JP7447619B2 - ophthalmology equipment - Google Patents

Description

The present disclosure relates to an ophthalmologic apparatus for obtaining the axial length of an eye to be examined.

Ultrasonic and optical interference type axial length measurement devices are used for prescription of intraocular lenses.

The ultrasonic axial length measuring device is a contact type, and measurement is performed by bringing a probe into contact with the cornea.

In optical interference type axial length measurement devices, two methods are mainstream: a TD method (time domain method) and an SS method (swept source method). In the TD method, a coherent light source is used, and in the SS method, a wavelength swept light source is used (see Patent Documents 1 and 2).

JP2012-224621A JP2019-063044A

In recent years, the increase in the prevalence of myopia, especially among young people, has become noticeable in all countries. Myopia progresses as the axial length of the eye increases, increasing the risk of blindness and has become a major social problem. Against this background, evaluation of myopia progression based on axial length is attracting attention. In order to appropriately perform tests on young people, it is desired that axial length measurement devices become widespread not only in cataract treatment facilities but also in more facilities (hospital facilities, school facilities, etc.).

However, since the ultrasonic axial length measuring device is a contact type, the number of examiners is limited and the burden on the examinee is heavy. Furthermore, the optical interference type axial length measuring device has an expensive device configuration such as a light source. Therefore, the cost of the device can be a hindrance to its widespread use in facilities.

In response, the inventors of the present invention have studied a new method for measuring the axial length of the eye and an apparatus configuration for realizing the new method.

The present disclosure has been made in view of the above circumstances, and a technical problem is to provide an ophthalmologic apparatus in which either a method for measuring the axial length of the eye or an apparatus configuration is novel.

An ophthalmological apparatus according to a first aspect of the present disclosure includes a first optical system that projects measurement light onto the fundus of an eye to be examined and obtains the ocular refractive power of the eye to be examined based on the fundus reflected light of the measurement light. , a second optical system for acquiring anterior eye segment information that is information about the shape of the anterior eye segment and that includes at least shape information of the crystalline lens; and a fixation target presentation that presents the fixation target. an optical system, controlling the first optical system, the second optical system , and the fixation target presentation optical system , and adding accommodation to the eye to be examined by the fixation target to obtain the eye refractive power. By controlling the respective acquisition timings of the eye refractive power and the anterior eye segment information so that the acquisition timings of the eye refractive power and the anterior eye segment information are the same between the time and the acquisition time of the anterior eye segment information, the eye refractive power and the anterior eye segment information are acquired at the same time. a control means that acquires the eye information with the accommodation in the crystalline lens being the same as each other, and the eye refractive power and the anterior eye information obtained with the accommodation in the crystalline lens being the same as each other. , the distance between the axial length of the eye to be examined and the corneal vertex of the eye to be examined, when a light beam entering the eye to be examined from a far point is refracted by the transparent body of the eye to be examined and intersects with the optical axis of the first optical system; and an axial length acquisition means for acquiring the axial length.
An ophthalmological apparatus according to a second aspect of the present disclosure includes a first optical system that projects measurement light onto the fundus of an eye to be examined and obtains the ocular refractive power of the eye to be examined based on the fundus reflected light of the measurement light. , a second optical system for acquiring anterior eye segment information that is information about the shape of the anterior eye segment and includes at least shape information of the crystalline lens; the first optical system and the second optical system; By controlling the system and synchronizing the acquisition timings of the eye refractive power and the anterior eye segment information, each of the eye refractive power and the anterior eye segment information can be adjusted to the same extent in the crystalline lens. The axial length of the eye to be examined is determined based on the control means acquired under the condition, and the eye refractive power and the anterior eye segment information acquired under the same state of accommodation in the crystalline lens. The apparatus further includes an axial length obtaining means for obtaining an axial length as a distance between a point of intersection when a light beam is refracted by a transparent body of the eye to be examined and intersects with the optical axis of the first optical system and a corneal vertex of the eye to be examined.

FIG. 1 is an external view showing a schematic configuration of an ophthalmologic apparatus according to an example. FIG. 2 is a schematic configuration diagram of an optical system of an ophthalmologic apparatus. FIG. 3 is a diagram showing an anterior segment cross-sectional image photographed by a cross-sectional photographing optical system. FIG. 3 is a side view of the measurement unit, and is a diagram for explaining the positional relationship between the index projector and the optical axis of the cross-sectional photographing optical system. FIG. 3 is a perspective view of the measurement unit, and is a diagram for explaining the positional relationship between the index projector and the optical axis of the cross-sectional photographing optical system. It is a flowchart for explaining the operation of the device. FIG. 3 is a schematic diagram for explaining a method for deriving an axial length by ray tracing. FIG. 7 is a diagram showing the refractive power in each meridian direction when SPH=-5D, CYL=-2D, and AXIS=30°.

"overview"
Embodiments of the present disclosure will be described. The items classified in <> below can be used independently or in conjunction. For example, in some embodiments, multiple items can be combined as appropriate. Furthermore, for example, items described regarding one embodiment can be applied to other embodiments.

"First embodiment"
First, an ophthalmologic apparatus and an axial length calculation program according to a first embodiment will be described. In the first embodiment, the ophthalmologic apparatus and the axial length calculation program include: the eye refractive power of the eye to be examined acquired through the first optical system; the anterior segment information acquired through the second optical system; The axial length of the eye to be examined is obtained based on the following.

<Device configuration>
The ophthalmologic apparatus according to the first embodiment includes at least a first optical system, a second optical system, and an arithmetic control section. The calculation control unit is an axial length acquisition unit and a control unit in the embodiment. The ophthalmologic apparatus may additionally include a fixation target presentation optical system.

An axial length calculation program is executed by the calculation control unit. For convenience, unless otherwise specified, in the following description of the embodiment, it is assumed that the axial length calculation program is executed in an ophthalmological apparatus (an example of an ophthalmological computer).

<First optical system>
The first optical system is used to obtain the eye refractive power of the eye to be examined. The first optical system projects measurement light onto the fundus of the eye to be examined. Ocular refractive power is acquired based on the fundus reflected light of the measurement light. The first optical system may be, for example, a measurement optical system of an objective eye refractive power measuring device such as an auto reflex camera or a wavefront sensor.

In this embodiment, the measurement light from the first optical system is assumed to be infrared light. However, the light is not necessarily limited to this, and visible light may also be used.

