beam splitter 132 directs the parallel laser beam to the lens 13.
It has a function of dividing the light beam toward the mirror 143 and the light beam toward the half mirror 143.

Half mirror 143 is standard mirror 144, reference mirror 1
Together with 45, it constitutes a Twyman type reference interference optical path 147. Here, the distance from the point Q1 of the half mirror 143 to the point Q2 of the reference mirror 144 is Dl, and the point Q1
Let the distance from Q3 to the reference mirror be D2, and DI
D2=D is defined as a reference optical path length. Reference mirror 144
serves as a reference object and the reference mirror 145
serves as a reference surface corresponding to a reference object, and the reflected laser beams reflected by each mirror 144 and 145 are combined by a beam splitter 143 and transmitted as interference light to a photosensor 146 as a second light receiving section via a beam splitter 132. guided by. The photosensor 146 outputs an interference signal based on the interference light, and the interference signal increases by 1!111
4g to the signal processing circuit 149. The configuration of this signal processing circuit 149 will be described later.

The parallel laser beam that has passed through the half mirror 132 is focused onto a pinhole plate 134 by a lens 133.

The pinhole plate 134 serves as a single point light source.

The laser beam that has passed through the pinhole plate 134 is guided to a beam splitter 135 as a measurement light beam. The beam splitter 135 has the function of splitting the measurement light flux, guiding a portion to a collimating lens 136 and guiding the remainder to a collimating lens 138.

The measurement light flux guided to the collimating lens 138 is made into a parallel light flux, reflected by the reference mirror 139, and returned to the beam splitter. The measurement light beam having a guiding force λ is guided to the collimating lens 136, and is guided to the focusing lens 137, passes through the dichroic mirror 115 and the objective lens 104, is guided to the eye 103 as a parallel light beam, and is converged on the fundus 160. The reflected light flux from the fundus 160 follows the same optical path, returns to the beam splitter 135 again, is combined with the reflected light flux from the reference mirror 139, and is guided to the aperture 140.

The diaphragm 140 is arranged at a conjugate position with the fundus 160, and the cornea 1
The aperture 140 serves to remove the light reflected from the lens 20 and the light reflected from the crystalline lens.The aperture 140 is also conjugate with the aperture 134, so even if the alignment of the length measuring device with respect to the eye to be examined is slightly misaligned, measurement can be performed without any problem. It is possible.

The light beam that has passed through the aperture 140 is transmitted through the lens 141.
The light beam is converted into an interference parallel light beam, and guided to a photosensor 142 as a first light receiving section. The photosensor 142 outputs an interference signal based on the interference light beam. The interference signal is input to the signal processing circuit 149 via the amplifier 15[1. Here, the beam splitter 135 and the collimating lens 13
6. Focusing lens 137, dichroic mirror 1151
The objective lens 104, the collimating lens 138, and the reference mirror 139 combine the reflected light flux from the fundus 160 as the measurement object and the reference mirror 13 as a reference surface corresponding to the measurement object.
A measurement interference optical path 151 is configured in which the reflected light beam from 9 interferes with each other.

Here, the distance from the point Q4 of the beam splitter 135 to the point Q5 of the reference mirror 139 is expressed as , and the optical axis distance from the point Q4 to the fundus 160 is expressed as Lt. At this time, the reference mirror 139 is virtually positioned on the optical axis ○.
39', it can be considered that the reflected light from this reference mirror 139' and the reflected light from the fundus 160 interfered, and L+L- is the difference between the reference mirror 139' and the reflected light from the fundus 160.
This is the air-equivalent optical path difference up to 9'.

Next, the principle of measurement from the measuring device to the fundus will be explained.

When the wavelength λ of the laser diode 130 is changed, the intensity of the interference light incident on the photodiode 146 is determined by the optical path difference 2 (DI D2) between the reflected light reflected by the reference mirror 144 and the reflected light reflected by the reference mirror 145. The intensity of the interference fringes formed on the photodiode 142 is determined by the phase difference corresponding to the optical path difference 2 between the reflected light reflected by the reference mirror 139 and the reflected light reflected by the fundus 160.
It is determined by the phase difference corresponding to (LiL-). If the wavelength of the laser light emitted from the laser diode 130 is constant, the intensity of the interference fringes of the photodiodes 142 and 146 exhibits a constant value.

