CN110680277B

CN110680277B - Ophthalmic optical imaging and biological parameter measuring instrument calibration tool and use method thereof

Info

Publication number: CN110680277B
Application number: CN201910871326.4A
Authority: CN
Inventors: 胡志雄; 王红婷; 刘文丽; 李飞; 李修宇; 洪宝玉; 李姣
Original assignee: National Institute of Metrology
Current assignee: National Institute of Metrology
Priority date: 2019-09-16
Filing date: 2019-09-16
Publication date: 2021-08-27
Anticipated expiration: 2039-09-16
Also published as: CN110680277A

Abstract

The invention relates to an ophthalmic optical imaging and biological parameter measuring instrument calibration tool and a using method thereof. The calibration tool comprises: a first lens having a first curved surface and a first plane; a second lens having a second curved surface and parallel second and third planes; and the PDMS mold body is internally provided with a cavity and resolution test microspheres which are uniformly distributed, wherein the first plane and the second plane are attached together, the third plane and the PDMS mold body are attached together, the cavity is adjacent to the third plane, and the first lens, the second lens, the PDMS mold body and the cavity have a common axis, wherein the curvature radius of the first lens is smaller than that of the second lens, the bottom radius of the PDMS mold body is smaller than that of the third plane, the second curved surface is provided with a view angle scale and a resolution line pair pattern, and the third plane is provided with a spoke-shaped resolution test pattern and an image registration fine line.

Description

Ophthalmic optical imaging and biological parameter measuring instrument calibration tool and use method thereof

Technical Field

The application relates to the technical field of instrument detection, in particular to a calibration tool for ophthalmic optical imaging and biological parameter measuring instruments and a using method thereof.

Background

The fundus optical imaging obtains the structural information of human eyes by a two-dimensional or three-dimensional imaging technology, and is widely applied to clinical diagnosis with the advantages of no wound and high precision. The fundus imaging diagnosis device mainly comprises a posterior segment optical coherence tomography scanner, a fundus camera and the like, and an optical coherence tomography scanner with a fundus photographing function, an ophthalmologic optical biological measuring instrument and the like. The maximum measurable field angle of the fundus imaging medical equipment influences the imageable range, and the resolution determines the minimum distinguishable structural size, which are important parameters for representing the measurement and diagnosis capability of the equipment; the depth measurement accuracy is related to the accuracy of thickness measurement of structures below the fundus retina; the measuring accuracy of the eye axis length influences the effect of ophthalmic optical surgery, especially cataract; the signal-to-noise ratio affects the quality of the imaging. These indicators affect the validity and reliability of the final diagnosis result, so a calibration tool or a calibrator is needed to test the imaging device, and further evaluate the measurement accuracy of the field angle, the lateral resolution, the axial resolution, the depth measurement capability, the signal-to-noise ratio and the eye axis length. There is currently no single calibration tool that can detect or calibrate the above parameters of an ophthalmic instrument.

ISO standard 169971 provides a standard and calibration tool for a posterior segment optical coherence tomography scanner, and the parameters involved include resolution, field angle, depth measurement, signal-to-noise ratio, and the like. Fig. 1 is a schematic diagram of the structure of a calibration tool given in ISO standard 169971. As shown in fig. 1, the calibration tool includes a lens 101, an aperture 102, a barrel 103 having a length of 17mm, a thin line 104, a neutral density filter 105, a glass plate 106 having a thickness of 1mm, and a scale 107. The scale of the scale 107 is directly used for detecting the field angle of the OCT instrument. However, the actual OCT imaging scan is not planar, especially when imaging at large field angles. Therefore, the calibration tool given by ISO standard 169971 is only suitable for paraxial small angle detection, and cannot meet the requirement of OCT for field angle detection of tens of degrees. Therefore, in practical detection, the calibration tool is not practical for detecting the OCT parameters, and needs to be improved.

The difficulty of fundus camera equipment detection is analyzed in detail in a paper of fundus camera optical performance detection and solution research in the Chinese medical apparatus information 2017 13 by Li Ning et al. The international standard IS010940 for fundus camera, ophthalmology instrument fundus camera, provides a method for measuring resolution, field angle, etc. by placing a graduated scale at a position 1 meter away from the fundus camera and calculating the field angle from the read length. However, in actual detection, the resolution of the fundus camera to a scale at a distance of 1 meter is low, and image distortion at the edge of the field of view and the resulting blur make it difficult to read the numerical result. The detection method given by IS010940 IS not practical. CN107647845A "A model eye for fundus examination and its application method" designs a model eye with a lens and an angle scale of field of view and a resolution negative film for fundus camera examination. The view field angle scale and the resolution ratio line are aligned on the negative plate, and the precise alignment of the negative plate and the model eye is difficult to control when the model eye is actually developed, so that the measurement precision of the view field angle is difficult to guarantee; the resolution line pair of the invention can only be used for transverse two-dimensional resolution detection, and cannot detect axial resolution.

