JP2007007297A - Method of measuring object to be examined and ophthalmological device using the method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of measuring an object to be examined using spectrum interference, capable of eliminating autocorrelation signals included in light receiving signals and obtaining sharp images by simple constitution, and an ophthalmological device. <P>SOLUTION: In the method of measuring the object to be examined for irradiating the object to be examined with a part of the light of a low coherent length, turning reflected light to object light, also synthesizing a part of the light of the low coherent length with the object light as reference light, making it interfere, performing the spectroscopy of obtained interference light into a prescribed frequency component, receiving it, obtaining the light receiving signals, performing Fourier transformation or inverse Fourier transformation of the light receiving signals and performing the tomography of a phase object or the measurement of an optical surface profile, the power spectrum of the light of the low coherent length is obtained beforehand, the autocorrelation function of the reference light included in the light receiving signals is removed on the basis of the power spectrum obtained beforehand, the Fourier transformation or the inverse Fourier transformation is performed to the light receiving signals from which the autocorrelation signals of the reference light are removed, and thus the image information of the object to be examined is obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a measurement method for measuring optical tomographic imaging and optical surface profile of a test object (phase object) using optical coherence tomography (OCT), and a measurement apparatus equipped with the method, More particularly, the present invention relates to an ophthalmologic apparatus for measuring optical tomography and an optical surface profile of an eye to be examined.

2. Description of the Related Art Conventionally, apparatuses for measuring optical tomographic images of an eye to be examined and measuring optical surface profiles by optical coherence tomography (OCT) using spectral interference are known. Since such an apparatus does not drive the reference mirror, high-speed measurement is possible as compared with a normal OCT apparatus that does not use spectral interference. Such an OCT apparatus using spectral interference obtains information in the depth direction of the test object by Fourier-transforming the interference signal of the light beam split into frequency components by the spectrometer unit, thereby obtaining a tomographic image of the test object. Is known (see Patent Document 1).
JP 11-325849 A

However, in such an OCT apparatus using spectral interference, the obtained light reception signal includes an autocorrelation signal as a noise component, and it is difficult to obtain a sharp image due to the influence of such an autocorrelation signal. .
In view of the above-mentioned problems of the prior art, with a simple configuration, the autocorrelation signal included in the received light signal can be removed, and a measurement method of the object to be measured using spectral interference that can obtain a sharp image, and An object of the present invention is to provide an ophthalmologic apparatus using the method.

In order to solve the above problems, the present invention is characterized by having the following configuration.
(1) A part of light having a low coherent length is irradiated on a test object to make reflected light as object light, and a part of the light having low coherent length is combined with the object light as reference light to cause interference. The obtained interference light is dispersed into a predetermined frequency component and received to obtain a received light signal, and the received light signal is subjected to Fourier transform or inverse Fourier transform to perform tomographic imaging of a phase object or measurement of an optical surface profile. In the test object measuring method, the power spectrum of the light of the low coherent length is obtained in advance, and the autocorrelation function of the reference light included in the light reception signal is divided based on the power spectrum obtained in advance, Image information of the object to be examined is obtained by performing Fourier transform or inverse Fourier transform on the received light signal from which the autocorrelation signal of the reference light has been removed.
(2) In the test object measuring method according to (1), the power spectrum is obtained by performing an inverse Fourier transform on a coherent function obtained based on a result of quantitatively measuring the light of the low coherent length. And
(3) In the test object measuring method according to (1), the power spectrum is obtained by receiving only the reference light.
(4) irradiating a test object with a part of light having a low coherent length to make reflected light as object light, and combining a part of the light with low coherent length as reference light with the object light to cause interference; An ophthalmologic apparatus that obtains a received light signal by dispersing the obtained interference light into a predetermined frequency component to obtain a received light signal, and taking a tomographic image of a phase object by performing Fourier transform or inverse Fourier transform on the received light signal. The measurement method of (3) is used.