Two points are the virtual reference mirror 139' and the corneal apex 120.
Assuming that the distance from P on the optical axis ○ is Px as shown in Fig. 7, this Px can be calculated using the corneal distance detection system.
It can be obtained by detecting 0P. This is because if the distance from the reference position Y to the corneal apex position 120P is measured, the distance from the reference position Y to the corneal apex position 120P is measured, and the distance between the reference position Y and the virtual reference mirror 1 is measured.
This is because the relationship with 39' can be determined in advance by design.

Therefore, if Lt-Lr can be obtained, the air-equivalent axial length AL can be obtained, where the average refractive index is nA, and AL=(Lt Lr Px)/n.

It can be found as

Lt-Lr can be obtained by performing measurements based on the principle described below.

The wavelength of the laser light is assumed to be λ, and the wavelength λ of this laser light is changed by a laser driving section which will be described later. If the amount of wavelength change is Δλ, then the photosensor 14 of the reference interference optical path
The phase difference of the laser beam before the wavelength change at 6 is 2π・
2(DI-D2)/λ. The phase difference after changing the wavelength by Δλ is 2π・2 (DI D2) / (λ+
Δλ).

Therefore, if the wavelength is changed by Δλ, the phase difference will be 2π/λ
It will change by 2π·2 (DI-D2) / (λ + Δλ) from . Here, if the wavelength change amount Δλ is extremely small with respect to the wavelength λ, the phase difference after the wavelength change is 2π・2 (DI D2) by series expansion.
・It can be approximated as (1/λ−Δλ/λ2), and the amount of change in the phase difference is 2π・2 (DI D2)・Δλ/λ2.

Similarly, the amount of change in the phase difference at the photosensor 142 in the measurement interference optical path 151 is 2π·2 (Lt L,)·Δλ/λ2.

Now, if the change in phase difference in the photosensor 142 is vl, and the change in phase difference in the photosensor 146 is v2, 'F+=4 π (DI D2) · Δ2. /
λ2 (1)v2=4π (Lt L-)
・Δλ/12 (2), and by eliminating Δλ/λ2 from the above equation, L i L
It can be expressed as −= v+ / v2. (3) This formula can be used to calculate the distance from the virtual reference plane 139' to the fundus 160 (Lt L
−) means that it can be measured.

Here, assuming that the wavelength change Δλ is continuous, a general interference equation will be considered.

The general interference equation is: I=I++lz+2 (I+・12)l/2・CO8δ
It is expressed as (4).

Here, ■ is the intensity of the interference light on the photodiode 142.14S,
δ is the phase difference between the light beams that interfere with each other; for example, δ is 4π(DI D2)(1/λ−Δλ/λ2).

Focusing on equation (4), when the wavelength λ is continuously changed, the value of the third term in equation (4) changes periodically every time the phase difference δ changes by 2π, so the intensity of the interference fringe It can be seen that ■ changes periodically.

Here, the number of cycles of intensity change is the value obtained by dividing the change in phase difference by 2π, and vl/v2 obtained from equation (3) is the ratio of the number of cycles of intensity change of the interference fringes obtained by the photosensors 142 and 146. It shows. Therefore, photosensor 1
4! , 146 shows the ratio of the number of periods of intensity change of the interference fringes obtained by .

Therefore, if the number of cycles of intensity change of the interference fringes obtained by the photosensors 142 and 146 is measured, (Lt L=)
is calculated, and the distance to the fundus is calculated as described above.

In other words, the change in the intensity of the interference fringes due to the change in wavelength can also be seen as a change in the phase of the interference fringes themselves at specific locations on the photosensors 142 and 146.

Next, wavelength modulation of a laser diode will be explained.

