JP3116972B2 - Eye axis length measuring device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a measuring optical system in which a measuring light beam is corrected by a correcting optical system in accordance with the refractive power of an eye to be inspected, and is radiated to the eye to be inspected. The present invention relates to an apparatus for measuring an axial length of an eye to be inspected using reflected light incident on the measuring optical system.

[0002]

2. Description of the Related Art Conventionally, there has been known an axial length measuring apparatus which irradiates a measuring light to an eye to be examined and makes the reflected light reflected by the fundus of the eye to interfere with a reference light serving as a reference to measure the axial length. Are known.

In this eye axial length measuring apparatus, a refractive power correcting optical system for correcting the refractive power of the eye to be examined is provided so that the measuring light can always be focused on the fundus irrespective of the refractive power of the eye to be examined. This is because if the irradiated measurement light is not sufficiently focused on the fundus, the reflected light obtained will be weak, and the wavefront of the reflected light of the fundus and the wavefront of the reference light will be significantly different, and sufficient interference light will be obtained. Therefore, accurate measurement of the axial length is hindered, which is intended to prevent this.

[0004]

However, when the eye to be examined is accompanied by astigmatism, the refractive power correcting optical system cannot sufficiently collect the measurement light on the fundus, and it is difficult to accurately measure the measurement light due to the shortage of reflected light. There is a problem that it becomes impossible to measure the eye axial length.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide an axial length that allows measurement light to be condensed on the fundus even when the eye to be examined is astigmatic. It is to provide a measuring device.

[0006]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention corrects a measurement light beam according to the refractive power of an eye to be inspected by a correction optical system and irradiates the light to the eye to be inspected. An eye axial length measuring apparatus that includes a measuring optical system on which reflected light is incident, and measures an axial length of an eye to be inspected using reflected light incident on the measuring optical system, wherein the eye cornea is ring-shaped. A ring illumination optical system that illuminates the cornea, a corneal measurement optical system on which corneal reflection light reflected by the cornea of the eye is incident, and a radius of curvature of the cornea of the eye to be calculated from the corneal reflection light incident on the cornea measurement optical system. Corneal curvature calculating means for obtaining the astigmatic intensity and the astigmatic axis, and the correction optical system rotate with respect to the optical axis.
The astigmatism correction optical system is provided rotatably, the correction intensity and the direction of the astigmatism axis change according to the amount of rotation, and the astigmatism correction optical system based on the astigmatism intensity and the astigmatism axis calculated by the corneal curvature calculation means. Rotating means for rotating and correcting astigmatism of the cornea of the eye to be examined.

[0007]

According to the present invention, with the above arrangement, the ring illumination optical system forms a ring virtual image inside the cornea of the eye to be inspected, the corneal measurement optical system receives the corneal reflection light reflected by the cornea, and the corneal curvature calculating means includes: Calculate the radius of curvature of the cornea of the eye to be examined from the corneal reflected light, calculate the astigmatic intensity and the astigmatic axis, and rotate the astigmatism correcting optical system based on the astigmatic intensity and the astigmatic axis to correct the astigmatism of the cornea of the eye to be examined. I do.

[0008]

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

FIG. 1 shows an arrangement of an optical system of an eye axial length measuring apparatus. This optical axis length measuring apparatus includes an optical axis length measuring optical system (measuring optical system) 10 and a corneal curvature measuring optical system ( Corneal measurement optical system) 100.

The axial length measuring optical system 10 has a measuring optical system 20 for emitting a laser beam toward the eye E to be examined, and a reference interference optical system 70 having a reference optical path.

The measuring optical system 20 includes a semiconductor laser (laser light source) 11 for emitting laser light, a collimator lens 12 for converting the laser light into a parallel light beam, and an optical isolator for preventing reflected light from entering the semiconductor laser 11. and Les chromatography motor 13, a beam splitter 14 which leads to the reference interference optical system 70 of one of the laser beam is divided into two laser beams, measuring interference optical system to irradiate toward the other side of the laser beam onto the eye E 30 And A heating / cooling plate (not shown) is attached to the semiconductor laser 11, and a Peltier effect element (not shown) is attached to the heating / cooling plate. And
By controlling the Peltier effect element, the temperature of the semiconductor laser 11 chip is controlled.

The measurement interference optical system 30 is a beam splitter for splitting the other laser beam split by the beam splitter 14 into a corneal irradiation laser beam and a fundus irradiation laser beam.
15, a corneal irradiation optical system 40 for converging the corneal irradiation laser light to a vertex of the cornea of the eye E through an objective lens 17 and irradiating the cornea Ea, and the fundus irradiation laser light through the objective lens 17 The light is focused on the fundus Er of the eye E to be examined and the fundus Er is collected.
And a light receiving optical system 60 that receives interference light between the fundus reflection light reflected by the fundus Er and the cornea reflection light reflected by the cornea Ea.

