JPH0496727A - Dimension measuring device for living body eye - Google Patents

Abstract

PURPOSE:To easily execute the superior observation of interference streaks by allowing the reflected light flux supplied from the first measurement object surface and the reflected light flux supplied from the second measurement object surface to interfere with each other. CONSTITUTION:The ultrared light irradiated from an ultrared ray LED 32 is reflected by a half mirror 33, and led into a beam splitter 55, and the reflected light flux is formed to a parallel light flux by an objective lens 56, and led into a living body eye 31, and reflected by a corona 38, and then passes through the objective lens 56 again, and reflected by the beam splitter 55, and led into a CCD camera 34. The optical axis O1 for the corona top point P is positioned, and when the alignment distance is set, the converged light flux P2' is reflected by the corona 38, and the reflected light flux P3 is reflected to an original light path. While, the parallel light flux P1' is led is as converged light flux to an eye bottom 42 by the corona 38 and a lens 41, and a spot is formed by shifting a refraction force correcting lens 29, and the reflected light flux P4 is reflected to the original light path. The reflected light fluxes P3 and P4 are led to a bream splitter 22, and form a planary wave. Accordingly, the number of interference streaks is made nearly constant, and made rough, and the superior observation is facilitated.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention provides a method for detecting the first image of a living eye by observing interference fringes.
The present invention relates to an improvement in a living eye dimension measuring device that can measure the axial length, anterior chamber depth, crystalline lens thickness, etc., as dimensions from a measurement target surface to a second measurement target surface, in a non-contact manner.

(Prior art) Conventionally, the axial length, anterior chamber depth, crystalline lens thickness, etc., as dimensions from the first measurement target surface to the second measurement target surface of the living eye, are measured using ultrasound. Ocular size measuring devices are known.

This biological eye measurement device projects ultrasound from the front of the eye, draws the reflected waves from the front surface of the cornea, front surface of the crystalline lens, back surface of the crystalline lens, and fundus surface on a cathode ray tube, and records the echogram drawn on the cathode ray tube. It is measured by

By the way, since the measurement accuracy of conventional living eye size measuring devices is about ±0.2 mm, for example, the axial length obtained as a result of measurement is used to calculate l0L (Intraocuja).
r Lens), the measurement accuracy of the axial length was insufficient.

In addition, the conventional ultrasound-based eye dimension measuring device requires a probe to be brought into contact with the living eye during measurement, which is troublesome and requires preventive measures against infection and the like.

Therefore, in recent years, by observing interference fringes, axial length and
BACKGROUND ART A living eye size measuring device that can measure the depth of the anterior chamber, the thickness of the crystalline lens, etc. in a non-contact manner has been proposed.

Figure 5 shows an example of a living eye size measuring device used to measure the axial length.
cher et al, (OPTTC5LETTER
, VOL, 13 N.

3 PP, 186-188 <March
1988 0ptical 5ociety
This is a technology described in the United States of America).

This living eye size measuring device is roughly composed of a semiconductor laser 1, a collimating lens 2, two parallel plane plates 3 and 4, a beam splitter 5, a condensing lens 6, and an imaging camera 7.

A laser beam emitted from a semiconductor laser 1 is converted into a parallel beam by a collimating lens 2 and guided to two parallel plane plates 3 and 4. The parallel light flux (referred to as light flux ■) that has passed through the two parallel plane plates 34 is guided as convergent light to the fundus 9 of the living eye 8 via the beam splitter 5, and is reflected by the fundus 9 to form a substantially parallel light flux (plane wave). It is emitted from the living eye 8 as . The emitted plane wave is reflected by the reflecting surface 10 of the beam splitter 5 in the direction of the condenser lens 6, and is condensed by the condenser lens 6 and guided to the imaging camera 7.

