Placido patterns for corneal topographers

Abstract

In certain embodiments, an ophthalmic system for determining the topography of the anterior surface of the cornea of ​​an eye includes an illuminator, a camera, and a computer. The illuminator illuminates the anterior surface of the cornea of ​​the eye with a Placido pattern. The Placido pattern includes a plurality of rings. Each ring of the plurality of rings has a distinguishing feature that distinguishes it from adjacent rings. The anterior surface of the cornea reflects the Placido pattern. The camera captures an image of the reflected Placido pattern. The computer analyzes the image to detect distortions of the rings that are indicative of an anterior corneal surface abnormality, identifies the rings of the plurality of rings according to the distinguishing features of the rings, and generates a topography of the corneal surface including the abnormality.

Description

Technical Field

[0001] The present disclosure generally relates to a corneal topographer, and more particularly to a platy pattern for a corneal topographer.

Background Art

[0002] Corneal topography depicts the shape of the corneal surface. For example, a platy topographer projects a pattern of equally spaced concentric rings onto the anterior corneal surface and analyzes the reflections of the rings to determine the shape of the surface. If the surface is an ideal sphere, the reflected rings will match the projected pattern of equally spaced rings. If there are deformations on the surface, regions where the reflected rings are closer to each other indicate a greater corneal curvature, and regions where the rings are farther apart indicate a flatter region. In addition, clear and well-shaped rings indicate that the corneal surface is smooth.

[0003] Platy topographers rely on analyzing images of the reflected pattern, which can be difficult. In certain situations, known patterns are not easily analyzed.

Summary of the Invention

Means for Solving the Problems

[0004] In certain embodiments, an ophthalmic system for determining the topography of the anterior surface of the eye's cornea includes an illuminator, a camera, and a computer. The illuminator illuminates the anterior surface of the eye's cornea with a platy pattern. The platy pattern includes a plurality of rings. The rings among the plurality of rings have an identification feature that identifies the ring from adjacent rings. The anterior surface of the cornea reflects the platy pattern. The camera captures an image of the reflected platy pattern. The computer analyzes the image to detect distortion of the rings indicating an abnormality of the anterior surface of the cornea, identifies the rings among the plurality of rings according to the identification feature of the rings, and generates a topography of the corneal surface including the abnormality.

[0005] The embodiments may not include any of the following features, or they may include one, some, or all of them.

[0006] Ring identification features that distinguish a ring from adjacent rings may include a ring color different from the color of the adjacent ring, a ring thickness different from the thickness of the adjacent ring, and / or a distance between a ring and an adjacent ring that is different from the distance between the adjacent ring and the next ring.

[0007] The ring may have marker features indicating a position on the ring. A computer can determine the location of a strain on the ring according to these marker features. The marker features may include gaps within the ring or markings on the ring.

[0008] In certain embodiments, a Placido pattern for determining the topography of the anterior surface of the cornea of ​​the eye includes a plurality of rings. Each of the rings has a distinguishing feature that identifies it from adjacent rings. The rings also have marker features that indicate their position on the ring.

[0009] The embodiments may not include any of the following features, or they may include one, some, or all of them.

[0010] Ring identification features that distinguish a ring from adjacent rings may include a ring color different from the color of the adjacent ring, a ring thickness different from the thickness of the adjacent ring, and / or a distance between a ring and an adjacent ring that is different from the distance between the adjacent ring and the next ring.

[0011] Marker features may include gaps within the ring or markings on the ring.

[0012] In a particular embodiment, a method for determining the topography of the anterior surface of the cornea of ​​an eye includes illuminating the anterior surface of the cornea of ​​an eye with a Placido pattern. The Placido pattern includes a plurality of rings. The rings among the plurality of rings have identification features that distinguish the ring from adjacent rings. The anterior surface of the cornea reflects the Placido pattern. An image of the reflected Placido pattern is captured. A computer analyzes the image to detect distortions in the rings that indicate anomalies on the anterior surface of the cornea, to identify the rings among the plurality of rings according to the ring identification features, and to generate a topography of the corneal surface containing the anomalies.