<Second optical system>
The second optical system is used to obtain anterior segment information, which is information regarding the shape of the anterior segment.

In the first embodiment, anterior segment information regarding the cut plane may be acquired via the second optical system. At this time, the optical axis of the first optical system is arranged on the cut surface.

The second optical system may be a cross-sectional imaging optical system such as a Scheimpflug optical system, or may be another optical system. When the Scheimpflug optical system is used as the second optical system, the optical axis of the illumination light in the second optical system and the optical axis of the measurement light in the first optical system are arranged coaxially. is required.

<Example of anterior segment information>
The anterior segment information may include shape information of a transparent body in the anterior segment. The anterior segment information may be an image of the anterior segment. From the anterior segment information, the shape of the transparent body in the anterior segment can be specified. For example, two or more of the corneal thickness, the anterior corneal radius of curvature, the posterior corneal radius of curvature, the anterior chamber depth, the crystalline lens thickness, the anterior lens radius of curvature, and the posterior lens radius of curvature can be specified based on the anterior segment information. It is desirable that there be. Of course, these values that specify the shape of the transparent body may themselves be the anterior segment information.

The anterior segment information acquired via the second optical system may include at least shape information of the crystalline lens. Further, the shape of the measurement area by the first optical system may be specified by anterior segment information acquired via the second optical system. The measurement area is an area where the eye refractive power is measured by the first optical system.

<Fixation target presentation optical system>
The ophthalmologic apparatus may include a fixation target presentation optical system. The fixation target presentation optical system is an optical system that presents a fixation target to the subject's eye, and may be used during the respective operations of the first optical system and the second optical system.

The fixation target presentation optical system in this embodiment may be capable of changing the presentation distance of the fixation target. Such a fixation target presentation optical system may be used to fog the subject's eye when measuring refractive power using the first optical system. The first optical system may also be utilized to add accommodation within the eye.

<Derivation method of axial length (axial length calculation program)>
In the first embodiment, the calculation control unit acquires the axial length of the eye to be examined based on the eye refractive power and anterior segment information.

The eye refractive power and anterior segment information may be acquired based on measurement or photography. Moreover, what is measured or photographed by a separate device may be acquired by being stored in a memory.

At this time, the axial length may be acquired based on the on-plane ocular refractive power, which is the eye refractive power on the cut plane, and the anterior segment information regarding the cut plane. When the eye refractive power and the information for specifying the shape of the anterior segment are information regarding the same cutting plane, the ocular axial length can be easily derived appropriately. Note that at this time, the axial length can be determined more appropriately by using information that specifies the shape of the measurement area by the first optical system as the anterior segment information regarding the cut plane.

Here, for example, the calculation control unit may derive the axial length by ray tracing calculation. In the ray tracing calculation, the far point location may be determined based on the on-plane ocular power.

In ray tracing calculations, when a ray that enters a predetermined position in the anterior segment from a far point is refracted by a transparent body and then intersects on the optical axis, the distance between the intersection point and the corneal apex is derived as the axial length. Ru. At this time, the eye refractive power at the cut plane (on-plane refractive power) may be used instead of the equivalent spherical power that is generally used when specifying the far point in the ophthalmology field. Thereby, the position of the far point of the light beam passing on the cut plane can be more appropriately specified. As a result, the axial length can be determined more appropriately. At this time, a ray tracing calculation may be performed for each of the plurality of light rays, and the axial length may be determined as a result of the ray tracing calculation for each ray. For example, the average value (a weighted average may be used) of the axial lengths obtained by each ray tracing calculation may be determined as the axial length of the eye to be examined.

In addition, in the ray tracing calculation, the incident position of the ray with respect to the boundary surface of each transparent body and the angle change at the boundary surface are determined by considering the shape of the transparent body at the cut plane specified from the anterior segment information. be done. A more detailed explanation of the ray tracing method will be given in Examples below.

Furthermore, the arithmetic control unit may take into account the eccentricity of the transparent body of the anterior segment when deriving the axial length from the eye refractive power and anterior segment information regarding the same cutting plane. Eccentricity is identified based on anterior segment information. As a result of taking into account the eccentricity of the light-transmitting body within the cutting plane, the axial length can be determined more appropriately. In this case, for example, a ray tracing calculation is performed on each of a plurality of rays including at least a first ray and a second ray to determine the axial length of each ray, and the final axial length is determined based on the plurality of axial lengths. You may also obtain a measured value. The first light ray and the second light ray are light rays arranged on the cutting plane with the eye axis in between.

<Specific example of second optical system: cross-sectional imaging optical system>
In the first embodiment, the second optical system may be a cross-sectional photographing optical system that photographs a cross-sectional image of a cut plane set in the anterior segment of the subject's eye. The cross-sectional imaging optical system may be, for example, a Scheimpflug optical system or an OCT optical system. From the cross-sectional image, it is possible to specify not only the shape of the boundary surfaces (surfaces) of each transparent body but also the distance between the boundary surfaces. As a result, the axial length can be determined with higher accuracy. When the second optical system is a cross-sectional photographing optical system, it is preferable that the photographing range of the cross-sectional photographing optical system includes from the anterior surface of the cornea of the subject's eye to at least the anterior surface of the crystalline lens. Needless to say, it is more preferable if the imaging range includes from the anterior surface of the cornea to the posterior surface of the crystalline lens. Since the corneal thickness, the anterior corneal radius of curvature, the posterior corneal radius of curvature, the anterior chamber depth, the crystalline lens thickness, the anterior lens radius of curvature, and the posterior lens radius of curvature can be obtained without omission, the axial length can be obtained more appropriately.

Note that when the second optical system is a Scheimpflug optical system, the projection optical axis of the illumination light needs to be arranged coaxially with the projection optical axis of the measurement light in the first optical system. Further, the light projecting optical system of the Scheimpflug optical system may emit slit light as illumination light. The irradiation area of the slit light is set as a cutting plane. Further, the light receiving optical system of the Scheimpflug optical system includes a lens system and an image sensor arranged in a Scheimpflug relationship with the cutting surface. The light-receiving optical system is provided with a light-receiving optical axis that is inclined with respect to the cutting surface.

Visible light or infrared light may be irradiated as the slit light. Visible light is more likely to be scattered by a transparent material than infrared light. On the other hand, when infrared light is irradiated, the burden on the subject during imaging can be suppressed.