  According to the present invention, an autocorrelation signal included in a light reception signal can be removed with a simple configuration, and a sharp image can be obtained.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an optical system of an ophthalmologic apparatus using spectral interference OCT used in the present embodiment. Note that the ophthalmologic apparatus of the present embodiment uses an ophthalmologic photographing apparatus that photographs an anterior segment cross section. The optical system shown in FIG. 1 includes a measurement light projection optical system, a reference light optical system, an interference signal detection optical system, and an observation optical system. Note that the ophthalmologic apparatus of the present embodiment also has an alignment optical system for positioning the apparatus in a predetermined relationship with respect to the eye to be examined. Conventionally, an optical system similar to a known alignment optical system used for an objective eye refractive power device or the like may be used, and the description thereof is omitted.

<Measurement light projection optical system>
A measuring light projection optical system 100 shown in FIG. 1 includes a light source 1, a collimator lens 2, a beam splitter 3, a galvano mirror 4, an objective lens 5, and a beam splitter 6.
The light source 1 is a light source that emits low-coherent infrared light such as SLD (Super luminescent Diode). The low coherent light emitted from the light source 1 is converted into a parallel light beam by the collimator lens 2 and then transmitted through the beam splitter 3. The light beam that has passed through the beam splitter 3 is reflected by the galvanometer mirror 4, and then converges near the apex of the cornea of the eye E through the objective lens 5 and the beam splitter 6. The galvanometer mirror 4 can be rotationally driven in a predetermined direction (in this embodiment, the direction in which the light beam is scanned in the vertical direction with respect to the eye to be examined). Further, the reflection surface of the galvanometer mirror 4 is disposed at the back focal position of the objective lens 5 so that the optical path length is not changed by driving.

<Reference light optical system>
A reference optical system 200 shown in FIG. 1 includes a light source 1, a collimator lens 2, a beam splitter 3, mirrors 7 to 9, a condenser lens 10, and a reference mirror 11 from the light source side. The measurement light projecting optical system 100 shares the light source 1 to the beam splitter 3.
After the low-coherent light emitted from the light source 1 passes through the collimator lens 2, a part of the light beam is reflected by the beam splitter 3 and travels to the mirror 7. The light beam reflected by the mirror 7 is further turned back by the mirrors 8 and 9, and then condensed on the reference mirror 11 by the condenser lens 10.

<Interference signal detection optical system>
An interference signal detection optical system 300 shown in FIG. 1 includes an optical system for receiving reflected light (object light) from the eye E and an optical system for receiving reflected light (reference light) from the reference mirror 11. Consists of
An optical system that receives object light from the eye to be examined includes a beam splitter 6, an objective lens 5, a galvano mirror 4, a beam splitter 3, a condensing lens 13, an expander lens 14, a grating mirror (diffraction grating) from the front of the eye E. ) 15, a condenser lens 16, a cylindrical lens 17, and a light receiving element 18. The grating mirror 15 is placed at the front focal position of the condenser lens 16, and the light receiving element 18 is placed at the rear focal position.

The light receiving element 18 used in the present embodiment is a one-dimensional element having sensitivity in the infrared region. The measurement light projecting optical system 100 shares the beam splitter 10 to the beam splitter 15.
The reflected light (object light) of the light beam condensed near the cornea of the eye E to be examined by the measurement light projection optical system 100 passes through various optical members of the measurement light projection optical system 100 again, and then is reflected by the beam splitter 3. Some reflected light is reflected. The object light reflected from the beam splitter 3 is once condensed through the condenser lens 13. The object light condensed by the condensing lens 13 is expanded by the expander lens 14 and then split into frequency components by the grating mirror 15. The object light split into the frequency components is condensed on the light receiving surface of the light receiving element 18 through the condenser lens 16 and the cylindrical lens 17. The beam diameter after passing through the expander lens 14, the grating interval of the grating mirror, the condensing lens 16, and the light receiving element 18 are optimized in consideration of the measurement range and resolution in the optical axis direction of the eye to be examined.

  The optical system for receiving the reflected light (reference light) reflected by the reference mirror 11 includes a reference mirror 11, a condenser lens 10, mirrors 7 to 9, a beam splitter 3, a condenser lens 13, and an expander lens. 14, a grating mirror 15, a condenser lens 16, a cylindrical lens 17, and a light receiving element 18.

