Optical tomographic image photographing apparatus and optical tomographic image photographing program

An optical tomographic image photographing apparatus for acquiring information on a tissue inside a specimen, the apparatus includes: a synthesis unit configured to generate a interference beam by synthesizing a measuring beam reflected from the tissue and a reference beam; and a detector configured to detect the generated first interference beam as a first interference signal, the first interference beam being detected for each scanning position of the measuring beam. The optical tomographic image photographing apparatus acquires tomographic information for each scanning position of the specimen by using the detected first interference signal and acquiring tomographic image data of the specimen expressed by polar coordinates by using the tomographic information; and converts the tomographic image data of the specimen expressed by the acquired polar coordinates into image data expressed by rectangular coordinates.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of Japanese Patent Application No. 2013-248734 filed on Nov. 29, 2013, the contents of which are incorporated herein by reference in its entirety.

BACKGROUND

The present invention relates to an optical tomographic image photographing apparatus which photographs a tomographic image of a tissue of a specimen, and an optical tomographic image photographing program.

In the related art, as an apparatus which is capable of photographing a tomographic image in a predetermined portion of a specimen, an apparatus employing an optical coherence tomography (OCT) has been known. An optical tomographic image photographing apparatus which employs the OCT divides the light beam emitted from a light source into a measuring beam and a reference beam and the irradiates tissue of the specimen with the divided measuring beam. The measuring beam reflected from the tissue is synthesized with the reference beam, and the information on the tissue in the depth direction is acquired through the interference signal of the synthesized light. The optical tomographic image photographing apparatus can generate the tomographic image by using the acquired information of the tissue in the depth direction.

An optical tomographic image photographing apparatus which photographs the tomographic image of the tissue in the specimen by emitting the measuring beam from a tip end of a probe which can be inserted into the specimen has been proposed. In such an optical tomographic image photographing apparatus, the specimen is scanned with the measuring beam by the rotation of an optical fiber in the probe and thereby the image data is acquired by a detector for each scanning angle set in advance (for example, JP-A-2000-131222).

SUMMARY

Meanwhile, the image data acquired by rotation of the optical fiber is a collection of primary image data regulated by a polar coordinate system. The tomographic image (the image data expressed by polar coordinates) is generated by assuming a horizontal axis to be the scanning angle (θ) and arranging the primary image data items in a line for each scanning line. The tomographic image generated in this manner is different from the form (shape) of an actual fundus of an eye. For this reason, for example, the length is different from the actual length, and thus it is difficult to measure the thickness of an optic stratum in some cases.

The present invention was made in consideration of the above described circumstance, and an object thereof is to provide an optical tomographic image photographing apparatus and an optical tomographic image photographing program capable of acquiring useful information for diagnosing an object eye.

In order to solve the above problems, the present invention includes the following configurations.

(1) An optical tomographic image photographing apparatus for acquiring information on a tissue inside a specimen in a depth direction, the apparatus comprising:

a light source configured to emit a light beam;

a dividing unit configured to divide the emitted optical flux into a measuring beam and a reference beam;

a attaching unit to which a probe is to be attached, the probe being configured to irradiate an inside of the specimen with the measuring beam and rotatably scan the inside of the specimen with the measuring beam;

a synthesis unit configured to generate a first interference beam by synthesizing the measuring beam reflected from the tissue inside the specimen and the reference beam;

a detector configured to detect the generated first interference beam as a first interference signal, the first interference beam being detected for each scanning position of the measuring beam;

a processor; and

memory storing a computer executable program, when executed by the processor, causing the optical tomographic image photographing apparatus to execute:

a tomographic image acquiring instruction of acquiring tomographic information for each scanning position of the specimen by using the detected first interference signal and acquiring tomographic image data of the specimen expressed by polar coordinates by using the tomographic information; and

a coordinate conversion instruction of converting the tomographic image data of the specimen expressed by the acquired polar coordinates into image data expressed by rectangular coordinates.

A computer readable recording medium storing a program for an optical tomographic image photographing apparatus which acquires information on a tissue inside a specimen in a depth direction, the optical tomographic image photographing apparatus including: a attaching unit to which the probe is attached; a synthesis unit configured to generate a first interference beam by synthesizing the measuring beam reflected from the tissue inside the specimen and the reference beam; a detector configured to detect the generated first interference beam as a first interference signal, the first interference beam being detected for each scanning position of the measuring beam; and a processor, the program when executed by the processor causing the optical tomographic image photographing apparatus to execute:

a tomographic image acquiring instruction of acquiring tomographic information for each scanning position of the specimen by using the detected first interference signal and acquiring tomographic image data of the specimen expressed by polar coordinates by using the tomographic information; and

a coordinate conversion instruction of converting the tomographic image data of the specimen expressed by the acquired polar coordinates into image data expressed by rectangular coordinates.

DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The outline of the present example will be described. An optical tomographic image photographing apparatus1of the example acquires information on a tissue inside a specimen in a depth direction. The optical tomographic image photographing apparatus1mainly includes dividing means (for example, a coupler14), a attaching unit16, synthesis means (for example, the coupler14), a detector18, tomographic image acquiring means (for example, a control unit20and a CPU21), and coordinate conversion means (for example, the control unit20and the CPU21).

The dividing means divides an optical flux emitted from a light source into a measuring beam and a reference beam. The attaching unit mounts a probe2irradiating an inside of a specimen with the measuring beam divided by the dividing means and rotatably scanning the inside of the object with the measuring beam thereon. Here, “rotatably scanning” includes a case of the rotary scanning with the measuring beam performed by rotating an optical member (a fiber4and the like) in the probe2around a shaft of the probe2and the rotary scanning performed by an optical scanner which is provided at a tip end of the probe2.

The synthesis means generates an interference beam by synthesizing the measuring beam (a first measuring beam) which is emitted from the probe2and reflected from the inside of the specimen and the reference beam divided by the dividing means.

The detector18detects the interference beam generated by synthesizing the first measuring beam and the reference beam by the synthesis means as a first interference signal for each scanning position of the measuring beam. For example, the interference beam is detected for each scanning angle of the measuring beam.

The tomographic image acquiring means acquires tomographic information for each scanning position of the specimen by using the first interference signal detected by the detector18and tomographic image data of the specimen expressed by polar coordinates by using the tomographic information.

The coordinate conversion means converts the tomographic image data of the specimen expressed by the polar coordinates acquired by the tomographic image acquiring means into image data expressed by rectangular coordinates.

The apparatus1converts an image expressed by polar coordinates into an image expressed by rectangular coordinates. Accordingly, it is possible for the specimen in reality to have the same form as that of the specimen in the image.

In addition, when the image data expressed by the polar coordinates is converted into the image data expressed by rectangular coordinates, the apparatus may perform the conversion of the image data on the basis of the position of a rotation axis when the inside of the specimen is rotatably scanned with the measuring beam. For example, the image data may be converted by setting the position of the rotation axis as an origin of a polar coordinates system when the inside of the specimen is rotatably scanned with the measuring beam.

In this case, for example, the synthesis means may generate the interference beam obtained by synthesizing the measuring beam (a second measuring beam) which is emitted from the light source and reflected from the inside of the probe without being applied to the inside of the specimen and the reference beam divided by the dividing means. In addition, the interference beam may be detected as a second interference signal. The tomographic image acquiring means may acquire the positional information of the inside of the probe from which the measuring beam is reflected by using the second interference signal detected by the detector18. The coordinate conversion means may acquire a shaft position of a rotation axis when the probe rotatably scans the inside of the specimen with the measuring beam by using the positional information on the inside of the probe which is acquired by the tomographic image acquiring means. Then, the coordinate conversion means may convert the tomographic image data of the specimen expressed by the polar coordinates into tomographic image data expressed by the rectangular coordinates by setting the position of the acquired rotation axis as an origin of a polar coordinates system.

Meanwhile, the probe2may include an optical fiber (referred to as a fiber in some cases)4and a shielding member inside thereof. The fiber4guides the measuring beam emitted from the light source of the apparatus1to the specimen. The shielding member (for example, an external cylinder61) is an optical member shielding the measuring beam emitted from the optical fiber4. In this case, the synthesis means may synthesize the measuring beam, as the second measuring beam, reflected from the shielding member and the reference beam. The detector18may detect the interference beam obtained by synthesizing the measuring beam reflected from the shielding member and the reference beam as the second interference signal. The coordinate conversion means may acquire the positional information of the optical member (the shielding member or the like) from which the measuring beam is reflected through the second interference signal. Then, the coordinate conversion means may acquire the shaft position of the rotation axis when the probe2rotatably scans the inside of the specimen with the measuring beam by using the positional information of the optical member from which the measuring beam is reflected. Further, the coordinate conversion means may perform the conversion of the tomographic image data of the specimen by setting the acquired shaft position of the rotation axis as an origin of a polar coordinates system.

