JP2823660B2 - Length measuring device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a length measuring device, and more particularly, to a corneal vertex position obtained by using an optical system utilizing a geometrical optical principle, and a fundus position to be determined by a physical optical principle. The present invention relates to a length measuring device suitable for measuring the axial length from the fundus oculi to the corneal apex, obtained by using an interference optical system as an optical system utilizing the method.

(Prior art) Conventionally, a light beam from a laser diode LD is applied to an eye to be examined, and a plane wave reflected from the fundus and a spherical wave reflected from the cornea interfere with each other. The interference signal is used between the fundus and the cornea. A length measuring device for measuring the distance (axial length) of the eye, for example, an axial length measuring device is known.

(Problems to be Solved by the Invention) However, in the conventional length measuring device, when a reflected plane wave from the fundus and a reflected spherical wave from the cornea interfere with each other,
Strict alignment accuracy is required for alignment of the measuring device with respect to the eye to be inspected, and this is a fatal drawback, particularly in the measurement of a constantly moving eyeball. Also, if the alignment of the measuring device is slightly deviated with respect to the eye to be examined, the position of the interference fringes will greatly deviate, and at the place where the observation has been made, the number of the interference fringes will increase rapidly and it will be determined whether interference is occurring. Was difficult.

(Means for Solving the Problems) The present invention has been made in view of the above circumstances, and a configuration of a length measuring apparatus according to claim 1 is a laser light source that emits a laser beam whose wavelength can be changed. And a measurement interference optical path for causing the laser light reflected by the measurement object and the laser light reflected by the measurement object corresponding reference surface to interfere with each other, and having a longer optical path length than the measurement interference optical path and being reflected by the reference object. A beam splitter for forming a reference interference optical path for interfering the laser light reflected by the reference object-corresponding reference surface and the laser light from the laser light source to the measurement interference optical path and the reference interference optical path. A first light receiving unit that receives light guided as interference light via the measurement interference light path, and a second light reception unit that receives light guided as interference light via the reference interference light path A laser driving unit that changes an emission wavelength of the laser light source; a periodic wave that forms a periodic wave signal by sampling an output signal of the first light receiving unit using an output signal of the second light receiving unit as a timing signal. A signal forming unit; and a calculating unit for calculating a distance to a measurement object based on an optical path length of the reference interference optical path and a cycle of the periodic wave signal.

According to a third aspect of the present invention, there is provided a laser light source that emits a laser beam whose wavelength can be changed, and a measurement that causes the laser beam reflected by the fundus of the eye to be examined to interfere with the laser beam reflected by the reference surface corresponding to the fundus. Forming an interference optical path and a reference interference optical path having a longer optical path length than the measurement interference optical path and causing the laser light reflected by the reference object and the laser light reflected by the reference object corresponding reference surface to interfere with each other; A beam splitter that guides laser light from a laser light source to the measurement interference light path and the reference interference light path; a first light receiving unit that receives light guided as interference light via the measurement interference light path; A second light receiving unit that receives light guided as interference light via an optical path, a laser driving unit that changes an emission wavelength of the laser light source, and an output signal of the second light receiving unit A periodic wave signal forming unit that samples an output signal of the first light receiving unit using the timing signal and forms a periodic wave signal; and a sensor for generating a periodic wave signal based on an optical path length of the reference interference optical path and a period of the periodic wave signal. A fundus position measuring unit for determining a distance, an irradiation optical system for irradiating a cornea of the eye to be examined with a light beam, a light receiving optical system for guiding reflected light from the cornea to a third light receiving unit, and an output of the third light receiving unit. A corneal position measuring unit for determining a corneal position of the eye to be examined based on the eye axis length of the eye to be examined.

(Operation) According to the length measuring device of the first aspect of the present invention, if the 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 unit, the distance to the object to be measured can be obtained. The distance can be determined.

According to the length measuring device of the third aspect of the present invention, the corneal vertex position is measured using the irradiation optical system and the light receiving optical system using the geometric optical principle, and the fundus position uses the physical optical principle. The measurement is performed using the interference optical system thus determined, whereby the axial length of the eye is obtained.

Embodiment 1 FIG. 1 shows an embodiment in which a ring image is projected on the cornea to obtain a corneal vertex position as a corneal distance measuring system.

In FIG. 1, reference numeral 100 denotes a corneal distance measurement system, 101 denotes an interference optical system, 102 denotes a ring-shaped light source projection unit as an irradiation optical system for irradiating a cornea with a light beam, 103 denotes an eye to be inspected, and 104 denotes an objective lens. . The corneal distance measurement system 100 has a first optical path 105 and a second optical path 106. The first optical path 105 includes a two-dimensional image sensor 107 as a third light receiving unit, an imaging lens 108, a half mirror 109, an aperture 110, a lens 111, a total reflection mirror 112, and a lens.
The optical system generally comprises 113, a half mirror 114, a dichroic mirror 115, and an objective lens 104. The second optical path 106 generally includes a lens 117, total reflection mirrors 116, 118, 119, and a diaphragm 124.

The ring-shaped light source projection unit 102 includes a ring-shaped light source and a pattern plate (not shown), and here projects illumination light such that meridional sectional rays are parallel to the eye to be examined. Radiant illumination light may be projected. When this illumination light is irradiated toward the subject's eye 103, the subject's eye 103
A ring-shaped virtual image 121 is formed on the cornea 120. Here, the wavelength of the illumination light of the ring-shaped light source projection unit 102 is 900 nm to 10 nm.
00 nm. The dichroic mirror 115 has a role of transmitting the illumination light and reflecting a laser light described later.