Also, a part of the parallel light beam that has passed through the parallel plane plate 3 is reflected by the parallel plane plate 4 and returns to the parallel plane plate 3 as a reflected light beam (referred to as a light beam ■), and is reflected again by the parallel plane plate 3 to become a parallel light beam. The light reflected by the cornea 11 that passes through the face plate 4 and the beam splitter 5 and is guided to the cornea 11 of the living eye 8 is guided to the beam splitter 5 as diverging light (spherical wave), and is focused on the reflecting surface 10. The light is reflected in the direction in which the light lens 6 exists, is condensed by the condenser lens 6, and guided to the camera 7.

In addition, in FIG. 5, 12 is a light receiving sensor for monitoring the amount of light of the semiconductor laser I.

In this conventional device, the distance d between the parallel plane plate 3 and the parallel plane plate 4 is made variable, and the distance d between the parallel plane plate 3 and the parallel plane plate 4 is made variable.
The refractive index of the substance existing between is n, the refractive index of the intraocular substance is N, and the axial length obtained by measurement (distance from the vertex of the cornea H to the fundus 9) is X, and the equation nd=NX When the distance d is adjusted so as to satisfy the equation, the light beams ■ and ■ have equal optical path lengths, and the camera 7 observes interference fringes. Therefore, the axial length X can be determined by obtaining the distance d at which the interference fringes are observed as a measured value.

(The problem that Bimei is trying to solve) However, in a living eye size measurement device that measures the axial length by observing interference fringes, the reflected light flux from the corneal surface mj is approximately a spherical wave. Since the reflected light flux from the fundus of the eye is a substantially flat mj wave, the number of interference fringes increases as the distance from the corneal apex to the periphery increases, making it impossible to observe interference fringes well. There is a problem.

In particular, the light reflected from the fundus of the eye cannot actually be considered to be a plane wave due to the refractive power of the eye, and on top of that, the number of interference fringes is limited due to the fact that the interference fringes are concentrated in the center. It was difficult to read.

In addition, this living eye size measuring device requires accurate alignment of the optical axes of the condenser lens 6 and camera 7 with respect to the living eye 8, but there is also the problem that alignment is extremely troublesome. .

The present invention has been made in view of the above-mentioned problems, and its purpose is to facilitate good observation of interference fringes, and to improve measurement accuracy without being affected by the refractive power of the eye to be examined. It is an object of the present invention to provide a dimension measuring device for a living eye, which can be expected to improve.

(Means for Solving the Problems) In order to achieve the above object, the living eye dimension measuring device according to the present invention projects a light beam with a short coherence length onto the living eye, and comprises the following steps: In the biological eye dimension measuring device that measures the dimension from the first measurement target surface to the second measurement target surface based on the interference between the reflected light flux from the and the second measurement target surface, the coherence length The short light beam of It has a light beam projecting means for projecting light onto the living eye, and a wavefront shape of the reflected light beam from the first measurement object surface and a wavefront shape of the reflected light beam from the second measurement object surface are provided between the optical path splitting member and the optical path combining member. A refractive power correction optical system is provided to make the wavefront shape of the reflected light beam substantially the same in the optical path splitting member, and the reflected light beam from the living eye passes through the optical path of both the projected light beams in reverse, and the optical path splitting member The optical path is synthesized by the member, and the first
It is characterized in that the light beam reflected from the surface to be measured and the light beam reflected from the second surface to be measured are caused to interfere with each other.

(Function) According to the living eye dimension measuring device according to the present invention, the refractive power correction optical system allows the wavefront shape of the reflected light beam from the first measurement object surface and the wavefront shape of the reflection light beam from the second measurement object surface to be adjusted. Since the optical path splitting member allows the interference fringes to be substantially the same, the number of interference fringes is small or substantially constant, making observation easier.

(Embodiment 1) FIG. 1 shows an optical system of a first embodiment of the living eye dimension measuring device according to the present invention, which is used to measure the axial length as the dimension of the living eye.