In addition, the probe2may include the optical member which is coupled with the optical fiber4and guides the measuring beam emitted from the fiber to the inside of the specimen in the inside thereof. In addition, the detector18may detect, as a second interference signal, the interference beam obtained by synthesizing the measuring beam (second measuring beam) which is reflected from an interface between the fiber4and the optical member and the reference beam divided by the dividing means by the synthesis means.

Meanwhile, the apparatus1may be provided with distance calculating means. The distance calculating means may calculate the distance between two points in the specimen based on the tomographic image data which is coordinate-converted by the coordinate conversion means.

Note that, the apparatus1may include a display unit31and display control means (for example, the control unit20). The display unit31displays the tomographic image. The display control means causes the display unit to display the tomographic image data as the tomographic image. In addition, the display control means may cause the display unit to display the tomographic image data, coordinate-converted into the rectangular coordinates by the coordinate conversion means, as the tomographic image.

Meanwhile, the control unit20may include a processor (for example, the CPU21) for controlling a variety of control processes and a storage medium for storing a program. The processor may cause the optical tomographic image photographing apparatus1to execute a dividing step, a rotary scanning step, a synthesizing step, a detecting step, a tomographic image acquiring step, a coordinate conversion step or the like. The dividing step divides the optical flux emitted from the light source into the measuring beam and the reference beam. The rotary scanning step causes the probe2to irradiate the inside of the specimen with the measuring beam divided in the dividing step and rotatably scanning the inside of the specimen with the measuring beam. The synthesizing step generates the interference beam by synthesizing the measuring beam which is emitted from the probe2and is reflected from the tissue inside the specimen and the reference beam which is divided in the dividing step. The detecting step detects the interference beam generated in the synthesizing step as the first interference signal for each scanning position of the measuring beam. The tomographic image acquiring step acquires tomographic information for each scanning position of the specimen through the first interference signal detected in the detecting step and tomographic image data of the specimen expressed by polar coordinates by using the tomographic information. The coordinate conversion step converts the tomographic image data of the specimen expressed by the polar coordinates acquired in the tomographic image acquiring step into image data expressed by rectangular coordinates.

Example

Hereinafter, description is given of an example of the present invention with reference to the drawings. First, a schematic configuration of an optical tomographic image photographing apparatus1according to the present embodiment is described with reference toFIG. 1. The optical tomographic image photographing apparatus (an optical coherence tomographic device)1of the embodiment photographs a tomographic image of a tissue inside the specimen by using a probe2being inserted into the specimen. According to the embodiment, the description is made by exemplifying an ophthalmologic photographing apparatus which photographs the tomographic image of the tissue (for example, the retina) inside an object eye E. However, the present invention may be applied to an apparatus which photographs tomographic images of specimens (for example, internal organs or an ear) other than an eye. The optical tomographic image photographing apparatus1includes a measuring unit10and a control unit20.

The measuring unit10is configured to have an optical coherence tomography (OCT). The measuring unit10of the present embodiment includes a measuring light source11, an aiming light source12, a coupler13, the coupler14, a reference optical system15, the attaching unit16, a fiber rotation motor17, and the detector (a light receiving element)18.

The measuring light source11emits light so as to acquire a tomographic image. As an example, the optical tomographic image photographing apparatus1of the embodiment acquires the tomographic image through a Swept-source OCT (SS-OCT) measurement by including the measuring light source11which is capable of changing the wavelength of a laser beam to be emitted at a high speed. The measuring light source11of the embodiment is configured to have a laser medium, a resonator, a wavelength selection filter, or the like. As the wavelength selection filter, for example, a combination of a diffraction grating and a polygon mirror, or a filter using Fabry-Perot etalon is employed.

The aiming light source12emits an aiming beam which is visible light for indicating an irradiation position of a measuring beam (in other words, an acquiring position of information in the depth direction, or a photographing position of the tomographic image when photographing the tomographic image). The aiming light source12of the embodiment can cause a color of the aiming beam (the wavelength) to change within a range from green to red. In addition, the aiming light source12can cause a period of flashing of the aiming beam to vary by switching between flashing of the aiming beam and constant lighting.