Further, when the second optical system is an OCT optical system, it may be possible to image not only the anterior segment OCT but also the fundus OCT. In this case, it is not necessary that anterior segment OCT and fundus OCT can be imaged at the same time; by switching a part of the OCT optical system, anterior segment OCT and fundus OCT can be imaged separately. It's okay to be.

<Specific example of second optical system: Purkinje image acquisition optical system>
Instead of the cross-sectional imaging optical system, a Purkinje image acquisition optical system may be applied as the second optical system. The Purkinje image acquisition optical system consists of an index projector that projects a measurement index based on a certain pattern (called a pattern index) onto the anterior segment of the eye from the front facing the subject's eye, and a frontal photographing optical system that photographs the Purkinje image using the pattern index. and, including. At this time, the first Purkinje image (image reflected by the anterior surface of the cornea), the second Purkinje image (image reflected by the posterior surface of the cornea), the third Purkinje image (image reflected by the anterior surface of the crystalline lens), and the fourth Purkinje image (image reflected by the posterior surface of the crystalline lens) image) can occur, respectively. It is conceivable to find the shape of the boundary surface corresponding to each Purkinje image based on the position information of each Purkinje image. However, corneal thickness, anterior chamber depth, crystalline lens thickness, etc. cannot be obtained from only the position information of the Purkinje image. In other words, the distance between the boundary surfaces of the transparent body cannot be obtained. On the other hand, a cross-sectional imaging optical system is more advantageous in obtaining the distance between boundary surfaces. In addition, the third Purkinje image (an image reflected by the front surface of the crystalline lens) occurs near the optical axis of the frontal photographing optical system compared to the first, second, and fourth Purkinje images, so the difference in the shape of the front surface of the crystalline lens is caused by the difference in the shape of the front surface of the lens. 3 It is difficult to see this because of the difference in the appearance position of Purkinje's image. Therefore, a cross-sectional imaging optical system whose imaging range includes from the anterior surface of the cornea of the subject's eye to at least the anterior surface of the crystalline lens is more effective in obtaining shape information of the anterior surface of the lens than a Purkinje image acquisition optical system. It's advantageous.

Note that the pattern index projected from the index projector may be a ring-shaped pattern, a line, or another two-dimensional pattern formed by a plurality of points. For example, a plurality of point indicators arranged on the circumference may be projected as pattern indicators. Further, a plurality of patterns may be combined.

<Measurement control>
In order to appropriately determine the axial length using the above method, it is desirable that the anterior segment information includes shape information of more types of light-transmitting bodies. At this time, it is conceivable that at least the shape information of the crystalline lens is included in the anterior segment information. In this case, the eye refractive power measured by the first optical system and the crystalline lens shape information included in the anterior segment information are each unavoidably influenced by intraocular accommodation. Therefore, in order to ensure the accuracy and reproducibility of the ocular axial length, it is required to take into account the state of accommodation within the eye and acquire the ocular refractive power and anterior segment information, respectively.

On the other hand, in the present embodiment, the arithmetic control unit controls the first optical system and the second optical system so that the eye refractive power and the anterior segment information are acquired with the same intraocular accommodation. The optical system may also be controlled.

If each of the eye refractive power and anterior segment information is acquired with the same intraocular accommodation, each of the acquired information will be equally affected by the accommodation, so the axial length can be adjusted. You can ask for it appropriately.

At this time, the arithmetic control unit adjusts the eye refractive power and anterior segment so that the accommodation addition given to the subject's eye by the fixation target is the same between the time of acquiring the eye refractive power and the time of acquiring the anterior eye segment information. The acquisition timing of each eye information may be controlled. The acquisition timing may be controlled in conjunction with the control to change the presentation distance of the fixation target.

For example, the acquisition timings may be controlled such that the presentation position of the fixation target is the same between when acquiring the eye refractive power and when acquiring the anterior segment information.

Further, for example, the calculation control unit may synchronize the acquisition timings of the eye refractive power and the anterior segment information. Synchronization here does not necessarily require that the respective acquisition timings be completely simultaneous. For example, there may be a time difference between the respective acquisition timings that does not cause a significant difference in the adjustment state.

The arithmetic control unit adds fog to the subject's eye by controlling the fixation target presentation optical system, and displays each of the eye refractive power and anterior segment information when the subject's eye is in an unaccommodated state. You may obtain it. It is better to calculate the axial length based on the eye refractive power and anterior eye segment information obtained in the non-accommodative state than to calculate the axial length from the eye refractive power and anterior eye segment information measured in the accommodative state. In comparison, the accuracy and reproducibility of the axial length are further improved.

By the way, as described above, the second optical system used to obtain anterior ocular segment information may be a Scheimpflug optical system, in which case visible light is irradiated to the anterior ocular segment as illumination light, A case is assumed in which a cross-sectional image of the anterior segment of the eye is photographed. On the other hand, infrared light is used as measurement light to measure eye refractive power.

When a cross-sectional image is photographed using the Scheimpflug optical system, relatively strong visible light is irradiated as photographing light. At this time, the strong visible light irradiation may surprise the subject, and as a result, the alignment state may change.

On the other hand, the arithmetic control unit may first perform the operation of acquiring the eye refractive power, and at the timing when the acquisition operation is completed, execute the operation of acquiring the anterior segment information. This suppresses misalignment between the time of acquiring the eye refractive power and the time of acquiring the cross-sectional image which is the anterior segment information. Further, at this time, the order of execution of each operation may be: fog ⇒ acquisition of eye refractive power ⇒ acquisition of anterior segment information. In addition, the completion timing of the eye refractive power acquisition operation and the execution timing of the anterior eye segment information acquisition operation are approximately the same time, as described above, so that the eye refractive power can be adjusted for each of the accommodation state and alignment state. Discrepancies are unlikely to occur between the time of acquisition and the time of acquisition of a cross-sectional image that is anterior segment information. As a result, the accuracy and reproducibility of the axial length is improved.

As described above, in the ophthalmologic apparatus of the first embodiment, the axial length is measured using a novel method and a new device configuration that are different from conventional axial length measurement apparatuses.

Here, the first optical system can acquire the eye refractive power of the eye to be examined, which is important in evaluating myopia. The ophthalmologic apparatus of the first embodiment can acquire important information in the evaluation of myopia, such as eye refractive power and axial length, with a single device.

In particular, in the first embodiment, when the Scheimpflug optical system is used as the second optical system, the device cost can be sufficiently suppressed compared to the optical interference type axial length measuring device, and the progression of myopia can be prevented. It is easy to satisfy the measurement accuracy of the axial length required for monitoring.