The corneal irradiation optical system 40 includes a total reflection mirror 41,
An optical path length correction plate 42 for matching the optical path lengths of the fundus illumination optical system 50 and the corneal illumination optical system 40, a condenser lens 43, and a corneal vertex Ea
Aperture located at a conjugate position to remove reflected light other than the cornea
44 and has. The optical path length correction plate 42 is composed of at least two members, and is configured such that the optical path length to be corrected differs depending on whether or not an astigmatism correction optical system described later exists in the optical path.

The fundus illuminating optical system 50 includes a condenser lens 52, an aperture 53 disposed at a position conjugate with the fundus Er for removing reflected light other than the fundus, a collimator lens 54, and a total reflection mirror 55.
When, and a correction optical system 56, and a beam scan splitter 57. The beam splitter 57 combines the light beam of the cornea irradiation optical system 40 with the light beam of the fundus irradiation optical system 50 and irradiates the eye E as coaxial light.

The correcting optical system 56 moves in the optical axis direction to correct the refractive power of the eye E, and an astigmatism correcting optical member (astigmatic correcting optical system) for correcting astigmatism of the eye E. 59 and has.

The astigmatism correcting optical member 59 can be moved from the solid line position shown in the drawing to the outside of the optical path shown by the broken line, and is composed of a cylindrical lens having the same absolute value and different signs.
It is composed of two cross cylinders 59a and 59b (see FIG. 2).

As shown in FIG. 2, the cross cylinders 59a and 59b are rotatable around the optical axis 50a. The cross cylinders 59a and 59b maintain the cross angle 2α of the cross cylinders 59a and 59b in the same direction. 59a, 59b cylindrical axis M,
By rotating the axis P in the intermediate direction of N around the optical axis 50a, the astigmatic axis of the eye E can be corrected.
Also, cross cylinders in opposite directions about axis P
The astigmatic strength of the eye E is corrected by adjusting the intersection angle 2α by rotating the 59a and 59b by the same angle.

As shown in FIG. 3, the cross cylinders 59a and 59b are held by rotary cylinders 3 and 4 rotatably fitted to both ends of a cylinder 2 fixed to a base 1. Rotating cylinder 3,
4 is rotated by motors 7 and 8 via gears 5 and 6, and the rotation of the rotary cylinders 3 and 4 causes the cross cylinder to rotate.
59a and 59b are rotated around the optical axis 50a. The base 1 is moved in the direction of the arrow by, for example, a solenoid (not shown), and the astigmatism correction optical member 59 is moved outside or inside the optical path by this movement.

When the astigmatism correcting optical member 59 is inserted into the optical path of the measuring optical system, the optical path length becomes longer by that amount. To prevent this from appearing as an error in the measurement result, tilt the optical path length correction plate 42 provided in the corneal irradiation optical system 40,
The optical path length of the corneal irradiation optical system 40 is configured to be longer by the same amount.

The reference interference optical system 70 includes a beam splitter 1
4, 71, a total reflection mirror 72, a total reflection mirror 73, a light receiver 74 and the like. And the beam splitter 14,
A reference interference optical path is formed by 71 and total reflection mirrors 72, 73, etc., and the laser light reflected by total reflection mirror 72 and the laser light reflected by total reflection mirror 73 are beam splitter 71.
The light receiving device 74 receives the interference light. The reference optical path difference 2 (L1-L2), which is the optical path difference from the beam splitter 14 to the total reflection mirror 72 and the total reflection mirror 73, is set to be sufficiently longer than the eye axis length Leye. The corneal curvature measurement optical system 100 includes a ring illumination optical system 101 that illuminates the cornea Ea of the eye E with light in a wavelength region different from the wavelength region of the laser beam and has a meridional cross section as parallel light. A dichroic mirror 102 that transmits the laser light and reflects the pattern light, a relay lens 103, and a total reflection mirror 104.
, An imaging lens 105, an aperture 106, and a CCD
And a three-dimensional imaging element 107.

Now, when a laser beam is emitted from the semiconductor laser 11 and reaches the beam splitter 15 of the measurement interference optical system 30 via the collimator lens 12, the optical isolator 13, and the beam splitter 14, the laser beam is irradiated with the corneal irradiation laser beam. And a fundus irradiation laser beam. Then, the corneal irradiation laser light is converged on the corneal apex by the corneal irradiation optical system 40 and irradiates the cornea Ea. The cornea irradiation laser light is reflected by the cornea Ea, and the reflected cornea reflected light travels back through the cornea irradiation optical system 40. Aperture of corneal irradiation optical system 40
44 removes light other than the corneal reflection, so that only the corneal reflected light passes through the diaphragm 44 to become a parallel light beam, and the beam splitter 15
To reach.