[0013] The embodiments may not include any of the following features, or they may include one, some, or all of them.

[0014] Ring identification features that distinguish a ring from adjacent rings may include a ring color different from the color of the adjacent ring, a ring thickness different from the thickness of the adjacent ring, and / or a distance between a ring and an adjacent ring that is different from the distance between the adjacent ring and the next ring.

[0015] The ring may have marker features indicating positions on the ring. A computer may perform the task of determining the location of strain on the ring according to these marker features. The marker features may include gaps within the ring or markings on the ring. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 shows an example of an ophthalmic system for determining the topography of the anterior surface of the cornea of ​​the eye, according to a specific embodiment. [Figure 2] Figure 2 shows an example of how the illumination ring of the illuminator in the system of Figure 1 illuminates the eye. [Figure 3A-C] Figures 3A-C show examples of Placido patterns that include rings with distinguishing features that differentiate them from adjacent rings. [Figure 4A-B] Figures 4A-B show an example of a Placido pattern that includes a ring with marker features that identify its position on the ring. [Figure 5] Figure 5 shows an example of a Placido pattern that includes a ring having one or more distinguishing features and / or one or more marker features. [Figure 6] Figure 6 shows an example of a method that can be performed by the system in Figure 1, according to a specific embodiment. [Modes for carrying out the invention]

[0017] Herein, exemplary embodiments of the disclosed apparatus, systems, and methods are described in detail with reference to the description and drawings. The description and drawings are not intended to be exhaustive or to limit the claims to any particular embodiment shown in the drawings or disclosed in the description. The drawings represent possible embodiments, but they are not necessarily to scale, and certain features may be simplified, exaggerated, omitted or partially divided to better illustrate the embodiments.

[0018] Placido topographers rely on analyzing images of reflected Placido patterns. Certain embodiments provide Placido patterns that can be analyzed more easily. In embodiments, the Placido pattern includes a plurality of rings. At least one ring has an identification feature that distinguishes the ring from adjacent rings, and the identification feature can be used to identify the ring. In addition, at least one ring also has a marker feature that indicates a position on the ring, and the marker feature can be used to identify a position on the ring.

[0019] Figure 1 shows an example of an ophthalmic system 10 for determining the topography of the anterior surface of the cornea of ​​an eye 12, according to a specific embodiment. In the example, the system 10 includes an illuminator 20, a camera 22, and a computer 24. In summary, the illuminator 20 illuminates the anterior surface of the cornea with a Placido pattern. The Placido pattern includes a plurality of concentric rings. At least one ring has an identification feature that distinguishes the ring from adjacent rings, and at least one ring has at least one marker feature that indicates a position on the ring.

[0020] To continue the overview, the corneal surface reflects the Placido pattern. Camera 22 generates an image of the reflected Placido pattern. Computer 24 analyzes the image to detect ring distortion, which typically indicates an anomaly on the corneal surface. Computer 24 identifies rings with distortion according to the ring's identifying features. For example, rings may have color, thickness, spacing, and / or other suitable identifying features that distinguish them from adjacent rings. Computer 24 determines the location of the distortion on the ring according to marker features. For example, the location may have gaps, markings, or other suitable marker features that identify the location on the ring. Computer 24 generates a topography of the corneal surface, including the location of the anomaly.

[0021] In part of the system 10, the illuminator 20 illuminates the corneal surface with a Placido pattern, which may be called an "illumination Placido pattern" or "illumination pattern" having an "illumination ring". Examples of Placido patterns are described with reference to Figures 3A to 5. The illuminator 20 may include any suitable arrangement of one or more light sources configured to illuminate the corneal surface with a Placido pattern. In a particular embodiment, the illuminator 20 includes an illuminator ring 26, each illuminator ring 26 illuminating the corneal surface with a ring of Placido pattern. In another embodiment, the illuminator 20 includes a pixel illuminator, each pixel illuminating the corneal surface with a pixel of light. The pixels are coupled to produce a Placido pattern. The computer 24 may turn specific pixel illuminators on and off to produce specific Placido patterns.