<Obtaining axial length from multiple cut planes>
In the above description, the axial length is determined using anterior segment information regarding one cut plane. However, the present invention is not necessarily limited to this, and a plurality of pieces of anterior segment information may be acquired for each of a plurality of cut planes. In this case, the axial length may be derived for each cut plane using the above method. For example, the average value of the axial lengths obtained for each cut plane may be determined.

In addition, in the Scheimpflug optical system, as a method of photographing a plurality of cut planes, a method of rotating the light receiving optical system around the light emitting optical axis and photographing the light receiving optical system is known, and this may be used.

“Second embodiment”
Next, a second embodiment will be described.

The ophthalmologic apparatus according to the second embodiment further includes a third optical system in addition to the apparatus configuration of the first embodiment. That is, the ophthalmologic apparatus according to the second embodiment includes a first optical system, a second optical system, a third optical system, and an arithmetic control section.

Regarding configurations common to the first embodiment, the description of the first embodiment will be used as appropriate, and details will be omitted. However, in the second embodiment, the second optical system is an anterior segment cross-sectional photographing optical system, and will be described as a Scheimpflug optical system unless otherwise specified.

In the second embodiment, the third optical system includes an index projector that projects a pattern index for measuring the corneal shape from the front facing the eye to be examined onto the anterior segment of the eye. Additionally, the third optical system may include a front imaging optical system that captures a corneal Purkinje image using the pattern index. The corneal Purkinje image may be captured as a frontal image of the anterior segment of the eye.

In the second embodiment, the arithmetic control unit may acquire the axial length based on the eye refractive power and anterior segment information regarding the cut plane, and the corneal shape information based on the corneal Purkinje image.

Here, corneal shape information, including at least the radius of curvature of the anterior surface of the cornea, can be derived with higher accuracy from the corneal Purkinje image than from the anterior segment cross-sectional image taken by the Scheimpflug optical system. For this reason, for example, in the axial length calculation, part of the information regarding the cornea in the anterior segment information may be replaced by corneal shape information derived from the corneal Purkinje image. Further, part or all of the anterior segment information may be corrected based on the corneal shape information. As a specific example of correction, the entire anterior segment cross-sectional image is transformed so that the corneal shape of the anterior segment cross-sectional image matches the corneal shape based on the corneal Purkinje image, and then each transparency based on the transformed image is The shape of the light object may be used to calculate the axial length of the eye.

In this way, in the axial length calculation, the corneal shape information derived from the corneal Purkinje image is taken into consideration, so that the axial length can be determined more appropriately.

In the second optical system, which is a Scheimpflug optical system, the smaller the inclination of the optical axis with respect to the cutting plane (object surface), the easier it is to expand the imaging range in the depth direction. In other words, the smaller the inclination of the light-receiving optical axis (photographing optical axis) of the second optical system with respect to the cutting plane (object surface), the more advantageous it is for the second optical system to photograph the area from the anterior surface of the cornea to the posterior surface of the crystalline lens. . However, if the light-receiving optical axis is tilted to the extent that images can be taken from the anterior surface of the cornea to the posterior surface of the crystalline lens, the light-receiving optical system of the second optical system and the index projector of the third optical system will spatially interfere with each other. There is a risk that this may occur.

This will be explained in more detail. Normally, in keratometry, which is one of the methods for measuring the shape of the cornea, one or more circumferential regions of the cornea within the range of 2 mm to 4 mm are often used as the measurement region. At this time, the light flux forming the pattern index is projected at an angle in the range of 14° (corresponding to φ2 mm) to 29° (corresponding to φ4 mm) with respect to the eye axis.

On the other hand, when attempting to photograph the area from the anterior surface of the cornea to the posterior surface of the crystalline lens using the Scheimpflug optical system, which is the second optical system, it is desirable to make the angle between the light receiving optical axis of the second optical system and the cutting surface smaller. Conventional Scheimpflug cameras for ophthalmology are mainly used in anterior segment analysis devices, and because low distortion and high resolution are prioritized, the above angle is around 45° or larger. Ta. On the other hand, the angle in the Scheimpflug optical system of this embodiment is desirably about 40 degrees or less, giving priority to being able to photograph deeper. Therefore, each light beam output position in the index projector and the light receiving optical axis of the second optical system can be arranged on substantially the same circumference with respect to the visual axis. If the sizes of the optical elements in each part are taken into account in addition, the above-mentioned interference problem may occur.

On the other hand, in the second embodiment, the target projector of the third optical system is arranged so as to avoid the light receiving optical axis of the second optical system. More specifically, the third optical system is designed to avoid the normal direction of the cut plane of the anterior segment formed by the second optical system (at least the direction in which the light-receiving optical system of the second optical system is placed). An indicator projector may also be arranged. For example, if the normal direction is the vertical direction, the index of the third optical system is A projector may be arranged.

The pattern index projected from the index projector is formed avoiding positions in the ±90° direction (with the horizontal direction being 0°) with respect to the optical axis of the third optical system. The pattern index may have a pattern shape that is symmetrical with respect to the optical axis of the third optical system. For example, it may be a two-dimensional pattern formed by lines or a plurality of points. For example, a plurality of point indicators arranged on the circumference may be projected as pattern indicators. Further, a plurality of patterns may be combined.

"Example"
Next, one example corresponding to the first and second embodiments will be described with reference to FIGS. 1 to 7.

<Overall configuration of example>
First, with reference to FIG. 1, a schematic configuration of an ophthalmologic apparatus 10 according to an embodiment is shown.

In the present embodiment, the ophthalmologic apparatus 10 is a composite device including an objective eye refractive power measuring device (particularly, in the present embodiment, an autorefractometer) and a Scheimpflug camera. In this embodiment, the ophthalmological apparatus 10 is a stationary examination apparatus, but is not necessarily limited to this, and may be a hand-held type.

As shown in FIG. 1, the ophthalmologic apparatus 10 includes at least a measurement unit 11, a base 12, an alignment drive section 13, a face support unit 15, a monitor 16, and a control section 50.

The measurement unit 11 includes a measurement system, an imaging system, etc., which are used to examine the eye to be examined. In this embodiment, the optical system shown in FIG. 2 is arranged.

The alignment drive section 13 may be able to move the measurement unit 11 three-dimensionally with respect to the base 12.