On the other hand, the fundus irradiating laser beam split by the beam splitter 15 is applied to the fundus
r and is irradiated to the fundus Er. Then, the fundus irradiation laser light is reflected by the fundus Er, and the reflected fundus reflected light is reflected by the fundus irradiation optical system 50. Since the stop 53 of the fundus illumination optical system 50 removes light other than the fundus reflection, only the fundus reflection light passes through the stop 53 and reaches the beam splitter 15 as a parallel light flux. Then, the cornea reflected light and the fundus reflected light interfere with each other at the beam splitter 15, and the interference light is guided to the light receiving optical system 60.

The light receiving optical system 60 includes an image forming lens 61 and a light receiving device.
62, the interference light interfered by the beam splitter 15 is condensed on the light receiving surface 62a of the light receiver 62 by the imaging lens 61, and an interference fringe is formed on the light receiving surface 62a. And the receiver
62 outputs a light receiving signal according to the intensity of the interference fringes.

On the other hand, the laser beam split by the beam splitter 14 and incident on the reference interference system 70 is further split by the beam splitter 71 and reaches the total reflection mirrors 72 and 73, where it is reflected and again transmitted to the beam splitter 71. Reach. In the beam splitter 71, the reflected lights are combined to cause interference with each other, and the interference light is received by the light receiver 74, and the light receiver 74 outputs a light reception signal according to the intensity of the interference light.

Here, the light receiving device when the wavelength of the laser light emitted from the semiconductor laser 11 is changed within a certain range
The axial length is obtained based on the output signals of 62 and 74.

The reciprocating optical path from the beam splitter 15 of the measurement interference optical system 30 to the fundus Er via the fundus irradiation optical system 50 and the reciprocal optical path from the beam splitter 15 to the cornea Ea via the corneal irradiation optical system 40 are described. The optical path difference is determined by the fundus illumination optical system.
Since the optical path of 50 and the optical path of the corneal irradiation optical system 40 are the same, it is 2Leye (a value obtained by converting the axial length of the eye to air).

The optical path difference of the reference optical path of the reference interference optical system 70 is L
= 2 (L1−L2), the wavelength of the laser beam is λ, and the amount of change in wavelength is △ λ (L is constant), the initial phase difference at the photodetector 74 is 2π (L / λ), The phase difference is 2π ｛L
/ (Λ + {λ)}, and by continuously changing the wavelength, the phase difference is changed from 2π (L / λ) to {L / (λ + △).
λ)｝. Here, if λ >> △ λ, the phase difference after the wavelength change is 2π (L / λ−L △ λ / λ
² ) , the change of the phase difference is 2π (L △ λ / λ ² ), and the intensity of the interference fringe observed by the light receiver 74 periodically changes due to the wavelength change.

Similarly, in the light receiver 62, the change in the phase difference is 2
π (2Leye △ λ / λ ² ), and the intensity of interference fringes observed by the light receiver 62 changes. The axial length is calculated from the signals of these periodically changing intensities.

The change in the phase difference at the photodetector 62 is φ1,
Assuming that the change in the phase difference at 74 is φ2, φ1 = 2π (2Leye △ λ / λ ² ) (1) φ2 = 2π (L △ λ / λ ² ) (2) From these, when △ λ / λ ² is eliminated, Leye = L · φ1 / 2φ2 (3), and Leye can be calculated by calculating the amount of change in the phase difference between the signals obtained by the photodetectors 62 and 72 (L Is known). When Leye is found, the refractive index eyee inside the eyeball
The axial length is determined by dividing by (average value in consideration of the structure and composition).

Eye axial length (AL) = Lye / neye (4) Next, the wavelength change and signal processing will be described.

The semiconductor laser 11 is pulsed (FIG. 5 (a)
Reference). When the semiconductor laser is turned on,
The temperature of the semiconductor laser 11 chip rises, and it takes time for the temperature to reach equilibrium. When the temperature of the semiconductor laser 11 chip changes, the oscillation wavelength changes, and the relationship between the temperature and the wavelength corresponds one-to-one except at the position where the mode hop occurs. That is, the semiconductor laser 11
When turned on, the temperature of the semiconductor laser 11 chip changes, and the wavelength of the emitted laser beam changes accordingly.

This temperature change is represented by a square wave signal in FIG.
As shown in (1), the change immediately after the start of oscillation is abrupt and gradually converges. After a certain time, the semiconductor laser 11 is turned off to return the temperature to the original state, and the irradiation of the laser beam is stopped. By the pulse driving of the semiconductor laser 11, the average irradiation light amount can be reduced to increase the measurement light amount. The pulse width is determined in consideration of the width of the wavelength change. For example, when the semiconductor laser 11 is driven in a rectangular shape at a speed of about 1 KHz, it is possible to use a main part whose wavelength changes with a change in temperature, and also has reproducibility.