  The reference light reflected by the reference mirror 11 passes through the condenser lens 10, returns in order through the mirror 9, the mirror 8, and the mirror 7, passes through the beam splitter 3, and is combined with the object light from the eye to be examined. The reference light combined with the object light from the eye to be examined passes through the condensing lens 13 and the expander lens 14, and then is split into frequency components by the grating mirror 15, and passes through the condensing lens 16 and the cylindrical lens 17 to receive the light receiving element 18. Condensed to Thus, the spectrometer unit is formed by the grating mirror 15, the condenser lens 16, the cylindrical lens 17, and the light receiving element 18. The light receiving surface of the light receiving element 18 has a conjugate relationship with the eye cornea to be examined. The cylindrical lens 17 serves to widen the diameter of the light beam in the width direction of the light receiving element 18 and is used to cause the light receiving surface to receive the light beam regardless of the installation error of the light receiving element 18.

<Observation optics>
An observation optical system 400 shown in FIG. 1 includes a beam splitter 6, an objective lens 19, an imaging lens 20, and a light receiving element 21 having sensitivity in the infrared region from the front of the eye E to be examined. Note that the pupil position of the eye E and the light receiving element 21 have a conjugate positional relationship via the lens. Reference numeral 22 denotes an infrared LED for illuminating the eye E to be examined.

FIG. 2 is a block diagram showing a control system in the ophthalmologic apparatus used in the present embodiment.
Reference numeral 30 denotes a control unit that performs drive control of the apparatus according to the present embodiment. The control unit 30 is connected to the light receiving element 18, the light receiving element 21, the monitor 31, the arithmetic processing unit 32, the storage unit 33, and the like. The arithmetic processing unit 32 performs analysis based on information obtained by the light receiving element, and is used to form a cross-sectional image of the eye to be examined. The storage unit 33 stores a photographed cross-sectional image of the eye E.

Next, a measurement method for obtaining a cross-sectional image of an object to be examined (in this embodiment, eye E) based on a light reception signal of a light beam split into frequency components obtained by the light receiving element 18 in the present embodiment ( The analysis method will be described below. For ease of explanation, the simple optical layout shown in FIG. 3 is used. In the figure, SLD is a light source, BS is a beam splitter, RM is a reference mirror, M is a mirror, and G is a grating mirror.
The electric field at the BS position of the light emitted from the light source at time t

far. The reason why the integral display relating to the angular frequency ω is used is to indicate that the light source has a wavelength distribution. If the optical path length from the BS reflected by the RM to the BS again is 2L, the electric field of the reference light at the BS position is

As

It can be expressed. C is the speed of light. Further, the measurement high speed has a corneal apex at a position distant by Z0 from RM, and the energy reflectivity at a depth Z position measured therefrom can be expressed as R (Z) as follows.

here,

And considering that the depth direction of the phase object (eye) and the time axis of light are the same direction,

It was. Here, r (τ) is an even real function. Then Equation 4 becomes

And can be expanded. The final expression is expressed using convolution integration. This Fourier transform is obtained for later. Assuming that the Fourier transform is represented by the symbol ~

It becomes. The reference light and the object light interfere with each other by being coaxial with the BS, but are separated by a spectrometer comprising a grating mirror G, a lens, and a CCD, so that an interference spectrum pattern for each wavelength component is generated on the CCD. Therefore, it is expressed by Fourier transform and is as follows.

Note that * represents a complex conjugate. Although the diffraction angle by the grating mirror G is proportional to the minute shift amount of the wavelength, the above equation is written as a function of the angular frequency ω corresponding to the Fourier transform with respect to time. this is,

Is obtained by differentiating.

This is because a proportional relationship is established between the diffraction angle and the minute angular frequency deviation via the wavelength. Note that f is a focal length and λ is a frequency. The depth information r (t) of the phase object is obtained by performing an inverse Fourier transform on the interference spectrum formed on the CCD with respect to ω, and the intensity I (t) is

It becomes. A represents autocorrelation. Since r (t) is an even real function,

Is used. In Equation 12, the first and second terms represent the autocorrelation functions of the reference light and the object light, respectively, and in Equation 12, the phase object depth information to be obtained in the third and fourth terms is the autocorrelation of the reference light. The function (the coherent length of the light source) appears as a point response function.