[0022] The anterior surface of the cornea 12 typically has a tear film. The interface between the tear film and air reflects the platy pattern, which may be referred to as a "reflected platy pattern" or "reflected pattern" having a "reflected ring". The reflected platy pattern can indicate the shape of the corneal surface. The camera 22 generates an image of the reflected platy pattern. The camera 22 can be any suitable camera that captures and records an image. For example, the camera 22 can be a digital camera that includes an image sensor that detects light reflected from an object, an image processor that converts the sensor output into digital data representing the image, and a memory that records the digital data.

[0023] The computer 24 determines the topography of the corneal surface from the image of the reflected platy pattern. The computer 24 detects the distortion of the reflected ring, and the distortion of the ring typically indicates an abnormality of the surface. If the surface is an ideal sphere, the reflected pattern should match the illumination pattern. If there is a deformation on the surface, the reflected pattern may be distorted from the illumination pattern. The distortion can be any suitable difference between the reflected pattern and the illumination pattern that indicates the difference between the anterior surface of the cornea and the desired surface, such as a spherical surface. For example, the distortion can be a difference in the spacing between the rings. Reflected rings that are closer to each other than the corresponding illumination rings indicate a greater corneal curvature. Reflected rings that are farther apart than the corresponding illumination rings indicate a flatter region. As another example, the distortion can be a difference in the shape of the rings. Reflected rings that are more elliptical or have a shape that deviates from the shape of the corresponding illumination ring can indicate astigmatism. As another example, the distortion can be a difference in the edges of the rings. Reflected rings having clear and focused edges indicate a smooth corneal surface. Reflected rings having a wavy or an edge that deviates from the edge of the corresponding illumination ring can indicate surface irregularities.

[0024] Computer 24 determines the position of the distortion of the reflected pattern to determine the position of the abnormality on the corneal surface. The position of the reflected pattern corresponds to the position of the anterior corneal surface. In certain embodiments, the illumination pattern is centered on the axis of the eye 12 (e.g., the visual axis or the optical axis), and the reflected pattern is also centered on that axis. The image of the reflected pattern may include features of the eye (e.g., the pupil, the eyelid) that help to align the position of the reflected pattern with the position on the corneal surface.

[0025] In certain embodiments, computer 24 determines the position of the distortion by (1) identifying a ring having a distortion, i.e., a distorted ring, and (2) determining the position of the distortion on the ring. In certain embodiments, computer 24 identifies the distorted ring according to the identification features of the ring. For example, the ring may have a color, thickness, spacing, and / or other suitable identification features that distinguish the ring from one or more other rings, such as adjacent rings and / or other rings. The identification features may enable the user and / or the image processing logic to more easily identify the ring having the distortion.

[0026] Computer 24 determines the position of the distortion on the ring according to marker features. For example, the position may have a gap, marking, or other suitable marker feature that identifies a position on the ring. The marker features may enable the user and / or the image processing logic to more easily identify the position of the distortion on the ring. After determining the position of the distortion of the reflected pattern, the position of the abnormality on the surface can be determined. Computer 24 generates a topography of the corneal surface, and the topography of the corneal surface includes the abnormality and the position of the abnormality.

[0027] Figure 2 shows an example of how the illuminator ring 26 of the illuminator 20 illuminates the eye 12. In the example, the illuminator ring 26 illuminates a ring 30 of the Placido pattern onto the anterior surface of the cornea of ​​the eye 12. The surface reflects the ring 30. The camera 22 detects the reflected ring 30. If there are no abnormalities on the surface reflecting the ring 30, the reflected ring 30 detected by the camera 22 will have a shape that generally matches the intended shape, for example, the shape of the illumination ring 30 before reflection. That is, the front surface does not distort the ring 30. If there is an abnormality on the surface reflecting the ring 30, the reflected ring 30 detected by the camera 22 may have a distortion that indicates the presence of the abnormality.

[0028] Figures 3A-3C show examples of Placido patterns 40 (40a-40c) including a ring 30 having an identification feature that distinguishes the ring from adjacent rings. The identification feature has an appropriate color, dimensions, placement, and / or other features that enable the user and / or software to distinguish the ring from one or more other rings, for example, from adjacent rings.

