Patent Description:
Ophthalmic apparatuses configured to capture tomographic images of inside of a subject eye have been developed. For example, <CIT> discloses an optical tomographic device including a measurement optical system, a reference optical system, a calibration optical system, a light-receiving element and an arithmetic logic unit. Further, an ophthalmic apparatus of <CIT> is provided with a measurement optical system configured to irradiate a subject eye with light outputted from a light source and guide reflected light from the subject eye, and a reference optical system configured to irradiate a reference surface with the light outputted from the light source and guide reflected light from the reference surface. In measurement, a tomographic image of the subject eye is generated from an interference light being a combination of the reflected light guided by the measurement optical system and the reflected light guided by the reference optical system.

When a subject eye is measured using an ophthalmic apparatus such as that described in <CIT>, an abnormality might occur in an interference signal obtained from the interference light. As an example, this may happen when vibration and/or shock cause an abnormality in the interference signal, and/or when a change in current that drives the light source or a change in a temperature of the light source lead to a change in oscillation wavelength (so-called mode hop). It is impossible to measure a subject eye accurately in a situation where such abnormality is occurring. However, there has been a problem that when the interference signal from measurement light that has measured the subject eye wobbles as compared to its normal state, it is difficult to determine what has caused the abnormality, i.e., whether the abnormality is caused due to a capturing state, that is, how the image of the subject eye was captured, or the abnormality is caused due to a presence of a lesion or the like in the subject eye. The present disclosure discloses a technique that determines image of the subject eye was captured, or the abnormality is caused due to a presence of a lesion or the like in the subject eye. The present disclosure discloses a technique that determines whether or not there was an abnormality in a capturing state when a subject eye was being measured.

An ophthalmic apparatus disclosed herein may comprise: a light source; a measurement optical system configured to irradiate a subject eye with light from the light source and to guide reflected light from the subject eye; a reference optical system configured to guide the light from the light source so as to use the light from the light source as reference light; an abnormality detection optical system configured to have an optical path length adjusted to a predetermined length and to guide the light from the light source so as to use the light from the light source as abnormality detection light; a light receiving element configured to receive measurement interference light and abnormality detection interference light, the measurement interference light being a combination of the reflected light from the subject eye and the reference light, the abnormality detection interference light being a combination of the abnormality detection light and the reference light; a processor; and a memory storing computer-readable instructions therein, wherein the computer-readable instructions, when executed by the processor, cause the ophthalmic apparatus to execute determining whether the measurement interference light is abnormal based on a waveform of an abnormality detection interference signal, the abnormality detection interference signal being outputted from the light receiving element when the light receiving element receives the abnormality detection interference light.

Some of the features characteristic to below-described embodiment will herein be listed. It should be noted that the respective technical elements are independent of one another, and are useful solely or in combinations. The combinations thereof are limited to those described in the claims.

An ophthalmic apparatus disclosed herein comprises: a light source; a measurement optical system configured to irradiate a subject eye with light from the light source and to guide reflected light from the subject eye; a reference optical system configured to guide the light from the light source so as to use the light from the light source as reference light; an abnormality detection optical system configured to have an optical path length adjusted to a predetermined length and to guide the light from the light source so as to use the light from the light source as abnormality detection light; a light receiving element configured to receive measurement interference light and abnormality detection interference light, the measurement interference light being a combination of the reflected light from the subject eye and the reference light, the abnormality detection interference light being a combination of the abnormality detection light and the reference light; a processor; and a memory storing computer-readable instructions therein, wherein the computer-readable instructions, when executed by the processor, cause the ophthalmic apparatus to execute determining whether the measurement interference light is abnormal based on a waveform of an abnormality detection interference signal, the abnormality detection interference signal being outputted from the light receiving element when the light receiving element receives the abnormality detection interference light.

In the above ophthalmic apparatus, by comprising the abnormality detection optical system separately from the measurement optical system, the abnormality detection interference light is generated simultaneously with the measurement interference light when the subject eye is measured. Since the optical path length of the abnormality detection optical system is already known, it is possible to distinguish between a signal generated from the abnormality detection interference light and a signal generated from the measurement interference light. Further, since the abnormality detection interference light is known irrespective of a state of the subject eye, a signal waveform of the abnormality detection interference light can be used to determine whether an abnormality is occurring in the abnormality detection interference light. Because the measurement interference light and the abnormality detection interference light are obtained simultaneously, by detecting the abnormality in the abnormality detection interference light, an abnormality in a capturing state in measurement can be determined, as a result of which an abnormality in the measurement interference light can also be determined.