The face support unit 102 is used to fix the subject's face in front of the measurement unit 11. The face support unit 102 is fixed to the base 12 and supports the subject's face.

An arithmetic control unit (also referred to as a processor; hereinafter simply referred to as a control unit) 50 controls the entire ophthalmologic apparatus 10 . It also processes various test results obtained via the measurement unit 11.

<Optical system>
Next, with reference to FIG. 2, the optical system in the ophthalmologic apparatus 10 will be described.

As an example, the ophthalmologic apparatus 10 includes a measurement optical system 100, a fixation target presentation optical system 150, a frontal photographing optical system 200, cross-sectional photographing optical systems 300a and 300b, and a target projection optical system 400. It also includes beep splitters 501, 502, and 503 that split and combine the optical paths of each optical system.

<Measurement optical system>
The measurement optical system 100 objectively measures the eye refractive power of the eye E to be examined. For example, each value of SPH: spherical power, CYL: cylindrical power, and AXIS: astigmatic axis angle may be acquired as the measurement result of the eye refractive power.

The measurement optical system 100 includes a projection optical system 100a and a light receiving optical system 100b.

The projection optical system 100a includes at least a measurement light source 111, and projects a spot-shaped measurement light onto the fundus of the eye E through the center of the pupil P or the corneal vertex of the eye E. In this embodiment, infrared light is used as the measurement light. However, the measurement light is not necessarily limited to this, and the measurement light may be visible light. The measurement light source 111 may be an SLD light source, an LED light source, or another light source.

In this embodiment, a prism 115 is arranged on a common path of the projection optical system 100a and the light receiving optical system 100b. By rotating the prism 115 around the optical axis L1, the projection light beam on the pupil is eccentrically rotated at high speed. As an example, in this embodiment, the projection light beam is eccentrically rotated in a region of φ2 mm to φ4 mm on the pupil. This area becomes the measurement area of the eye refractive power in this example.

The light receiving optical system 100b includes at least a ring lens 124 and an image sensor 125. As shown in FIG. 2, the measurement optical system 100 may include other optical elements such as lenses and apertures. The light receiving optical system 100b extracts a reflected light beam of the measurement light beam reflected from the fundus of the eye in a ring shape through the peripheral part of the pupil. The ring lens 124 is placed at a pupil conjugate position, and the image sensor 125 is placed at a fundus conjugate position. The ring image formed on the image sensor 125 via the ring lens 124 is analyzed to derive the eye refractive power.

As mentioned above, in this embodiment, the measurement light is eccentrically rotated on the pupil at high speed, so the output image from the image sensor 125 is based on an exposure time sufficiently long than the rotation period, or the image from the image sensor 125 is Analysis processing is performed on the summed image of the image data that is sequentially output, and the eye refractive power is derived. In this embodiment, at least the values of SPH: spherical power, CYL: cylindrical power, and AXIS: astigmatic axis angle are acquired as a result of the analysis process.

<Fixation target presentation optical system>
The fixation target presentation optical system 300 presents a fixation target to the eye E to be examined. The fixation target is presented on the optical axis of the measurement optical system 100. The fixation target presentation optical system 300 is used to cause the subject's eye to fixate. It is also used to apply fog and accommodative load to the eye to be examined. For example, the fixation target presentation optical system 300 includes at least a light source 151 and a fixation target plate 155. The fixation target plate 155 is movable along the optical axis by the drive unit 155a. Thereby, the presentation distance (presentation position) of the fixation target with respect to the eye E to be examined can be changed.

<Front photographing optical system>
The front photographing optical system 200 photographs a front image of the anterior segment of the eye E to be examined. For example, the front photographing optical system 200 includes an image sensor 205 and the like. An observation image of the anterior segment of the eye may be acquired as the frontal image. The observed image is used for alignment and the like. Further, an index image (pattern index image) based on the pattern index projected onto the cornea of the eye to be examined from the index projection optical system 400 is photographed by the front photographing optical system 200.

<Cross-sectional imaging optical system>
The cross-sectional photographing optical systems 300a and 300b are used to photograph cross-sectional images of the anterior segment of the eye. The cross-sectional photographing optical systems 300a and 300b include an irradiation optical system 300a and a light receiving optical system 300b. The irradiation optical system 300a is coaxial with the projection optical axis (optical axis L1) of the measurement light of the measurement optical system 100, and irradiates the anterior segment of the eye with slit light. The irradiation optical system 300a includes a light source 311, a slit 312, and the like. In this embodiment, the slit light that is the illumination light is visible light. For example, the light source 311 may be a visible light source that emits blue light.

In this embodiment, the cross section through which the slit light passes through the anterior segment of the eye is referred to as a "cutting surface." The cut plane becomes the object plane of the cross-sectional photographing optical systems 300a, 300b. In FIG. 2, the opening of the slit 312 has a horizontal direction (the depth direction of the paper in FIG. 2) as its longitudinal direction. Therefore, in this embodiment, the horizontal plane (XZ cross section) including the optical axis L1 is set as the cutting plane. In this embodiment, a cut plane is formed at least between the anterior surface of the cornea and the posterior surface of the crystalline lens.

The light receiving optical system 300b includes a lens system 322, an image sensor 321, and the like. In the light receiving optical system 300, the lens system 322 and the image sensor 321 are arranged in a Scheimpflug relationship with a cutting plane set in the anterior segment of the eye. That is, the optical arrangement is such that the cut plane, the main plane of the lens system 322, and each extension surface of the imaging surface of the image sensor 321 intersect at one line of intersection (one axis). A cross-sectional image of the anterior segment of the eye (see FIG. 3) is acquired based on the signal from the image sensor 321.

<Indicator projection optical system>
In this embodiment, the target projection optical system 400 includes a plurality of point light sources 401. In this embodiment, each point light source 401 emits infrared light. However, visible light may also be used. As shown in FIGS. 4A and 4B, in this embodiment, the target projection optical system 400 is arranged as a target projector 410 in front of the measurement unit 11. The index projection optical system 400 projects a pattern index for measuring the shape of the cornea onto the anterior segment of the eye from the front facing the eye to be examined. In this embodiment, a pattern index consisting of four point images symmetrical with respect to the optical axis L1 is projected onto the cornea. The circumferential region onto which the pattern index is projected is the region where the corneal shape is measured by the index projection optical system 400 and the front photographing optical system 200. As an example, in this example, when a corneal model eye with a predetermined radius of curvature is placed at a position at a predetermined working distance, a circumferential area of 3 mm in diameter of the corneal model eye forms each point image constituting the pattern index. is projected. Note that in this embodiment, the pattern index is composed of four point images, but the number of indexes is not necessarily limited to this. The pattern index may be composed of a plurality of point images of three or more points, or may include a linear index image or the like.