Disclosure of Invention

The invention discloses a calibration tool for an ophthalmic optical imaging and biological parameter measuring instrument and a using method thereof, aiming at solving the problem that the existing single calibration tool cannot detect or calibrate parameters such as an angle of view, resolution, depth measurement, eye axial length, signal to noise ratio and the like of the ophthalmic imaging device and the ophthalmic biological parameter measuring instrument.

According to a first aspect of the present invention, there is provided a calibration tool for an ophthalmic optical imaging and bio-parameter measurement instrument, comprising:

a first lens having a first curved surface and a first plane;

a second lens having a second curved surface and parallel second and third planes; and

a PDMS mold body, a hollow chamber and resolution test microspheres which are uniformly distributed are arranged in the PDMS mold body,

wherein the first plane and the second plane are attached together, the third plane and the PDMS body are attached together, the void is adjacent to the third plane, and the first lens, the second lens, the PDMS body and the void share a common axis,

wherein the radius of curvature of the first lens is smaller than that of the second lens, and the bottom radius of the PDMS mold body is smaller than that of the third plane,

wherein the second curved surface has a field angle scale and a resolution line pair pattern thereon, and the third plane has a spoke-shaped resolution test pattern and a fine image registration line thereon.

In one embodiment, the number of the empty chambers is plural, or the empty chambers have plural depths.

In one embodiment, the effective focal length of the calibration tool is in the range of 8-22 mm.

In one embodiment, the radius of curvature of the second lens is in the range of 7-30 mm.

In an embodiment, the view angle scale is distributed on the second curved surface in a petal shape, and is symmetric about the center of the third plane, each petal includes a plurality of concentric arcs, two boundary lines, and angle divisions of the boundary lines, the number of the concentric arcs is 2 to 20, the covered angle of view is 2 to 180 degrees, the angle values of the corresponding angles of view between each two adjacent concentric arcs are equal, and short lines perpendicular to the angle divisions are arranged on the angle divisions as view angle subdivision scale lines.

In an embodiment, the resolution line pair pattern is distributed between every two petals of the field angle scale and is symmetrical about a center of the third plane, the resolution line pair pattern comprises a combination of 25lp/mm, 40lp/mm, 60lp/mm, 80lp/mm and 100lp/mm, and a plurality of the combinations are included between every two petals of the field angle scale.

In one embodiment, the second curved surface has a positioning mark thereon.

In one embodiment, the resolution test microspheres have a diameter in the range of 10nm to 2 μm and the distance between the centers of adjacent microspheres is greater than 2 times the diameter of the microspheres.

In one embodiment, the depth of the void chamber ranges from 300 μm to 3 mm.

According to a second aspect of the present invention, there is provided a method of using the calibration tool described above, comprising:

placing the first curved surface of the calibration tool opposite to the ophthalmic optical imaging and biological parameter measuring instrument to be detected at the measuring position of the calibration tool, and adjusting the position and the angle of the calibration tool to enable the optical axis of the calibration tool to be superposed with the optical axis of the ophthalmic optical imaging and biological parameter measuring instrument and to be imaged clearly;

setting the ophthalmic optical imaging and biological parameter measuring instrument to be in a line scanning mode, enabling a scanning preview line of the ophthalmic optical imaging and biological parameter measuring instrument to be consistent with the image registration fine line of the calibration tool in the angles, the x direction and the y direction, and checking a scanning signal of the ophthalmic optical imaging and biological parameter measuring instrument to enable the scanning signal to display the complete length of the image registration fine line;

making an angular line of the angular scale of field of view parallel to the x-axis of the ophthalmic optical imaging and biometric measurement instrument imaging;

combining all xz images obtained from different y positions to obtain an xyz three-dimensional image, and obtaining an xy two-dimensional image through the obtained three-dimensional image;

reading the reading of the field angle ruler of the calibration tool on the xy image to obtain the imaging field angles of the ophthalmic optical imaging and biological parameter measuring instrument in the x direction and the y direction;