[0029] Figure 3A shows a Placido pattern 40a including rings 30 with different spacings between adjacent rings 30. In this example, the spacing 31a between rings 30a and 30b is greater than the spacing 31b between rings 30b and 30c.

[0030] Figure 3B shows a Placido pattern 40b including rings 30 having different colors. Although not clear in the black and white drawing, rings 30a, 30d, 30g, and 30j are red, rings 30b, 30e, and 30h are blue, and rings 30c, 30f, and 30i are green. In certain embodiments, a sequence of a certain number of adjacent rings 30 may have a sequence of different colors. The sequence of colors may be repeated for the next number of rings. In the example, a sequence of three adjacent rings 30a, 30b, and 30c has a sequence of different colors: red, blue, and green. That is, ring 30a is red, ring 30b is blue, and ring 30c is green. The sequence of colors is repeated for the next three rings 30d, 30e, and 30f.

[0031] Figure 3C shows a Placido pattern 40c including rings 30 having different thicknesses. In a particular embodiment, a sequence of a certain number of adjacent rings 30 may have a sequence of different thicknesses. The sequence of thicknesses may be repeated for the next number of rings. In the example, a sequence of two adjacent rings 30a, 30b has a sequence of different thicknesses. The sequence of thicknesses is repeated for the next two rings 30c, 30d.

[0032] Figures 4A–4B show examples of Placido patterns 40 (40d–40e) including rings 30 having marker features 34 that identify positions on the ring. Rings 30 having marker features 34 may be called marked rings 30.

[0033] Figure 4A shows a Placido pattern 40d including rings 30 having marker features 34 with gaps 34a to 34i. The gaps may have any suitable length detectable by the user and / or software to pinpoint their position on the rings 30, e.g., values ​​within the range of 0.5 to 1, 1 to 1.5, 1.5 to 2, and / or 2 to 5 millimeters. In certain embodiments, a sequence of a certain number of adjacent rings 30 may have marker features 34 placed, for example, equidistant from each other within the sequence. The sequence of marker features 34 may be repeated for the next number of rings. For ease of explanation, angle A is assumed to have the vertex of the center of the rings 30 and the direction shown in the drawing. In the example, a sequence of four adjacent rings 30a to 30d has gaps 34a to 34d equidistant from each other. Specifically, gap 34a is at approximately 180°, gap 34b is at approximately 90°, gap 34c is at approximately 0°, and gap 34d is at approximately 270°. The sequence for gaps 34e to 34h is repeated for rings 30e to 30h.

[0034] Figure 4B shows a Placido pattern 40e including a ring 30 having a marker feature 34 including a marking. The marking may have any suitable shape and size that can be detected by the user and / or software to pinpoint its position on the ring 30. For example, the marking may have an average diameter in the range of 0.5–1, 1–1.5, 1.5–2, and / or 2–5 millimeters. Examples of shapes include circles, polygons (e.g., squares, rectangles), and stars.

[0035] In the example, the markings are dots 34a to 34i, and the sequence of three adjacent rings 30a to 30c has dots 34a to 34c equidistant from each other. That is, dot 34a is at approximately 0°, dot 34b is at approximately 120°, and dot 34c is at approximately 240°. The sequence of dots 34d to 34f is repeated for rings 30d to 30f.

[0036] Figure 5 shows an example of a Placido pattern 40 (40f) including rings 30 (30a-30i) having one or more distinguishing features and / or one or more marker features 34. Although not clear in the black and white drawing, rings 30a, 30d and 30g are red, rings 30b, 30e and 30h are blue, and rings 30c, 30f and 30i are green. In the example, the rings 30 have different colors and spacing 31 that distinguish them from at least adjacent rings 30. In addition, the rings 30 have gaps 34 that indicate their position on the ring. In certain embodiments, the rings 30 may have distinguishing features or marker features, neither or both.

[0037] Figure 6 shows an example of a method that can be performed by the system 10 of Figure 1 according to a particular embodiment. In the embodiment, the computer 24 may perform a particular step by sending instructions to the components of the system 10.