By the way, the eyeball of the subject's eye 103 is expanding and contracting due to pulsation. That is, the eyeball repeats expansion and contraction 60 to 80 times per minute, and the amount of variation is about 3 μm. Therefore, when converted to the number of interference fringes, it is approximately 8 degrees per pulsation, and the movement of approximately 16 interference fringes back and forth is observed, so if one period of pulsation is 80 times/60 seconds = 1°33 Hz, then 21
．． The output of the interference fringes changes at a cycle of 33 Hz.

Therefore, a method was adopted in which the laser diode 130 was subjected to high-speed wavelength modulation to perform measurements at sufficiently short intervals compared to the pulsation period.

The laser diode 130 is controlled by a laser driver 152, as shown in FIGS. 6 and 8.

The second laser driving section 152 outputs a pulse current shown in FIG. 9(a) toward the laser diode 130. The temperature of the laser diode 130 changes (increases) due to this pulsed current, and a temperature change curve T shown in FIG. 9(b) is drawn. This temperature change requires about several milliseconds to stabilize.

The laser diode 130 changes temperature and emission wavelength,
Used in areas where there is a one-to-one correspondence. However, since temperature changes are nonlinear with respect to time, the emission wavelength also changes nonlinearly. Therefore, the photosensor 14
The phase change of the interference fringes received at 2.146 is also affected by the nonlinearity of this temperature change.

That is, as shown in FIG. 9(c), the photodiode 1
The interference waveform Cs of the interference signal outputted from 42 has a short period in the early stage when the temperature rise change is rapid, and has a long period in the latter stage when the temperature change is gradual. Photodiode 1
The same applies to the interference waveform C1 of the interference signal output from 46. Here, the reason why the frequency of the interference waveform CI is higher than the frequency of the interference waveform C@ is that the optical path difference (DID2) in the reference interference optical path 147 is the optical path difference (L
This is because it is designed to be sufficiently larger than tL=). Here, the reference optical path difference (DI D2) is (Lt
L,) is set to approximately 6 times. Note that when designing the reference interference optical path 147, an optical fiber can be used to extend its optical distance.

The reference interference optical path 147 and the measurement interference optical path 151 are split from the same laser beam by the beam splitter 132, so the wavelength change of the laser beam is the same.

Therefore, the ratio of the period of the interference signal of the photodiode 142 and the period of the interference signal of the photodiode 146 is the ratio of the measurement optical path difference, t-L, ) to the reference optical path difference (DI D2), (DI D2)/( Lt-L-). Let this ratio be K.

In order to obtain this ratio K, the signal processing circuit 149 is configured to sample the interference signal of the photosensor 142 based on the interference signal of the photosensor 146.

That is, the signal processing circuit 149 is connected to the trigger circuit 153.
have. This trigger circuit 153 is synchronously controlled by the laser drive section 152, and slices the interference waveform C1 at the slice level ■ shown in FIG. It has a function of generating a timing clock signal C2. The interference signal from the photodiode 142 is input to the A/D converter 154 of the signal processing circuit 149. A/D converter 154
Based on the timing clock signal C2 of the trigger circuit 153, the output value of the interference waveform Ca is A/D converted and outputted to the memory 155.

This makes it possible to know how many samples the interference waveform C@ makes up one cycle. In other words, it is possible to know which period of the photodiode 142 corresponds to one period of the photodiode 146. 9th
FIG. 5(f) is a diagram showing the interference waveform C11 at equal intervals using the sampling values stored in the memory 155. Therefore, the signal processing circuit 149 functions as a periodic wave signal forming section that samples the output signal of the first light receiving section and forms a periodic wave signal using the output signal of the second light receiving section as a timing signal.

In double mode, one period is composed of six sampling values, so K=6. Therefore, this K is calculated by the calculation circuit 1
56, and the formula of K= (Lt L-)/(DI D2) was transformed into (Lt L=) = (DI D2)/K
If you calculate , (DI D2) is known, so
(Li Lr) can be obtained. Therefore, the calculation circuit 156 functions as a calculation unit that calculates the distance to the measurement target based on the optical path difference of the reference interference optical path and the periodic wave signal, and also functions as a fundus position measurement unit when determining the axial length. It will work.