In an aspect of the ophthalmic apparatus disclosed herein, the light receiving element is configured to output the abnormality detection interference signal generated from the abnormality detection interference light to the processor, and the computer-readable instructions, when executed by the processor, may cause the ophthalmic apparatus to execute: detecting a position in a depth direction of a peak of the waveform of the outputted abnormality detection interference signal, and determining that the abnormality detection interference signal and the measurement interference signal are abnormal when the detected position is out of a predetermined range, the predetermined range being set based on a position in the depth direction corresponding to the predetermined length. There may be a case where, if an abnormality is occurring in a capturing state while the subject eye is being measured, the position in the depth direction of the abnormality detection interference signal could be displaced. With the above configuration, however, when the abnormality detection interference signal is out of the predetermined range, it is possible to determine the capturing state as being abnormal, and determine that an abnormality is occurring in the received interference signal (abnormality detection interference signal and measurement interference signal).

In an aspect of the ophthalmic apparatus disclosed herein, the light receiving element is configured to output the abnormality detection interference signal generated from the abnormality detection light to the processor, and the computer-readable instructions, when executed by the processor, may cause the ophthalmic apparatus to execute: detecting a peak shape of the outputted abnormality detection interference signal; and determining that the abnormality detection interference signal and the measurement interference signal are abnormal when the detected peak shape is out of a predetermined range, the predetermined range being set based on a normal peak shape, the normal peak shape being detected at a position corresponding to the predetermined length when no abnormality is occurring. There may be a case where, if an abnormality is occurring in the capturing state while the subject eye is being measured, the peak shape of the abnormality detection interference signal may wobble. With such a configuration, however, when the peak shape of the abnormality detection interference signal is out of the predetermined range, it is possible to determine the capturing state as being abnormal, and determine that an abnormality is occurring in the received interference signal (abnormality detection interference signal and measurement interference signal).

In an aspect of the ophthalmic apparatus disclosed herein, the computer-readable instructions, when executed by the processor, may cause the ophthalmic apparatus to execute: detecting a height of the peak shape of the abnormality detection interference signal; and determining that the abnormality detection interference signal and the measurement interference signal are abnormal when the detected height of the peak shape is out of a predetermined range, the predetermined range being set based on a height of the normal peak shape.

In an aspect of the ophthalmic apparatus disclosed herein, the computer-readable instructions, when executed by the processor, may cause the ophthalmic apparatus to execute detecting a width of the peak shape of the abnormality detection interference signal; and determining that the abnormality detection interference signal light and the measurement interference signal are abnormal when the detected width of the peak shape is out of a predetermined range, the predetermined range being set based on a width of the normal peak shape.

Hereinbelow, an ophthalmic apparatus <NUM> according to an embodiment will be described. As shown in <FIG>, the ophthalmic apparatus <NUM> includes a measurement unit <NUM> configured to examine a subject eye <NUM>. The measurement unit <NUM> includes an interference optical system <NUM> configured to cause reflected light reflected from the subject eye <NUM> and reference light to interfere with each other, an observation optical system <NUM> configured to observe an anterior part of the subject eye <NUM>, and an alignment optical system (not shown) configured to align the measurement unit <NUM> in a predetermined positional relationship with the subject eye <NUM>. Since an alignment optical system used in a known ophthalmic apparatus may be used as the alignment optical system, a detailed description thereof will be omitted.

The interfering optical system <NUM> is configured of a light source <NUM>, a measurement optical system, a reference optical system, an abnormality detection optical system, and a light receiving element <NUM>. The measurement optical system is an optical system configured to irradiate inside of the subject eye <NUM> with light from the light source <NUM> and guide reflected light therefrom. The reference optical system is an optical system configured to irradiate a reference surface 22a with light from the light source <NUM> and guide reflected light therefrom. The abnormality detection optical system is an optical system configured to irradiate a reflective surface 70a with light from the light source <NUM> and guide reflected light therefrom. The light receiving element <NUM> receives measurement interference light being a combination of the reflected light guided by the measurement optical system and the reflected light guided by the reference optical system, and abnormality detection interference light being a combination of the reflected light guided by the abnormality detection optical system and the reflected light guided by the reference optical system.