drawing a circle of a minimum distinguishable area at the edge of the spoke on the spoke pattern of the xy image by taking the center of the spoke as the center of a circle, and dividing the circumference by the number of the spokes to obtain the transverse resolution of the central field of view of the ophthalmic optical imaging and biological parameter measuring instrument;

reading the minimum resolution line pair capable of being resolved on the xy image to obtain the transverse resolution of the non-central field of view of the ophthalmic optical imaging and biological parameter measuring instrument;

reading the half-height widths of the point spread functions corresponding to the resolution microspheres in the three-dimensional image in the directions of x, y and z to obtain the transverse resolution and the axial resolution of the central field area of the ophthalmologic optical imaging and biological parameter measuring instrument;

obtaining a z-direction depth measurement of the void on an xz image;

reading the distance between the first curved surface and the third plane on the xz image to obtain an eye axis length measurement value; and

and inserting a neutral density filter between the ophthalmic optical imaging and biological parameter measuring instrument and the calibration tool, testing the PDMS mold body, and counting the signal light intensity and the background noise signal of the resolution test microspheres at different depths in the PDMS mold body to obtain a curve of the signal-to-noise ratio changing along with the depth.

Compared with the prior art, the above aspects of the present invention may have the following advantages or beneficial effects:

the single calibration tool covers the functions of detecting multiple parameters such as an angle of view, fundus transverse resolution, fundus axial resolution, transverse and axial resolution at a certain depth of the fundus retina, depth measurement, signal-to-noise ratio, eye axial length and the like; and the calibration tool has stable structure and can be used for a long time.

Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by the practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and together with the description serve to explain the principles of the invention and not to limit the invention.

In the drawings, like parts are designated with like reference numerals, and the drawings are schematic and not necessarily drawn to scale.

Fig. 1 is a schematic diagram of the structure of a calibration tool given in ISO standard 169971.

Fig. 2 is a schematic structural diagram of a calibration tool for an ophthalmic optical imaging and biological parameter measuring instrument according to an embodiment of the present invention.

Fig. 3 is an expanded plan view of the rear surface of the second lens according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of a resolution line pair pattern according to an embodiment of the invention.

FIG. 5 is a schematic diagram of resolution circle rendering of a spoke image

Detailed Description

The following detailed description of the embodiments of the present invention will be provided with reference to the drawings and examples, so that how to apply the technical means to solve the technical problems and achieve the technical effects can be fully understood and implemented. It should be noted that, as long as there is no conflict, the embodiments and the features of the embodiments of the present invention may be combined with each other, and the technical solutions formed are within the scope of the present invention.

In the following description, for purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the embodiments of the invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without some of these specific details or with other methods described herein.

The following disclosure provides many different embodiments, or examples, for implementing different features of the invention. Specific examples of components and arrangements are described below to simplify the present disclosure. These are, of course, merely examples and are not intended to be limiting. For example, the formation of a first feature "over" or "on" a second feature in the description that follows may include embodiments in which the first and second features are formed in direct contact, and may also include embodiments in which additional features may be formed between the first and second features, such that the first and second features may not be in direct contact.

Furthermore, spatially relative terms (such as "upper," "lower," "front," "rear," "left," "right," and the like) are used herein to describe one element or component's relationship to another element or component as illustrated in the figures for ease of description. These spatially relative terms are intended to encompass different orientations of the device or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as "above" other elements or features would then be oriented "below" the other elements or features.

As described above, the invention discloses a calibration tool for ophthalmic optical imaging and biological parameter measuring instruments and a use method thereof, wherein the detection range of the calibration tool covers parameters such as field angle, transverse resolution, axial resolution, depth measurement, eye axial length, signal to noise ratio and the like.

Fig. 2 is a schematic structural diagram of a calibration tool for an ophthalmic optical imaging and biological parameter measuring instrument according to an embodiment of the present invention. Wherein, the left half of fig. 2 is a schematic diagram of the overall structure of the calibration tool, and the right half of fig. 2 is an enlarged view of the structure in the oval frame in the left half, so as to more clearly show the structure of the calibration tool. The calibration tool may also be referred to as a simulated eye.