By the way, in this embodiment, the light receiving optical axis L2 in the cross-sectional photographing optical system 300 is arranged directly below the optical axis L1 (in the −90° direction). In order to achieve an imaging range from the anterior surface of the cornea to the posterior surface of the crystalline lens, the inclination of the light-receiving optical axis (imaging optical axis) of the second optical system with respect to the cutting plane is sufficiently small. , the light beam of the pattern index projected from the index projection optical system 400 and the light receiving optical axis L2 are placed in a close positional relationship (see FIG. 4A).

Here, in FIG. 4B, the index projector 450 that is virtually arranged (not actually arranged) in the measurement section 13 is shown by a broken line. Indicator projector 450 projects the Mayer ring onto the same circumferential area as indicator projector 400 . When the light beam of the pattern indicator and the light receiving optical axis L2 are in a close positional relationship, when trying to project the pattern indicator on a ring such as a Mayer ring, the light receiving optical axis L2 interferes with the indicator projector 450. You can see that this happens.

On the other hand, the index projector 410 is arranged so as to avoid being below the optical axis L1. For example, in FIG. 4B, a device in which a light source 401 and a mirror 402 for adjusting the angle (not shown in FIG. 2) are arranged at four positions, upper right, lower right, upper left, and lower left of the optical axis L1. The configuration is illustrated. In this embodiment, a pattern index consisting of four point images symmetrical with respect to the optical axis L1 is projected onto the cornea. In this embodiment, as a result of the arrangement of the index projector 410, it is possible to simultaneously capture a wide range of images using the cross-sectional imaging optical system 300 and obtain the corneal shape using a Purkinje image.

<Alignment index projection optical system>
Furthermore, the ophthalmologic apparatus 10 includes an alignment light source 600. One alignment light source 600 may be provided on each side. For example, a light beam is projected along a horizontal plane including the optical axis L1. In this embodiment, the alignment target projection optical system is formed by the target projection optical system 400 and the light source 600. Diffused light is projected from one of the target projection optical system 400 and the light source 600, and parallel light is projected from the other. The working distance may be adjusted by moving in the front-back direction so that the Purkinje image of the cornea using parallel light and the Purkinje image using diffused light are captured at a predetermined ratio.

<Control operation>
Next, the control operation of the ophthalmologic apparatus 10 will be explained with reference to the flowchart of FIG. 5.

In this embodiment, the ophthalmological apparatus 10 sequentially performs corneal curvature measurement, imaging of an anterior segment cross-sectional image, and eye refractive power measurement, and obtains the axial length based on the measurement and imaging results. I will explain it as a thing.

First, alignment of the measurement unit 11 with respect to the eye E to be examined is performed (S1). The examiner instructs the subject to place his or her face on the face support unit 15. Furthermore, presentation of the fixation target and acquisition of anterior segment observation images are started.

Thereafter, the eye to be examined and the device are adjusted to a predetermined positional relationship, for example, based at least on the observation image of the anterior segment obtained through the frontal photographing optical system 200. More specifically, alignment in the XY directions is performed so that the optical axis L1 coincides with the corneal vertex of the eye E to be examined. Further, alignment in the Z direction is performed so that the distance between the eye to be examined and the device is a predetermined working distance. At this time, an alignment index (not shown) may be projected onto the cornea, and the alignment may be adjusted based on the alignment index detected in the observed image.

Next, the corneal shape is measured (S2). A pattern index is projected from the index projector 410 (index projection optical system 400), and a corneal Purkinje image of the pattern index is photographed by the front photographing optical system 200. Corneal shape information is acquired based on the corneal Purkinje image. Corneal shape information is derived based on the image height of the corneal Purkinje image. In this embodiment, at least each value of corneal curvature, astigmatic power, and astigmatic axis angle is acquired as corneal shape information.

Next, in this example, the eye refractive power is measured (S3). For example, a preliminary measurement may be performed first, and then a main measurement may be performed.

In the preliminary measurement, the eye refractive power of the eye E to be examined is measured with the fixation target placed at a predetermined presentation distance. At the time of measurement, the fixation target plate 155 may be placed at an initial position that is optically far enough away from the eye E to be examined and corresponds to the far point of the 0D eye. A ring image captured by the image sensor 125 based on the measurement light irradiated in this state is image-analyzed by the calculation control unit 50. As an analysis result, the value of refractive power in each meridian direction is determined. By performing predetermined processing on the refractive power in each meridian direction, at least the spherical power in the preliminary measurement is obtained.

Subsequently, the control unit 50 moves the fixation target plate 155 to the fog start position where the eye to be examined E is in focus, according to the preliminary measurement of the spherical power of the eye to be examined E. As a result, the fixation target can be clearly observed in the eye E to be examined. Thereafter, the control unit 50 adds fog to the eye E by moving the fixation target from the fog start position. This causes the accommodation of the eye E to be examined to be released.

The main measurement is performed with a cloud added to the eye E to be examined. A predetermined analysis process is performed on the ring image captured for the subject's eye E to which fog has been added, thereby obtaining the objective value of the subject's eye: SPH: spherical power, CYL: cylindrical power, AXIS: astigmatic axis angle. is obtained.

Next, a cross-sectional image of the anterior segment of the eye is photographed (S4). At this time, the photographing operation is executed immediately after the main measurement of the eye refractive power is completed. For example, the completion of the main measurement of the eye refractive power may be used as a trigger to perform the operation of photographing a cross-sectional image. That is, immediately after the main measurement is completed, visible illumination light is irradiated from the irradiation optical system 300a, and a cross-sectional image of the anterior segment of the eye formed on the image sensor 321 is acquired. Since the cross-sectional image of the anterior segment of the eye is executed immediately after the main measurement of the eye refractive power is completed, misalignment between the time of measuring the eye refractive power and the time of photographing the cross-sectional image is reduced.

Furthermore, in this embodiment, visible light is not irradiated before the cross-sectional image is photographed, so that miosis is suppressed when the cross-sectional image is photographed. As a result, a cross-sectional image in which the anterior segment of the eye is photographed deeper is more likely to be photographed satisfactorily.