The light reflected by the cornea 120 is guided to the half mirror 114 via the objective lens 104 and the dichroic mirror 115,
The light is branched into an optical path 105 and a second optical path 106. The reflected light guided to the first optical path 105 is once formed as a ring-shaped aerial image 122 by a lens 113, and further passes through a total reflection mirror 112, a lens 111, a diaphragm 110, a half mirror 109, and an imaging lens 108. And the ring image i ₂ (second
(See the figure). Incidentally, the imaging magnification of the ring image i ₂ is here, and 0.5 times. The reflected light guided to the second optical path 106 is reflected by a total reflection mirror 119, is once formed as an aerial image 123 by an objective lens 104, and is totally reflected mirror 118, lens 117, total reflection mirror 116, aperture 124, half mirror 109, via the image forming lens 108 is imaged as a ring image i ₁ into a two-dimensional image sensor 107. In addition,
Imaging magnification of the ring image i ₁ is set larger than the imaging magnification of the ring image i _2.

The stop 110 serves as a second stop, and the lens 1
11, relayed to the rear focal position of the objective lens 104 by the lens 113, a conjugate image 125 is formed at the rear focal position of the objective lens 104, and the optical system of the first optical path 105 is telecentric on the object side. The aperture 124 serves as a first aperture, and is relayed in front of the eye 103 (in front of the objective lens 104) by a lens 117. In this case, a conjugate image (real image) 126 is 25 mm to 50 mm in front of the eye to be inspected. Formed at the location.

Here, the relationship between the objective lens 104 and the apertures 110 and 124 will be described with reference to FIGS. Now, as the position of the origin G on the optical axis O of the conjugate image 126 of the diaphragm 124 is formed to define a reference position Y at a position distant in the optical axis direction from the origin G by a distance L _1. The reference position Y is determined so that the ring images i ₁ and i ₂ are not out of focus. Then, an object having an object height h (corresponding to the radius of the ring image i) is placed at the reference position Y. In this case, y ₁ the image height formed on the viewing surface 127 (position of the two-dimensional image sensor 107) by the second optical path 106, the image height is formed on the observation surface 127 by the first optical path 105 and y _2. Then, by moving the known object distance X _0, the image height y ₁ at this time ', y _2' to. The distance from the observation surface 127 to the point Z is L ₁ ′, the distance from the reference position Y to the point Z ′ is L ₂ , and the distance from the stop 110 to the observation surface 127 is L ₂ ′. Further, the angular magnifications are set as β ₁ and β ₂ .

 Then, the following equation is obtained.

h / L ₁ = y ₁ · β ₁ / L ₁ ′ h / (L ₁ + X ₀ ) = (y ₁ ′ · β ₁ ) / L ₁ ′ h / L ₂ = y ₂ / (β ₂ · L ₂ ′ ) H / (L ₂ + X ₀ ) = y ₂ ′ / (β ₂ · L ₂ ′) In the formula, the angular magnification β ₁ , distances L ₁ and L ₁ ′ are constants, and K ₁ = (β ₁・ L ₁ ) / L ₁ ′ K ₂ = β ₁ / L ₁ ′, the equation is transformed into the following equation.

h = K ₁ · y ₁ h = K ₁ · y ₁ ′ + K ₂ · y ₁ ′ · X _{0 Further} , in the formula, the angular magnification β ₂ , the distance L ₂ , L ₂ ′
Is a constant, and if K ₃ = L ₂ / (L ₂ ′ · β ₂ ) and K ₄ = 1 / (L ₂ ′ · β ₂ ), the equation is transformed into the following equation.

_{h = K 3 · y 2 h} = K 3 · y 2 '+ K 4 · y 2' · X 2 , where the constant _{K 1, K 2, K 3} , K 4 is the object height h, and the image height y measured By doing so, it can be determined.

That is, the following equation is obtained by modifying the equation.

K ₁ = h / y ₁ K ₂ = (h / y ₁ ) · (y ₁ −y ₁ ′) / (y ₁ ′ · X ₀ ) K ₃ = h / y ₂ K ₄ = (h / y ₂ ) (Y ₂ −y ₂ ′) / (y ₂ ′ · X ₀ ) Therefore, by actually measuring the object height h and the image height of the known object, the constants K ₁ , K ₂ , K ₃ , and K _{4 are obtained.} Is required.

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

In this case, the place where in the formula, the distance X in place of the distance X _0. Also, y ₁ ′ and y ₂ ′ are replaced with y ₁ and y ₂ .

 Then, the following equation is obtained.

The _{h = K 1 · y 1 +} K 2 · y 1 · X h = K 3 · y 2 + K 4 · y 2 · X above simultaneous equations, the distance X, and solving for the object height h, X = (K ₃ · y ₂ -K ₁ · y ₁ ) / (K ₂ · y ₁ -K ₄ · y ₂ ) h = K ₁ · y ₁ + K ₂ · y ₁ · X = (K ₂ · K ₃ -K ₁ · K ₄ ) Y ₁ · y ₂ / (K ₂ · y _1- K ₄ · y ₂ ) Therefore, by measuring the image heights y ₁ and y ₂ , the distance from the reference position Y to the object can be measured.

Next, the measurement of the corneal curvature radius R and the vertex position will be described with reference to FIG.