The light source <NUM> is a wavelength-sweeping light source, and is configured to change a wavelength of the light emitted therefrom at a predetermined cycle. When the wavelength of the light emitted from the light source <NUM> changes, a reflected position of reflected light that interferes with the reference light, among reflected light from respective parts of the subject eye <NUM> in a depth direction, changes in the depth direction of the subject eye <NUM> in accordance with the wavelength of the emitted light. Due to this, it is possible to specify positions of respective parts (such as a crystalline lens <NUM> and a retina <NUM>) inside the subject eye <NUM> by measuring the interference light while changing the wavelength of the emitted light.

The measurement optical system is configured of a beam splitter <NUM>, a beam splitter <NUM>, a focal point adjustment mechanism <NUM>, a Galvano scanner <NUM>, and a hot mirror <NUM>. Light emitted from the light source <NUM> enters the subject eye <NUM> through the beam splitter <NUM>, the beam splitter <NUM>, the focal point adjustment mechanism <NUM>, the Galvano scanner <NUM>, and the hot mirror <NUM>. Reflected light from the subject eye <NUM> is guided to the light receiving element <NUM> through the hot mirror <NUM>, the Galvano scanner <NUM>, the focal point adjustment mechanism <NUM>, the beam splitter <NUM>, and the beam splitter <NUM>.

The focal point adjustment mechanism <NUM> is provided with a convex lens <NUM> disposed on a light source <NUM> side, a convex lens <NUM> disposed on a subject eye <NUM> side, and a second driver <NUM> (shown in <FIG>) configured to move the convex lens <NUM> back and forth with respect to the convex lens <NUM> in an optical axis direction. The convex lens <NUM> and the convex lens <NUM> are disposed on an optical axis and are configured to change a position of a focal point of incident parallel light from the light source <NUM>. When the second driver <NUM> drives the convex lens <NUM> in directions of arrow A in <FIG>, the position of the focal point of the light radiated to the subject eye <NUM> changes in the depth direction of the subject eye <NUM>, the position of the focal point of the light radiated to the subject eye <NUM> is adjusted.

The Galvano scanner <NUM> includes a Galvano mirror 46a, and third driver <NUM> (shown in <FIG>) configured to tilt the Galvano mirror 46a. An irradiation position of the measurement light to the subject eye <NUM> is scanned by the third driver <NUM> tilting the Galvano mirror 46a.

The reference optical system is configured of the beam splitter <NUM> and a reference mirror <NUM>. A part of light outputted from the light source <NUM> is reflected by the beam splitter <NUM>, is directed to the reference surface 22a of the reference mirror <NUM>, and then is reflected by the reference surface 22a of the reference mirror <NUM>. Light reflected by the reference mirror <NUM> is guided to the light receiving element <NUM> through the beam splitter <NUM>. The reference mirror <NUM>, the beam splitter <NUM>, and the light receiving element <NUM> are disposed in an interferometer <NUM>, and their positions are fixed. Therefore, in the ophthalmic apparatus <NUM> of the present embodiment, a reference optical path length is constant and does not change.

The abnormality detection optical system is configured of the beam splitter <NUM>, the beam splitter <NUM>, and a mirror <NUM>. Light outputted from the light source <NUM> is reflected by the beam splitter <NUM> through the beam splitter <NUM>, is directed to the reflective surface 70a of the mirror <NUM>, and is reflected by the reflective surface 70a of the mirror <NUM>. Light reflected by the mirror <NUM> is guided through the beam splitters <NUM> and <NUM> to the light receiving element <NUM>. In the ophthalmic apparatus <NUM> of the present embodiment, a position of the mirror <NUM> is fixed. Therefore, an optical path length of the light guided by the abnormality detection optical system (may be referred to as abnormality detection light) is constant and does not change.

Further, as shown in <FIG>, in the abnormality detection optical system, the position of the mirror <NUM> is set with a zero point as a reference thereof and has been set such that an optical path length L1 from the zero point is longer than a distance from the zero point to the retina <NUM> of the subject eye <NUM> when the zero point is set to a position on the light source <NUM> side relative to the subject eye <NUM>. The zero point means a point at which an optical path length of the reference optical system (reference optical path length) coincides with an optical path length of the measurement optical system (measurement optical path length). In the present embodiment, the position of the zero point is set to a predetermined position (for example, a position subtly displaced to the light source <NUM> side from an anterior surface of a cornea <NUM>). By setting the optical path length L1 of the abnormality detection optical system from the zero point to be longer than the distance from the zero point to the retina <NUM> of the subject eye <NUM>, the reflective surface 70a of the mirror <NUM> can be detected without overlapping a measurement area of the subject eye <NUM> (area from the cornea <NUM> anterior surface to the retina <NUM>). Due to this, a position of the reflective surface 70a can be easily specified.