In FIG. 1, 20 is a semiconductor laser, 21 is a collimating lens, and 22 and 23 are beam splitters. The semiconductor laser 2o has a relatively short coherence length of about O.bnm. this is,
This is because if a lens with a long coherence length is used, interference fringes will be obtained even if the optical path difference is largely shifted, and the accuracy of measuring the axial length will deteriorate. In addition, if an extremely short coherence length is used, interference fringes cannot be obtained even if the optical path difference is slightly shifted, and it is difficult to obtain interference fringes.
However, it takes time for one measurement.

The laser beam emitted from the semiconductor laser 20 is made into a parallel beam by the collimating lens 21. This parallel light flux is transmitted through a beam streak 2 notch 220 as an optical path splitting member.
A parallel light beam P1 guided to the beam splitter 23 and a parallel light beam P guided to the optical path length changing member 25 by the reflective surface 24.
It is divided into 2. The optical path length changing member 25 has a reflective surface 26
．． 27, and has a function of changing the optical path length of the parallel light beam P2 by moving it in the direction of the arrow. When the optical path length changing member 25 is moved by (ΔL/2) in the direction of the arrow, the optical path length of the parallel light beam P2 changes by the shift amount ΔL.

The beam splitter 23 has a reflective/transmissive surface 28 and functions as an optical path combining member. A refractive power correction lens 2 is provided between the beam splitter 23 and the beam splitter 22.
9 is provided. The refractive power correction lens 29 has a function of guiding the parallel light beam P1 that has passed through the beam splitter 22 to the reflective/transmissive surface 28 of the beam splitter 23 as a convergent light beam PI-. Further, the parallel light beam P2 from the optical path length changing member 25 is guided to the bims splitter 23. This parallel light beam r]2 is reflected by the reflective/transmissive surface 28 to become a parallel light beam P2-, and the parallel light beam P2 and the convergent light beam P1' are guided to the objective lens 56 via the beam splitter 55. With this objective lens 56, when the eye to be examined is a normal eye, the convergent light flux P, - becomes a parallel light flux P1'', and the parallel light flux P2
- becomes a convergent light beam P2'' and both are guided to the living eye 31.

The convergent light beam P2' becomes a light beam directed toward the center of corneal curvature 40.

The main body of the device is aligned with the living silver 31 using an infrared LED 32, and the CCD camera 34 is
Used for observing the anterior segment of the eye. Infrared light emitted from the infrared LED 32 passes through a condenser lens 36, a pinhole 37, and a relay lens 49, is reflected by a half mirror 33, and is guided to a beam splitter 55. The light beam reflected by the reflective surface 30 of the beam splitter 55 becomes a parallel light beam by the objective lens 56 and is guided to the biological silver 31. The beam splitter 55 has a function of transmitting semiconductor laser light and reflecting other light.

The infrared light is applied to the cornea 38 which is the first measurement target surface of the living silver 31.
The beam is reflected by the beam splitter 55, passes through the half mirror 33, passes through the imaging lens 35, and is guided to the CCD camera 34. The CCD camera 34 is connected to a TV monitor 44, which will be described later. The alignment of the optical system with respect to the living silver 31 is performed by observing the reflected bright spot of the infrared reflected light beam displayed on the TV monitor 44, and is aligned vertically and horizontally within a plane perpendicular to the optical axis direction of the optical system. By moving the optical system, the optical axis O0 of the optical system is aligned with the corneal vertex P.

When the alignment distance in the optical axis direction of the optical system with respect to the living silver 31 is set so that the convergent light beam P2'' enters toward the corneal curvature center 40 of the cornea 38 of the living silver 31, the second
As shown in the figure, the convergent light beam P2'' is reflected by the cornea 38, and the reflected light beam P, is reflected back to the original optical path.On the other hand, the parallel light beam P,'' guided to the living body silver 31 is reflected by the cornea 38 and the crystalline lens. 41, the light beam is guided as a convergent light beam to the fundus 42, which is the second measurement target surface.

By moving the refractive power correction lens 29, a spot is formed on the fundus 42, and the reflected light beam P4 reflected by the fundus 42 is transferred to the lens 41 and the cornea 3 again.
8 and is reflected back to the original optical path.