The coupler13combines a light beam emitted from the measuring light source11and the aiming beam emitted from the aiming light source12so as to coincide optical axes of the two light beams with each other. The coupler14divides the light from the coupler13into the measuring beam (sample light) and the reference beam. The measuring beam is wave-guided to the probe2which is attached to the attaching unit16. A reference beam is wave-guided to the reference optical system15. In addition, the coupler14generates an interference beam by synthesizing the measuring beam (a reflected measuring beam) reflected from the object eye E and the reference beam generated by the reference optical system15. The coupler14causes the generated interference beam to be received in the detector18.

The reference optical system15returns the reference beam which is wave-guided by the coupler14to the coupler14. The reference optical system15may be a Michelson type or may be a Mach-Zehnder type. According to the embodiment, the reference optical system15causes the reference beam guided from the coupler14to be reflected from a reflecting optical system including a reference mirror or the like so as to return the reference beam to the coupler14. As described above, the reference beam which is returned to the coupler14is synthesized with the reflected measuring beam which is reflected from the object eye E. The configuration of the reference optical system15can be changed. For example, the reference optical system15may cause the reference beam guided from the coupler14not to be reflected but be transmitted to the detector18by a transmission optical system such as the optical fiber.

A rear end portion (a base end portion) of the fiber4in the probe2is detachably attached to the attaching unit (for example, a connector)16. The probe2of the embodiment includes the fiber4, a handpiece5, and an insertion portion (for example, a needle)6. The fiber4wave-guides the measuring beam and the aiming beam guided from the coupler14of the measuring unit10to the tip end of the insertion portion6. The fiber4is coated with a torque coil (not shown) and is rotatable with respect to the handpiece5. The handpiece5is a substantially cylinder-shaped member which is grasped by an operator (for example, an inspector or a technician). The insertion portion6is provided at a tip end of the handpiece5and has an outer diameter smaller than the outer diameter of the handpiece5. The tip end of the insertion portion6is inserted into the specimen (for example, the object eye E). The fiber4is connected to a rear end portion of the handpiece5and extends to the tip end of the insertion portion6. The probe2can emit the measuring beam and the aiming beam which are wave-guided by the fiber4from the tip end thereof while scanning the specimen with the measuring beam and the aiming beam. The description for a structure of the tip end in the probe2will be made in detail with reference toFIG. 2.

The fiber rotation motor17can cause the attaching unit16to which the fiber4in the probe2is attached to rotate around an axis of the fiber4. In other words, the fiber rotation motor17causes the attaching unit16to rotate with the fiber4, and thus the scanning is performed with the measuring beam and the aiming beam.

The detector18detects an interference state between the reflected measuring beam and the reference beam. In other words, the detector18detects an interference signal of the interference beam generated by the coupler14. More specifically, in a case of a Fourier domain OCT, spectrum intensity of the interference beam is detected by the detector18and then a depth profile (a scan signal A) in a predetermined range is acquired through a Fourier transform with respect to data of the spectrum intensity. As described above, the optical tomographic image photographing apparatus1of the embodiment employs an SS-OCT. However, the optical tomographic image photographing apparatus1may employ various types of OCTs. For example, any one of a Spectral-domain OCT (SD-OCT), a Time-domain OCT (TD-OCT), and the like may be employed in the optical tomographic image photographing apparatus1. In a case where the SS-OCT is employed, it is preferable that a balanced detector including a plurality of light receiving elements be employed as the detector18. When the balanced detector is used, the optical tomographic image photographing apparatus1can obtain a difference of interference signals from the plurality of light receiving elements, and thus it is possible to reduce unnecessary noise included in the interference signal. As a result, a quality of the tomographic image is improved.

Meanwhile, the measuring unit10is configured to change an optical path length difference between the measuring beam and the reference beam. The measuring unit10of the present embodiment changes the optical path length difference by moving the optical member (for example, the reference mirror) included in the reference optical system15in the optical axis direction. Here, the configuration for changing the optical path length difference may be disposed in the middle of the optical path of the measuring beam. In addition, the optical tomographic image photographing apparatus1further includes a variety of configurations such as an optical system for performing focus adjustment of the measuring beam, but the description thereof will not be made.

The control unit20includes the CPU (a processor)21, a RAM22, a ROM23, a non-volatile memory24, or the like. The CPU21controls the optical tomographic image photographing apparatus1and peripheral devices. The RAM22temporarily stores a variety of information. In the ROM23, a variety of programs, an initial value, and the like are stored. The non-volatile memory24is a non-transitory storage medium capable of saving the stored contents even when the power supply is cut off. For example, a hard disk drive, a flash ROM, and a USB memory which is detachably mounted on the optical tomographic image photographing apparatus1can be used as the non-volatile memory24. A photographing control program for controlling a process executed by the CPU21is stored in the non-volatile memory24. In addition, in the non-volatile memory24, a variety of information such as a photographed tomographic image and the distance between a tip end of the probe2and a tissue is stored.