In FIG. 5, the radius of the ring image i (the major axis or minor axis of the ellipse when the ellipse is approximated) is defined as the object height h. At this time, the object height h is determined by the meridional light beam.
If the diameter of the ring image is about 3 mm, the angle φ is 20
゜, and the paraxial calculation formula described below cannot be used.

h = (R · sin φ) / 2 Therefore, the distance L _{2 is set} to be sufficiently large so that the angle φ is always constant, and the object height h measured on the second optical path 106 passing through the diaphragm 124 is used. Then, an expression based on the following reflection law can be used.

h = R · sin (φ / 2) By modifying the above equation, R = h / sin (φ / 2) The distance L ₁ is such that the angle formed by the ray passing through the stop 110 and the ray passing through the stop 124 does not become large. by setting, the object height h obtained from not believed to large error be used in the above formula by, as the distance P _X position of the corneal vertex 120P from the reference position Y, P _X = X- ( (R−h / tanφ) The formula for calculating the corneal vertex position is affected by spherical aberration because the ring image is on the optical axis of the spherical surface, but the amount is considered to be so large. However, it is also possible to make corrections based on experimental values. In addition,
In Figure 5, O 'is spherical optical axis when the cornea curvature center, A ₁ is the regarded normal, A ₂ is a cornea 120 and spherical, A ₃ is cornea 120
Is the incident light beam on

Next, the interference optical system will be described with reference to FIGS.

The interference optical system 101 includes a laser diode 130 as a laser light source, a collimator lens 131, and a beam splitter.
132, lens 133, pinhole plate 134, beam splitter 1
35, collimating lens 136, focusing lens 137, collimating lens 138, reference mirror 139, pinhole plate 140, lens 1
41, a photodiode 142, a beam splitter 143, a reference mirror 144, a reference mirror 145, and a photodiode 146. The laser diode 130 having a long coherent length and capable of changing the wavelength (for example, a single mode) is used. The laser light emitted from the laser diode 130 is converted into a parallel light beam by the collimator lens 131 and guided to the beam splitter 132. The beam splitter 132 has a function of splitting the parallel laser light into a light beam going to the lens 133 and a light beam going to the half mirror 143.

The half mirror 143 forms a Twyman-type reference interference optical path 147 together with the reference mirror 144 and the reference mirror 145. Here, from the point Q ₁ of the half mirror 143 to the reference mirror 1
D ₁ the distance of a point to Q ₂ of 44, the distance from point Q ₁ to the point Q ₃ of the reference mirror and D _2, is defined as reference optical path length D ₁ -D ₂ = D. The reference mirror 144 serves as a reference object, the reference mirror 145 serves as a reference surface corresponding to the reference object, and the reflected laser beams reflected by the mirrors 144 and 145 are combined by the beam splitter 143 to generate interference. The light is guided to a photosensor 146 as a second light receiving unit via a beam splitter 132. The photo sensor 146 outputs an interference signal based on the interference light, and the interference signal is output to the amplifier 148.
Is input to the signal processing circuit 149 via the. The configuration of the signal processing circuit 149 will be described later.

The parallel laser light that has passed through the half mirror 132 is converged on the pinhole plate 134 by the lens 133. The pinhole plate 134 serves as a quasi-point light source. The laser light that has passed through the pinhole plate 134 is guided to the beam splitter 135 as a measurement light beam. The beam splitter 135 has a function of splitting the measurement light beam, guiding a part of the light beam to the collimator lens 136, and guiding the rest to the collimator lens 138.

The measurement light beam guided to the collimator lens 138 is converted into a parallel light beam, reflected by the reference mirror 139, and returned to the beam splitter. The measurement light beam guided to the collimating lens 136 is guided to the focusing lens 137, and the dichroic mirror 115,
The light is guided to the subject's eye 103 as a parallel light beam via the objective lens 104, and converged on the fundus 160. The reflected light flux from the fundus 160 follows the same optical path and returns to the beam splitter 135 again,
The light is combined with the light beam reflected from the reference mirror 139 and guided to the stop 140. The diaphragm 140 is located at a position conjugate with the fundus 160 and the cornea
It plays the role of removing the reflected light from 120 and the reflected light from the crystalline lens. Further, since the stop 140 is also conjugate to the stop 134, even if the alignment of the length measuring device with respect to the eye to be examined is slightly shifted, the measurement can be performed without any trouble.

The light beam that has passed through the stop 140 is converted into an interference parallel light beam by the lens 141, and the photosensor as the first light receiving unit is used.
Guided to 142. The photo sensor 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 150. Here, a beam splitter 135, a collimating lens 136, a focusing lens 137, a dichroic mirror 115, an objective lens 104, a collimating lens 138, and a reference mirror 139 are used as a fundus 160 as an object to be measured.
Interference light path 151 that causes the reflected light beam from the mirror to interfere with the reflected light beam from reference mirror 139 as the reference surface corresponding to the measurement object.
Is composed.

Here, the reference mirror from the point Q ₄ of the beam splitter 135 1
The distance to the point Q ₅ 39 and L _r, the optical axis distance from point Q ₄ to the fundus 160 and L _t. At this time, assuming that the reference mirror 139 has a reference mirror 139 'virtually at a position on the optical axis O, it can be considered that the reflected light of the reference mirror 139' and the reflected light from the fundus 160 interfere. Yes, L _t −L _r is 16
This is the optical path difference in air conversion from 0 to the reference mirror 139 '.

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

When the wavelength λ of the laser diode 130 is changed, the intensity of the interference light incident on the photodiode 146 is
The intensity of the interference fringes formed on the photodiode 142 is determined by the phase difference corresponding to the optical path difference 2 (D ₁ −D ₂ ) between the reflected light reflected by the reference light 44 and the reflected light reflected by the reference mirror 145. is determined by the phase difference corresponding to the optical path difference 2 (L _t -L _r) of the reflected light reflected by the reflection light and the fundus 160 is reflected by the reference mirror 139. 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 shows a constant value.