Each reflected light beam P3. P4 passes through the original optical path and is guided to the beam splitter 22 (see FIG. 1). Both incident light beams P3 at the beam splitter 22. P4
becomes a plane wave with a substantially flat wavefront shape. The reflected light beam P4 is reflected by the reflecting surface 24 of the beam splitter 22, passes through the imaging lens 46, forms an image on the confocal diaphragm 47, and is guided to the CCD camera 43 as a parallel light beam by the collimating lens 48. The CCD camera 43 is connected to a TV monitor 44.

The measurement of this living silver using the size measuring device is performed as described below.

First, the known reference axial length is assumed to be X8. This reference axial length XB includes the average axial length of living silver 31 (22 mm to 24 m).
m) is used. Here, a model having an average axial length is placed with the eye at a predetermined position, and the optical path length changing member 25 is moved in the direction of the arrow (the first
Suppose that when the optical path length changing member 25 is moved to a position shown in FIG. Parallel light flux P for parallel light flux P at this time
The optical path difference of 2 is defined as a reference optical path difference e. Now, the optical path length of the parallel light beam P1 from point 2 to point 2 is set to 2, and the parallel light beam P2 is reflected at point 1 and passes through the optical path length changing member 25 to point 2. If the optical path length is 1 to 3 + K3 to 4 + K4 to 2, the reference optical path difference L[] is L8'' (KIK3+ to 3 to 4+ to 4 to 2 KIK2+
It is. Note that the predetermined position of the optical path length changing member 25 when the reference optical path difference Le is reached is the reference position.

Furthermore, if the average refractive index of the living silver 31 is N, the optical path difference based on the reference axial length Xe is N-Xe, so that between the quasi-optical path difference L8 and the reference axial length x8, there is L, =N−X,
・・・・・・■ The following relationship holds true.

Next, the optical system is aligned with respect to the living body silver 31 having an unknown axial length X. Assume that no interference fringes are displayed on the TV monitor 44 at this time. Therefore, the optical path length changing member 25 is moved in the direction of the arrow. Assume that interference fringes are displayed on the TV monitor 44 when the optical path length changing member 25 is moved from the reference position by b (ΔL/2).

The optical path length based on the axial length −...■ becomes.

Therefore, the unknown axial length X can be obtained by substituting and transforming the 0 equation into the 0 equation as follows: X=X8+(ΔL/N).

By the way, the interference fringes displayed on the TV monitor 44 are
If the amount of reflected light beam P4 from the fundus 42 and the amount of reflected light beam P3 from the cornea 38 are significantly different, the contrast will be low. This is because the contrast of the interference fringes is
This is because it is best when the amounts of light beams that interfere with each other are equal. Therefore, in this optical system, the reflectance of the reflective surface 24 of the beam splitter 22 is adjusted to increase the amount of reflected light beam P3 from the cornea 38 and the reflected light beam P4 from the fundus 42.
In order to make the amount of light approximately equal to that of the beam splitter 22
The beam splitter 22 is designed so that the amount of laser light reflected by the beam splitter 22 is smaller than the amount of laser light that passes through the beam splitter 22. However, since there are individual differences among the three biological models, the amount of light reflected from the fundus 42 may vary depending on the individual differences.

Therefore, in this embodiment, the beam splitter 22
A variable density filter 45 is provided between the refractive power correction lens 29 and the refractive power correction lens 29 . When the contrast of the interference fringes is low, the variable density filter 45 is rotated to adjust the amount of the reflected light beam P4 from the fundus 42 and the reflected light beam P3 from the cornea 38.
The amount of light is adjusted to be approximately the same as the amount of light, so that interference fringes with good contrast can be obtained. In addition, when measuring the depth of the anterior chamber or the thickness of the crystalline lens, use beam splitter 2.
An optical path length changing member 50 with a high refractive power is inserted between the refractive power correction lens 29 and the refractive power correction lens 29, and the measurement is performed by shortening the optical path length difference between the parallel light beam P1 and the parallel light beam P2.

