JP2007252413A - Measuring instrument for ophthalmology - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To execute measurement satisfying requested measurement accuracy even when using a plurality of light receiving parts of a smaller pixel density than the condition of satisfying the measurement accuracy requested for a measurement area. <P>SOLUTION: A first light source part 1 emits a luminous flux for illuminating the fundus. A first illumination optical system 10 illuminates the luminous flux from the first light source part 1 on the fundus of an eye 100 to be measured as roughly a point image. A first light receiving optical system 20 has a first light receiving part 21-1 to a fourth light receiving part 21-4 of the smaller number of pixels than the number of pixels for satisfying the measurement accuracy requested for the measurement area, and the luminous flux from a measurement object area is divided and received by the first light receiving part 21-1 to the fourth light receiving part 21-4. A measurement part measures the aberration of the eye 100 to be measured of the entire measurement area on the basis of output from the first light receiving part 21-1 to the fourth light receiving part 21-4. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an ophthalmic measuring apparatus, and more particularly to an ophthalmic measuring apparatus that can repeatedly perform wavefront measurement in a short time.

In conventional ophthalmic optical devices, Patent Documents 1 and 2 disclose devices that measure the wavefront aberration of an eye using two Shack-Hartmann wavefront sensors.
In Patent Document 1, the first light receiving portion and the third light receiving portion correspond to the Shack-Hartmann wavefront sensor in FIG. 12, but the first light receiving portion receives the reflected light beam from the cornea and measures the shape of the cornea. The three light receiving units are different from each other so as to receive the reflected light beam from the retina and measure the optical characteristics.
Patent Document 2 discloses a configuration in which reflected light from the retina is received by a low-sensitivity Shack-Hartmann wavefront sensor and a high-sensitivity Shack-Hartmann wavefront sensor. Here, the two Shack-Hartmann wavefront sensors differ in sensitivity and are not intended for high-speed shooting.
Patent Document 3 synchronizes the start time of the dead time of the first camera and the end time of the dead time of the second camera, and sets the light emission start time of the first light emission immediately before the start of the dead time of the first camera. On the other hand, a high-speed continuous shooting system is disclosed in which the light emission start time of the second light emission is within the dead time of the first camera and after the dead time of the second camera is over.
Patent Document 4 receives scattered light from each of these light sources, a light source that generates a plurality of light beams, an optical imaging system that projects light beams to different positions in the target optical system, and each of the scattered lights. A system for measuring aberrations of a three-dimensional structure is disclosed that includes a wavefront sensor that detects the wavefront of the three-dimensional structure.
Furthermore, Patent Document 5 discloses an aberration analysis from end to end of a visual system by a pre-correction system that is positioned between the projection optical system and the eye and compensates for the light beam incident on the eye to be measured with respect to the aberration of the eye. A possible dynamic range expansion technique for wavefront sensors is disclosed.

JP-A-11-137520 JP 2004-81725 A Japanese Patent Laying-Open No. 2005-275305 JP 2005-506107 A JP-T-2004-500195

The measured eye aberration varies with eye movement. In addition, tears on the cornea also change over time, which also causes aberration changes. Further, the lens is adjusted according to the distance when looking at near or far away objects, and this also changes the aberration. Although this change has various frequency components, it is considered that the maximum frequency is about 20 Hz. Considering the sampling theorem, the number of measurements in the time direction needs to be measured, for example, 40 times or more per second, and the need for high-speed measurement of eye aberrations is increasing.
The Shack-Hartmann wavefront sensor uses a CCD to capture an image. The CCD used here is required to have a specification that can capture weak light with low noise. For example, the Shack-Hartmann wavefront sensor has a lenslet array having lenslets arranged in two dimensions (the lenslet array is composed of small lenses of about 0.2 mm square, for example), and typically has a size of 1000 × 1000 pixels. It consists of a digital CCD. Wavefront aberration measurement using a Shack-Hartmann wavefront sensor can be measured with high accuracy when measured with a digital CCD having a low noise of about 1000 × 1000.