According to the embodiment, a personal computer (hereinafter, referred to as “PC”) connected to the measuring unit10is used as the control unit20. However, without using the PC, the measuring unit10and the control unit20may be integrally formed as one device. In addition, the control unit20may be configured of a plurality of control units (that is, a plurality of processors). For example, the control unit20of the optical tomographic image photographing apparatus1may be configured of a first control unit provided in the PC and a second control unit provided inside the measuring unit10. In this case, for example, the first control unit provided in the PC may instruct the second control unit to perform the start and end of the photographing based on an operation of an operating unit connected to the PC. The second control unit may control operations of the measuring light source11, the aiming light source12, the fiber rotation motor17, or the like following instructions from the first control unit. In addition, an image generating process or the like based on the interference signal may be performed in both of the first control unit and the second control unit.

The peripheral devices, such as a display unit31, an operating unit32, a speaker33, a vibration unit34, a foot switch35, and a surgical operation microscope36are electrically connected to the control unit20. A screen for work (not shown) or the like is displayed on the display unit31. The display unit31may be a display unit of the PC or may be a dedicated display unit for the optical tomographic image photographing apparatus1. Alternately, a plurality of display units may be used in combination. The operating unit32is a device for identifying a variety of instructions for operations by an operator. As for the operating unit32, for example, at least any one of a mouse, a joy-stick, a keyboard, a touch panel, and the like may be used. The speaker33generates sounds. The vibration unit34can generate vibration which is felt by an operator.

The foot switch35is disposed at an operator's feet. The operator can operate the foot switch35while observing the probe2or the like. The surgical operation microscope36magnifies and displays (by photographing in the embodiment) the inside of the specimen (the object eye E in the embodiment) during surgery or diagnosis, or during the training thereof. The operator performs the surgery or the diagnosis, or the training thereof (according to the embodiment, these are collectively referred to as “operation”) while looking into the surgical operation microscope36. In addition, according to the embodiment, the control unit20can acquire the image photographed by the surgical operation microscope36so as to display the image on the display unit31. During operation, an assistant or the like of the operator can check an operation state or the like through the image displayed on the display unit31. Note that, it is possible to realize the present invention without using the surgical operation microscope36. For example, an observation optical system for photographing the image inside the specimen may be provided in the measuring unit10. In this case, the operator can operate while checking the image photographed by the observation optical system. Further, the present invention is applied to a case where the operator observes the proximity of the tip end of the probe2by the naked eye.

With reference toFIG. 2, a structure of the tip end of the insertion portion6of the probe2will be described in detail. An external cylinder61, a cover66, a holding portion68, a condensing portion71and the like are provided in the tip end of the insertion portion6.

The external cylinder61covers the periphery of the tip end of the fiber4(particularly, in the periphery of the holding portion68and the condensing portion71). According to the embodiment, a shape of an external cylinder61is a substantially cylindrical shape having a hemispherical occluding part at the tip end. The external cylinder61is formed of a material having a function of shielding the measuring beam and the aiming beam. In the external cylinder61, an opening62, which has the predetermined width in the scanning direction (the direction around the axis) of the measuring beam and the aiming beam, is formed in the proximity of a portion at which the condensing portion71is positioned in the axial direction. The optical flux is emitted from the condensing portion71is transmitted to the outside in an area63(hereinafter, referred to as “a transmission area63”) inside the opening62, but is shielded by the external cylinder61in an area64(hereinafter, referred to as “a shielding area64”) where the opening62is not formed.

According to the embodiment, an inner surface of the external cylinder61is subjected to a roughing process. In other words, a large number of minute irregularities are formed in the inner surface of the external cylinder61. In this case, the light applied to the inner surface of the external cylinder61is scattered in the shielding area64. Accordingly, the reflected light reflected from the shielding area64is less likely to return to the condensing portion71compared with a case where the light is not easily scattered in the inner surface of the external cylinder61(for example, the inner surface is subjected to a polishing process). In other words, in a case of being subjected to the polishing process or the like, if the light is reflected toward a different direction from the condensing portion71, the reflected light is not incident on the condensing portion71. When the reflected light is scattered, the reflected light is easily returned to the condensing portion71. Therefore, the optical tomographic image photographing apparatus1can perform more reliable detection by using the reflected light reflected from the shielding area64when detecting a state where the shielding area64is irradiated with the measuring beam.