When the parallel light beam P,'' is projected onto the fundus 42, the biological type 31
When the refractive power of the eye is not normal, the reflected light flux P4 from the fundus 42 deviates from a plane wave, and the reflected light flux P4 from the fundus 42
The wavefront shape of the reflected light beam P3 from the cornea 38 is no longer the same as the wavefront shape of the reflected light beam P3. Correction of the refractive power at this time can be performed by the refractive power correction lens 29. In other words, the refractive power correction lens 29 generates a light beam that is shifted from the parallel light beam P1 according to the refractive power based on individual differences in the living body type 31, so that a small spot is formed on the fundus 42, that is, both wavefront shapes are the same. The refractive power correction lens 29 is moved and adjusted so that.

Therefore, the wavefront shape of both reflected light beams is
They are almost the same and will interfere.

(Example 2) FIG. 3 shows a second example of the biological type dimension measuring device according to the present invention, in which the reflected light flux from the first measurement target surface and the reflected light flux from the second measurement target surface are The unknown axial length X is determined by electrically detecting the interference state.

In the optical system of the dimension measuring apparatus shown in FIG. 3, instead of providing the CCD camera 43, a diaphragm 52, an imaging lens 53, and a photodetector 54 are provided as detection means.

The aperture 52 is provided with a circular optical aperture 56 at its center. Instead of the circular optical aperture 56, a cross slit may be provided to convert the interference light beam into a slit light beam. This diaphragm 52 is selected so that the peak of the interference detection signal S, which will be described later, is appropriate, and the reflected light beam P4 passing through the diaphragm 52
is incident on the photodetector 54.

Measurement by the living body size measuring device according to the second embodiment is performed as described below.

First, as in the first embodiment, the optical path length changing member 25 is adjusted using the known reference axial length X8, and the known reference axial length X8 is adjusted.
. The reference position of the optical path length changing member 25 when the optical path length changing member 25 is obtained is determined in advance.

Next, the biological mold 31 having an unknown ocular axial length X with respect to the reference ocular axial length X8 is set, and the optical path length changing member 25 is moved in the direction shown by the arrow. In response to the movement of the optical path length changing member 25, the photodetector 54 outputs an interference detection signal S as shown in FIG.

That is, as the difference between the optical path length NX corresponding to the unknown axial length The output of the signal S is started, and as the difference approaches zero, the peak of the interference detection signal S becomes larger. Then, the optical path length changing member 25 is further moved in the same direction. Then, the difference between the optical path length NX and the optical path difference increases, the peak of the interference detection signal S becomes smaller, and eventually no change in the interference detection signal S is detected.

Now, assuming that the time when the change in the interference detection signal S begins to appear is t3, and the time when the change in the interference detection signal S ends is t2, for example,
If we decide to obtain the measured value of the axial length X between time t and time t2, then tm = (t 1 + t2) / 2
At the time of , the optical path length changing member 2 from the reference optical path difference L8
By detecting the deviation amount ΔL (equal to the moving distance from the reference position) of 5 and performing calculations based on the following formula, the unknown axial length
can be found.

NX= L8+△L=L, +△L(tmlX=(L8+
ΔL)/N = X, ΔL/N The reason why the interference detection signal S fluctuates is as follows.

The reflected light flux P3 and the reflected light flux P4 are guided to a predetermined area of the photodetector 54 via the aperture 52, so if a bright spot of the interference fringe is located in the predetermined area, the interference detection signal S becomes a positive peak, and the interference fringe When the dark spot of is located, it becomes a negative peak.

According to this second embodiment, based on the electrical detection means,
The cornea 38, which is the first measurement target surface,
Since the state of interference with the reflected light beam from the fundus 42, which is the surface to be measured, can be detected, the dimensions of the living eye 31 can be measured quickly and accurately.

Further, the confocal diaphragm 47 is provided to remove noise on the CcD camera 43.