However, in the case of a CCD having such a specification, it is conceivable that there is a performance limitation that the time for reading out the electric charge stored in the CCD after exposure cannot be made very fast. For example, in the case of a digital CCD of about 1000 × 1000, the current number of repeated measurements is about 20 times per second. This is determined by the sum of the exposure time and the image data read time. The time required for reading the image data is determined as follows. The readout speed per pixel is typically about 66 MHz for measurement at present. For example, since the true pixel count of a 1000 × 1000 CCD, that is, a 1 million pixel CCD is 1280 × 1024, the readout time is about 20 ms as shown in the following equation.
(Time required to read one screen) = 1280 × 1024/66000000
= 0.019859
In other words, when an exposure of about 20 ms is applied, a total time of about 40 ms takes a total of about 40 ms per image, and information is captured at about 25 frames per second (FPS). Furthermore, even if the effort is made to reduce the exposure time so that the exposure time is almost zero, it is assumed that the number of captures only increases to about 50 FPS. Thus, in such a CCD in which the data transfer time is longer than the exposure time, the number of images obtained per second does not increase so much even if the exposure time is shortened.
In view of the above points, the present invention performs measurement that satisfies the required measurement accuracy even when a plurality of light receiving units having a smaller pixel density than the condition that satisfies the measurement accuracy required for the measurement area is used. It is an object of the present invention to provide an ophthalmic measurement apparatus to be performed. In addition, the present invention uses a plurality of, in particular, four Shack-Hartmann wavefront sensors to increase the number of images, and uses four CCDs with a small number of pixels without degrading the performance of aberration measurement. An object of the present invention is to provide an ophthalmic measurement apparatus that can shorten the reading time and capture more images per unit time.

According to the first solution of the present invention,
A light source unit that emits a light beam for illuminating the fundus;
An illumination optical system that illuminates the light flux from the light source unit as a substantially point image on the fundus of the eye to be measured;
It has a plurality of light receiving portions having a number of pixels smaller than the number of pixels satisfying the measurement accuracy required for the measurement area, and the light beams from the measurement target area are divided and received by the plurality of light receiving portions. Receiving optical system,
Based on outputs from the plurality of light receiving units, a measuring unit that measures the wavefront aberration of the eye under measurement in the entire measurement area;
An ophthalmic measurement apparatus is provided.

  Conventionally, the number of required CCD pixels was originally about 1000 × 1000 pixels. However, in the present invention, for example, four VGA level 640 × 480 CCDs can realize a high-speed sensor with the same accuracy. Further, in the present invention, when the number of pixels of the CCD is about 1000 × 1000 pixels, data reading of about 20 ms can be read out in about 5 ms with the same data amount and pixel clock.

1. Apparatus Configuration 1.1 Optical System 1.1.1 First Embodiment (Half Mirror Type)
FIG. 1 shows a diagram of an optical system using a half mirror as a mirror.
This apparatus includes a first light source unit 1, a first illumination optical system 10, a first light receiving optical system 20, an anterior ocular segment observation unit 30, an anterior ocular segment illumination unit 40, and a target optical unit 50. And the eye 100 to be measured is measured.
The first light source unit 1 emits light at a predetermined timing and emits a light beam having a first wavelength. The first light source unit 1 preferably has high spatial coherence and not high temporal coherence. Here, as an example, the first light source unit 1 employs an SLD (super luminescence diode), and a point light source with high luminance can be obtained. Note that the first light source unit 1 is not limited to the SLD, and even the one having high coherence in both space and time, such as a laser, can be used by appropriately reducing the time coherence by inserting a rotating diffusion plate or the like. it can. And even if the LED does not have high coherence in space and time, it can be used by inserting a pinhole or the like at the position of the light source in the optical path as long as the amount of light is sufficient. Moreover, the wavelength of the 1st light source part 1 for illumination can use near infrared light (about 840 nm) or the wavelength (for example, 780 nm) of an infrared region, for example.

