Ophthalmological device

An ophthalmological device according to one aspect of the present disclosure includes a support structure, an illumination light source, an observation optical system, and a controller. The support structure is configured to support a subject's face. The illumination light source is configured to illuminate a subject's eye. The observation optical system includes an imaging element configured to receive light reflecting off the subject's eye. The controller is configured to acquire, from the imaging element, a first image captured when the illumination light source is on and a second image captured when the illumination light source is off and determine whether the subject's face is placed on the support structure based on a difference between the first image and the second image.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of Japanese Patent Application No. 2018-170716 filed with the Japan Patent Office on Sep. 12, 2018, and the disclosure of which is incorporated herein by reference.

BACKGROUND

The present disclosure relates to an ophthalmological device.

As disclosed in Japanese Unexamined Patent Application Publication No. 2000-254098, ophthalmological devices configured to detect subjects have been already known. In such a known ophthalmological device, a light emitting element is turned on and off at a specific frequency so as to emit index light. A light-received signal from a light receiving element is inputted to a bypass circuit. A signal with a specific frequency is selectively extracted from the light-received signal by the bypass circuit. When a subject is present, a component of the index light reflecting off the subject is extracted. The ophthalmological device determines the presence/absence of the subject based on the extracted signal.

One type of ophthalmological devices are also known in which sensors for determining the presence/absence of subjects are provided on chin rests on which subjects' faces are to be placed.

SUMMARY

To detect subjects, the conventional devices include physical structures such as special-purpose circuits that are not directly related to ophthalmological examinations.

Accordingly, it is desirable that one aspect of the present disclosure provides an ophthalmological device that can detect a subject using a structure used for ophthalmological examinations.

The ophthalmological device according to one aspect of the present disclosure comprises a support structure, an illumination light source, an observation optical system, and a controller. The support structure is configured to support a subject's face. The illumination light source is configured to illuminate a subject's eye. The observation optical system comprises an imaging element configured to receive light reflecting off the subject's eye. The observation optical system is provided for observing the subject's eye.

The controller is configured to turn on and off the illumination light source. The controller is configured to acquire a first image from the imaging element. The first image is captured by the imaging element when the illumination light source is on. The controller is configured to acquire a second image from the imaging element. The second image is captured by the imaging element when the illumination light source is off. The controller is configured to determine whether the subject's face is placed on the support structure based on a difference between the first image and the second image.

The ophthalmological device according to one aspect of the present disclosure can determine whether the subject's face is placed on the support structure through the use of the illumination light source and the observation optical system, which are used for ophthalmological examinations.

In one aspect of the present disclosure, the controller may be configured to determine whether the subject's face is placed on the support structure based on a difference in brightness between the first image and the second image.

In one aspect of the present disclosure, the controller may be configured to determine that the subject's face is placed on the support structure when the difference in brightness between the first image and the second image is equal to or larger than a reference value, and determine that the subject's face is not placed on the support structure when the difference in brightness is smaller than the reference value.

In one aspect of the present disclosure, the ophthalmological device may further comprise a driving system configured to change a position of the observation optical system relative to the support structure. The controller may be configured to control the driving system to align the observation optical system with the subject's eye on condition that the subject's face is determined to be placed on the support structure.

In one aspect of the present disclosure, the controller may be configured to detect a position of a pupil of the subject's eye based on an image captured by the imaging element when the illumination light source is on, and control the driving system to align the observation optical system with the subject's eye based on the position of the pupil.

In one aspect of the present disclosure, the ophthalmological device may further comprise a position detection system configured to apply light to a cornea of the subject's eye and receive reflected light so as to detect a position of an apex of the cornea. The controller may be configured to perform a rough alignment processing and a fine alignment processing so as to align the observation optical system with the subject's eye in a stepwise manner.

The rough alignment processing may comprise detecting a position of a pupil of the subject's eye based on an image captured by the imaging element when the illumination light source is on, on condition that the subject's face is determined to be placed on the support structure, and controlling the driving system based on the position of the pupil detected so as to align the observation optical system with the subject's eye.