Note that the ratio is generally a fraction. In this case, data for one period of the interference signal of the photodiode 142 may be obtained by, for example, interpolation, and the number of periods of the interference signal of the photodiode 146 included in one period of the interference signal of the photodiode 142 may be obtained.

Although the first embodiment has been described above, the interference optical system 10
If an ND filter is provided at an appropriate location in 1 to adjust the light amount, the interference signal in the measurement interference optical path 151 can be appropriately extracted.

According to this IJ/I11 embodiment, since the position of the corneal apex is measured using a double ring image, it is possible to originally measure the radius of curvature of the cornea as shown in equation 0, and therefore, it is possible to measure the corneal shape. It has the advantage of being able to be used as a device (kerato device).

(Embodiment 2) FIG. 10 shows an optical system for determining the corneal vertex position using an alignment optical system as a corneal distance measuring system.

In FIG. 10, an alignment optical system 200 consists of a first optical system 201 and a second optical system 202. 1st
The optical system 201 and the second optical system 202 are symmetrical with respect to the optical axis 01. An objective lens 203, a mirror 204, and an imaging lens 205 are provided on the optical axis 01. The objective lens 203 and the imaging lens 205 are used when observing the anterior segment of the eye 103 to be examined. Mirror 204 is a half mirror.
Or a bandpass mirror is used, and mirror 204 is the first
It has the function of reflecting laser light during measurement using the interference optical system shown in Figure 1. The configuration of this interference optical system will be described later.

The first optical system 201 includes a point light source 206 as an irradiation optical system;
The second optical system 202 has a half mirror 207 and a lens 208, and the zero point light source 206 has a point light source 209 as an irradiation optical system, a half mirror 210, and a lens 211. A point light source 209 is placed at the focal point of a lens 211 via a half mirror 210. Point light source 206
The light from the point light source 209 is projected onto the cornea 120 of the subject's eye 103 as a parallel light beam by the lens 208, and the light from the point light source 209 is projected onto the cornea 120 by the lens 211 as a parallel light beam.

The parallel light beam from the lens 211 is reflected by the surface of the cornea 120, and the reflected light beam passes through the lens 208 and the half mirror 207, is guided to the total reflection mirror 212, and is reflected by the total reflection mirror 212. On the other hand, the parallel light beam from the lens 208 is reflected by the surface of the cornea 1200 as diverging light from the focal position of the cornea, and the reflected light beam passes through the lens 211 and the half mirror 210 and is guided to the total reflection mirror 213. It is reflected by mirror 213. This corneal specular reflection Nijotte angle ll1
120 niha, point 1 [bright spot image 21 based on 206, 209 niha
4.215 is formed.

A physically telecentric aperture 216 is installed in front of the total reflection mirror 212 in the reflection direction, and the total reflection mirror 213
In front of the reflection direction is a physically telecentric aperture 21.
7 is installed, and the telecentric aperture 216.217 is located at the back focus of the lens 208.211.

Here, a lens 208, a total reflection mirror 212) an aperture 21
6 (lens 211, total reflection mirror 213, aperture 217)
constitutes a light receiving optical system. Total reflection mirror 212.2
The reflected light reflected by 13 passes through apertures 216 and 217 and is guided to lenses 218 and 219, respectively. The aperture 216.217 is conjugate with the image sensor 221 for each lens 218.219, and the aperture 216.217
is at the focal point of each lens 218,219. Lens 218. 219 is telecentrically installed on the image side, and the reflected light guided by lenses 218 and 219 is imaged on a two-dimensional image sensor 221 as a third light receiving section.

According to this alignment optical system 200, as shown in FIG. Alignment optical system 20 when the angle θ1 with the principal ray does not deviate from the working distance
0 and the principal ray, and the optical axis 01 of the alignment optical system 200 on the image side
The angle θ2 between the principal ray and the optical axis o1 of the alignment optical system 200 is equal to the angle θ2 between the principal ray and the optical axis o1 of the alignment optical system 200 when the working distances are not shifted.