The first illumination optical system 10 includes, for example, a lens such as an adjustment unit 11, a beam splitter 12, a condenser lens, an objective lens, a cylinder lens, and / or a relay lens. The first illumination optical system 10 illuminates the light beam from the first light source 1 as a substantially point image on the fundus of the eye 100 to be measured. The adjustment unit 11 moves the roof-shaped mirror in accordance with the sphericity of the eye 100 to be measured, and forms a focused point image on the first light receiving unit 21-1 to the fourth light receiving unit 21-4. Adjust as follows. The beam splitter (B2) 12 reflects visible light and reflects S-polarized light and transmits P-polarized light in a region of about 810 nm to 870 nm, for example, for the purpose of wavefront measurement.
Incident light from the first light source unit 1 to the eye 100 to be measured is decentered to change the incident position of the light flux in a direction perpendicular to the optical axis, and can prevent noise from being reflected by preventing the vertex reflection of the lens and cornea. The stop has a diameter smaller than the effective range of the Hartmann plate of the conversion member, and can perform so-called single-pass aberration measurement in which the aberration of the eye affects only the light receiving side.
In addition, after the incident light beam emitted from the first light source unit 1 has a common optical path with the measurement light beam diffusely reflected from the fundus, it travels in the same manner as the measurement light beam diffusely reflected from the fundus. To do. However, in the single pass measurement, the diameters of the respective light beams are different, and the beam diameter of the incident light beam is set to be considerably smaller than the measurement light beam. Specifically, the beam diameter of the incident light beam may be, for example, about 1 mm at the pupil position of the eye 100 to be measured, and the beam diameter of the measurement light beam may be about 7 mm. Note that double-pass measurement can also be performed by appropriately arranging the optical system.

The first light receiving optical system 20 includes a first light receiving unit (Hartmann sensor 1) 21-1 to a fourth light receiving unit (Hartmann sensor 4) 21-4, and separation reflection units (half mirrors) 22 to 24. The first light receiving optical system 20 is for branching the reflected light from the eye 100 to be measured into a plurality of optical paths and guiding the light to the first light receiving unit 21-1 to the fourth light receiving unit 21-4. The separation reflection units 22 to 24 are half mirrors, and separate the light beam so that the light beam from the measurement area can be divided and received in a partially overlapping state. The first light receiving unit 21-1 to the fourth light receiving unit 21-4 are arranged eccentrically in each optical path. For example, it is conceivable that the first light receiving portions 21-1 and 21-2 are generally disposed on the front side of the paper, and the light receiving portions 21-3 and 21-4 are generally disposed on the other side of the paper. The first light receiving unit 21-1 to the fourth light receiving unit 21-4 may be arranged so as to straddle each optical axis so that the light beams can be divided and received in a partially overlapping state.
The first light receiving unit 21-1 to the fourth light receiving unit 21-4 include, for example, a CCD and a conversion member (eg, Hartmann plate). The conversion member is a wavefront conversion member having a lens unit for converting the reflected light beam into at least 17 plural beams. As the conversion member, a plurality of micro Fresnel lenses arranged in a plane orthogonal to the optical axis can be used. The reflected light from the fundus is condensed on the CCD via the conversion member.

The anterior ocular segment observing unit 30 includes, for example, a fifth light receiving unit 31 including a relay lens and a CCD, and a reflecting mirror (B1) 32. For example, the pattern of the anterior ocular segment illuminating unit 40 such as platide ring and kerat ring However, the light beam reflected and returned from the anterior eye part of the eye 100 to be measured is observed. If a telecentric diaphragm is provided, the pupil diameter can be measured accurately. The reflecting mirror 32 is a dichroic mirror that reflects only 900 nm or more, for example.
The anterior ocular segment illumination unit 40 includes a second light source unit that emits a light beam having a second wavelength, and irradiates the anterior eye segment with a predetermined pattern using, for example, platid ring or kerat ring, with the light beam from the second light source unit. To do. In the case of keratoling, a pattern only near the center of curvature of the cornea can be obtained from the kerato image. Here, for example, the second wavelength of the light beam emitted from the second light source unit is different from the first wavelength (here, about 840 nm), and near infrared light having a long wavelength of about 940 nm can be selected.
The target optical unit 50 includes, for example, a landscape chart of the eye 100 to be measured, an optical path for projecting a target for fixation or clouding, and includes a fixation target 51, a reflecting mirror 52, and a relay lens. Prepare. The fixation target 51 can be irradiated onto the fundus with the light flux from the first light source unit 1, and the image of the eye 100 to be measured is observed. The fixation target 51 is illuminated with visible light. The reflecting mirror 52 is a dichroic mirror that transmits visible reflection, for example, 900 nm or more.
Although the above-described optical system has been mainly described as a single path with a thin incident light beam, the present invention can also be applied to an ophthalmic measurement apparatus as a double path with a large incident light beam. At this time, the optical system is arranged in a double-pass configuration, but the measurement / calculation processing by the calculation unit is the same.
(Conjugate relationship)
The CCD of each of the fundus of the eye 100 to be measured, the first light source unit 1, and the first light receiving unit 21-1 to the fourth light receiving unit 21-4 is conjugate. Further, the pupil (iris) of the eye 100 to be measured, the respective conversion members of the first light receiving unit 21-1 to the fourth light receiving unit 21-4, the stop on the measurement light incident side of the first illumination optical system 10, the front The eye observation unit 30 is conjugate.