[0038] The method begins in step 110, when the illuminator 20 illuminates the corneal surface with a Placido pattern. The Placido pattern includes multiple rings. At least one ring has an identification feature that distinguishes it from adjacent rings, and at least one ring has a marker feature that indicates its position on the ring. The corneal surface reflects the Placido pattern.

[0039] In step 112, camera 22 detects the reflected Placido pattern and generates an image of the reflected Placido pattern. In step 114, computer 24 analyzes the image to detect ring distortion. Distortion typically indicates an anomaly on the corneal surface. In step 116, computer 24 identifies the ring according to its identification features. For example, the ring may have color, thickness, spacing, and / or other suitable identification features that distinguish it from adjacent rings. In step 120, computer 24 determines the location of the distortion according to its marker features. For example, its location may have gaps, markings, or other suitable marker features that identify its location on the ring. In step 122, computer 24 generates a topography of the corneal surface. The topography depicts the anomaly and its location. Computer 24 may output the topography to a user interface, such as a display. The method then ends.

[0040] The components of the systems and apparatus disclosed herein (such as computer 24) may include interfaces, logic, and / or memory, any of which may include computer hardware and / or software. Interfaces can receive inputs to a component and / or transmit outputs from a component and are typically used to exchange information between, for example, software, hardware, peripherals, users, and combinations thereof. User interfaces (e.g., graphical user interfaces (GUIs)) are a type of interface that can be used for a user to interact with a computer. Examples of user interfaces include displays, touchscreens, keyboards, mice, gesture sensors, microphones, and speakers.

[0041] Logic can perform the actions of components. Logic may include one or more electronic devices that process data, for example, by executing instructions to produce an output from an input. Examples of such electronic devices include computers, processors, microprocessors (e.g., central processing units (CPUs)), and computer chips. Logic may also include computer software that encodes instructions that can be executed by electronic devices to perform actions. Examples of computer software include computer programs, applications, and operating systems.

[0042] Memory may include tangible, computer-readable and / or computer-executable storage media capable of storing information. Examples of memory include computer memory (e.g., random-access memory (RAM) or read-only memory (ROM)), mass storage media (e.g., hard disks), removable storage media (e.g., compact discs (CDs) or digital video or multi-purpose discs (DVDs)), databases, network storage (e.g., servers), and / or other computer-readable media. Certain embodiments may involve memory encoded using computer software.

[0043] While this disclosure has described specific embodiments, modifications to the embodiments (e.g., altered, replaced, added, omitted, and / or other modifications) will be apparent to those skilled in the art. Thus, modifications to the embodiments can be made without departing from the scope of the invention. For example, modifications can be made to the systems and apparatus disclosed herein. As will be apparent to those skilled in the art, the components of the systems and apparatus may be integrated or separated, or the operation of the systems and apparatus may be performed by more, fewer, or other components. As another example, modifications can be made to the methods disclosed herein. As will be apparent to those skilled in the art, the methods may include more, fewer, or other steps, and the steps may be performed in any suitable order.