1 is measured using the optical system shown in FIG. 1 as a phase object, and the analysis is performed using Equation 12 based on the received light signal obtained by the spectrometer unit, FIG. An image as shown will be obtained. Here, the first and second terms in Equation 12 correspond to the peak portions in the figure, the fourth term is the position where r (t) is moved to the + side by τ 0, the third term is the fourth term t = Appears at a position folded with respect to the 0 axis. In the above, Equation 9 is inverse Fourier transformed to derive Equation 12. However, the present invention is not limited to this, and the variable of the autocorrelation function between the reference light and the object light can also be obtained by Fourier transform of Equation 9. Since the only difference is that the phase is inverted, the depth information of the phase object can be obtained in the same manner, regardless of whether Fourier transform or inverse Fourier transform is performed on Equation 9.
In Expression 13, it is assumed that r (t) is an even real function. Then

Therefore, Equation 9 is

And can.

  In Equation 15, if cos (ωτ0) can be set to 0 (in other words, the contribution of the signal from the test object becomes 0), only the autocorrelation signal (peak signal that becomes noise) between the reference light and the object light can be obtained. It will remain. By removing the obtained value from Equation 9 or Equation 12, an image from which the peak signal has been removed (in this embodiment, a tomographic image of the eye) can be obtained.

  Note that τ0 is an unequal optical path difference (time) between the object optical path and the reference optical path. This τ0 is the distance from the center of the image to the vertex position of the depth profile of the test object obtained using Equation 12 (in this embodiment, the corneal vertex that is the forefront of the test object) by image processing. It can be obtained by obtaining and converting to time. In the present embodiment, τ0 is obtained by obtaining the distance from the image center to the corneal apex by image processing, but is not limited thereto. For example, a mechanism for detecting the working distance can be provided separately, and τ0 can be obtained from the result of the working distance detection. When obtaining a two-dimensional cross-sectional image of the eye to be examined, a corneal curvature measuring device (curvature corresponding to the obtained cross-sectional image) obtained by this device is obtained in advance using a corneal shape measuring device which is an existing device. Each τ 0 for the two-dimensional cross-sectional image can be obtained based on the corneal apex.

If the value of τ0 is obtained, the process returns to Equation 15 and only the power spectra of the reference light and the object light are obtained (estimated) from the interference intensity on the CCD at the angular frequency ω such that cos (ωτ0) becomes zero. it can. If the obtained value is subtracted from Equation 9 and Fourier transform (or inverse Fourier transform) is performed, the autocorrelation signal that becomes annoying noise is removed, and only the depth information of the phase object to be obtained is obtained. On the contrary, after the Fourier transform, the power spectra of the reference light and the object light may be subtracted from the obtained values.
The interference intensity distribution at the stage where the power spectrum distributions of the reference light and the object light are subtracted from the interference intensity distribution on the CCD is expressed by Equation 16 below.

It can be expressed as When this is multiplied by -tan (ωτ0) using the above-mentioned known τ0, the following equation 17 is obtained.

Here, Expression 16 is a value having a real part and Expression 17 is an imaginary part, and Expression 18 is derived.

When inverse Fourier transform is performed on the obtained Equation 18,

It becomes. Since the obtained equation 19 has no term indicating the autocorrelation function of the reference light and the object light and no term indicating the depth information of the phase object to be a virtual image, only the real image can be obtained by using the equation 19. It becomes possible.

  By using such a measurement method (analysis method), it is possible to widen the measurement range in the depth direction because the left and right sides of the screen are not discarded. Note that a tomographic image of a phase object obtained as a double image folded at the center may be converted into an original image (one image) by image processing. In such image processing, an image obtained when the obtained double image is folded and overlapped at the center is used as an original image, and the double image is overlaid or one image is erased. Find an image to do.

The operation of the apparatus having the above configuration will be briefly described below.
While looking at the monitor 31 shown in FIG. 2, the examiner moves the apparatus in the up / down / left / right and front / rear directions using an operation means such as a joystick (not shown), and the apparatus is moved to a predetermined eye E with respect to the eye E shown in FIG. Place it in a positional relationship. In the present embodiment, the light receiving surface of the light receiving element 21 and the pupil position of the eye E to be examined are in a conjugate relationship. In FIG. 1, the measurement reference position is the corneal apex position. However, since the measurement range is a predetermined range in the front-rear direction from the reference position, when the tomographic image is to be obtained in the widest possible range, the above-described reference beam is used. The optical path length difference between the object light and the object light is set to satisfy τ0 <0.