As shown in fig. 2, the calibration tool includes a first lens 201, a second lens 202, and a PDMS mold 203 in this order from front to back (left to right in fig. 2). The first lens 201 is a plano-convex lens, the front surface of which is a curved surface, and the rear surface of which is a first plane 207. The second lens 202 is a plano-convex lens with a truncated spherical cap, and has a front surface formed by a second plane 204 and a rear surface including a third plane 205 and a curved surface portion 206. It is obvious that the first plane 207, the second plane 204 and the third plane 205 are all circular planes, and the three are parallel. The PDMS mold body 203 is internally provided with resolution test microspheres 209 which are uniformly distributed, and is also provided with a hollow chamber 210. For example, the PDMS mold body 203 and the hollow chamber 210 may have a cylindrical shape, a rectangular parallelepiped shape, or the like.

The first plane 307 and the second plane 204 are attached together, the third plane 205 and the PDMS mold body 203 are attached together, and the void 210 is adjacent to the third plane 205. The first lens 201, the second lens 202, the PDMS mold body 203, and the hollow chamber 210 have a common axis, i.e., a horizontal dashed line in fig. 2. The first lens 201, the second lens 202, the PDMS mold body 203, and the chamber 210 are all symmetric about this axis.

As shown in fig. 2, the radius of curvature of the first lens 201 is smaller than the radius of curvature of the second lens 202, i.e., the first plane 207 is smaller in area than the second plane 204. The bottom radius of the PDMS mold body 203 is smaller than the radius of the third plane 205.

In one embodiment, the effective focal length of the calibration tool is in the range of 8-22 mm. For example, the effective focal length of the calibration tool may be 17 mm.

In one embodiment, the radius of curvature of the second lens 202 is in the range of 7-30 mm. For example, the radius of curvature of the second lens 202 is 8.8 mm.

Resolution test microspheres 209 disposed within the PDMS phantom 203 may be used to measure the three-dimensional resolution of the central field of view region. The resolution test microspheres 209 have a diameter in the range of 10nm to 2 μm, for example 0.5 μm, and the distance between the centers of adjacent microspheres is greater than 2 times the diameter of the microspheres. If the diameter of the resolution test microsphere 209 is too small, the signal-to-noise ratio is too low, and if the diameter is too large, the point spread function is too wide, so that the test result cannot reflect the real resolution condition of the instrument to be tested. When the distance between the centers of the adjacent microspheres is too small, the point spread functions of the adjacent microspheres are overlapped; when the distance between the centers of adjacent microspheres is too large, the number of points in an imaging field is too small. By limiting the diameter of the microspheres to be within the range of 10nm-2 mu m and limiting the sphere center distance of adjacent microspheres to be greater than 2 times of the diameter of the microspheres, higher signal-to-noise ratio can be realized, microsphere images can be easily and quickly found within the imaging visual field range, and a point spread function capable of reflecting the level of an instrument to be detected can be obtained.

The empty chamber 210 arranged in the PDMS mold body 203 can be used for detecting the accuracy of the axial depth small-size measurement of the instrument to be detected. The relevant information can be obtained by measuring the depth of the empty chamber 210. In one embodiment, a plurality of chambers 210 may be disposed within the PDMS mold body 203. In another embodiment, the interior of the PDMS mold body 203 may be provided with complex-structured chambers 210 having multiple depths. The depth of the empty chamber 210 may be selected to have one or more values in the range of 300 μm-3mm, for example 1 mm.

To more clearly show the pattern on the rear surface of the second lens 202, further reference is now made to fig. 3. Fig. 3 is an expanded plan view of the rear surface of the second lens according to an embodiment of the present invention. As shown in fig. 2 and 3, the curved surface portion 206 of the second lens 202 has the field angle scale 208 and the resolution line pair pattern 306 thereon, and the third plane 205 has the spoke-shaped resolution test pattern 308 thereon. In fig. 3, in addition to the rear surface of the second lens 202 as a whole, the third plane 205 of the second lens 202 and a part of the field angle scale 208 are also shown enlarged. The invention can detect the accuracy of the measurement of the wide-angle view field angle by designing the view field angle scale on the curved surface, and has more practicability.

In one embodiment, the field angle scale 208, the resolution line pair pattern 306, and the spoke-shaped resolution test pattern 308 may all be made by laser cleaning a metal film. Thus, the position accuracy of the formed pattern is high, thereby making the measurement result more reliable.

As shown in fig. 3, the angular scale of field 208 is distributed in a petal shape on the curved surface portion 206 of the second lens 202, and is symmetrical about the center of the third plane 205. Each petal comprises a plurality of concentric arcs 301, two border lines 302, and angular bisectors 303 of the border lines 302.