The fine alignment processing may comprise controlling the driving system based on the position of the apex of the cornea acquired from the position detection system so as to align the observation optical system with the subject's eye. The fine alignment processing may be performed after the rough alignment processing.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An ophthalmological device1, shown inFIG. 1, according to the present embodiment is configured to function as a pachymeter that measures the thickness of a cornea of an eye of a subject (subject's eye E) and as a tonometer that measures the intraocular pressure of the subject's eye E. The ophthalmological device1comprises a head portion3, a main body5, a support structure7, and a display9.

The head portion3is attached to the main body5in a manner movable in X (left-right), Y (up-down), and Z (front-rear) directions relative to the main body5. The support structure7is configured to support the face of the subject (subject's face), specifically, the chin of the subject, and is secured to the main body5. The display9is disposed in a rear portion of the head portion3, which is on the opposite side of a front portion that faces the subject.

In an ophthalmological examination, the subject's face is placed on the support structure7. The position of the subject's eye E is stabilized by the subject's face being supported by the support structure7. Moreover, in the eye examination, the head portion3is moved in the XYZ directions relative to the main body5so that an optical system incorporated in the head portion3is aligned with the subject's eye E.

As shown inFIG. 2, the head portion3comprises an alignment optical system100, an observation optical system300, a visual fixation optical system400, a first measurement optical system500, and a second measurement optical system600as the aforementioned optical system.

The main body5comprises a controller700, a storage device710, an XYZ-direction driving system720, and an operation system740. The controller700is configured to generally control the entirety of the ophthalmological device1and to process measurement data of the subject's eye E.

The controller700comprises, for example, a processor701and a memory703. The processor701is configured to perform processes in accordance with computer programs stored in the storage device710.

It may be understood that the processes performed by the controller700, which will be described below, are achieved by the processor701performing the processes in accordance with the computer programs. The storage device710is composed of, for example, a nonvolatile memory such as a flash memory in which data can be electronically rewritten.

The XYZ-direction driving system720is configured to move the head portion3in the XYZ directions relative to the main body5based on instructions from the controller700. The operation system740comprises a joystick741through which an examiner's operation is received.

In addition, a touchscreen (not shown) may be provided on the screen of the display9as part of the operation system740. The display9is configured to be controlled by the controller700so as to show the examiner an image of the subject's eye E and various information including the intraocular pressure and the thickness of the cornea measured.

As shown inFIG. 3, the alignment optical system100incorporated in the head portion3comprises a light source101, a hot mirror102, an objective lens103, and a hot mirror104. The light source101is configured to output alignment light.

The alignment light from the light source101reflects off the hot mirror102, passes through the objective lens103, and reflects off the hot mirror104. Subsequently, passing through an eyepiece200, the alignment light is transmitted toward the cornea of the subject's eye E. The light source101is, for example, an LED that outputs infrared rays.

The eyepiece200comprises a nozzle201and a planar glass plate205. The nozzle201comprises a transparent window member201a, which faces the subject's eye E, and an aperture201c. The aperture201cis formed as an ejection path for compressed air and defines an ejection port201bin the center of the window member201a.

When the intraocular pressure is measured, the compressed air is ejected from the ejection port201bthrough the aperture201ctoward the subject's eye E. The alignment light reflecting off the aforementioned hot mirror104passes through the planar glass plate205of the eyepiece200and the aperture201cof the nozzle201and is applied to the subject's eye E.

The light reflects off the cornea of the subject's eye E is transmitted inside the observation optical system300disposed on a main optical axis O1. The observation optical system300comprises a two-dimensional imaging element306. The light reflecting off the cornea of the subject's eye E is received by the two-dimensional imaging element (CCD)306. Accordingly, the reflected light that corresponds to the alignment light is captured by the two-dimensional imaging element306.

An image signal from the two-dimensional imaging element306that includes the captured image of the reflected light is processed by the controller700. The controller700is configured to detect the position of the apex of the cornea of the subject's eye E in the XY directions based on the image of the reflected light included in the image signal. In this manner, the alignment optical system100and the observation optical system300function as the position detection system.

The XYZ-direction driving system720is configured to move the head portion3based on the detected position of the subject's eye E in the XY directions so as to align the head portion3with the subject's eye E in the XY directions.