In addition, the two-dimensional image sensor 221 has each point light #120.
6. Bright spot images i, l i21 based on 209 are the 14th
As shown in the figure, it is formed by splitting at symmetrical positions with respect to the center 02. On the other hand, although the working distance coincides with the corneal vertex 120P, if the alignment of the measuring device deviates in the left-right direction with respect to the eye 103 to be examined, as shown in FIG. The angle θ1 between the optical axis 01 and the principal ray of the alignment optical system 200 is equal to the angle θ1 between the optical axis 01 of the alignment optical system 200 and the principal ray when the working distance is not shifted, and the alignment optical system 200 on the image side The angle θ2 between the optical axis O1 and the principal ray of the alignment optical system 200 is equal to the angle θ2 between the optical axis 01 of the alignment optical system 200 and the principal ray when the working distances are not shifted.In this case, the bright spot image 11. 12 is not separated, but the position of the two-dimensional image sensor 221 from the origin 02 is shifted.

Here, the focal length of the lens 208 is f+, and the lens 218
The focal length of the lens is assumed to be f2, and the aperture 216 is considered as a reference. In Fig. 12, when the working distance shifts by ΔZ, the position of the chief ray changes by Δ compared to when the working distance does not shift.
It deviates by Z-sin θ1.

Furthermore, since the optical system formed by the lens 208, the aperture 216, and the lens 218 is telecentric on the physical and image side as shown in FIG.
and the distance ΔX from the center 02 to the bright spot i, l, or 12' on the two-dimensional image sensor 221 are in a proportional relationship.

Therefore, if the magnification of this optical system is β, then ΔZsinθ
There is a relationship of 1=β·ΔXcosθ2.

Here β=□ Therefore, the working distance deviation ΔZ is f + sinθ1 It is expressed as

Note that when the bright spot image 11 is on the right side of the bright spot image 12, Δ
If X is positive and vice versa, ΔX is determined to be negative.

By the way, since the bright spot images i1'i2' are not particularly distinguishable, the two-dimensional image sensor 221
If they are formed overlapping each other, it is impossible to distinguish between them, and even if it is possible to distinguish them, if they overlap each other, their positions cannot be determined accurately. Therefore, the point light source 206 corresponding to the bright spot image 11' is caused to emit light, the image data of the two-dimensional image sensor 221 of the bright spot image iI' is stored in the frame memory, and then the point light source 206 corresponding to the bright spot image 12' is stored in the frame memory. Point light source 2
09, the image data of the bright spot image 12' is stored in the frame memory, and the distance of the bright spot image i+i2' is determined based on this image data. If the interval 2ΔX between the bright spot images of the two-dimensional image sensor 221 is measured, f+, f
2) Since θ1 and θ2 are known, the working distance deviation △Z
is determined, and the distance from the corneal apex 120P to the reference position of the measuring device is obtained.

Note that if the lens 218 is slightly shifted upward in the direction perpendicular to the page and the lens 219 is shifted downward in the direction perpendicular to the page, as shown in FIG. 12' is formed on the two-dimensional image sensor 221 in a vertically split state, so measurement can be performed even when the point light sources 206 and 209 are turned on at the same time. However, if we consider it strictly, the chief ray of the bright spot image L+'12' deviates from the vertical plane of the observation surface of the two-dimensional image sensor 221, so ΔX and ΔZ
Although the relationship between the two values is slightly different, the error due to this effect is so small that it can be ignored.

Since the interference optical system 101 is substantially the same as that used in the first embodiment, the same components are given the same reference numerals and detailed explanation thereof will be omitted.

(Example 3) Figure 11116 shows an example using a confocal optical system as a corneal distance measuring system.

The corneal distance measurement system includes a light source 300, a condensing lens 301, a pinhole plate 302 as a first aperture, a collimating lens 303 as a relay lens, and a beam splitter 304.
, an objective lens 305, a lens 306, a spatial filter 307, and a light receiver 308. light source 300
The emitted light is condensed by a condenser lens 301 and converged onto a pinhole plate 302 . The pinhole plate 302 serves as a secondary point light source, and the light passing through the pinhole of the pinhole plate 302 is reflected by the beam splitter 304 and converted into a parallel light beam by the collimating lens 303.