1.1.2 Second Embodiment (Kirikaki Mirror Type)
FIG. 2 shows a diagram of an optical system composed of sharp mirrors.
The apparatus includes a first light source unit 1, a first illumination optical system 10, a second light receiving optical system 20 ′, an anterior ocular segment observation unit 30, an anterior ocular segment illumination unit 40, and a target optical unit 50. And the eye 100 to be measured is measured. The optical system is the same as the half mirror type optical system shown in FIG. 1 except that a mirror with a clear mirror of the second light receiving optical system 20 ′ is used.
The second light receiving optical system 20 ′ includes a first light receiving portion (Hartmann sensor 1) 21-1 to a fourth light receiving portion (Hartmann sensor 4) 21-4, divided reflection portions (cutting mirrors) 22-2 and 23-2. , 24-2. The division | segmentation reflection parts 22-2 to 24-2 exist only in a required place, and reflect the reflected light from the to-be-measured eye 100 partially. Although there are other combinations of how to split the dividing reflector, one implementation example will be described here. The split reflection part 22-2 exists only on the other side of the page. As can be seen in the figure, the split reflection section 23-2 is only on one side across the optical axis. The same applies to the divided reflection section 24-2. Although it is difficult to understand in the figure, the first light receiving parts 21-1 and 21-2 correspond to the arrangement of the divided reflection parts 22-2, 23-2, and 24-2. It can be considered that 21-3 and 21-4 are generally arranged on the other side of the drawing.

1.2 Arrangement of 4 CCDs FIG. 3 is an explanatory diagram showing the arrangement of 4 CCDs. FIG. 3A shows the case of a half mirror, and FIG. 3B shows the case of a scratched mirror.
When a half mirror is used as in the optical system of the first embodiment, the images captured by the CCDs partially overlap as shown in FIG. On the other hand, when a scratch mirror is used as in the optical system of the second embodiment, the captured images do not overlap as shown in FIG.

1.3 Electrical System FIG. 4 is a block diagram of an ophthalmic measuring apparatus.
The electrical system of the present embodiment includes a measurement unit 600, a control unit 610, a first drive unit 620, a display unit 700, and a memory 800. The measurement unit 600 includes a signal (2) from the fifth light receiving unit 31 of the anterior segment observation unit 30, a signal (4) from the first light receiving unit 21-1, and a second light receiving unit 21-2. Signal (5), a signal (6) from the third light receiving unit 21-3, and a signal (7) from the fourth light receiving unit 21-4 are input.
The measurement unit 600 measures the aberration of the eye 100 to be measured at short intervals based on the outputs from the first light receiving unit 21-1 to the fourth light receiving unit 21-4. The measuring unit 600 includes a signal (4) from the first light receiving unit 21-1, a signal (5) from the second light receiving unit 21-2, a signal (6) from the third light receiving unit 21-3, and a fourth light receiving unit. The signal (7) from the unit 21-4 and the signal (2) from the fifth light receiving unit 31 of the anterior segment observation unit 30 are input, and the optical characteristics of the eye 100 to be measured are obtained based on, for example, the tilt angle of the luminous flux. . The signal from the fifth light receiving unit 31 of the anterior ocular segment observation unit 30 is necessary to obtain information for misalignment of the eye and the measuring device, correction of eccentricity, and analysis at the center of the pupil. The measurement unit 600 appropriately outputs signals or other signals / data corresponding to the calculation results to the control unit 610 that controls the electric drive system, the display unit 700, and the memory 800, respectively.
Based on the control signal from the measurement unit 600, the control unit 610 controls turning on / off of the second light source unit of the first light source unit 1 and the anterior segment illumination unit 40, or the first light receiving unit 21-1. To control exposure / read-out of the CCD of the fourth light receiving unit 21-4. The control unit 610 outputs a signal (1) to the first light source unit 1 based on a signal corresponding to the calculation result in the measurement unit 600, and outputs a signal (3) to the anterior ocular segment illumination unit 40. The signal (4) is output to the first light receiving unit 21-1, the signal (5) is output to the second light receiving unit 21-2, and the signal is output to the third light receiving unit 21-3. (6) is output, the signal (7) is output to the fourth light receiving unit 21-4, and the signal (8) is output to the adjustment unit 11.
The first drive unit 620 is controlled by the measurement unit 600 and the control unit 610, and moves the roof-shaped mirror according to the sphericity of the eye 100 to be measured, so that the first light receiving units 21-1 to 21-1 of each Hartmann sensor. The fourth light receiving unit 21-4 is adjusted so that a focused point image can be formed.
The display unit 700 displays a result (aberration analysis or the like) during or after the arithmetic processing as a diagram, a table, data, a graphic, a moving image / still image, or the like. Or, output to another device.
The memory 800 appropriately stores various data such as measured data, intermediate data, and calculation result data, and preset values such as an exposure time t and the number of measurements P as necessary. Measurement unit 600 reads / writes data to / from memory 800 as appropriate.