Here, when P _X to indicate the distance on the optical axis O of the virtual reference mirror 139 'and the corneal vertex 120P in Figure 7,
The P _X can be determined by detecting the corneal vertex 120P with corneal distance detection system. That is, if the distance from the reference position Y to the corneal vertex position 120P is measured,
This is because the distance from the reference position Y to the corneal vertex 120P is measured, and the relationship between the reference position Y and the virtual reference mirror 139 'can be determined in advance by design. Therefore, if L _t −L _r can be obtained, the eye axis length in air conversion
AL can be obtained, axial length AL is the average refractive index n _A, it can be obtained as _{AL = (L t -L r -P} X) / n A.

L _t −L _r can be obtained by performing measurement based on the principle described below.

Let the wavelength of the laser light be λ, the wavelength λ of this laser light
Is changed by a laser driver described later. Assuming that the wavelength change amount is Δλ, the photosensor 14 in the reference interference optical path
The phase difference of the laser beam before the wavelength change at 6 is 2π ·
2 (D ₁ −D ₂ ) / λ. The phase difference after changing the wavelength by Δλ is 2π · 2 (D ₁ −D ₂ ) / (λ + Δλ).

Therefore, if the wavelength is changed by Δλ, the phase difference becomes 2π
/ Λ by 2π · 2 (D ₁ −D ₂ ) / (λ + Δλ). Here, assuming that the wavelength change amount Δλ is extremely small with respect to the wavelength λ, the phase difference after the wavelength change is
By the series expansion, 2π · 2 (D ₁ −D ₂ ) · (1 / λ−Δλ)
/ Λ ² ), and the amount of change in the phase difference is 2π · 2 (D ₁ −D ₂ ) · Δλ / λ ² .

Similarly, the amount of change in phase difference in the photosensor 142 of the measured interference path 151 becomes _{2π · 2 (L t -L r} ) · Δλ / λ 2.

Now, ₁ change in the phase difference in the photosensor 142 [psi, when a change in the phase difference and [psi ₂ in the photosensor _{146, Ψ 1 = 4π (D} 1 -D 2) · Δλ / λ 2 (1) Ψ 2 = 4π ( L _t −L _r ) · Δλ / λ ² (2) When Δλ / λ ² is eliminated from the above equation, L _t −L _r = Ψ ₁ / Ψ ₂ can be expressed. (3) This equation, by obtaining the amount of change in the phase difference of the interference light, which means that can measure the distance (L _t -L _r) from the virtual reference surface 139 'to the fundus 160. Here, assuming that the wavelength change Δλ is continuous, a general interference equation will be considered.

Wherein the common interference is expressed as _{I = I 1 +1 2 +2 (} I 1 · 1 2) 1/2 · COSδ (4).

Here, I is the intensity of the interference light on the photodiode 142, 146, I _1, 1 ₂ is the intensity of the interfering light beams with one another, [delta] is the phase difference of the interfering light beams with one another, for example, [delta] is 4 [pi] (D ₁₋ D ₂ ) (1 / λ−Δλ / λ ² ).

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

Here, the number of periods of the intensity change is a value obtained by dividing the change of the phase difference by 2π, and Ψ ₁ / Ψ ₂ obtained by the equation (3) is the number of periods of the intensity change of the interference fringes obtained by the photosensors 142 and 146. Is shown. Therefore, the ratio of the number of periods of the intensity change of the interference fringes obtained by the photo sensors 142 and 146 is shown.

Therefore, by measuring the number of periods of intensity change of the interference fringes obtained by the photo sensors 142 and 146, (L _t −L _r ) is obtained,
The distance to the fundus is obtained as described above.

In other words, the change in the intensity of the interference fringes based on the change in the wavelength can be regarded as a change in the position of the interference fringes at specific locations of the photosensors 142 and 146, in other words.

Next, wavelength modulation of the laser diode will be described.

By the way, the eyeball of the subject's eye 103 is expanding and contracting due to pulsation. That is, the eyeball repeatedly expands and contracts 60 to 80 times per minute, and its fluctuation amount is about 3 μm. Therefore, when converted to the number of interference fringes, it is about eight, and
Since movement of about 16 interference fringes is observed, if one cycle of pulsation is set to 80 times / 60 seconds = 1.33 Hz, the output of the interference fringes changes at a cycle of 21.33 Hz.

Therefore, a means for performing high-speed wavelength modulation of the laser diode 130 and performing measurement at intervals sufficiently short as compared with the period of the pulsation is employed.

The laser diode 130 is controlled by a laser driver 152 as shown in FIGS. The laser driver 152 outputs a pulse current shown in FIG. The temperature of the laser diode 130 changes (rises) due to the pulse current, and a temperature change curve T shown in FIG. 9B is drawn. This temperature change takes about several ms to stabilize.

The laser diode 130 has a temperature change and an emission wavelength,
Use in areas that have a one-to-one correspondence. However, since the temperature change is non-linear with respect to time, the emission wavelength also changes non-linearly. Therefore, the photo sensor 14
The phase change of the interference fringes received at 2, 146 is also affected by the nonlinearity of the temperature change.