The second parallel beam passes through the objective lens 305 through the lens 306.
The light is reflected toward the subject's eye 103 as a convergent light beam. The objective lens 305 plays the role of condensing the parallel light flux onto a focal point 309 using geometric optics.The pinhole plate 302 and the focal point 309 are conjugate with respect to the collimating lens 303 and the objective lens 305, 309 and the spatial filter 307 are conjugate with respect to the objective lens 305 and the lens 306. That is, the focal point 309
is confocal, and the corneal distance measuring system constitutes a confocal optical system.

This confocal optical system has an optical property that light emitted from a point other than the vicinity of the confocal cannot pass through the spatial filter 307. Note that the objective lens 305 functions as an objective lens unit that changes the position of the condensing point 309.

Here, the lens 308 is movable back and forth in the direction of the optical axis 03, and a linear encoder 310 as a position detection mechanism faces the lens 306.
The output of 0 is input to the position detection circuit 311. The linear encoder 310 and the position detection circuit 311 are the lens 3
The output of the photoreceiver 308, which serves to detect the position of the sensor 06, is input to a signal processing circuit 313 via an amplifier 312. The signal processing circuit 313 has a function of outputting a trigger signal and a timing signal.

The trigger signal is the laser diode 130 of the interference optical system.
The timing signal is used when the position detection circuit 311 specifies the lens position.The zero position detection circuit 311 sends the lens position detection signal to the calculation circuit 15
Output towards 6. The arithmetic circuit 156 calculates the lens position and the device/focal point 3, which have been associated with each other in advance.
It has a function of calculating the distance from the reference position of the measuring device to the corneal apex 120P based on the distance relationship between 09 and 09.

Now, when the condensing point 309 is at the position shown in FIG. As shown in FIGS. 17(b) and 17(c), when the subject's eye 103 is approached in the direction of the optical axis 03, the surface of the cornea 120 is The reflected light from the beginning begins to pass through the spatial filter 307.

Therefore, the output of the light receiver 308 begins to gradually increase and becomes maximum when the focal point 309 coincides with the surface of the cornea 120.

That is, when the focal point 309 coincides with the surface of the cornea 120, the first peak appears. Then, as the lens 306 is brought even closer to the eye 103 to be examined, a peak appears in the output from the light receiver 308 based on reflected light from the back surface of the cornea 120, the surface of the crystalline lens 315, and the like.

Therefore, if the signal processing circuit 313 is made to output a trigger signal and a timing signal based on the first peak, the position detection circuit 311 detects the position of the lens 306 when the focal point 309 is on the surface of the cornea 120. However, the calculation circuit 156 calculates the distance from the reference position to the corneal vertex 120P based on the position of the lens 306.

At the same time, distance measurement to the fundus of the eye is started based on the trigger signal.

According to this confocal optical system, if the numerical aperture (N, A) of the objective lens 305 is designed to be large enough, the focal point 309 will be perpendicular to the optical axis 03, as shown in FIG. Even if the corneal apex 120P is slightly deviated from the corneal apex 120P in the
As long as the surface of the cornea 20 coincides with the focal point 309, the light receiver 308 can receive almost all of the reflected light from the surface of the cornea 120, and therefore the alignment error of the measuring device with respect to the cornea 120 can be tolerated. .

For example, if the radius of curvature R of the cornea 120 is 7.7 mm,
If the numerical aperture NA at which no reflected light enters the objective lens 305 is 0.25, the amount of deviation Δ of the condensing point 309 from the corneal apex 120 P in the direction orthogonal to the optical axis 03 is 1. It becomes 93mm. However, in the direction perpendicular to the optical axis 03, the focal point 309 is 1.
If the deviation is 93 mm, as shown in FIG. 19, the position of the condensing point 309 will be deviated by 0.25 mm with respect to the actual corneal apex 120P in the direction of the optical axis 03, so the amount of deviation Δ should be reduced to 1. 93m
Although it is not possible to design as large as 0.0 m, the deviation amount Δ can be set to 0. If designed to be about 5 am, the positional deviation of the condensing point 309 with respect to the actual corneal apex 120P in the optical axis direction is about 0,016 + * + m, ignoring the positional deviation of the condensing point 309 in the optical axis direction. can. Note that in FIG. 18, the shaded area indicates the reflected light from the cornea.