The observation optical system300further comprises a light source301, a light source302, an objective lens303, a Dichroic mirror304, and an imaging lens305. The light sources301,302are disposed so as to illuminate an anterior segment area of the subject's eye E. For the light sources301,302, LEDs are used which output infrared rays with shorter wavelengths as compared to that of the alignment light from the light source101. Hereinafter, the light from the light sources301,302will be referred to as observation light.

The observation light from the light sources301,302reflects off the subject's eye E. The reflected light penetrates the hot mirror104, passes through the objective lens303, the Dichroic mirror304, and the imaging lens305, and is received by the two-dimensional imaging element (CCD)306. The receipt of the reflected light causes the two-dimensional imaging element306to capture an image of the anterior segment area of the subject's eye E. The image signal representing the captured image is outputted from the two-dimensional imaging element306. The controller700controls the display9based on the image signal from the two-dimensional imaging element306to show the image of the anterior segment of the subject's eye E on the display9.

Moreover, the visual fixation optical system400comprises a light source401, a relay lens403, and a reflective mirror404. The light source401is configured to transmit light that facilitates visual fixation of the subject (hereinafter referred to as visual fixation light).

The visual fixation light passes through the relay lens403and reflects off the reflective mirror404. Subsequently, the visual fixation light reflects off the Dichroic mirror304, passes along the main optical axis O1through the objective lens303and the hot mirror104. As a result, an image is formed on the retina of the subject's eye E. Due to the visual fixation light, the subject's eye E is brought into a fixed state which enables examination of ocular characteristics, such as an intraocular pressure examination. For the light source401, an LED is used which outputs light visible to the subject.

The first measurement optical system500for measuring the intraocular pressure comprises a light source501, a semi-reflective mirror502, a condenser lens503, and a light receiving element504. Light from the light source501(hereinafter referred to as first measurement light) penetrates the semi-reflective mirror502, the hot mirror102, and the objective lens103, and reflects off the hot mirror104. Subsequently, the first measurement light passes along the main optical axis O1and through the planar glass plate205and the aperture201cof the nozzle201, and is applied to the cornea of the subject's eye E.

The light applied to the cornea of the subject's eye E reflects off the cornea and travels as if it goes back through the route that it has once traveled. The reflected light passes through the aperture201cof the nozzle201and the planar glass plate205and then reflects off the hot mirror104. The light further passes through the objective lens103and the hot mirror102and reflects off the semi-reflective mirror502so as to pass through the condenser lens503and to be received by the light receiving element504.

In the intraocular pressure test, the compressed air is ejected from the nozzle201toward the cornea of the subject's eye E. In response to the ejection of the compressed air, the cornea of the subject's eye E is displaced and deformed, and thus the amount of light received by the light receiving element504changes. The intraocular pressure of the subject's eye E is calculated from the degree of such change in amount of the light.

For the light source501, an LED is used which outputs infrared rays with wavelengths that are longer than that of the observation light and shorter than that of the alignment light. The wavelengths of the alignment light, the observation light, the visual fixation light, and the first measurement light are set as described above, and the reflection and/or transmission characteristics of the hot mirrors102,104, and the Dichroic mirror304are suitably set so that these four types of light are respectively transmitted along the suitable paths.

The second measurement optical system600for measuring the thickness of the cornea comprises a light source601, a lens602, a cylindrical lens603, and a light receiving element604. The light from the light source601(hereinafter referred to as second measurement light) is first collimated by the lens602. Then, the second measurement light passes through the transparent window member201aof the eyepiece200and is applied to the cornea of the subject's eye E. The second measurement light applied to the cornea reflects off the corneal endothelium and the corneal epithelium of the subject's eye E. The light reflected at these points passes through the transparent window member201aof the eyepiece200and the cylindrical lens603so as to be received by the light receiving element604. For the light source601, a coherent super-luminescent diode (SLD) is used, for example. For the light source601, not only the SLD, but also a coherent light source (diode), such as a laser diode (LD), may be alternatively used.

If a coherent light source is used as the light source601, speckle noise may be generated and the accuracy in measuring the thickness of the cornea may be reduced. Nevertheless, it is possible to reduce the speckle noise by allowing the passage of the second measurement light that has reflected off the corneal endothelium and the corneal epithelium of the subject's eye E through the cylindrical lens603as described above so as to linearly shape the second measurement light.