This noise is caused by the fact that the reflected light flux P3 and the reflected light flux P4 from the living eye 31 are not in the original optical path of the irradiation light flux P and the irradiation light flux P2, and that the reflected light flux P3 is the optical path of the reflected light flux P4, or the reflected light beam P4 is the reflected light beam P3. This occurs when the light enters the optical path of However, the light flux that has passed through an optical path different from the original optical path and is related to noise not only has a different optical path length but is not imaged on the confocal aperture 47, so the confocal aperture 47 The amount of light passing through the pinhole is small and the noise is minute.

By the way, in each example, the cornea 3 which is the first measurement target surface
Although the irradiation position on the cornea 8 is set at the center of curvature 40 of the cornea 38, similar results can be obtained even if the irradiation position is set at the vertex P of the cornea 38.

Although each embodiment has been described above, the reference optical path difference LI3
If is set in accordance with the thickness of the crystalline lens from the front surface to the back surface of the crystalline lens 41, the thickness of the crystalline lens as a dimension of the living eye 31 can be measured. Similarly, if the reference optical path difference Le is set to correspond to the anterior chamber depth from the cornea 38 to the front surface of the crystalline lens 41, the anterior chamber depth can be measured.

(Effects) As explained above, the living eye dimension measuring device according to the present invention uses the refractive power correction optical system to adjust the wavefront shape of the reflected light beam from the first measurement target surface and the reflected light flux from the second measurement target surface. Since the optical path splitting member is used to make the wavefront shapes substantially the same and cause interference, the number of interference fringes becomes approximately constant and becomes coarse, making it easy to observe the interference fringes well.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an optical system of a first embodiment of a living eye size measuring device according to the present invention. FIG. 2 is a diagram showing the reflected light flux from the living eye shown in FIG. 1. FIG. 3 is a diagram showing an optical system of a second embodiment of the living eye dimension measuring device according to the present invention. FIG. 4 is an explanatory diagram of an interference detection signal output from the photodetector shown in FIG. 3. FIG. 5 is a diagram showing an optical system of a conventional living eye dimension measuring device. 22... Beam splitter (optical path splitting member) 23...
・Beam splitter (optical path combining member) 25 2 optical path length changing members ・Refractive power correction lens (refractive power correction optical system) 31 ・
...Living eye 38...Cornea (first measurement target surface) 42...Fundus (second measurement target surface) 52...Aperture

Claims (3)

[Claims] (1) A light beam with a short coherence length is projected onto the living eye, and based on the interference between the reflected light beam from the first measurement object surface of the living eye and the reflected light beam from the second measurement object surface, the first measurement object In a living eye dimension measuring device that measures the dimension from a surface to the second measurement target surface, the light beam with the short coherence length is projected into the first measurement target surface and the second measurement target surface. a light beam projecting means that divides the projected light beam into the projected light beam by an optical path dividing member, combines the optical paths again by an optical path combining member, and projects the light onto the living eye; In between, a refractive power correction optical system is provided for making the wavefront shape of the reflected light flux from the first measurement target surface and the wavefront shape of the reflected light flux from the second measurement target surface substantially the same by the optical path splitting member. The reflected light beam from the living eye passes through the optical paths of both the projected light beams in reverse, and the optical paths are combined by the optical path splitting member,
A dimension measuring device for a living eye, characterized in that a reflected light flux from a measurement target surface and a reflected light flux from the second measurement target surface are caused to interfere with each other. (2) The apparatus further comprises a detection means for electrically detecting an interference state between the reflected light beam from the first measurement object surface and the reflection light beam from the second measurement object surface. A device for measuring the dimensions of the living eye. (3) The light beam projecting means includes an optical path length changing member, the detecting means includes a photodetector that outputs an interference detection signal, and the size of the living eye is determined based on the interference detection signal and the position of the optical path length changing member. 3. The living eye dimension measuring device according to claim 2, wherein the device measures dimensions of a living eye.