That is, as shown in FIG.
142 interference waveform C ₀ of the interference signal output from the period at the stage of temperature rise changes suddenly initial short, period becomes longer at the temperature change is gradual late phase. Photodiode 146
The same applies to the interference waveform C ₁ of the interference signal output from. Here, the frequency of the interference waveform C ₁ is higher than the frequency of the interference wave C ₀ is the optical path difference between the reference interference optical path 147 (D ₁ -D
₂₎ because is designed sufficiently larger than the optical path difference at the measured interference path 147 (L _t -L _r). Here, the reference optical path difference (D ₁ −D ₂ ) is set to be about 6 times (L _t −L _r ). In designing the reference interference optical path 147, an optical fiber can be used to extend the optical distance.

Since the same laser light is divided by the beam splitter 132 in the reference interference light path 147 and the measurement interference light path 151, the method of changing the wavelength of the laser light is the same. Therefore, the ratio of the period of the interference signal of the photodiode 142 to the period of the interference signal of the photodiode 146 is the ratio of the measured optical path difference (L _t −L _r ) to the reference optical path difference (D ₁ −D ₂ ), (D ₁ −D ₂ ) / (L _t −L _r ). This ratio is defined as K.

In order to obtain the ratio K, the signal processing circuit 149 is configured to sample the interference signal of the photo sensor 142 based on the interference signal of the photo sensor 146. That is, the signal processing circuit 149 includes the trigger circuit 153. The trigger circuit 153 is synchronously controlled by a laser drive unit 152, FIG. 9 slicing the interference waveform C ₁ by slice level V shown in (d), one every cycle, Figure 9 of the interference waveform C ₁ (e) It has a function of generating a timing clock signal C ₂ shown. The interference signal of the photodiode 142 is input to the A / D converter 154 of the signal processing circuit 149. A / D converter
154 on the basis of the timing clock signal C ₂ of the trigger circuit 153, the output value of the interference waveform C ₂ A / D-converts and outputs toward the memory 155. This results in either an interference waveform C ₀ constitute one cycle at some sampling number is found. That is, it is possible to know how many periods of the photodiode 142 correspond to one period of the photodiode 142. 9 (f) is a view showing equally spaced interference waveform C ₀ using the sampled value stored in the memory 155. Therefore, the signal processing circuit 149 functions as a periodic wave signal forming unit that samples the output signal of the first light receiving unit using the output signal of the second light receiving unit as a timing signal and forms a periodic wave signal.

Here, since one cycle is composed of six sampling values, K = 6. Therefore, this K is
Was calculated by 156, by calculating the _{K = (L t -L r)} / obtained by modifying the formula _{(D 1 -D 2) (L} t -L r) = (D 1 -D 2) / K, ( Since (D ₁ −D ₂ ) is known, (L _t −L _r ) can be obtained. Therefore, the arithmetic circuit 156 functions as an arithmetic 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 as a fundus position measuring unit when calculating the axial length. Will work.

In general, the ratio K is a fraction. In this case,
Data of one cycle of the interference signal of the photodiode 142 may be obtained by, for example, an interpolation method, and the number of one cycle of the interference signal of the photodiode 146 included in one cycle of the interference signal of the photodiode 142 may be obtained.

The first embodiment has been described above.
If an ND filter is provided at an appropriate position in (1) to adjust the light amount, an interference signal in the measurement interference optical path 151 can be properly extracted.

According to the first embodiment, since the position of the corneal apex is measured using the double ring image, the radius of curvature of the cornea can be originally measured as shown in the equation, and therefore, the corneal shape measuring device ( (Kerat apparatus).

Embodiment 2 FIG. 10 shows an optical system for obtaining a corneal apex position using an alignment optical system as a corneal distance measuring system.

In FIG. 10, the alignment optical system 200 includes a first optical system 201 and a second optical system 202. First optical system 20
1 and the second optical system 202 is symmetrical to the boundary of the optical axis O _1. optical axis
O ₁ on the objective lens 203, a mirror 204, an imaging lens 205
Is provided. The objective lens 203 and the imaging lens 205 are used when observing the anterior segment of the eye 103 to be inspected. As the mirror 204, a half mirror or a band-pass mirror is used.
Reference numeral 204 has a function of reflecting a laser beam at the time of measurement using the interference optical system shown in FIG. The configuration of this interference optical system will be described later.

The first optical system 201 has a point light source 206, a half mirror 207, and a lens 208 as an irradiation optical system, and the second optical system 202 has a point light source 209, a half mirror 210, and a lens as an irradiation optical system.
Has 211. The point light source 206 is installed at the focal position of the lens 208 via the half mirror 207, and the point light source 209 is installed at the focal position of the lens 211 via the half mirror 210.
Light from the point light source 206 is projected by the lens 208 as a parallel light beam onto the cornea 120 of the eye 103 to be inspected, and light from the point light source 209 is projected onto the cornea 120 as a parallel light beam by the lens 211.

The parallel light beam by 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 and is guided to the total reflection mirror 212.
Reflected by 12. On the other hand, the parallel light beam by the lens 208 is reflected by the surface of the cornea 120 as divergent 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, The light is reflected by the reflection mirror 213. Bright spot images 214 and 215 based on point light sources 206 and 209 are formed on the cornea 120 by the corneal specular reflection.

A telecentric stop 216 is installed on the object side in front of the reflection direction of the total reflection mirror 212, a telecentric stop 217 is installed on the object side in front of the reflection direction of the total reflection mirror 213, and the telecentric stops 216 and 217 are lenses 208. , 211
Is located at the rear focal point. Here, the lens 208, the total reflection mirror 212, the aperture 216 (the lens 211, the total reflection mirror 213,
The stop 217) forms a light receiving optical system. Total reflection mirror 2
The light reflected by the light sources 12 and 213 passes through the apertures 216 and 217 and is guided to the lenses 218 and 219, respectively. Aperture 216, 2
Reference numeral 17 relates to each of the lenses 218 and 219, which is conjugate with the image sensor 221. The stops 216 and 217 are located at the focal positions of the respective lenses 218 and 219. The lenses 218 and 219 are installed telecentrically on the image side, and the reflected light guided to the lenses 218 and 219 forms an image on a two-dimensional image sensor 221 as a third light receiving unit.