Meanwhile, a shape of the transmission area63of the embodiment is substantially rectangular, but needless to say, a size, a shape, the number, or the like of the transmission area63can be changed. In addition, a specific method for forming the transmission area63and the shielding area64can be also changed. For example, the transmission area63and the shielding area64may be formed by combining a material transmitting the measuring beam and the aiming beam and a material shielding the measuring beam and the aiming beam for manufacturing the external cylinder61.

The cover66is formed of the material transmitting the measuring beam and aiming beam and blocks the outside of the external cylinder61. Accordingly, the cover66allows the light transmission to be performed between the inside and the outside of the transmission area63while preventing blood, a tissue of vitreous body, or the like from intruding inside the external cylinder61from the opening62. Meanwhile, the cover66may be positioned on the inner side of the external cylinder61. In addition, the cover66may be configured to block only the opening62of the external cylinder61.

A holding portion68is a member having a substantially cylindrical outer shape and is fixed with respect to the external cylinder61. An insertion hole69which inserts the fiber4being in a rotatable state is formed in a center portion of a shaft of the holding portion68. The holding portion68holds the fiber4to be rotatable in a state where the position of the fiber4on the shaft with respect to the external cylinder61is constant.

The condensing portion71is provided in the tip end of the fiber4. The condensing portion71causes the light beam emitted from the tip end of the fiber4to be deflected and concentrated on the tissue of the specimen. In addition, the reflected measuring beam reflected from the tissue is received in the condensing portion71and incident on the fiber4. The condensing portion71of the present embodiment causes the light beam to be deflected at an angle of about 70° with respect to the fiber4in the axial direction, but the deflection angle can be properly changed. Meanwhile, in the fiber4, a shaft73serving for suppression of a distortion or the like of the fiber4is provided in the outer periphery of a portion on the rear end side from the holding portion68.

FIG. 3is a diagram illustrating a state of scanning when measuring, for example, a horizontal step (for example, block gauge BG) by the optical tomographic image photographing apparatus1in the embodiment. When data acquired by the rotary scanning as illustrated inFIG. 3is imaged, an image is generated by arranging data items, acquired at scanning angles as illustrated inFIG. 4A, in a line. In this manner, the image data expressed by the polar coordinates is displayed in a different form from the actual. For example, a flat one is displayed to be largely curved and a resolution of a horizontal pixel is changed depending of the depth. As illustrated inFIG. 4A, the horizontal step ends up being curved. In this way, with the image data expressed by the polar coordinates, an inspector cannot observe a tomographic shape of the retina in actuality and thus it is difficult to measure the distance on the image.

Accordingly, according to the embodiment, by coordinates-converting the image acquired from the polar coordinates system into the rectangular coordinates system, the data is converted into the same image as that of the actual form of the specimen. Therefore, an intuitively understandable display is realized. In addition, the tomographic image which is coordinate-converted into the rectangular coordinates system is advantageous in measuring the length (the distance) of a portion of the specimen (described later in detail).

Hereinafter, as an example of an image processing method of the present example, a method of creating a table for conversion so as to coordinates-convert the tomographic image acquired by the polar coordinates system into the rectangular coordinates will be described. In the example, the image conversion is performed by calculating the polar coordinates corresponding to the coordinates system of the image (for example, the rectangular coordinates system) to be calculated and then performing an interpolation from the original image.

For example, the table for conversion is created by identifying which pixel (xi, yj) configuring the image data (hereinafter, referred to as “secondary image data” in some cases) (xi, yj) expressed by the rectangular coordinates system after coordinate conversion corresponds to which position of the coordinate system of the image data (hereinafter, referred to as “primary image data” in some cases) before the coordinate conversion.

FIG. 4Ais a diagram illustrating the image data before coordinate conversion when the horizontal step is photographed. Generally, each of the sample points (ri, θj) of the primary image data I (ri, θj) before coordinate conversion is expressed by the polar coordinates system having an upper right end as the origin. In other words, the position of each of the sample points (ri, θj) is expressed by the polar coordinates system. For example, each of the sample points (ri, θj) is expressed by an angle θ of a scanning line and a length r from a rotation center to each of the sample points on the respective scanning lines.