Next, the calculation control unit 50 calculates the axial length of the eye to be examined based on the information or images acquired in each step of S2 to S4.

In this embodiment, the axial length is derived based on ray tracing calculations on the cut plane.

As shown in FIG. 6, a light ray entering the subject's eye from the far point FP (for example, the light ray Lx in FIG. 6) is traced, and the intersection point when the light ray is refracted by each transparent body of the subject's eye and intersects with the optical axis. Find the position of. The distance between the obtained intersection point and the corneal apex is derived as the ocular axial length. In this example, for convenience of explanation, it is assumed that the refractive index of each light-transmitting body (cornea, aqueous humor, and crystalline lens) is constant, and there is no change in refraction inside each of them. However, it is not necessarily limited to this, and the axial length may be derived by taking into account changes in the refractive index inside the light-transmitting body (for example, changes in the refractive index between the inside and outside of the crystalline lens). .

Furthermore, in addition to the cross-sectional image that is the anterior segment information, refractive index information regarding the refractive index of the transparent body may be acquired, and the refractive index information may be used to derive the ocular axial length. That is, when acquiring the axial length, the refractive index of the light-transmitting body based on the refractive index information may be further taken into consideration. Regarding the refractive index information, for example, it is known that the refractive index of the crystalline lens changes with age. Therefore, the device may include a calculation formula or lookup table in which the refractive index of the crystalline lens is associated with each age. In this case, by inputting the age, a refractive index according to the age is acquired. Ray tracing calculation may be performed using this refractive index.

In this method, the following parameters are used in addition to the position of the far point FP. The following parameters are obtained based on the Scheimpflug image and corneal shape information.
Ra : Radius of curvature of the anterior surface of the cornea Rp : Radius of curvature of the posterior surface of the cornea CT : Corneal thickness ACD : Depth of the anterior chamber ra : Radius of curvature of the anterior surface of the crystalline lens rp : Radius of curvature of the posterior surface of the crystalline lens LT : Lens thickness In addition, the measurement results of the ocular refractive power Based on this, the position of the far point FP of the eye to be examined relative to the corneal vertex is determined. For example, if the eye E to be examined has no astigmatism, SPH=-5D, and VD=12 mm, then the distance from the corneal vertex to the far point FP is 12+1000/5=212 mm. It is thought that the light rays from here form an image on the fundus of the eye to be examined. Note that the VD of 12 mm is a constant value indicating the distance between the corneal vertices on the assumption that spectacle lenses are worn. VD may vary from device to device.

By the way, in the widely used expression format of eye refractive power using SPH, CYL, and AXIS, SPH indicates the refractive power regarding the strong principal meridian (or weak principal meridian), so in ray tracing on a cutting plane, It is not necessarily an appropriate value. For example, consider a case where SPH=-5D, CYL=-2D, and AXIS=30°. In this case, if a horizontal cross section is obtained using the optical system example above, the refractive power at this cross section is neither -5D nor -7D with CYL added.

In contrast, in this embodiment, the on-plane ocular refractive power, which is the ocular refractive power on the cut plane, is determined, and the position of the far point FP is set based on the on-plane refractive power. Here, the refractive power on any surface is expressed by the following formula.

P(θ)=S+C×[sin ² (θ−A)]
However, θ is an angle with respect to a horizontal plane, and the horizontal direction is assumed to be 0°. The cut plane in this example is a horizontal plane (θ=0°). Therefore, when SPH=-5D, CYL=-2D, and AXIS=30°, P(0°)=-5.5D is calculated (see FIG. 7). In this case, 12+1000/5.5=194 mm is the distance from the corneal vertex to the far point FP on the cutting plane.

Here, the light ray from the far point FP thus set is traced. For example, a light ray (for example, the light ray Lx in FIG. 6) is guided from the far point FP toward a certain position (for example, a position of φ6 mm at the position of the pupil of the eye to be examined (approximately 3 mm deep into the cornea)). Note that setting the fixed position to φ6 mm at the position of the pupil of the eye to be examined is only an example, and can be changed as appropriate.

This light ray undergoes initial refraction at the anterior surface of the cornea. The intersection of the ray and the anterior surface of the cornea is calculated based on the radius of curvature Ra of the anterior surface of the cornea, the position of the far point FP, and the ray angle at the far point FP. Furthermore, the angle of incidence of the light beam at the intersection is calculated. Light rays that reach the front surface of the cornea change direction at a fixed refraction angle relative to the angle of incidence, based on Snell's law. In this way, the light rays at each transparent body boundary surface are sequentially traced. At that time, various parameters (Ra, Rp, CT, ACD, ra, rp, LT) acquired based on the Scheimpflug image and corneal shape information are used as appropriate to provide the intersection of each boundary surface and the light ray. be done. In this embodiment, the point that intersects with the axis of the eye (here, the visual axis) after exiting the posterior surface of the crystalline lens is finally determined. The distance from the intersection to the corneal apex (here, the origin) is used as the axial length AL.

Note that when using the above various parameters (Ra, Rp, CT, ACD, ra, rp, LT) in the ray tracing calculation, in this example, at least the radius of curvature Ra of the anterior surface of the cornea is determined by the corneal Purkinian pattern index. The values based on the image are used, and for the remaining values, the values based on the Scheimpflug image are used. This is because, in general, the measurement accuracy based on the corneal Purkinje image is higher than the measurement accuracy based on the Scheimpflug image regarding the anterior surface shape of the cornea. Note that, as described above, in this embodiment, at least each value of corneal curvature, astigmatic power, and astigmatic axis angle is acquired as corneal shape information. The corneal curvature (curvature of the front surface of the cornea) at the cut plane can be determined from these values using a method similar to the method used to determine the refractive power for the cut plane. The reciprocal of the obtained value is used as Ra.

As described above, the axial length of the eye can be determined by tracing the rays toward a certain position. However, the ray tracing method is not limited to the above method. For example, a point that forms an image from a far point may be determined by paraxial calculation. Further, the point at which the image is formed from the far point may be determined by considering a plurality of light rays that enter the subject's eye at different positions. For example, ray tracing for each ray of a paraxial ray and a ray directed toward a fixed position different from the paraxial ray may be combined. When ray tracing of multiple rays is performed, the final measured value (calculated value) of the axial length may be the average value of the axial lengths obtained by each ray tracing (it may be a weighted average value). good).