According to this alignment optical system 200, as shown in FIG. 12, even when the working distance of the measuring device is shifted in the optical axis direction with respect to the eye 103 to be inspected, the optical axis O of the alignment optical system 200 on the object side is shifted. The optical axis O ₁ of the alignment optical system 200 when the angle θ _{1 formed} between ₁ and the principal ray does not deviate from the working distance.
And equal to the angle theta ₁ for the principal ray, also, the alignment optical system 200 when the angle formed theta ₂ for the optical axis O ₁ and the principal ray of the alignment optical system 200 of the image side is not deviated working distance equal to the angle theta ₂ for the optical axis O ₁ and the principal ray. The two-dimensional image sensor 221 has each point light source 206,
Bright spot images i ₁ ′ and i ₂ ′ based on 209 are split at symmetrical positions with respect to the center O ₂ as shown in FIG. On the other hand, the working distance matches the corneal vertex 120P,
When the alignment of the measuring device is shifted in the left-right direction with respect to 103, as shown in FIG. 13, the angle θ _{1 formed} between the optical axis O ₁ of the alignment optical system 200 and the principal ray on the object side.
20 when the working distance is not shifted
It is equal to the angle θ ₁ between the optical axis O _{1 of} 0 and the principal ray, and
The angle formed between the order to the angle theta ₂ is the optical axis O ₁ and the principal ray of the alignment optical system 200 when no shift working distance between the optical axis O ₁ and the principal ray of the alignment optical system 200 of the image side theta
Equal to ₂ . In this case, luminescent spot image i _1, i ₂ is without separation, shifts the position of the origin O ₂ of the two-dimensional image sensor 221.

Here, the focal length of the lens 208 is f ₁ , the focal length of the lens 218 is f ₂ , and the aperture 216 is considered as a reference. In FIG. 12, when the working distance is shifted by ΔZ, the position of the chief ray becomes ΔZ · sin θ ₁ compared to the case where the working distance is not shifted.
Just shift.

The optical system formed by the lens 208, the stop 216, and the lens 218 is telecentric on the object side and the image side as shown in FIG. Bright point i ₁ ′ or i ₂ ′ from center O ₂
Is a proportional relationship.

Therefore, when the magnification of the optical system beta, a relationship of ΔZsinθ _{1 =} β · ΔXcosθ _2.

Therefore, the deviation ΔZ of the working distance is It is expressed as

Incidentally, when the luminescent spot image i ₁ is to the right of the bright spot image i _2, [Delta] X
Is positive and vice versa when ΔX is negative.

By the way, since the bright spot images i ₁ ′ and i ₂ ′ are not particularly distinguishable, if they are formed on the two-dimensional image sensor 221 at the same time, the distinction cannot be made. Even if they can be distinguished from each other, if they overlap each other, the position cannot be accurately obtained. Accordingly, 'to emit light 206 point corresponding to its reflexes i _1' luminescent spot image i ₁ to accumulate image data of the two-dimensional image sensor 221 of the frame memory, then luminescent spot image i ₂ ' Is caused to emit light, and the image data of the bright spot image i ₂ ′ is accumulated in the frame memory,
The distance between the bright spot images i ₁ ′ and i ₂ ′ is obtained based on the image data. If the interval 2ΔX between the bright spot images of the two-dimensional image sensor 221 is measured, f ₁ , f ₂ , θ ₁ , and θ ₂ are known, and thus the working distance deviation ΔZ is obtained. The distance to the reference position is obtained.

When the lens 218 is slightly shifted upward in the direction perpendicular to the paper and the lens 219 is shifted downward in the direction perpendicular to the paper, when the working distance is predetermined as shown in FIG.
Since the bright point images i ₁ ′ and i ₂ ′ are formed on the two-dimensional image sensor 221 in a vertically split state, the point light source 20
The measurement can be performed even when both 6, 209 are turned on. However, strictly speaking, the principal rays of the bright spot images i ₁ ′ and i ₂ ′ deviate from the vertical plane of the observation surface of the two-dimensional image sensor 221, so that the relationship between ΔX and ΔZ slightly deviates. Is negligibly small.

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

Embodiment 3 FIG. 16 shows an embodiment using a confocal optical system as a corneal distance measuring system.

The corneal distance measurement system includes a light source 300, a condenser lens 301, a pinhole plate 302 as a first stop, a collimator lens 303 as a relay lens, a beam splitter 304, and an objective lens.
305, lens 306, spatial filter 307, light receiver 308
Consists of The light emitted from the light source 300 is collected by a condenser lens 301.
And is converged on the pinhole plate 302. The pinhole plate 302 serves as a secondary point light source, and light passing through the pinholes of the pinhole plate 302 is reflected by the beam splitter 304 and is converted into a parallel light beam by the collimator lens 303.

The parallel light beam is reflected toward the objective lens 305 via the lens 306, and is guided to the eye 103 as a convergent light beam.
The objective lens 305 geometrically optically focuses the parallel
It plays the role of condensing light. Pinhole plate 302 and focal point 3
09 is conjugate with respect to the collimating lens 303 and the objective lens 305, and the light-converging point 309 and the spatial filter 307 are conjugate with respect to the objective lens 305 and the lens 306. In other words, the condensing 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 points other than near the confocal point 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 focal point 309.