A light-received signal transmitted from the light receiving element604is processed by the controller700. The controller700is configured to measure the thickness of the cornea of the subject's eye E based on the difference between the positions on the light receiving surface to receive first reflected light and to receive second reflected light that are identified from the light-received signals. The first reflected light is the light reflecting off the corneal endothelium of the subject's eye E. The second reflected light is the light reflecting off the corneal epithelium.

In addition, the second measurement optical system600is used as a Z-direction alignment optical system prior to ophthalmological examinations. A light receiving position at which the light receiving element604receives the reflected light changes depending on the position of the cornea of the subject's eye E in the Z direction. The controller700detects the position of the cornea of the subject's eye E in the Z direction based on the light receiving position. The XYZ-direction driving system720adjusts the position of the head portion3in the Z direction relative to the subject's eye E based on the detected position.

In the ophthalmological device1, alignment of the head portion3in the Z direction with the subject's eye E is automatically performed based on, for example, the image of the anterior segment of the subject's eye E shown by the image signal from the two-dimensional imaging element306(rough alignment), and then automatically and accurately performed based on the second measurement light (fine alignment).

As described above, alignment of the head portion3in the XY directions with the subject's eye E is also automatically performed in a similar manner based on the image of the anterior segment of the subject's eye E shown by the image signal from the two-dimensional imaging element306(rough alignment), and then is automatically and accurately performed based on the alignment light (fine alignment). If it is not possible to automatically perform the rough alignment, the rough alignment is manually performed by the examiner using the joystick741.

With reference toFIG. 4, the detail of the alignment process performed by the controller700will be described below. The controller700repeatedly performs the alignment process shown inFIG. 4while the subject's face is placed on the support structure7so as to automatically align the head portion3with the subject's eye E.

When the alignment process is initiated, the controller700determines whether it is possible to perform the fine alignment processing (S110). If the position of the head portion3relative to the subject's eye E is within a range where the fine alignment processing can be performed, the controller700makes an affirmative determination in S110. If the relative position of the head portion3is elsewhere, the controller700makes a negative determination in S110.

To determine whether it is possible to perform the fine alignment processing, the controller700may transmit the alignment light from the light source101and acquire the image signal from the two-dimensional imaging element306. If the image signal includes a component of the reflected light that correspond to that of the alignment light, and the position of the apex of the cornea is detected from the component of the reflected light, the controller700may determine that it is possible to perform the fine alignment processing.

Determining in S110that it is possible to perform the fine alignment processing (S110: Yes), the controller700performs the fine alignment processing in S220. Then, the alignment process is completed.

Making the negative determination in S110, the controller700turns on and off the light sources301,302(S120). The controller700further acquires the image signal from the two-dimensional imaging element306respectively when the light sources301,302are on (ON-state) and when the light sources301,302are off (OFF-state) (S120). The image signal acquired in the ON-state represents the image (light receiving image) captured by the two-dimensional imaging element306in the ON-state. The image signal in the OFF-state represents the image (light receiving image) captured by the two-dimensional imaging element306in the OFF-state.

Based on the acquired image signal, the controller700calculates a brightness B1of the image captured in the ON-state and a brightness B2of the image captured in the OFF-state (S130). The controller700further calculates the difference in brightness BD=B1−B2between the brightness B1in the ON-state and the brightness B2in the OFF-state (S140).

The brightness B1and the brightness B2may be the sum or the average of the brightness of the pixels in the entire captured image, or may alternatively be the sum or the average of the brightness of the pixels located in a predefined central portion of the captured image.

Based on the brightness difference BD calculated as described above, the controller700determines whether the subject's face is placed on the support structure7(S150). As shown inFIG. 5, if the subject's face is not placed on the support structure7, the light that reaches the two-dimensional imaging element306is mostly background light transmitted from outside of the ophthalmological device1through the eyepiece200, and thus the brightness of the image captured by the two-dimensional imaging element306is low irrespective of whether the light sources301,302are on. InFIG. 5, the low brightness state is represented by hatching.