The semiconductor laser 11 has a mode hop interval wider than the wavelength change width, and the reference temperature of the semiconductor laser 11 shown in FIG. 4 is set so that the mode hop does not occur during the temperature change during the pulse period. The control circuit 201 controls the Peltier device (not shown). That is, the reference wavelength of the laser beam is controlled.

In response to this temperature change, the oscillation output changes (there is a transition period until the output is stabilized when a rectangular input is applied and turned on, and the output fluctuation portion that is the transition period is omitted in FIG. 5A). ) Converges very quickly, so that it can be said that there is almost no change in intensity during the pulse period (therefore, actually, it is used from the point of time after this transition period). However, the change in the wavelength at this time is not linear, but changes first and then gradually decreases. Therefore,
The frequency of the resulting signal is very high initially and gradually decreases over time.

As can be seen from FIGS. 5C and 5D, the frequencies of the light receiving signals S1 and S2 output from the light receivers 62 and 54 are also high in the initial period, and gradually decrease with time. Therefore, the signals S1 and S1 shown in (c) and (d) of FIG.
2 is subjected to A / D conversion using a trigger of a constant frequency as it is, and if this is used as data, the signal is recorded as a signal whose frequency is high in the initial period and gradually decreases as time passes. Cannot accurately calculate the period of the signal.

Now, when the equation (3) is modified, 2Leye / L = φ1 / φ2 (5)

This means that the ratio of the change in the phase difference between the reference optical path and the measurement optical path is the same as the ratio of the optical path difference. In other words, if the wavelength changes by a certain amount, the change in the phase difference is proportional to the optical path difference, so when comparing the signal in the reference optical path and the signal in the measurement optical path, the ratio of the phase change always becomes the ratio of the optical path difference at the same time. I have. This is true no matter how the wavelength of the semiconductor laser 11 changes if it is continuous. Therefore, if the optical path difference of the reference optical path is made sufficiently long with respect to the measurement optical path, and the interference signal from the reference optical path is used as a trigger signal to sample the interference signal of the measurement optical path, and the sampled data is arranged in order, the apparent A signal with an equal period is obtained.

That is, one trigger signal is generated every one cycle of the interference signal from the reference optical path, and the measurement signal is sampled and written into the memory by this trigger signal. It means to think by replacing with an address. Since the ratio between the measurement signal cycle and the trigger cycle is constant, the signal on the memory is an equal cycle signal. Thus, the signal is stored in the memory for each pulse.

Next, the periodic analysis is performed from the stored data. Since an actual signal contains electrical noise, random noise is removed by averaging a plurality of pulses, for example, 128 pulses. , Perform periodic analysis.

The period T obtained here means the ratio φ1 / φ2 = T with respect to the trigger of the signal. Therefore, when the period T is obtained, Leye is immediately obtained from the equation (5). In practice, since the signal is also riding with different reflective surfaces or these reflected light of internal eye are sorted during cycle analysis.

FIG. 4 shows the eye axis length Ley by the above method.
FIG. 4 is a block diagram showing a configuration of a signal processing circuit for obtaining e.

The configuration and operation will be described below with reference to the waveforms shown in FIG.

[0043] In FIG. 4, 201 denotes a semiconductor laser by the Peltier-effect element (not shown) together with driving the semiconductor laser 11 supplies the semiconductor laser 11 to <br/> Pulse current (see (a) of FIG. 5) 11 is a drive control circuit for controlling the temperature of the chip, 202 is a trigger circuit and
The trigger signal Sg is output as shown in (e) of FIG. 5 for each cycle of the light receiving signal S2 output via the signal line 03. The light receiving signal S1 output from the optical receiver 62 via the amplifier 205 is changed to the trigger signal Sg output from the trigger circuit 202.
The A / D converter 204 performs A / D conversion at the timing shown in FIG. Reference numeral 206 denotes a memory for storing the digital value A / D converted by the A / D converter 204. As shown in FIG. 5F, the memory stores a digital value corresponding to the amplitude value of the signal S1. Go.

Then, the arithmetic circuit 207 performs a period analysis based on the data stored in the memory 206 to obtain a period T, and calculates the axial length AL from the period T according to the equations (5) and (4). .

In the method described above, when irradiating the fundus Er with measurement light, it is necessary to sufficiently condense the measurement light on the fundus Er. If the measurement light is not sufficiently condensed on the fundus Er, the light reflected on the fundus Er no longer has the same wavefront as the irradiation light, and is difficult to pass through the diaphragm 53. Further, the wavefronts of the fundus reflection light and the corneal reflection light synthesized by the beam splitter 15 are not the same, and the interference efficiency of the reflected lights decreases, and the efficiency of the interference signal output from the light receiver 62 decreases. .