The light receiving element <NUM> is configured to detect the measurement interference light being the combination of the light guided by the reference optical system and the light guided by the measurement optical system and the abnormality detection interference light being the combination of the light guided by the reference optical system and the light guided by the abnormality detection optical system. The light receiving element <NUM> is configured to output interference signals according to the measurement interference light and the abnormality detection interference light when the light receiving element <NUM> receives the measurement interference light and the abnormality detection interference light. That is, a signal generated from the measurement interference light (measurement interference signal) and a signal generated from the abnormality detection interference light (abnormality detection interference signal) are outputted. These signals are inputted to a processor <NUM>. A photodiode can be implemented for example as the light receiving element <NUM>.

The observation optical system <NUM> irradiates the subject eye <NUM> with observation light through the hot mirror <NUM> and captures reflected light that is reflected from the subject eye <NUM> (that is, reflected light of the observation light). Here, the hot mirror <NUM> reflects the light from the light source <NUM> and transmits light from a light source of the observation optical system <NUM>. As a result, in the ophthalmic apparatus <NUM> of the present embodiment, it is possible to perform the measurement by the interference optical system <NUM> and the observation of the anterior part of the eye by the observation optical system <NUM> at the same time. An observation optical system used in a well-known ophthalmic apparatus can be used as the observation optical system <NUM>. For this reason, detailed configuration thereof is not explained herein.

Further, the ophthalmic apparatus <NUM> of the present embodiment is provided with a position adjuster <NUM> (shown in <FIG>) configured to adjust a position of the measurement unit <NUM> with respect to the subject eye <NUM>, and a first driver <NUM> (shown in <FIG>) configured to drive the position adjuster <NUM>. The position of the measurement unit <NUM> with respect to the subject eye <NUM> is adjusted by driving the first driver <NUM>.

Next, a configuration of a control system of the ophthalmic apparatus <NUM> according to the present embodiment will be described. As shown in <FIG>, the ophthalmic apparatus <NUM> is controlled by the processor <NUM>. The processor <NUM> includes a microcomputer (microprocessor) configured of CPU, ROM, RAM, and the like. The processor <NUM> is connected to the light source <NUM>, the first to third drivers <NUM> to <NUM>, a monitor <NUM>, and the observation optical system <NUM>. The processor <NUM> is configured to control on/off of the light source <NUM>, and drive the position adjuster <NUM>, the focal point adjustment mechanism <NUM>, and the Galvano scanner <NUM> by controlling the first to third drivers <NUM> to <NUM>. Further, the processor <NUM> is configured to control the observation optical system <NUM> to display an image of the anterior eye part captured by the observation optical system <NUM> on the monitor <NUM>.

Further, the processor <NUM> is connected with the light receiving element <NUM>, and interference signals according to intensities of the interference light (i.e., measurement interference light and abnormality detection interference light) detected by the light receiving element <NUM> are inputted to the processor <NUM>. The processor <NUM> performs Fourier transform on the interference signals from the light receiving element <NUM>, and specifies positions of respective parts of the subject eye <NUM> (anterior and posterior surfaces of the cornea <NUM>, anterior and posterior surfaces of the crystalline lens <NUM>, a surface of the retina <NUM>) and of the reflective surface 70a of the mirror <NUM>, and uses these specified positions to calculate an axial length of the subject eye <NUM>.

Subsequently, a process to detect abnormality of a measurement state when the subject eye <NUM> is measured by using the ophthalmic apparatus <NUM> according to the embodiment will be described. When the subject eye <NUM> is measured, an abnormality occurs in the interference signals due to, for example, vibration or shock acting on the ophthalmic apparatus <NUM>, and/or due to a change in oscillation wavelength (so called mode hop) that is caused by a change in current that drives the light source <NUM> or a change in the temperature of the light source <NUM>. Thus, in a state where these abnormalities are occurring, the subject eye <NUM> cannot be accurately measured. Therefore, even if a tomographic image is generated using measured data of the subject eye <NUM> in such a state, the state of the subject eye <NUM> cannot be correctly grasped. The ophthalmic apparatus <NUM> according to the present embodiment is configured to detect an abnormality in the aforementioned measurement states and to generate a tomographic image by excluding data measured during when an abnormality is occurring and using only data measured in a normal state. Hereafter, with reference to <FIG>, the process of detecting an abnormality in the measurement state when the subject eye <NUM> is being measured will be described.