On the other hand, if the subject's face is placed on the support structure7, the light from the light source301and the light from the light source302reflect off the subject's face, particularly the subject's eye E, and each of the reflected light is received by the two-dimensional imaging element306. Accordingly, the brightness of the captured image is low during the OFF-state, whereas the brightness is high during the ON-state. Utilizing such a phenomenon, the controller700determines, in S150, whether the subject's face is placed on the support structure7based on the brightness difference BD.

Specifically, the controller700determines that the subject's face is placed on the support structure7(S150: Yes) if the brightness difference BD is equal to or larger than a predetermined threshold, and determines that the subject's face is not placed on the support structure7(S150: No) if the brightness difference BD is not equal to or larger than the threshold.

Determining that the subject's face is not placed on the support structure7(S150: No), the controller700again turns on and off the light sources301,302(S120) and then performs the processing of S130to S150again. When the light sources301,302are turned on and off again, the turn-on and turn-off may be performed at a specified interval from the previous turn-on and turn-off.

Determining that the subject's face is placed on the support structure7(S150: Yes), the controller700places the head portion3in a position where the point of origin in the Z direction is located (to be referred to as origin point position) and captures an image of the subject's eye E so as to detect the pupil (S160).

Specifically, the controller700first causes the XYZ-direction driving system720to move the head portion3to the origin point position in the Z direction. The origin point position corresponds to a position which is within a range where the image of the pupil of the subject's eye E can be captured and where the head portion3is positioned the farthest from the subject's eye E in the Z direction. The head portion3is placed in the origin point position at this stage so as to inhibit the head portion3from contacting the subject (particularly, the subject's eye E) in a later stage when the head portion3is moved.

Subsequently, while the head portion3being placed in the origin point position, the controller700turns on the light sources301,302so as to capture the image of the subject's eye E, and acquires the image signal in the ON-state from the two-dimensional imaging element306. The image signal basically represents the captured image of the anterior segment area of the subject's eye E. The controller700analyzes the acquired image signal and detects a black circular area in the captured image of the anterior segment area shown by the image signal so as to detect the pupil of the subject's eye E and the position of the pupil in the XY directions.

If the pupil is detected, the controller700makes an affirmative determination in S170and performs the processing of S180. On the other hand, if the pupil is not detected, the controller700makes a negative determination in S170and performs the processing of S120again.

In S180, the controller700performs the rough alignment processing in the XY directions based on the position of the detected pupil. Specifically, the controller700causes the XYZ-direction driving system720to move the head portion3in the XY directions such that the head portion3is aligned with the center of the detected pupil.

Subsequently, the controller700determines whether it is possible to perform the rough alignment processing in the Z direction (S190). Specifically, the controller700analyzes the image signal from the two-dimensional imaging element306and determines whether it is possible to calculate a distance D between the position of the reflected light of the light source301reflected in the pupil and the position of the reflected light of the light source302reflected in the pupil.

The image signal to be analyzed may be the image signal acquired through the capturing after the rough alignment processing in the XY directions (S180) is performed. More specifically, in order to make the aforementioned determination, the controller700may newly acquire, while the light sources301,302are on, the image signal in the ON-state from the two-dimensional imaging element306in S190and may analyze the newly acquired image signal. In an alternative example, the determination in S190may be made based on the image signal acquired through the processing in S160that is performed prior to the rough alignment processing in the XY directions.

In the present embodiment, the light sources301,302are disposed on the left side and the right side of the subject's eye E. Thus, when it is possible to calculate the distance D, the position of the subject's eye E in the Z direction can be approximately located from the distance D although the calculated distance D includes an error caused by the difference in curvature of eyes of individual subjects.

For example, if the distance D is long as shown inFIG. 6A, it means that the distance between the subject's eye E and the head portion3is closer as compared to a case where the distance D is short as shown inFIG. 6B. The hatched circular areas shown inFIGS. 6A and 6Beach represent the subject's eye E, and the white circular areas therein represent images of the reflected light reflected in the subject's eye E. A relational equation of the distance D and the position of the subject's eye E in the Z direction can be derived from an experiment run in advance or a theoretical calculation.

If the calculated distance D is within a predetermined normal range, the controller700determines that it is possible to perform the rough alignment processing in the Z direction. If the calculated distance D is not in the normal range, the controller700determines that it is not possible to perform the rough alignment processing in the Z direction.