Lens 306, where is can move back and forth in the optical axis O ₃ direction, the lens 306 is facing the linear encoder 310 as a position detection mechanism, the output of the linear encoder 310 is input to the position detection circuit 311 I have. Linear encoder 3
10 and the position detection circuit 311 serve to detect the position of the lens 306. The output of the light receiver 308 is input to the signal processing circuit 313 via the amplifier 312. The signal processing circuit 313 has a function of outputting a trigger signal and a timing signal.
The trigger signal is used when starting driving of the laser diode 130 of the interference optical system, and the timing signal is used when specifying the lens position by the position detection circuit 311. The position detection circuit 311 outputs a lens position detection signal to the arithmetic circuit 156. The arithmetic circuit 156 has a function of calculating the distance from the reference position of the measuring device to the corneal vertex 120P based on the distance relationship between the lens position and the device / focal point 309 that has been previously associated.

Now, when the focal point 309 is at the position shown in FIG. 17 (a), the light reflected from each reflecting surface of the eye cannot pass through the spatial filter 307 and hardly enters the light receiver 308.
The lens 306 is moved along the optical axis O ₃ as shown in FIGS.
When the focusing point 309 approaches the surface of the cornea 120 in a direction close to the subject's eye 103, the cornea 120
The light reflected from the surface starts to pass through the spatial filter 307. Therefore, the output of the light receiver 308 starts 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 first appears.
When the lens 306 is further moved closer to the subject's eye 103, the output from the light receiver 308 includes the back surface of the cornea 120 and the lens 31.
A peak based on the reflected light from the surface 5 appears.

Therefore, if the signal processing circuit 313 outputs the trigger signal and the 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. Then, the arithmetic 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 is started based on the trigger signal.

According to the confocal optical system, if sufficiently large design numerical aperture of the objective lens 305 (NA), as shown in FIG. 18, a direction perpendicular focal point 309 with respect to the optical axis O ₃ Even if the corneal vertex 120P slightly deviates from the corneal apex 120P, as long as the surface of the cornea 120 and the focal point 309 coincide, the light receiver 308 can receive almost all the reflected light from the surface of the cornea 120, , The alignment error of the measuring device with respect to

For example, the radius of curvature R of the cornea 120 is 7.7 mm, and the numerical aperture NA at which reflected light does not enter the objective lens 305 at all is 0.25.
When the shift amount of the focal point 309 with respect to the direction perpendicular to the corneal vertex 120P with respect to the optical axis O ₃ delta becomes 1.93 mm. However, the focal point 30 with respect to the corneal vertex 120P in a direction perpendicular to the optical axis O ₃
When 9 is shifted 1.93 mm, as shown in FIG. 19, with respect to the actual corneal vertex 120P to the optical axis O ₃ direction position of the focal point 309 0.25 m
m, the shift amount Δ cannot be designed to be as large as about 1.93 mm. However, if the shift amount Δ is designed to be about 0.5 mm, the position of the focal point 309 with respect to the actual corneal vertex 120P in the optical axis direction can be reduced. The displacement is about 0.016 mm, and the displacement of the focal point 309 in the optical axis direction can be ignored. In FIG. 18, the hatched portions indicate the reflected light from the cornea.

Since the configuration of the interference optical system 101 is substantially the same as in the first and second embodiments, the same components are denoted by the same reference numerals. In FIG. 16, reference numeral 314 denotes a dichroic mirror, lens 306 corresponds to the lens 137 of the first embodiment, and lens 303 corresponds to the collimating lens 136 of the first embodiment.

In the above embodiment, the model eye unit 141 is formed by the two surfaces of the cornea and the fundus, and the measurement of the axial length has been described. However, by setting this to each surface of the crystalline lens or the inner surface of the cornea, etc. The present invention can be applied to measure the intraocular length between them.

(Effect) 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 component.

As described above, in the length measuring device according to claim 3 of the present invention, the corneal vertex is measured using the geometric optical system, and the fundus position is measured using the interference optical system. Even if strict alignment accuracy is not required, the axial length of the eye can be accurately measured.

[Brief description of the drawings]

1 to 9 are explanatory views for explaining a first embodiment of a length measuring apparatus according to the present invention, and FIG. 1 is a view showing an optical system of the length measuring apparatus according to the present invention. FIG. 2 is a diagram showing a ring image formed on the two-dimensional image sensor shown in FIG. 1, and FIGS. 3 and 4 are diagrams for schematically explaining the operation of the corneal distance measuring optical system shown in FIG. FIG. 5 is an explanatory diagram for explaining corneal vertex position detection, FIG. 6 is an optical diagram for explaining the operation of the interference optical system, and FIG. 7 is an ocular axis based on a corneal vertex position and a 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 according to the present invention. FIG. 10 is a diagram showing a second embodiment of the long device, FIG. 10 is an optical diagram showing a corneal distance measuring system, FIG. 11 is a diagram showing the interference optical system, FIGS. 12 and 13 are optical schematic diagrams showing the operation of the corneal distance measuring system, and FIGS. 14 and 15 are luminescent 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 corneal distance measuring system thereof. FIG. 18 and FIG. 19 are explanatory diagrams showing a change in the position of the converging point of FIG. 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 lenses 107, 221, 308: two-dimensional image sensor ( Third light receiving unit) 110: diaphragm (second diaphragm), 124: diaphragm (first diaphragm) 120: cornea, 120P: corneal vertex 130: laser diode 132: beam splitter 139: reference mirror ( Surface for measuring object) 144 Reference mirror (reference object) 142 Photosensor (first light receiving unit) 146 Photosensor (second light receiving unit) 145 Reference mirror (surface for reference object) 147 ... Reference interference light path 160... Fundus 149... Signal processing circuit (periodic wave signal forming unit) 151... Measurement interference light path 156. , 217, 301, 302… Aperture 303… Collimating lens (relay lens) 304… Beam Splitter, 305 …… Objective lens