Therefore, the refractive power of the eye E to be inspected is corrected by the refractive power correcting lens 58 provided in the fundus illuminating optical system 50, so that the fundus irradiating laser light is constantly applied to the fundus Er regardless of the refractive power of the eye E. It is possible to collect light sufficiently. However, when the eye E has astigmatism, the laser light irradiating the fundus cannot be sufficiently focused on the fundus Er. Therefore, the astigmatism correction optical member 59 is provided in the correction optical system 56.

The astigmatism correcting optical member 59 corrects the astigmatic axis and the astigmatic strength of the eye E based on the rotation angles of the cross cylinders 59a and 59b as described above. This correction can be used if the astigmatism intensity and the axis of astigmatism are not known in advance.
Since the correction is performed by trial and error, there is a problem that the operation is very troublesome and takes a long time.

Therefore, in this embodiment, the astigmatism intensity and the astigmatism axis are measured to automatically correct the astigmatism. In astigmatism, astigmatism caused by a difference in the radius of the corneal curvature in the radial direction, that is, corneal astigmatism occupies a large portion, and the corneal astigmatism is measured by the corneal curvature measuring optical system 100.

When the ring illumination optical system 101 of the corneal curvature measurement optical system 100 illuminates the eye-shaped cornea Ea with a ring-shaped pattern light, a ring virtual image I is formed inside the cornea Ea by the light reflected by the cornea Ea. You. The virtual image reflected light forming the ring virtual image I passes through the objective lens 17 and is reflected by the dichroic mirror 102. The virtual image reflected light reflected by the dichroic mirror 102 passes through a relay lens 103, a total reflection mirror 104, an imaging lens 105, and an aperture 106 to form a ring image on a two-dimensional image sensor 107. Since the imaging magnification of the corneal curvature radius measurement optical system 200 is known, the corneal curvature radius can be calculated by examining the radius of the ring image formed on the two-dimensional image sensor 207. The corneal curvature radius is calculated by the curvature calculation circuit 300.

When the eye E has astigmatism, the ring image has an elliptical shape. If the major axis, the minor axis, and the major axis of the ellipse are determined in the axial direction, the corneal astigmatism intensity and the astigmatic axis can be calculated. A method of calculating corneal astigmatism from a ring image by corneal reflection is well known and will not be described.

The controller 301 shown in FIG. 6 controls the rotation of the motors 7 and 8 via the drivers 302 and 303 according to the calculation result of the curvature calculation circuit 300. With this control, the rotating cylinders 3 and 4 shown in FIG. 3 are rotated by an angle corresponding to the calculation result. That is, the cross cylinders 59a and 59b are
It is rotated by an angle corresponding to the calculation result around 50a, that is, the axis P (see FIG. 2) in the intermediate direction between the cylindrical axes M and N of the cross cylinders 59a and 59b is matched with the astigmatic axis of the eye E to be examined. The intersection angle 2α between the cross cylinders 59a and 59b is set to an angle corresponding to the astigmatic intensity, and the astigmatic axis and the astigmatic intensity are corrected. The controller 301 and the motors 7 and 8 constitute a rotating unit.

By these corrections, even if the eye E is astigmatic, the fundus irradiating laser light emitted from the fundus irradiating optical system 50 can be sufficiently focused on the fundus Er, and as a result, the laser light output from the light receiver 62 can be obtained. The efficiency of the interference signal can be increased.

In this embodiment, a part of the optical axis 10a of the eye axis length measuring optical system 10 and a part of the optical axis 100a of the corneal curvature measuring optical system 100, that is, the optical axis from the eye E to the dichroic mirror 102 is made common. The corneal curvature radius measurement optical system 10
The axial direction of astigmatism calculated with respect to 0 is the axial direction with respect to the ocular axial length measurement optical system 10, and the astigmatic axis can be corrected using the value calculated by the curvature calculation circuit 300 as it is. It can be done easily.

FIG. 7 shows a second embodiment. In this embodiment, a corneal apex distance measuring function is added to a corneal curvature radius measuring function, a fundus distance measuring optical system 300 for measuring a distance from a reference position of the apparatus to the fundus, and a cornea for measuring a distance to the cornea. Corneal curvature measurement optical system 40 with distance measurement function
0.

First, the method for measuring the distance to the fundus will be described, and then the corneal distance measurement will be described.

In this embodiment, the axial length is obtained by measuring the distance to the fundus by an interferometry and calculating the difference between the measured value and the distance to the cornea obtained by the corneal curvature measuring optical system 400.

The fundus distance measuring optical system 300 comprises a measuring light irradiation optical system 310 for irradiating a laser beam having a single wavelength and a wavelength changeable toward the eye E, and a reference interference system 70.