Determining that it is possible to perform the rough alignment processing in the Z direction (S190: Yes), the controller700performs the rough alignment processing in the Z direction based on the position of the subject's eye E in the Z direction which is located from the aforementioned distance D (S200).

Specifically, the controller700causes the XYZ-direction driving system720to move the head portion3in the Z direction so as to align the head portion3with a position at a suitable distance away from the position of the subject's eye E in the Z direction (S200). Subsequently, the controller700makes the determination in S110. In this case, the position of the head portion3relative to that of the subject's eye E is basically within a rage where it is possible to perform the fine alignment processing. Accordingly, the controller700makes an affirmative determination in S110and performs the fine alignment processing (S220).

On the other hand, determining that it is not possible to perform the rough alignment processing in the Z direction (S190: No), the controller700prompts the examiner through the display9to manually perform the alignment in the Z direction. Upon receipt of operation through the joystick741, the controller700moves the head portion3relative to the main body5(S210). The examiner can manually align the head portion3with the subject's eye E based on the captured image of the anterior segment area of the subject's eye E shown on the display9.

Upon completion of the above-described manual operation, the controller700makes the determination in S110. If the head portion3is adjusted by the manual operation to a position where it is possible to perform the fine alignment processing, the controller700makes an affirmative determination in S110and performs the fine alignment processing (S220).

Alternatively, after the process proceeds to S210and when the rough alignment processing in the Z direction becomes possible as a result of the manual operation, the controller700stops receiving the manual operation and performs the rough alignment processing in the Z direction in the same manner as in S200. Subsequently, the controller700makes an affirmative determination in S110and performs the fine alignment processing (S220).

In the fine alignment processing (S220), the controller700detects the position of the apex of the cornea of the subject's eye E based on the component of the reflected light of the alignment light included in the image signal from the two-dimensional imaging element306. The controller700further causes the XYZ-direction driving system720to move the head portion3in the XY directions so as to align the head portion3with the detected position of the apex of the cornea of the subject's eye E.

Moreover, the controller700controls the second measurement optical system600to transmit the second measurement light from the light source601and acquires the light-received signals of the reflected light from the light receiving element604. The controller700causes the XYZ-direction driving system720to move the head portion3in the Z direction so as to suitably align the head portion3with the position of the subject's eye E in the Z direction that is located from the component of the reflected light included in the acquired light-received signals. Subsequently, the controller700completes the alignment process shown inFIG. 4. Upon completion of the alignment process, the controller700may perform ophthalmological examination processes, such as a process to measure the thickness of the cornea and a process to measure the intraocular pressure.

The ophthalmological device1according to the present embodiment described above can detect the subject's face placed on the support structure7by turning on and off the light sources301,302provided to illuminate the subject's eye E for observation. After the detection, the ophthalmological device1can perform the automatic alignment of the head portion3with the subject's eye E.

Accordingly, the ophthalmological device1can reduce the burden of ophthalmological examinations on the examiner and can promptly and automatically perform preparation for ophthalmological examinations. The automatic performance contributes to shorten the examination time. The present embodiment therefore can provide a highly convenient ophthalmological device.

In the present embodiment, the subject's face is automatically detected, and the head portion3is automatically aligned. This can inhibit the head portion3from being unnecessarily driven for alignment when the subject's face is not placed on the support structure7.

Moreover, in the present embodiment, special components are not required for detecting the subject's face. More specifically, without any special hardware, the ophthalmological device1can detect the subject's face merely through software processing, such as through the turn-on and turn-off of the light sources301,302and the analysis of the captured image(s). The present embodiment thus enables detection of the subject through the efficient utilization of the structure of the ophthalmological device used for ophthalmological examinations.

The example embodiment of the present disclosure is explained hereinbefore. Nevertheless, the present disclosure is not limited to the aforementioned embodiment and may be embodied in various modes. For example, functions of one component in the aforementioned embodiment may be divided into two or more components. Functions of two or more components may be integrated into one component. A part of the structure of the aforementioned embodiment may be omitted. It should be noted that any and all modes that are encompassed in the technical ideas identified by the languages in the claims are embodiments of the present disclosure.