────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Akihiro Arai 75-1, Hasunumacho, Itabashi-ku, Tokyo Topcon, Inc. (72) Inventor Hideki Hatanaka 75-1, Hasunumacho, Itabashi-ku, Tokyo Topcon, Inc. ( 56) References JP-A-2-4310 (JP, A) JP-A-2-22502 (JP, A) JP-A-3-269302 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 9/00-9/10 G01B 11/00-11/30 A61B 3/10

Claims (6)

(57) [Claims] 1. A laser light source that emits a laser beam whose wavelength can be changed, a measurement interference optical path for interfering a laser beam reflected by a measurement object and a laser beam reflected by a reference surface corresponding to the measurement object, and the measurement. Forming a reference interference optical path for causing the laser light reflected by the reference object and the laser light reflected by the reference object corresponding reference surface to have an optical path length longer than the interference light path, and forming a laser beam from the laser light source; A beam splitter that guides light to the measurement interference light path and the reference interference light path, a first light receiving unit that receives light guided as interference light via the measurement interference light path, and via the reference interference light path A second light receiving unit that receives light guided as interference light, a laser driving unit that changes an emission wavelength of the laser light source, and a timing of an output signal of the second light receiving unit A periodic wave signal forming unit that samples an output signal of the first light receiving unit using the signal as a signal and forms a periodic wave signal; and an object to be measured based on an optical path length of the reference interference optical path and a period of the periodic wave signal. And a calculation unit for calculating the distance of the length measurement device. 2. The length measuring apparatus according to claim 1, wherein the laser driving section changes the temperature of the laser light source by turning on the laser light source in a pulsed manner. A length measuring device having a configuration that is changed based on a change. 3. A laser light source that emits a laser beam whose wavelength can be changed, a measurement interference optical path that causes the laser light reflected by the fundus of the eye to be examined to interfere with the laser light reflected by the fundus-corresponding reference surface, and the measurement interference optical path. Forming a laser light reflected by the reference object having a longer optical path length and a reference interference light path for causing the laser light reflected by the reference object corresponding reference surface to interfere with the laser light from the laser light source; A beam splitter that guides the measurement interference light path and the reference interference light path, a first light receiving unit that receives light guided as interference light through the measurement interference light path, and an interference light that passes through the reference interference light path A second light receiving unit for receiving the light guided as a laser, a laser driving unit for changing the emission wavelength of the laser light source, and an output signal of the second light receiving unit as a timing signal. A periodic wave signal forming unit that samples an output signal of the first light receiving unit to form a periodic wave signal, and obtains a distance to a fundus based on an optical path length of the reference interference light path and a period of the periodic wave signal. A fundus position measuring unit, an irradiation optical system that irradiates a cornea of the eye with a light beam, a light receiving optical system that guides reflected light from the cornea to a third light receiving unit, and the light receiving unit that is based on an output of the third light receiving unit. A length measuring device, comprising: a corneal position measuring unit that obtains a corneal position of an eye examination; and measuring an axial length of the eye to be examined from the corneal position and a fundus position. 4. The length measuring device according to claim 3, wherein the light receiving optical system is configured to reflect the light reflected from the cornea of the eye to be examined through a first stop disposed at a position conjugate with the front of the objective lens. A first light receiving system for guiding the light to the third light receiving unit and a second light receiving system for guiding the reflected light from the cornea of the subject's eye to the third light receiving unit via a second stop disposed at a conjugate position with the back of the objective lens; The corneal position measurement unit is configured to obtain a corneal position from a position of the reflected light flux from the cornea of the eye to be examined passing through the first stop and the second stop at the third light receiving unit. Length measuring device 5. The length measuring apparatus according to claim 3, wherein the irradiation optical system is configured to irradiate a parallel light beam obliquely to the cornea of the eye to be examined, and the light receiving optical system is configured to irradiate the cornea of the eye to be examined. An objective lens unit for receiving reflected light obliquely from the lens, and a stop disposed at a rear focal position thereof, wherein the third light receiving unit receives light through the objective lens unit and the third stop. The corneal position measuring unit is configured to obtain a corneal position from a light receiving position at the third light receiving unit. 6. The length measuring device according to claim 3, wherein the irradiation optical system includes: a point light source for irradiating the cornea of the eye to be inspected; and an image of the point light source near the cornea of the eye to be inspected. An objective lens formed so as to be changeable in position, wherein the light receiving optical system is a beam splitter for separating reflected light from the cornea of the eye to be examined from the irradiation optical system after passing through the objective lens, and the objective lens unit. The second light receiving unit is formed from an image of the point light source and a second stop at a conjugate position, and is configured to receive light reflected from the cornea of the subject's eye via the second stop. The corneal position measuring unit is for obtaining the corneal position of the eye to be examined from the intensity of the signal of the second light receiving unit according to the change in the image position of the point light source formed by the objective lens unit, and the fundus position measuring unit Eye from corneal measurement unit Length measuring apparatus and obtaining the length.