The measurement light irradiation optical system 310 is a semiconductor laser 1
1, a collimator lens 12, an optical isolator 13, a beam splitter 14, a condenser lens 311 and a spatial filter 3.
12, a beam splitter 313 that divides the laser light that has passed through the beam splitter 14 into a fundus irradiation laser light and a reference laser light, and focuses the fundus irradiation laser light to the fundus Er via the objective lens 17. A measurement interference optical system 320 that irradiates the fundus Er and reflects the fundus reflection light reflected by the fundus Er, and a beam splitter 313 that reflects the reference laser light by a mirror (reference surface) 315 via a collimator lens 314. The reference optical system 330 returning to the beam splitter 3 and the fundus reflection light incident on the measurement interference optical system 320 and the reference laser light returned to the beam splitter 313
A light receiving optical system for generating interference and receiving the interference light at 13
340.

The measurement interference optical system 320 includes a collimator lens 3
21, a correction optical system 56, and a dichroic mirror 322 that reflects laser light and transmits ring illumination light.

The light receiving optical system 340 is configured to reflect the fundus reflected light and the reference surface 315.
An aperture 341 for removing reflected light other than the reference light reflected by the
It has an imaging lens 342 and a light receiver 343, and interference light interfered by the beam splitter 313 is condensed on the light receiving surface 343a of the light receiver 343 by the imaging lens 342, and interference fringes are formed on the light receiving surface 343a. You. Then, the light receiver 343 outputs a light receiving signal according to the intensity of the interference fringes.

[0061] With this configuration, interference light received by the light receiving unit 343, the difference in optical path length Lr from the optical path length Lt and bi chromatography beam splitter 313 from the beam splitter 313 to the fundus Er to the reference plane 315 2 It has twice the phase difference. Here, when the wavelength of the laser light emitted from the semiconductor laser 111 is changed within a certain range and the light receiving signals of the light receivers 343 and 74 are processed according to the same principle as in the first embodiment, the reference plane 210 ( The distance from the fundus R to the fundus R (Lt-L)
r) can be measured.

On the other hand, the corneal curvature measurement optical system 400 has a ring illumination optical system 101, a first imaging optical system 410, and a second imaging optical system 430.

The first image forming optical system 410 includes an objective lens 17,
Half mirror 411, relay lens 412, mirror 413
, Relay lens 414, aperture 415, and imaging lens 416
And a two-dimensional imaging element 417 and the like.

The second imaging optical system 430 includes the objective lens 17 and
Mirrors 431 and 432, relay lens 433, mirror 434,
Aperture 435, half mirror 436, imaging lens 416, 2
A three-dimensional image sensor 417 and the like.

When the eye E is illuminated with a ring-shaped pattern light by the ring illumination optical system 101, a ring virtual image I is formed inside the cornea Ea by the light reflected by the cornea Ea.

The virtual image reflected light forming the ring virtual image I passes through the objective lens 17 and the dichroic mirror 322 and reaches the half mirror 411. One virtual image reflected light split by the half mirror 411 is formed by the relay lens 412 as a ring-shaped aerial image Ia. Then, as shown in FIG. 8, a ring image I1 is formed on the light receiving surface 417a of the two-dimensional image sensor 417 via the mirror 413, the relay lens 414, the aperture 415, and the imaging lens 416. Here, the imaging magnification of the ring image I1 is 0.5.

The other virtual image reflected light split by the half mirror 411 reaches the mirror 431 of the second image forming optical system 430, is reflected there, and the ring-shaped aerial image Ib is rearward of the mirror 431 by the objective lens 17. It is imaged. And mirror 432,
Relay lens 433, mirror 434, aperture 435, half mirror 4
36, the light receiving surface of the two-dimensional imaging element 417 via the imaging lens 416
At 417a, a ring image I2 is formed as shown in FIG. Here, the imaging magnification of the ring image I2 is set to be larger than the imaging magnification of the ring I1.

The stop 415 serves as a second stop, and the relay lenses 414 and 412
The conjugate image 415 'is relayed to the rear focal position of 17 and formed at that position. The first imaging optical system 410 is telecentric on the object side.

The stop 435 serves as a first stop, and is relayed in front of the eye E (in front of the objective lens 17) by a relay lens 433. In this case, a conjugate image 435 'is 25 to 50 mm in front of the eye to be examined. Formed at the location.

Here, the relationship between the objective lens 17 and the apertures 415 and 435 will be described with reference to FIGS.

FIGS. 9 and 10 show the optical path of the second imaging optical system 430 and the optical path of the first imaging optical system 410. FIG.

Now, a position on the optical axis O where the conjugate image 435 'of the stop 435 is formed is defined as an origin G, and a reference position Y is set at a position separated from the origin G by a distance L1 in the optical axis direction. This reference position Y is determined at a position where neither the ring images I1 nor I2 is out of focus. The object height is h at the reference position Y.
(Corresponding to the radius of the ring image I). At this time,
The image height formed on the observation surface 417a (the position of the two-dimensional image sensor 417) by the second imaging optical system 430 is y1, and the image height formed on the observation surface 417a by the first imaging optical system 410 is y2. . Next, the known object is moved by the distance X0, and the image heights at this time are defined as y1 'and y2'.