The concentric arc 301 is a field angle coarse graduation line. The angle values of the corresponding field angles between every two adjacent concentric arcs 301 are equal, and

short lines

304, 305 perpendicular to the angular lines are arranged on the angular lines 303 as field angle subdivision graduation lines. The

stubs

304, 305 are spaced apart at unequal intervals in length, which facilitates reading registration.

In one embodiment, the number of the concentric arcs 301 may be 2-20, and the covered angle of view may be 2-180 degrees. In a specific embodiment, the number of concentric arcs 301 is 18, and the covered field angle is 72 degrees. At this time, the angle of the corresponding field angle between each two adjacent concentric arcs 301 is 2 degrees. Additionally, 10

short lines

304, 305 are disposed between each two adjacent concentric arcs 301, so that the angle of the corresponding field angle between each two adjacent short lines is 0.2 degrees.

With further reference to fig. 3, a spoke-shaped resolution test pattern 308 and a fine image registration line 309 are disposed on the third plane 205 of the second lens 202. By scan imaging the spoke-shaped resolution test pattern 308, the lateral resolution of the central field of view can be measured. In a particular embodiment, 36 spokes are uniformly arranged within 360 degrees, each spoke having a radius of 80 μm in length. The included angle between every two spokes is 10 degrees, each spoke occupies 5 degrees, and the arc length of the spoke edge is 7 mu m. An image registration thin line 309 is used for registration of the fundus preview image and the scan image. The diameter of the thin image registration line 309 may be 50-200 μm, preferably 100 μm.

With further reference to fig. 3, a resolution line pair pattern 306 is provided at the blank between each two petals of the field angle scale 208 for measuring the lateral resolution of the non-central field of view. The resolution line pair pattern 306 is also symmetrical about the center of the third plane 205. The resolution line pair pattern 306 includes a combination of 25lp/mm, 40lp/mm, 60lp/mm, 80lp/mm, and 100lp/mm, and a plurality of the combinations are included between each two petals of the field angle scale 208. FIG. 4 is a schematic diagram of a resolution line pair pattern according to an embodiment of the invention.

In an embodiment, further referring to fig. 3, a short line index marker 307 is disposed on the curved surface portion 206 of the second lens 202 centered at the field angle of 14 degrees. The positioning mark is beneficial to quickly finding the direction of the calibration tool according to the corresponding relation between the positioning mark and the image.

The specific structure of the calibration tool for ophthalmic optical imaging and bio-parameter measurement instrument according to the present invention has been described. It will be apparent to those skilled in the art that the various numbers/numbers described above are not limiting, but are exemplary and variations can be made.

The following describes in detail the method of use of the calibration tool for ophthalmic optical imaging and bio-parameter measurement instruments according to the present invention, comprising the following steps.

The first step, the first curved surface of the calibration tool is placed at the measurement position of the to-be-detected ophthalmic optical imaging and biological parameter measuring instrument, and the position and the angle of the calibration tool are adjusted to enable the optical axis of the calibration tool to be coincident with the optical axis of the ophthalmic optical imaging and biological parameter measuring instrument and to be imaged clearly.

And a second step of setting the ophthalmic optical imaging and biological parameter measuring instrument to be in a line scanning mode, enabling a scanning preview line of the ophthalmic optical imaging and biological parameter measuring instrument to be consistent with the image registration fine line of the calibration tool in the angles, the x direction and the y direction, and checking a scanning signal of the ophthalmic optical imaging and biological parameter measuring instrument to enable the scanning signal to display the complete length of the image registration fine line. The scan signal can show the full length of the image registration thread, indicating that the position of the calibration tool is within tolerance.

And thirdly, enabling one angular line of the view field angle scale to be parallel to the x axis of the ophthalmic optical imaging and biological parameter measuring instrument imaging.

And fourthly, combining all xz images obtained from different y positions to obtain an xyz three-dimensional image, and obtaining an xy two-dimensional image through the obtained three-dimensional image.

And fifthly, reading the reading of the field angle ruler of the calibration tool on the xy image to obtain the imaging field angles of the ophthalmic optical imaging and biological parameter measuring instrument in the x direction and the y direction.

And sixthly, drawing a circle of the minimum distinguishable area at the spoke edge on the spoke pattern of the xy image by taking the spoke center as the circle center, and dividing the circumference by the number of the spokes to obtain the transverse resolution of the central field of view of the ophthalmic optical imaging and biological parameter measuring instrument. Fig. 5 is a schematic diagram of resolution circle mapping for a spoke image, in which a minimum resolvable area circle (also referred to as a resolution circle) 501 is shown.