  When the apparatus is in a predetermined positional relationship with the eye E, the examiner uses an imaging switch (not shown) to display an anterior tomographic image of the eye E on the monitor 31. When the photographing switch is pressed, the control unit 30 emits infrared light from the light source 1 and drives the galvanometer mirror 4 to scan the eye E with infrared light.

  The reflected light (object light) of the light beam condensed near the cornea of the eye E to be examined by the measurement light projection optical system 100 passes through various optical members of the measurement light projection optical system 100 again, and then is reflected by the beam splitter 3. Some object light is reflected. The object light reflected from the beam splitter 3 is combined with the reference light passing through the reference light optical system, and then condensed once through the condenser lens 13. The light beam condensed by the condensing lens 13 is expanded in diameter by the expander lens 14, and then split into frequency components by the grating mirror 15. The light beam split into frequency components is condensed on the light receiving surface of the light receiving element 18 through the condenser lens 16 and the cylindrical lens 17.

  The light receiving element 18 receives light split into frequency components and outputs interference intensity for each frequency component. The arithmetic processing unit 32 monitors the interference intensity obtained by the object light received by the light receiving element 18 and the reference light. The light received by the light receiving element 18 includes reflected light from phase objects such as the back surface of the cornea and the front and back surfaces of the crystalline lens, in addition to the reflected light from the surface of the cornea. Therefore, the interference signal received by the light receiving element 18 is received as a function of frequency due to interference between the reflected light and the reference light.

  The arithmetic processing unit 32 analyzes the detection signal output from the light receiving element 18 when the intensity of the interference signal becomes the highest using the Fourier transform described above. Since the interference light includes reflected light from each phase object (for example, the front and rear surfaces of the cornea and the front and rear surfaces of the lens) in the eye E, the cornea, the lens and the like in the eye E are subjected to Fourier transform on the detection signal. The depth information of each phase object can be obtained. The arithmetic processing unit 32 normally deletes the peak signal (autocorrelation signal) that becomes noise from the data that forms the peak signal and the double image shown in FIG. 5 (b). Further, by using the analysis method described above, a cross-sectional image that finally becomes a virtual image is deleted, and a cross-sectional image of the anterior segment shown in FIG. 5C is obtained and displayed on the monitor 32. Note that the tomographic image to be examined shown in FIG. 5C may be finally obtained by performing image processing such that one of the double images is deleted or folded and superimposed. The obtained anterior segment tomogram is stored in the storage unit 33 by using a storage switch (not shown).

In the above embodiment, the measurement method of the test object using the spectrum interference that can remove the signal that becomes noise and expand the measurement range in the depth direction has been described. A method for obtaining an edge image will be described below. Since the optical system, the control system, and the apparatus operation are the same as those in the above-described embodiment, the description of each configuration is omitted, and the analysis method for obtaining an image will be described in detail below. Further, the symbols in each formula are synonymous with the symbols in each formula described above unless otherwise specified.
The interference intensity distribution on the light receiving element 18 shown in FIG.

It is expressed. Further, the depth information r (t) of the phase object obtained by inverse Fourier transform or Fourier transform of the equation 20 is the equation 12 described above.

It can be expressed as
According to Equation 12, the depth information of the phase object is in a form in which the autocorrelation of the reference light is convoluted, and the resolution is reduced accordingly. In order to avoid this in the present embodiment, the power spectrum of the reference light represented by the following formula 21 in advance.

Then, the equation 20 is divided by using the equation 21. As a result, the following formula 22

Is obtained. When inverse Fourier transform or Fourier transform is performed on the obtained Expression 22, the following Expression 23 is obtained.

Is obtained. In the obtained Expression 23, since the autocorrelation information is removed in advance, the original depth information of the phase object is not affected by the autocorrelation of the light source. For this reason, the image obtained using Expression 23 is a sharp image. A method for obtaining the power spectrum of the reference light will be described below.

According to Wiener-Khinchine's theorem, the power spectrum (the square of the absolute value of the Fourier transform of the original function, here expressed by Equation 21) representing the energy of the wave of the angular frequency ω is obtained by the Fourier transform of the autocorrelation function. On the other hand, it has been found that an autocorrelation function can be obtained by inverse Fourier transform of the power spectrum.
Further, the autocorrelation of the reference light is expressed by the following equation 24 using Γenv (t (ω)) as an envelope function of a coherent function (a coherent time whose half width corresponds to a coherent length).