As shown in <FIG>, firstly, the processor <NUM> obtains the interference signals (i.e., measurement interference signal and abnormality detection interference signal) (S12). The obtainment of the interference signals is performed by following procedures. Firstly, an examiner operates an operation member, which is not shown, such as a joystick to align the measurement unit <NUM> with respect to the subject eye <NUM>. That is, the processor <NUM> drives the position adjuster <NUM> by the first driver <NUM> in accordance with the examiner's operation on the operation member. Due to this, a position of the measurement unit <NUM> in xy-directions (vertical-horizontal directions) and a position thereof in a z-direction (a direction along which the measurement unit <NUM> moves back and forth) are adjusted with respect to the subject eye <NUM>. Further, the processor <NUM> drives the second driver <NUM> to adjust the focal point adjustment mechanism <NUM>. Due to this, a position of the focal point of light irradiated from the light source <NUM> to the subject eye <NUM> comes to be positioned at a predetermined position in the subject eye <NUM> (for example, at the anterior surface of the cornea <NUM>).

Then, the processor <NUM> takes in signals detected by the light receiving element <NUM>, while changing the frequency of light from the light source <NUM>. As has already been explained, the interference signals outputted from the light receiving element <NUM> each becomes a signal of which intensity changes over time as shown in <FIG>, and these signals include signals generated from an interference wave which is a combination of the reference light and reflected light from the respective parts (the anterior and posterior surfaces of the cornea <NUM>, the anterior and posterior surfaces of the crystalline lens <NUM>, the surface of the retina <NUM>) of the subject eye <NUM> and an interference wave which is a combination of the reference light and reflected light from the reflective surface 70a of the mirror <NUM>. The processor <NUM> performs the Fourier transform on the signals inputted from the light receiving element <NUM> to separate, from those signals, interference signal components respectively generated by the reflected light from the respective parts (the anterior and posterior surfaces of the cornea <NUM>, the anterior and posterior surfaces of the crystalline lens <NUM>, the surface of the retina <NUM>) of the subject eye <NUM> and from the reflective surface 70a (see graph at bottom of <FIG>). Due to this, the processor <NUM> can specify the positions of the respective parts of the subject eye <NUM> and of the reflective surface 70a.

Upon obtaining the interference signals, the processor <NUM> determines whether or not the abnormality detection interference signal (i.e., signal by the interference wave which is the combination of the reference light and the reflected light from the reflective surface 70a) is normal (S14). As mentioned above, the optical path length of the abnormality detection light is constant and does not change. Due to this, as shown in <FIG>, the abnormality detection interference signal after being subjected to the Fourier transform is constantly detected at a certain position in the depth direction. The optical path length L1 from the zero point of the abnormality detection optical system is set to be longer than the distance from the zero point to the retina <NUM> of the subject eye <NUM> (see <FIG>). Due to this, the position of the reflective surface 70a is detected out of the measurement area of the subject eye <NUM> (more specifically, a position deeper than the measurement area). Accordingly, by performing the Fourier transform on the interference signals which include the measurement interference signal and the abnormality detection interference signal, the abnormality detection interference signal can be specified from among the interference signals. Then, the processor <NUM> determines whether or not the specified abnormality detection interference signal is normal by determining whether or not the position in the depth direction of and a shape of a waveform (hereafter may be referred to as a peak shape) of the specified abnormality detection interference signal (more specifically, the signal waveform after the Fourier transform, for example, a point spread function signal waveform) are normal.