And seventhly, reading the pair of minimum resolution lines which can be resolved on the xy image to obtain the transverse resolution of the non-central field of view of the ophthalmic optical imaging and biological parameter measuring instrument.

And eighthly, reading the full widths at half maximum of the point spread functions corresponding to the resolution microspheres on the three-dimensional image in the directions of x, y and z to obtain the transverse resolution and the axial resolution of the central field area of the ophthalmologic optical imaging and biological parameter measuring instrument.

And a ninth step of obtaining a z-direction depth measurement value of the empty chamber on the xz image.

And step ten, reading the distance between the first curved surface and the third plane on the xz image to obtain an eye axis length measurement value.

And step eleven, inserting a neutral density filter between the ophthalmological optical imaging and biological parameter measuring instrument and the calibration tool, testing the PDMS mold body, and counting the signal light intensity and the background noise signal of the resolution test microspheres at different depths in the PDMS mold body to obtain a curve of the signal-to-noise ratio changing along with the depth.

The calibration tool for the ophthalmology optical imaging and biological parameter measuring instrument has the advantages that the detection range covers parameters such as an angle of view, transverse resolution, axial resolution, depth measurement, axial length of an eye, signal to noise ratio and the like, and the tool is multipurpose and can be used for detecting and calibrating the ophthalmology optical imaging and biological parameter measuring instrument such as a posterior segment optical coherence tomography scanner and the like. Currently, there is no calibration tool available in China to detect or calibrate both the axial resolution and depth measurements of ophthalmic optical imaging devices, or even more, for which measurements can be made with the calibration tool according to the present invention.

It is to be understood that the disclosed embodiments of the invention are not limited to the particular process steps or materials disclosed herein, but rather, are extended to equivalents thereof as would be understood by those of ordinary skill in the relevant art. Reference in the specification to "an embodiment" means that a particular feature, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase or "an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment.

Furthermore, the described features or characteristics may be combined in any other suitable manner in one or more embodiments. In the above description, certain specific details are provided, such as thicknesses, amounts, etc., to provide a thorough understanding of embodiments of the invention. One skilled in the relevant art will recognize, however, that the invention may be practiced without one or more of the specific details, or with other methods, components, materials, and so forth.

While the above examples are illustrative of the principles of the present invention in one or more applications, it will be apparent to those of ordinary skill in the art that various changes in form, usage and details of implementation can be made without departing from the principles and concepts of the invention. Accordingly, the invention is defined by the appended claims.

Claims

1. A calibration tool for ophthalmic optical imaging and biological parameter measurement instruments, comprising:

a first lens having a first curved surface and a first plane;

2. The calibration tool of claim 1, wherein the number of said empty chambers is plural or the empty chambers have a plurality of depths.

3. The calibration tool of claim 1, wherein the effective focal length of the calibration tool is in the range of 8-22 mm.

4. The calibration tool of claim 1, wherein the radius of curvature of the second lens is in the range of 7-30 mm.

5. The calibration tool of claim 1, wherein the view angle scale is distributed on the second curved surface in a petal shape and is symmetric about a center of the third plane, each petal comprises a plurality of concentric arcs, two boundary lines and angle division lines of the boundary lines, the number of the concentric arcs is 2-20, the covered angle of view is 2-180 degrees, the angle value of the corresponding angle of view between each two adjacent concentric arcs is equal, and short lines perpendicular to the angle division lines are arranged on the angle division lines as the view angle subdivision scale lines.

6. The calibration tool of claim 4, wherein the resolution line pair pattern is distributed between every two petals of the field angle scale and is symmetrical about a center of the third plane, the resolution line pair pattern comprises a combination of 25lp/mm, 40lp/mm, 60lp/mm, 80lp/mm, and 100lp/mm, and the field angle scale comprises a plurality of the combinations between every two petals.

7. The calibration tool of claim 1, wherein the second curved surface has a locating mark thereon.

8. The calibration tool of claim 1, wherein the resolution test microspheres have a diameter in the range of 10nm to 2 μ ι η and the center-to-center spacing of adjacent microspheres is greater than 2 times the microsphere diameter.

9. The calibration tool of claim 1, wherein the depth of the void chamber ranges from 300 μ ι η to 3 mm.

10. A method of using the calibration tool of any of claims 1-9, comprising:

obtaining a z-direction depth measurement of the void on an xz image;