The configuration of the interference optical system 101 is almost the same as in the first and second embodiments, so the same components are denoted by the same reference numerals. In FIG. 16, 314 is a dichroic mirror lens 306. is the lens 13 of the first embodiment
7, and the lens 303 corresponds to the collimating lens 136 of the first embodiment.

In the above embodiment, the model eye unit 141 was formed with two surfaces, the cornea and the fundus, and the measurement of the axial length was explained. The present invention can be applied to measure the intraocular length between.

(Effects) Since the length measuring device according to claim 1 of the present invention is configured as described above, there is an effect that the distance to the object to be measured can be accurately measured without moving the optical components.

As explained above, in the length measuring device according to claim 3 of the present invention, the corneal apex is measured using a geometrical optical system, and the fundus position is measured using an interference optical system. , even if strict alignment accuracy is not required,
Accurately measure axial length.

[Brief explanation of the drawing]

1 to 9 are explanatory diagrams for explaining a first embodiment of a length measuring device according to the present invention, and FIG. 1 is a diagram showing an optical system of the length measuring device according to the present invention. Figure 2 is a diagram showing a ring image formed on the two-dimensional image sensor shown in Figure 1, and Figures 3 and 4 are diagrams for schematically explaining the operation of the corneal distance measuring optical system shown in Figure 1. 5 is an explanatory diagram for explaining corneal apex position detection, FIG. 6 is an optical diagram for explaining the action of the interference optical system, and 7 is an optical diagram for explaining the corneal apex position and fundus position. Fig. 8 is a block diagram of a signal processing circuit, Fig. 9 is a timing chart for explaining the operation of the signal processing circuit, and Figs. 10 to 15 are measurement diagrams related to the present invention. Fig. 11 is an optical diagram showing the corneal distance measuring system;
The figure shows the interference optical system. Figures 12 and 13 are optical schematic diagrams showing the operation of the corneal distance measuring system. Figures 14 and 15 are bright spot images formed on the two-dimensional image sensor. 16 to 19 are diagrams showing a third embodiment of the length measuring device according to the present invention, FIG. 16 is an optical diagram thereof, and FIG. 17 is a collection of its corneal distance measuring system. FIGS. 18 and 19 are explanatory diagrams showing changes in the position of the light spot, and FIGS. 18 and 19 are explanatory diagrams of misalignment. 100... Corneal distance measurement system, 101... Interference optical system 102... Ring-shaped light source projection unit (irradiation optical system) 103
...Eye to be examined, 104...Objective lens 107, 22
1.308...Two-dimensional image sensor (third light receiving part) 110...Aperture (second aperture), 124...Aperture (first aperture) 120...Cornea, 120P...Cornea vertex 1
30...Laser diode 132...Beam splitter 139...Reference mirror (measurement object corresponding surface) 144...
... Reference mirror (reference object) 142 ... Photo sensor (first light receiving section) 146 ... Photo sensor (second light receiving section)
145... Reference mirror (reference object corresponding surface) 147.
... Reference interference optical path 160 ... Fundus 149 ... Signal processing circuit (periodic wave signal forming section) 151
...Measurement interference optical path 156...Calculation section (fundus position measurement section, corneal position measurement section) 206.209...Light source 216.217.301.302...Aperture 303...
・Collimating lens (relay lens part) 304... Beam splitter, 305... Objective lens Fig. 17 Fig. 18 Fig. 19 Fig. Q, 25 mm

Claims (6)