The distance from the observation surface 417a to the point Z is L1 ', the distance from the reference position Y to Z' is L2, and the distance from the stop 415 'to the observation surface is L2'. Further, the objective lens 17 of the first and second imaging optical systems 410 and 430
Are magnifications β1 and β2.

Then, the following equation is obtained.

H / L1 = (y1 · β1) / L1 ′ (1) h / (L1 + X0) = (y1 ′ · β1) / L1 ′ (2) h / L2 = y2 / (β2 · L2 ′) .. (3) h / (L2 + X0) = y2 ′ / (β2 · L2 ′) (4) In the equations (1) and (2), assuming that the angular magnification β1 and the distances L1 and L1 ′ are constants, K1 = ( If β1 · L1) / L1 ′ K2 = β1 / L1 ′, the equations (1) and (2) are transformed into the following equations.

H = K1 · y1 (5) h = K1 · y1 ′ + K2 · y1 ′ · X0 (6) Further, in the equations (3) and (4), the angular magnification β2 and the distance L2,
Assuming that L2 ′ is a constant, K3 = L2 / (β2 · L2 ′) and K4 = 1 / (β2 · L2 ′), the expressions (3) and (4) are as follows: h = K3 · y2 (7) H = K3.y2 '+ K4.y2'.X0 (8)

Here, the constants K1, K2, K3, and K4 are obtained by actually measuring the object height h and the image height y.

That is, by transforming the equations (5) and (6), the following equation is obtained.

K1 = h / y1 (9) K2 = (h / y1) · (y1-y1 ′) / (y1 ′ · X0) (10) K3 = h / y2 (11) K4 = (h) /Y2).(y2-y2')/(y2'.X0) (12) By measuring the object height h of the known object and its image height, the constants K1, K2, K3, and K4 are calculated. Ask for it.

Next, measurement when the image height h and the distance X from the reference position Y are unknown will be described. In this case,
In equations (2) and (4), distance X is set instead of distance X0. Also, y1 'and y2' are replaced with y1 and y2.

Then, the following equation is obtained.

H = K1 · y1 + K2 · y1 · X (14) h = K3 · y2 + K4 · y2 · X (15) When the above simultaneous equations are solved for the distance X and the object height h, X = (K3 · y2−K1 · y1) / (K2 · y1−K4 · y2) (16) h = K1 · y1 + K2 · y1 · X = (K2 · K3−K1 · K4) y1 · y2 / (K2 · y1−K4 ·) y2) (17) Since K1 to K4 have been determined, the image height y1,
By measuring y2, the distance from the reference position Y to the object can be measured.

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

In FIG. 11, 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. Assuming that the diameter of the ring image is about 3 mm,
The angle φ is about 20 °, and the following paraxial calculation formula cannot be used.

H = (r · sin φ) / 2 Therefore, the distance L 2 is set sufficiently large so that the angle φ is always constant, and the object height h is measured by the second imaging optical system 430 passing through the stop 435. If the above is used, an expression based on the following reflection law can be used.

H = r · sin (φ / 2) If this is modified, r = h / sin (φ / 2) (18)

If the distance L1 is set so that the angle formed by the light beam passing through the stop 415 and the light beam passing through the stop 435 does not become large, the object height h obtained by the equation (17) becomes equal to the above (1).
Since it is considered that there is no big error even if it is used for the expression 8),
The position of the corneal vertex EaP is expressed as Px = X− (r−h / tanφ) (19) as the distance Px from the reference position Y. Since the equation (19) for calculating the corneal vertex position is based on the premise that the ring image is on the optical axis of the spherical surface, it is affected by spherical aberration, but it may be corrected based on experimental values.

In FIG. 11, O ′ is the corneal curvature center, A
1, A2 is a normal of a spherical surface when the cornea Ea is regarded as a spherical surface,
A3 is a light ray incident on the cornea Ea.

FIG. 12 shows the relationship between the fundus distance, the corneal vertex distance and the axial length determined in this way.
This shows a case where the above-described reference position Y and the interference reference plane 315 match.

From the Lt-Lr obtained by the interferometry, Px
Is subtracted, a value Leye obtained by converting the axial length of the eye to air is obtained.
If the reference position Y and the interference reference plane 315 do not match, the difference may be obtained in advance and corrected at the time of calculation.

Also in the second embodiment, the measurement light for the interference measurement needs to be focused on the fundus R. For this purpose, the measurement interference optical system 320 is provided with the correction optical system 56. When the subject's eye is accompanied by astigmatism, the cross cylinders 59a, 59b
Rotate to correct. In this case, if the astigmatic intensity and the astigmatic axis are not known in advance, the correction must be made by trial and error.