Furthermore, the axial length may be determined by tracing the light rays directed toward the measurement area (φ2 mm to φ4 mm on the pupil) by the measurement optical system 100. For example, ray tracing may be performed for each of a plurality of light rays directed toward an area of φ2 mm to φ4 mm on the pupil, and the average value of the axial length determined by each ray tracing may be obtained as a calculation result. Since ray tracing is performed under more appropriate conditions, it becomes easier to obtain the axial length with higher accuracy.

Note that a predetermined offset value may be added to the axial length value obtained in this example. The offset value corrects the error between the calculated value and the actual measurement value.

Alternatively, ray tracing may be performed by tracing a ray that is emitted from a far point and passes through a circumferential region on which a pattern index for corneal shape measurement is projected. This makes the conditions for ray tracing more appropriate, making it easier to obtain the axial length with higher accuracy.

The determined axial length is displayed on the monitor 16. In this embodiment, the axial length is displayed along with at least one of the eye refractive power (SPH, CYL, AXIS) and corneal shape information. If there are past measurement results for the subject's eye, the current measurement results may be displayed together with the past axial length measurement results. For example, the measurement results may be displayed as a trend graph in which the horizontal axis is age (measurement date) and the vertical axis is axial length. Of course, the display mode of the measurement results is not limited to these.

<Transformation example>
Although the description has been made above based on the embodiments and examples, the present disclosure is not limited to the above embodiments, and various modifications are possible.

For example, in the above embodiment, actual measured values were used for various parameters (Ra, Rp, CT, ACD, ra, rp, LT) used in ray tracing. However, the present invention is not necessarily limited to this, and standard values (hypothetical values) may be used for some of the various parameters. The standard value may be an average value or a value employed in a predetermined eye optical model (for example, Gullstrand model eye model, etc.). A plurality of standard values may be prepared for at least one of age, gender, and region, and the examiner may be able to select which standard value is used to determine the axial length. .

Further, for example, in the above embodiment, the axial length of the eye to be examined is obtained as a result of arithmetic processing based on the eye refractive power and anterior segment information of the eye to be examined. However, the method is not necessarily limited to this, and the axial length may be obtained using a mathematical model trained by a machine learning algorithm. A mathematical model refers to, for example, a data structure for predicting the relationship between input data and output data. A mathematical model is constructed by being trained using a training dataset. The training data set is a set of input training data and output training data. Input training data is sample data that is input to the mathematical model. For example, the input training data uses the eye refractive powers of a plurality of eyes to be examined and anterior segment information acquired in the past. The output training data is sample data of values predicted by the mathematical model. For example, the axial length values of a plurality of eyes to be examined acquired in the past are used as the output training data. The axial length value may be a measured value obtained by an optical interference type or ultrasonic type axial length measuring device. A mathematical model is trained such that when certain input training data is input, corresponding output training data is output. In this embodiment, the arithmetic control unit may obtain the axial length value of the subject's eye as a predicted value by inputting the eye refractive power and anterior segment information into the mathematical model.

Furthermore, for example, in the embodiments and examples described above, anterior segment information including crystalline lens shape information may be sequentially acquired while the fixation target is moved in order to add fog. Thereby, changes in the shape of the crystalline lens may be detected from the anterior segment information, and based on the changes in shape, it may be confirmed whether or not fogging is being performed appropriately.

10 Ophthalmological apparatus 50 Control unit 100 Measurement optical system 300a, 300b Cross-sectional imaging optical system

Claims (4)

a first optical system that projects measurement light onto the fundus of the eye to be examined and obtains the eye refractive power of the eye to be examined based on the fundus reflected light of the measurement light;
a second optical system for acquiring anterior eye segment information, which is information regarding the shape of the anterior eye segment and includes at least shape information of the crystalline lens;
a fixation target presentation optical system that presents a fixation target;
The first optical system, the second optical system , and the fixation target presenting optical system are controlled to add accommodation to the eye to be examined using the fixation target when acquiring the eye refractive power and the anterior segment information. By controlling the respective acquisition timings of the eye refractive power and the anterior eye segment information so that they are the same between the acquisition times of the eye refractive power and the anterior eye segment information, the eye refractive power and the anterior eye segment information are each , control means for obtaining accommodation in the crystalline lens in mutually identical conditions;
Based on the eye refractive power and the anterior segment information obtained with the same accommodation in the crystalline lens , the axial length of the eye to be examined is determined so that the light beam incident on the eye to be examined from the far point transmits light through the eye to be examined. An ophthalmological apparatus comprising: an axial length obtaining means for obtaining an axial length as a distance between a point of intersection when refracted by a body and intersecting an optical axis of the first optical system and a corneal apex of an eye to be examined . The fixation target presentation optical system is capable of changing the presentation distance of the fixation target,
The control means performs fogging on the subject's eye by controlling the fixation target presentation optical system, and acquires each of the eye refractive power and the anterior eye segment information when the subject's eye is in the foggy state. The ophthalmological apparatus according to claim 1. a first optical system that projects measurement light onto the fundus of the eye to be examined and obtains the eye refractive power of the eye to be examined based on the fundus reflected light of the measurement light;
a second optical system for acquiring anterior eye segment information, which is information regarding the shape of the anterior eye segment and includes at least shape information of the crystalline lens;
By controlling the first optical system and the second optical system to synchronize the respective acquisition timings of the eye refractive power and the anterior eye segment information, the eye refractive power and the anterior eye segment information can be synchronized. a control means for obtaining each in the same state of accommodation in the crystalline lens ;
Based on the eye refractive power and the anterior segment information obtained with the same accommodation in the crystalline lens , the axial length of the eye to be examined is determined so that the light beam incident on the eye to be examined from the far point transmits light through the eye to be examined. An ophthalmological apparatus comprising: an axial length obtaining means for obtaining an axial length as a distance between a point of intersection when refracted by a body and intersecting an optical axis of the first optical system and a corneal apex of an eye to be examined . The first optical system irradiates infrared light as the measurement light,
The second optical system includes an irradiation optical system that irradiates the anterior eye segment with slit light, and a lens system that is arranged in a Scheimpflug relationship with respect to a cut plane set in the anterior eye segment by the slit light. The ophthalmologic apparatus according to any one of claims 1 to 3 , comprising: a light receiving optical system having a sensor and an image sensor, and obtains a cross-sectional image of the anterior segment based on a signal from the image sensor.

Images