In creating the table for conversion, an image area after the coordinate conversion into the rectangular coordinates system is set first. This image area can be set arbitrarily. For example, an allowable x-y domain is obtained from each of the sample points (ri, θj) according to the following Equation (1), and then the image area after the coordinate conversion may be set with reference to the domain.
[Equation 1]
r=r0+r′
x=rcos θ
y=rsin θ  (1)

From the image data obtained by an interference optical system, it is difficult to grasp the distance r between the rotation center of the fiber4and each of the sample points. If the distance r from the rotation center is not clear, it is not possible to perform the coordinate conversion according to Equation (2) described later. Therefore, in the example, a point at which a distance from the rotation center is clear is assumed to be a standard, and the distance r′ between the standard and each of the sample points is measured. Then, the length r between the rotation center and the sample point is calculated by adding the length r0 between the rotation center and the standard, and the distance r′ between the standard and the sample point.

In the example, the shielding area64is photographed as a line S1(refer toFIG. 4A). Since the distance between the shielding area64and the rotation center of the fiber4is known in terms of design, in the example, the shielding area64on the image is assumed to be a standard and then the distance to each of the sample points is measured based on the standard. Accordingly, as illustrated in the equation (1), the distance r between the rotation center and the sample point is calculated by assuming that r0 is the distance between the rotation center of the fiber4and the shielding area64and r′ is the distance between the shielding area64and the sample point.

FIG. 5is a diagram illustrating an x-y domain calculated from equation (1), for example, in a case where r (depth of the image data) is in the range of 0≦r≦a and θ (the scanning angle of the fiber4) is in the range of α≦θ≦β. The x-y domain satisfying the above conditions becomes in the range of a×cos β≦x≦a×cos α, and 0≦y≦a.

The image area after the coordinate conversion may be set to a range, for example, including all of the x-y domains or including some of x-y domains with reference to the calculated x-y domains. For example, the image area after the coordinate conversion as illustrated inFIG. 4Bis set to a wide range compared to the x-y domain.

In this manner, the image area can be set to be sufficient for a required image area with respect to the polar coordinates data by setting the image area after the coordinate conversion in consideration of the x-y domain. In addition, it is possible to display, for example, the image with sufficient resolution by setting a portion of the x-y domain to the image area. Surely, the x-y domain is not necessarily calculated and the image area is not necessary to be set in consideration of the x-y domain.

Meanwhile, in the image area, the CPU21may be automatically set or may be set by an input of the inspector. The image area may be stored in the ROM in advance. In addition, as described above, for example, the x-y domain is calculated from the CPU21by inputting an allowable range of r and θ, and thus the x-y domain may be taken into consideration.

If the image area is set, which pixel (xi, yj) of the secondary image data I (xi, yj) in the set area image corresponds to which position of the polar coordinates system of the primary image data I (ri, θj) are calculated. The following equation (2) is an example of the equation for calculating the position of the primary image data I (ri, θj) with respect to the pixels (xi, yj).
[Equation 2]
r=(x2+y2)1/2
θ=tan−1(y/x)  (2)

With respect to each of the pixels (xi, yj) of the secondary image data I (xi, yj), a corresponding position in the polar coordinates system is calculated according to the equation (2). Regarding the corresponding position as this calculation result, the sample point and the pixel may not be a one-to-one correspondence, but in this case, the value of each pixel may be interpolated from such values of the several sample points near the corresponding position.

Thus, the corresponding positions in the polar coordinate system for each pixel are calculated and then the calculated positions are written in the RAM22one after another. Therefore, the secondary image data I (xi, yj) is generated and then is read out from the RAM22to be displayed.

The image data (the primary image data) before the coordinate conversion is temporarily stored in the RAM22. The CPU21generates the secondary image data I (xi, yj) corresponding to a pixel matrix of the display screen of the display unit31from the primary image data I (ri, θj) which is stored in the RAM22. In a generation process of the secondary image data I (xi, yj), a correlation and an interpolation of the coordinates are required. The secondary image data I (xi, yj) generated from the CPU21is temporarily stored in the RAM22and then read out to the display unit31.

In the example, the corresponding positions in the polar coordinate system, before coordinate conversion, corresponding to each of all pixels (xi, yj) of the secondary image data I (xi, yj) are calculated at least before the start of the measurement and stored in RAM22in advance.

Next, a distance measuring method will be described by using the coordinate-converted image. In the image data after coordinate conversion, the actual distance with respect to the length of one pixel is determined. For example, when the number of pixels for photographing a range of 5 mm of image data obtained by the detector18is assumed to be 688 pixels, the actual distance per one pixel becomes 5/688 mm. Accordingly, it is possible to obtain the actual distance according to the number of pixels of a portion to be measured on distance.