Therefore, also in the case of the second embodiment, the intensity of corneal astigmatism and the axis of astigmatism are obtained using the corneal curvature radius obtained when measuring the position of the corneal apex, and the corneal astigmatism is obtained using these values. Make corrections. In this measurement method, astigmatism intensity to be corrected and its axis are also measured at the same time as the measurement of the axial length of the eye, so that the first measurement cannot correct astigmatism. However, conversely, if the astigmatism can be measured without requiring astigmatism correction in the first measurement, for example, because astigmatism is weak for a certain patient, then the astigmatism correction will not matter. Another advantage is that measurement can be continued.

In both the first and second embodiments, the interference measurement is performed by changing the wavelength of the light source and measuring the phase change of the interference light to measure the length. However, neither is limited to this. A method of obtaining the length by matching the optical path lengths using a light beam having a short interference distance may be used. Further, the astigmatism correction method used in each embodiment can be applied to any method as long as it is a method of concentrating the measurement light on the fundus of the subject's eye and measuring the axial length using the reflected light. .

[0094]

As described above, according to the present invention, even if the subject's eye is accompanied by astigmatism, the corneal curvature calculating means calculates the astigmatic intensity and the astigmatic axis, and the rotating means calculates the astigmatic intensity and the astigmatic axis. Since the astigmatism correction optical system is rotated based on the correction, the astigmatism of the cornea of the eye to be inspected is corrected, so that the measurement light can be sufficiently focused on the fundus, and the accurate measurement of the axial length of the eye can be performed.

[Brief description of the drawings]

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

FIG. 2 is an explanatory diagram showing a method of correcting astigmatism by a cross cylinder.

FIG. 3 is a perspective view showing a rotation mechanism of a cross cylinder.

FIG. 4 is a block diagram showing a signal processing circuit for obtaining an axial length based on a light receiving signal output from each light receiving device.

FIG. 5 is an explanatory diagram showing signals output from each circuit of the signal processing circuit.

FIG. 6 is a block diagram showing a configuration of a control system for controlling a motor.

FIG. 7 is an optical arrangement diagram showing an arrangement relationship of an optical system according to a second embodiment.

FIG. 8 is an explanatory diagram showing a ring image formed on a light receiving surface of a two-dimensional image sensor.

FIG. 9 is an explanatory view schematically showing a stop and an objective lens of a second imaging optical system.

FIG. 10 is an explanatory view schematically showing a stop and an objective lens of the first imaging optical system.

FIG. 11 is an explanatory diagram illustrating measurement of a corneal curvature radius and a vertex position thereof.

FIG. 12 is an explanatory diagram showing a relationship among a fundus distance, a corneal vertex distance, and an ocular axial length.

[Explanation of symbols]

 7, 8 Motor 10 Eye axis length measurement optical system (measurement optical system) 56 Correction optical system 59 Astigmatism correction optical member (Astigmatism correction optical system) 100 Corneal curvature measurement optical system (Cornea measurement optical system) 300 Curvature calculation circuit (Cornea curvature curvature) Calculation means) 301 controller

Claims (2)

(57) [Claims] A measuring optical system that corrects a measuring light beam according to a refractive power of an eye to be inspected by a correcting optical system and irradiates the light to the eye to be inspected; An eye axial length measurement device that measures an axial length of an eye to be inspected using reflected light incident on an optical system, wherein a ring illumination optical system that illuminates the eye to be examined in a ring shape, A corneal measurement optical system on which the reflected corneal reflected light is incident; a corneal curvature calculation means for calculating a radius of curvature of the cornea of the eye to be examined from the corneal reflected light incident on the corneal measurement optical system to obtain an astigmatic intensity and an astigmatic axis; The correction optical system is provided rotatably about its optical axis.
An astigmatism correction optical system that changes the correction strength and the direction of the astigmatism axis in accordance with the amount of rotation; and rotates the astigmatism correction optical system based on the astigmatism intensity and the astigmatism axis calculated by the corneal curvature calculation means. A rotation device for correcting astigmatism of the cornea of the optometry, and an eye axial length measurement device, comprising: 2. An eye axial length measuring apparatus according to claim 1, wherein
The measurement optical system is configured to irradiate a fundus of a subject's eye with a fundus illumination;
From the optical system and the corneal irradiation optical system that irradiates the cornea of the subject's eye
Is configured, the correction optical system, in addition to the optical path length correction light astigmatism correcting optical system
Having an optical element, the astigmatism correction optical system is provided in an optical path of the fundus illumination optical system.
So that it moves from within the optical path to outside the optical path
Is configured, the optical path length correcting optical element, the optical path of the cornea irradiation optical system
And the astigmatism correction optical system is provided in the fundus illumination light.
With the movement of the optical system from inside the optical path to outside the optical path, the fundus
There is a change in the optical path length difference between the irradiation optical system and the corneal irradiation optical system.
Eye length measurement device characterized in that correction is made so as not to occur.
Place.