[Claims] (1) Measurement interference in which a laser light source that emits a laser beam with a long coherence distance and a variable wavelength is used, and the laser beam reflected by the object to be measured interferes with the laser beam reflected by the reference surface corresponding to the object to be measured. forming an optical path and a reference interference optical path having an optical path length longer than the measurement interference optical path and causing the laser beam reflected by the reference object to interfere with the laser beam reflected by the reference surface corresponding to the reference object; a beam splitter that guides a laser beam from a light source to the measurement interference optical path and the reference interference optical path; a first light receiving section that receives the light guided as interference light via the measurement interference optical path; and the reference interference optical path. a second light receiving section that receives the light guided as interference light via the laser light source; a laser driving section that changes the emission wavelength of the laser light source; and a laser driving section that uses the output signal of the second light receiving section as a timing signal to a periodic wave signal forming section that samples the output signal of the first light receiving section and forms a periodic wave signal, and a calculation section that calculates the distance to the measurement target based on the optical path length of the reference interference optical path and the period of the periodic wave signal. A length measuring device comprising: (2) In the length measuring device according to claim 1, the laser drive unit changes the temperature of the laser light source by lighting the laser light source in pulses, and the emission wavelength of the laser light source changes depending on the temperature change. A length measuring device characterized by having a configuration that changes based on the following. (3) A laser light source that emits a laser beam with a long coherence distance and a variable wavelength, and a measurement interference optical path that causes interference between the laser beam reflected by the fundus of the eye to be examined and the laser beam reflected by the reference surface corresponding to the fundus. forming a reference interference optical path having a longer optical path length than the measurement interference optical path and causing interference between the laser beam reflected by the reference object and the laser beam reflected by the reference surface corresponding to the reference object; a beam splitter that guides the laser beam to the measurement interference optical path and the reference interference optical path; a first light receiving section that receives the light guided as interference light via the measurement interference optical path; a second light receiving section that receives the light guided as interference light; a laser driving section that changes the emission wavelength of the laser light source; and a second light receiving section that uses the output signal of the second light receiving section as a timing signal to detect the first light receiving section a periodic wave signal forming section that samples the output signal of the section and forms a periodic wave signal; a fundus position measuring section that determines the distance to the fundus based on the optical path length of the reference interference optical path and the period of the periodic wave signal; an irradiation optical system that irradiates the cornea of the eye to be examined with a light beam; a light reception optical system that guides the reflected light from the cornea to a third light receiving section; and determining a corneal position of the eye to be examined based on the output of the third light receiving section. What is claimed is: 1. A length measuring device, comprising: a corneal position measuring section, and measures the axial length of the eye to be examined from the corneal position and the fundus position. (4) In the length measuring device according to claim 3, the light-receiving optical system passes the reflected light from the cornea of the subject's eye through a first diaphragm disposed at a position conjugate with the front of the objective lens to a third diaphragm. A first light receiving system that guides the light reflected from the cornea of the eye to be examined to the light receiving section, and a second light receiving system that guides the reflected light from the cornea of the subject's eye to the third light receiving section via a second diaphragm arranged at a position conjugate with the rear of the objective lens. The position measurement unit is configured to determine the corneal position from the position of the reflected light beam from the cornea of the eye to be examined, which has passed through the first diaphragm and the second diaphragm, at the third light receiving unit. Long device. (5) In the length measuring device according to claim 3, the irradiation optical system is configured to obliquely irradiate a parallel light beam to the cornea of the eye to be examined, and the light receiving optical system is configured to emit a parallel beam of light obliquely to the cornea of the eye to be examined. It is composed of an objective lens section that receives diagonally reflected light and a diaphragm placed at a focal position behind the objective lens section, and the third light receiving section is configured to receive light through the objective lens section and the third diaphragm, The length measuring device is characterized in that the corneal position measuring section is configured to determine the corneal position from the light receiving position at the third light receiving section. (6) In the length measuring device according to claim 3, the irradiation optical system includes a point light source for irradiating the cornea of the eye to be examined, and a position of the image of the point light source near the cornea of the eye to be examined. a beam splitter that separates reflected light from the cornea of the eye to be examined from the irradiation optical system after passing through the objective lens; an image of the point light source and a second aperture located at a conjugate position; the second light receiving section is configured to receive reflected light from the cornea of the eye to be examined via the second aperture; The measuring section determines the corneal position of the eye to be examined from the intensity of the signal of the second light receiving section according to the change in the image position of the point light source formed by the objective lens section, and the fundus position measuring section; A length measuring device characterized in that the axial length of the eye is determined from a corneal measuring section.