It is expressed. Therefore, the following equation 25

Holds.

Note that the coherent function can be obtained in advance from a measurement result obtained quantitatively by measuring the light emitted from the light source to be used (low-coherent light) using an interferometer or the like. . By substituting the obtained coherent function into Expression 25 and performing Fourier transform, the power spectrum of the reference light (measurement light) can be obtained. In addition, the power spectrum of the reference light is stored in advance in the storage unit in the device depending on the light source usage conditions such as temperature and current, and is stored in the storage unit according to the light source usage conditions when actually used. The stored power spectrum can be selected using a setting unit (not shown) or can be automatically selected and used.
In addition, by considering both of the analysis methods used in the first and second embodiments, it is possible to suppress noise light and expand the measurement range in the depth direction, and to obtain a sharp image. Yes.

  In the above embodiment, an ophthalmologic apparatus has been described as an example, but the present invention can be applied to an apparatus for taking a tomographic image of a phase object and measuring an optical surface profile in other fields. Further, when measuring the optical surface profile, two-dimensional scanning is performed using a galvano mirror and a polygon mirror, and an image is obtained by receiving light split into each frequency component using a two-dimensional CCD. do it.

  In the analysis method described above, reference is made from the interference intensity on the CCD at an angular frequency ω such that cos (ωτ0) is 0 using τ0 which is an unequal optical path difference (time) between the object optical path and the reference optical path. Although the power spectrum of the light and the object light is obtained or the power spectrum of the reference light is obtained using a coherent function and the autocorrelation signal is removed using this, the present invention is not limited to this. By designing an optical system that allows the light receiving element to receive the object light and the reference light separately, the respective power spectra (the power spectra of the object light and the reference light) can be obtained. Using the power spectrum values of the obtained object beam and reference beam, the autocorrelation signal component is removed from Equation 9 by subtracting the first and second terms of Equation 9 and dividing the third term. be able to. In addition, the power spectrum of the reference light obtained in Equation 22 described above may be applied. Further, when the autocorrelation signal component of the object light is sufficiently small with respect to the autocorrelation signal of the reference light to be negligible, the autocorrelation signal component of the object light may be ignored and not used.

It is the figure which showed the optical system of the ophthalmologic apparatus in this embodiment. It is the block diagram which showed the control system in this embodiment. It is the figure which showed the optical system used in order to demonstrate the measuring method in this embodiment. It is the figure which showed the image information corresponding to the formula used for an analysis. It is the figure which showed the analysis procedure of this embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Collimator lens 3 Beam splitter 4 Galvanometer mirror 5 Objective lens 6 Beam splitter 11 Reference mirror 15 Grating mirror 16 Condensing lens 18 Light receiving element 30 Control part 31 Monitor 32 Calculation processing part 100 Measurement light projection optical system 200 Reference optical system 300 Interference signal detection optical system 400 Observation optical system

Claims (4)

It was obtained by irradiating the object to be examined with a part of the light having a low coherent length and using the reflected light as the object light and combining the part of the light having the low coherent length with the object light as a reference light. The interference light is split into a predetermined frequency component and received to obtain a received light signal. The received light signal is subjected to Fourier transform or inverse Fourier transform to obtain a tomographic image of the phase object or measure an optical surface profile. In the measurement method, a power spectrum of the light having the low coherent length is obtained in advance, and an autocorrelation function of the reference light included in the light reception signal is divided based on the power spectrum obtained in advance, and the reference light A method for measuring an object to be detected, wherein image information of the object to be detected is obtained by performing Fourier transform or inverse Fourier transform on the received light signal from which the autocorrelation signal has been removed. 2. The object measurement method according to claim 1, wherein the power spectrum is obtained by performing an inverse Fourier transform on a coherent function obtained based on a result of quantitatively measuring the light having the low coherent length. Method for measuring specimen. 2. The method for measuring a test object according to claim 1, wherein the power spectrum is obtained by receiving only the reference light. An ophthalmologic apparatus characterized by obtaining a cross-sectional image of the anterior ocular segment to be examined using the measurement method according to claim 1.