For example, as illustrated inFIG. 7, it is assumed that points A and B on the image after the coordinate conversion are given by the inspector. The CPU21measures the number of pixels included in the distance between the pixel of the specified point A and the pixel of the point B in the horizontal direction and in the vertical direction. As described above, since the actual distance is determined with respect to the length of one pixel, it is possible to measure the distance between the point A and the point B. Meanwhile, a segment AB connecting the point A and the point B is oblique with respect to the image, the distance between the point A and the point B may be calculated by the Pythagorean theorem.

<Operation Method and Control Operation of the Apparatus>

Subsequently, an operation method of the apparatus and a control operation of the apparatus will be described. First, the CPU21creates the table for conversion based on the size of the image area set as described above, and then stores the table for conversion in the RAM22. It is preferable that the creation of the table for conversion be performed at least before the measurement.

After the table for conversion is stored in the RAM22, the inspector manipulates the foot switch35by inserting the probe2into the object eye. The foot switch35outputs the operation signal to the CPU21. The CPU21starts the measurement by receiving the operation signal from the foot switch35.

The CPU21causes the measuring beam to be emitted from the measuring light source and causes the fiber4to rotate. The measuring beam passing through the fiber4is applied to the inside of the object eye from the transmission area and then reflected from a fundus of the eye. The measuring beam reflected from the fundus of the eye enters the inside the insertion portion6again from the transmission area to pass through the fiber4. The measuring beam which is returned to the measuring unit by passing through the fiber4is combined with the reference beam from the reference optical system at the coupler14so as to become the interference beam, and the interference beam is detected by the detector18.

According to a scanning angle θj of the primary image data and an address ri of the pixels of the primary light receiving elements detected by the detector18for each the scanning angle θ set in advance, the CPU21writes the image data into the RAM22one after another based on the table for conversion stored in the RAM22.

The CPU21causes the display unit31to display, for example, the generated secondary image data. The inspector operates, for example, the foot switch35to capture the image which is being measured in real time. The CPU stores (records) the real time images in the non-volatile memory24as a still image when the operation signal is received from the foot switch35. Then, the CPU21causes the display unit31to display the still image stored in the non-volatile memory24on the screen.

The inspector selects a part to be measured on the distance of the still image which is displayed on the display unit31. For example, the inspector selects two points on the image by operating the operating unit32. The CPU21measures the actual distance from the pixel numbers between two points as described above. The CPU21displays, for example, the measured actual distance between two points on the display unit31.

Modification Example

Meanwhile, in the example, the shielding area64is assumed to be a standard, but the standard is not limited to the shielding area64. As long as there is a point capable of being a standard on the image, the measurement may be performed by using the point as the standard. For example, inFIGS. 4 and 7, a line S2is obtained by the measuring beam which is reflected from the optical member inside the probe and imaged on the tomographic image as a mirror image.

In this case, if the optical member from which the measuring beam is reflected is specified, it is possible to calculate the distance between each point and the rotation center of the fiber even with the line S2as a standard. In this manner, the rotation center of the probe may be calculated through the reflected light inside the probe as a standard.

In addition, in the above description, the conversion of the image data is performed by calculating the position of the rotation center of the fiber from the positional information of the inside of the probe, but is not limited thereto. For example, the conversion of the image data may be performed based on the length information of an interference optical path.

For example, with respect to the probe having the standard length between the attaching unit16and the tip end (for example, the condensing portion71), even in a case where the probe having a different length is attached, the rotation axis of the fiber4may be calculated by adjusting the reference mirror installed on the reference optical system15based on the difference of the length with respect to the probe having the standard length.

Meanwhile, in the above description, the table for conversion is created before measurement, but is not limited thereto. For example, the secondary image data may be calculated by substituting the acquired primary image data into the equation (2) instead of creating the table for conversion.

The table conversion is performed from the acquired image for each angle θ at all times, but is not limited thereto. For example, the conversion into the secondary image data may be performed by the table for conversion after the scanning is completed in the set scanning angle θ and data is completely acquired.

Meanwhile, in the example, the table for conversion is stored in the RAM22, but is not limited thereto. For example, the table for conversion may be stored in the ROM23in advance, or may be stored in the non-volatile memory24. In addition, the table for conversion may be created whenever the measurement is performed or one table for conversion may be used in a plurality of measurements. Further, a plurality of tables for conversion may be stored in the control unit20.