More specifically, the processor <NUM> determines that the abnormality detection interference signal is normal in a case where the position in the depth direction of the abnormality detection interference signal is within a predetermined range and also a height and width of the peak in the peak shape of the abnormality detection interference signal are within predetermined ranges (see <FIG>). On the other hand, the processor <NUM> determines that the abnormality detection interference signal is abnormal in a case where the position in the depth direction of the abnormality detection interference signal is out of the predetermined range, and/or where at least one of the height and width of the peak in the peak shape of the abnormality detection interference signal are out of the predetermined ranges (see <FIG>). Specifically, in the case where the position in the depth direction of the abnormality detection interference signal is out of the predetermined range, regardless of whether or not the peak shape of the abnormality detection interference signal is normal, the abnormality detection interference signal is determined as abnormal. On the other hand, in the case where the position in the depth direction of the abnormality detection interference signal is within the predetermined range, whether or not the abnormality detection interference signal is abnormal is determined based on the peak shape (peak height and width) of the abnormality detection interference signal. For example, even when the peak height of the peak shape of the abnormality detection interference signal is within the predetermined range, in a case where the width of the peak shape is out of the predetermined range, the abnormality detection interference signal is determined as abnormal. Similarly, even when the width of the peak shape of the abnormality detection interference signal is within the predetermined range, in a case where the peak height of the peak shape is out of the predetermined range, the abnormality detection interference signal is determined as abnormal. It should be noted that each of the "predetermined ranges" may not be limited to a particular range, but may be suitably selected.

In the case where the abnormality detection interference signal is determined as not normal (abnormal) (NO in Step S14), the processor <NUM> determines all the interference signals (i.e., measurement interference signal and abnormality detection interference signal) obtained at step S12 as abnormal (S16). When the ophthalmic apparatus <NUM> of the present embodiment performs measurement in a normal state, the abnormality detection interference signal after being subjected to the Fourier transform is detected in a known peak shape at a known position in the depth direction. In other words, if the abnormality detection interference signal is not detected normally, it can be determined that the measurement has not been performed in the normal state by the ophthalmic apparatus <NUM> due to some cause (e.g., vibration or shock, mode hop). When an abnormality occurs in the measurement as above, it can be determined that, not only the abnormality detection interference signal but also the measurement interference signal obtained simultaneously therewith has not been measured normally. Accordingly, the processor <NUM> determines that the measurement interference signal is also abnormal when the abnormality detection interference signal is determined as abnormal (NO in Step S14). Then, the processor <NUM> discards data of all the interference signals (measurement interference signal and abnormality detection interference signal) that have been determined as abnormal (S18).

On the other hand, in the case where the abnormality detection interference signal is determined as normal (YES in step S14), the processor <NUM> determines that all the interference signals (i.e., measurement interference signal and abnormality detection interference signal) obtained in step S12 have been measured normally (S20). That is, because the abnormality detection interference signal after being subjected to the Fourier transform is detected normally, the signal is determined as having been measured in the normal state. Due to this, the measurement interference signal obtained simultaneously with the abnormality detection interference signal is also determined as having been measured in the normal state. Then, the processor <NUM> stores data of all the interference signals (measurement interference signal and abnormality detection interference signal) in a memory (not shown) (S22).

The above processing is performed for each scan angle. As a result of this, since the data measured in the state where an abnormality is occurring is discarded, a tomographic image constituted of only the data measured in the normal state can be generated. When the data measured in the abnormal state is included in the tomographic image, the tomographic image will include a distortion. Such distortion makes it difficult to evaluate the state of the subject eye <NUM> correctly. By generating the tomographic image with the data measured in the abnormal state excluded such that a distortion caused by the abnormality in the measurement state can be excluded, the state of the subject eye <NUM> can be correctly evaluated.

Although in the present embodiment the zero point is set to the position on the light source <NUM> side relative to the subject eye <NUM>, and the optical path length L1 from the zero point of the abnormality detection optical system is set to be longer than the distance from the zero point to the retina <NUM> of the subject eye <NUM>, such configuration is non-limiting. The position of the reflective surface 70a only needs to be configured so as to be detected out of the measurement area of the subject eye <NUM>, for example, the optical path length from the zero point of the abnormality detection optical system may be set to be shorter than a distance from the zero point to the cornea <NUM> of the subject eye <NUM>. The zero point may be set to a position away from the light source <NUM> relative to the subject eye <NUM> and an optical path length L2 from the zero point of the abnormality detection optical system may be set to be longer than the distance from the zero point to the cornea <NUM> of the subject eye <NUM> (see <FIG>), and may be set to be shorter than the distance from the zero point to the retina <NUM> of the subject eye <NUM>. Further, the optical path length of the abnormality detection optical system may be longer than a distance from the light source <NUM> to the zero point, and may be set to a position at which the optical path length of the abnormality detection optical system becomes shorter than the distance from the light source <NUM> to the zero point. For example, the optical path length of the abnormality detection optical system may be longer by the optical path length L1 from the zero point (at a position shown in <FIG>), and set to be shorter by the same optical path length L1 from the zero point. In either case, since the distance from the zero point is the same, the abnormality detection interference signal can be detected in the same position in the obtained data.