[0044] To assist the Patent Office and readers in interpreting the claims in the claims, the applicant notes that, unless the terms “means for” or “steps for” are expressly used in a particular claim, no claim or element of a claim is intended to be subject to Section 112(f) of the U.S. Patent Act. The use of other terms in a claim (e.g., “mechanism,” “module,” “device,” “unit,” “component,” “element,” “member,” “apparatus,” “machine,” “system,” “processor,” or “controller”) is understood by the applicant to refer to a structure known to a person skilled in the art in the relevant field and is not intended to be subject to Section 112(f) of the U.S. Patent Act. This application encompasses the following aspects: [Aspect 1] An ophthalmic system for determining the topography of the anterior surface of the cornea of ​​the eye, An illuminator configured to illuminate the front surface of the cornea of ​​the eye with a Placido pattern, wherein the Placido pattern comprises a plurality of rings, each ring having an identification feature that distinguishes it from adjacent rings, and the front surface of the cornea reflects the Placido pattern; A camera configured to capture an image of the reflected Placido pattern, It is a computer, The process involves analyzing the aforementioned image to detect distortion of the ring, wherein the distortion indicates an abnormality in the anterior surface of the cornea. Identifying the ring among the plurality of rings according to the identification features of the ring, To generate the topography of the surface of the cornea including the aforementioned abnormality. A computer configured to perform the following actions An ophthalmic system including [Aspect 2] The ophthalmic system according to embodiment 1, wherein the identification feature of the ring that distinguishes the ring from the adjacent rings includes a color of the ring that is different from the color of the adjacent rings. [Aspect 3] The ophthalmic system according to embodiment 1, wherein the identification feature of the ring that distinguishes the ring from an adjacent ring includes a thickness of the ring that is different from the thickness of the adjacent ring. [Aspect 4] The ophthalmic system according to Embodiment 1, wherein the identification feature of the ring that distinguishes the ring from an adjacent ring includes a distance between the ring and the adjacent ring that is different from the distance between the adjacent ring and the next ring. [Aspect 5] The ring has marker features indicating a position on the ring, and The ophthalmic system according to embodiment 1, wherein the computer is configured to determine the position of the distortion on the ring according to the marker features. [Aspect 6] The ophthalmic system according to embodiment 5, wherein the marker feature of the ring includes a gap within the ring. [Aspect 7] The ophthalmic system according to embodiment 5, wherein the marker feature of the ring includes a marking on the ring. [Aspect 8] Placido patterns for determining the topography of the anterior surface of the cornea of ​​the eye, A plurality of rings, wherein each of the plurality of rings has an identification feature that distinguishes it from an adjacent ring, and each of the rings has a marker feature that indicates its position on the ring. Placido pattern including [Aspect 9] The Placido pattern according to embodiment 8, wherein the identification feature of the ring that distinguishes the ring from the adjacent rings includes a color of the ring that is different from the color of the adjacent rings. [Aspect 10] Placido pattern according to embodiment 8, wherein the identification feature of the ring that distinguishes the ring from an adjacent ring includes a thickness of the ring that is different from the thickness of the adjacent ring. [Aspect 11] Placido pattern according to embodiment 8, wherein the identification feature of the ring that distinguishes the ring from an adjacent ring includes a distance between the ring and the adjacent ring that is different from the distance between the adjacent ring and the next ring. [Aspect 12] The marker feature of the ring is a platy pattern according to embodiment 8, including a gap within the ring. [Aspect 13] The marker feature of the ring is a Placido pattern according to embodiment 8, wherein the marker feature of the ring includes a marking on the ring. [Aspect 14] A method for determining the topography of the anterior surface of the cornea of ​​the eye, Illuminating the front surface of the cornea of ​​the eye with a Placido pattern, wherein the Placido pattern comprises a plurality of rings, each ring having an identifying feature that distinguishes it from adjacent rings, and the front surface of the cornea reflects the Placido pattern. The image of the reflected Placido pattern is captured, By computer, The method involves analyzing the aforementioned image to detect distortion of the ring, wherein the distortion indicates an abnormality in the anterior surface of the cornea. Identifying the ring from among the plurality of rings according to the identification features of the ring, and To generate the topography of the surface of the cornea including the abnormality. To execute and A method that includes this. [Aspect 15] The method according to embodiment 14, wherein the identification feature of the ring that distinguishes the ring from the adjacent ring includes a color of the ring that is different from the color of the adjacent ring. [Aspect 16] The method according to embodiment 14, wherein the identification feature of the ring that distinguishes the ring from an adjacent ring includes a thickness of the ring that is different from the thickness of the adjacent ring. [Aspect 17] The method according to embodiment 14, wherein the identification feature of the ring that distinguishes the ring from an adjacent ring includes a distance between the ring and the adjacent ring that is different from the distance between the adjacent ring and the next ring. [Aspect 18] The ring has marker features indicating a position on the ring, and The above method is performed by the computer, The position of the distortion on the ring is determined according to the marker characteristics. The method according to embodiment 14, further comprising performing the following: [Aspect 19] The method according to embodiment 18, wherein the marker feature of the ring includes a gap within the ring. [Aspect 20] The method according to embodiment 18, wherein the marker feature of the ring includes a marking on the ring.