In the present embodiment, the positions of the zero point and the mirror <NUM> are fixed at predetermined positions, but such configuration is non-limiting. The position of the reflective surface 70a needs only to be detected out of the measurement area of the subject eye <NUM>, and for example the position of the zero point may be configured to be adjustable, and also the position of the mirror <NUM> may be configured to be adjustable. In such a case, by adjusting the position of the mirror <NUM> with the zero point as a reference after adjusting the position of the zero point and setting the optical path length from the zero point of the abnormality detection optical system to be a predetermined length as aforementioned, the position of the reflective surface 70a can be easily specified.

In the ophthalmic apparatus <NUM> of the present embodiment, the abnormality detection optical system is provided with the mirror <NUM>, but such configuration is non-limiting. The optical path length of the abnormality detection optical system only needs to be configured to guide known abnormality detection light, for example, the optical path length of the abnormality detection optical system may be configured to guide the known abnormality detection light by using optical fiber a fiber length of which is adjusted to be a predetermined length in advance. Further, in the abnormality detection optical system, a scatterer may be provided instead of the mirror <NUM>. By providing the scatterer in the abnormality detection optical system, axis displacement of the abnormality detection light can be suppressed.

In the present embodiment, whether or not the obtained interference signal(s) are normal is determined, and the data determined as abnormal is discarded, but such configuration is non-limiting. For example, the processor <NUM> may determine whether an interference signal at each scan angle is normal or not on one-by-one basis after having obtained (stored) all the interference signals at relevant scan angles. In this case, the processor <NUM> may not discard the data determined as abnormal, and may generate a tomographic image by selecting the data determined as normal without using the data determined as abnormal.

Further, in the present embodiment the processor <NUM> which the ophthalmic apparatus <NUM> comprises is configured to perform the abnormality detection process as described above, but such configuration is non-limiting. For example, data of the interference signals obtained by the ophthalmic apparatus <NUM> of the present embodiment may be inputted to an external processor which performs the abnormality detection process so as to generate a tomographic image.

Further, the ophthalmic apparatus <NUM> of the present embodiment is an ophthalmic apparatus of Fourier domain type (SS-OCT type) comprising the wavelength-sweeping light source <NUM>, but such configuration is non-limiting. For example, the ophthalmic apparatus may be of Spectral domain type (SD-OCT type) or may be of Time domain type (TD-OCT type).

Claim 1:
An ophthalmic apparatus (<NUM>) comprising:
a light source (<NUM>);
a measurement optical system configured to irradiate a subject eye (<NUM>) with light from the light source (<NUM>) and to guide reflected light from the subject eye (<NUM>), the measurement optical system having a measurement optical path length;
a reference optical system configured to guide the light from the light source (<NUM>) to form reference light, the reference optical system having a reference optical path length;
an abnormality detection optical system configured to have an abnormality detection optical path length (L1, L2) from a zero point adjusted to a predetermined length to an end position and to guide the light from the light source (<NUM>) to form abnormality detection light, the zero point being a point at which the reference optical path length coincides with the measurement optical path length;
a light receiving element (<NUM>) configured to receive measurement interference light and abnormality detection interference light, the measurement interference light being a combination of the reflected light from the subject eye (<NUM>) and the reference light, the abnormality detection interference light being a combination of the abnormality detection light and the reference light, the light receiving element (<NUM>) being configured to output measurement interference signals and abnormality detection interference signals according to the received measurement interference light and abnormality detection interference light;
a processor (<NUM>); and
a memory storing computer-readable instructions therein,
wherein
the end position of the optical path length (L1, L2) is set to be detected out of a measurement area of the subject eye (<NUM>), wherein the measurement area is an area from an anterior surface of a cornea (<NUM>) to a retina (<NUM>) of the subject eye (<NUM>),
the computer-readable instructions, when executed by the processor (<NUM>), cause the ophthalmic apparatus (<NUM>) to execute:
obtaining the measurement interference signal and the abnormality detection measurement signal;
determining that the abnormality detection interference light is abnormal when at least one of a position of a waveform in a depth direction and a shape of the waveform of an abnormality detection interference signal is out of a predetermined range, and
determining that the measurement interference signal is abnormal when it is determined that the abnormality detection interference light is abnormal.