Claims

1. An ophthalmic system for determining the topography of the anterior surface of the cornea of ​​the eye, An illuminator configured to illuminate the front surface of the cornea of ​​the eye with a Placido pattern, wherein the Placido pattern comprises a plurality of rings, each ring having an identification feature that distinguishes it from adjacent rings, and the front surface of the cornea reflects the Placido pattern; A camera configured to capture an image of the reflected Placido pattern, It is a computer, The process involves analyzing the aforementioned image to detect distortion of the ring, wherein the distortion indicates an abnormality in the anterior surface of the cornea. Identifying the ring among the plurality of rings according to the identification features of the ring, To generate the topography of the anterior surface of the cornea, including the aforementioned abnormality. A computer configured to do so Includes, The identification feature of the ring that distinguishes the ring from an adjacent ring includes a distance between the ring and the adjacent ring that is different from the distance between the adjacent ring and the next ring. Ophthalmic system.

2. The ophthalmic system according to claim 1, wherein the identification feature of the ring that distinguishes the ring from the adjacent rings includes a color of the ring that is different from the color of the adjacent rings.

3. The ophthalmic system according to claim 1, wherein the identification feature of the ring that distinguishes the ring from the adjacent ring includes a thickness of the ring that is different from the thickness of the adjacent ring.

4. The ring has marker features indicating a position on the ring, and The ophthalmic system according to claim 1, wherein the computer is configured to determine the position of the distortion on the ring according to the marker features.

5. The ophthalmic system according to claim 4, wherein the marker feature of the ring includes a gap within the ring.

6. The ophthalmic system according to claim 4, wherein the marker feature of the ring includes a marking on the ring.

7. Placido patterns for determining the topography of the anterior surface of the cornea of ​​the eye, A plurality of rings, wherein each of the plurality of rings has an identification feature that distinguishes it from adjacent rings, and each of the rings has a marker feature that indicates its position on the ring. Includes, The identification feature of the ring that distinguishes the ring from an adjacent ring includes a distance between the ring and the adjacent ring that is different from the distance between the adjacent ring and the next ring. Placido pattern.

8. The Placido pattern according to claim 7, wherein the identification feature of the ring that distinguishes the ring from the adjacent rings includes a color of the ring that is different from the color of the adjacent rings.

9. The Placido pattern according to claim 7, wherein the identification feature of the ring that distinguishes the ring from the adjacent ring includes a thickness of the ring that is different from the thickness of the adjacent ring.

10. The Placido pattern according to claim 7, wherein the marker feature of the ring includes a gap within the ring.

11. The Placido pattern according to claim 7, wherein the marker feature of the ring includes a marking on the ring.

12. A method for determining the topography of the anterior surface of the cornea of ​​the eye, Illuminating the front surface of the cornea of ​​the eye with a Placido pattern, wherein the Placido pattern comprises a plurality of rings, each ring having an identifying feature that distinguishes it from adjacent rings, and the front surface of the cornea reflects the Placido pattern. To capture an image of the reflected Placido pattern, By computer, The method involves analyzing the aforementioned image to detect distortion of the ring, wherein the distortion indicates an abnormality in the anterior surface of the cornea. Identifying the ring from among the plurality of rings according to the identification features of the ring, and To generate the topography of the anterior surface of the cornea, including the abnormality. To execute and Includes, The identification feature of the ring that distinguishes the ring from an adjacent ring includes a distance between the ring and the adjacent ring that is different from the distance between the adjacent ring and the next ring. method.

13. The method according to claim 12, wherein the identification feature of the ring that distinguishes the ring from the adjacent rings includes a color of the ring that is different from the color of the adjacent rings.

14. The method according to claim 12, wherein the identification feature of the ring that distinguishes the ring from the adjacent ring includes a thickness of the ring that is different from the thickness of the adjacent ring.

15. The ring has marker features indicating a position on the ring, and The above method is performed by the computer, The position of the distortion on the ring is determined according to the marker characteristics. The method according to claim 12, further comprising performing the following:

16. The method according to claim 15, wherein the marker feature of the ring includes a gap within the ring.

17. The method according to claim 15, wherein the marker feature of the ring includes a marking on the ring.

Images