2. Aberration Analysis 2.1 Comparison of Reading Time FIG. 5 is a diagram showing the effect of shortening the reading time of the CCD. FIG. 5A shows an example of a single CCD having about 1000 × 1000 pixels. FIG. 5B shows an example of a VGA level 640 × 480 CCD. As shown in FIG. 5B, compared with one CCD having about 1000 × 1000 pixels, four 640 × 480 CCDs having a VGA level have a short readout time for one exposure. It can be seen that a larger number of images can be captured by forming a single image using a plurality of these.

2.2 Flowchart FIG. 6 is a flowchart of wavefront aberration measurement.
The measurement unit 600 aligns the eye at the measurement position based on the anterior segment image obtained on the fifth light receiving unit 31 (step S01). Next, the measurement unit 600 captures images from the four light receiving units (Hartmann sensors) (step S03). For this purpose, the measurement unit 600 controls the four CCDs included in the first light receiving unit 21-1 to the fourth light receiving unit 21-4 by the control unit 610, exposes them, and captures an image. Next, the measurement unit 600 performs image processing on the image captured in step S03, and obtains a point image position (step S05). The measuring unit 600 reads the images captured by the first light receiving unit 21-1 to the fourth light receiving unit 21-4, and performs image processing on the images to obtain the point image position.
Next, the measurement unit 600 performs affine transformation using the calibration parameters of the apparatus stored in the memory 800 in advance, and converts the position of the point image obtained on the CCD into a position on the pupil. (Step S07). Here, the measurement unit 600 can execute two types of calibration as affine transformation, for example, calibration of the lenslet array of the Hartmann plate and calibration of the CCD placement error. In the present embodiment, the position of the point image obtained on each CCD can be converted to a position on the pupil by two-step affine transformation. In this example, the measurement unit 600 performs the two-stage affine transformation, but only one of the affine transformations may be used. Details of calibration parameters by affine transformation will be described later. Next, the measurement unit 600 obtains wavefront aberration by using a normal Shack-Hartmann wavefront sensor method (step S09). Next, the measurement unit 600 reads the obtained wavefront aberration analysis result from the memory (storage unit) 800, and based on the analysis result, for example, an eye aberration data map, a corneal aberration data map, an overhead view, A process for appropriately displaying numerical data, Zernike coefficients, polynomials, and the like is executed, displayed on the display unit 700, and stored in the memory 800 (step S10).
As described above, the measuring unit 600 calibrates the position of the point images of the plurality of images obtained by the four light receiving units and combines them into one image, and then, based on the synthesized one image, the wavefront aberration However, the measurement unit 600 obtains a plurality of wavefront aberrations for the plurality of images based on the plurality of images obtained by the four light receiving units, and then calibrates the position of the plurality of wavefront aberrations to obtain one sheet. It is also possible to synthesize the image. In the latter case, step S07 and step S09 in the illustrated flowchart may be interchanged so that step S09 is performed after the process of step S09 is performed as the processing order.

2.3 Wavefront aberration analysis (Zernike analysis and RMS)
The details of the method for obtaining the wavefront aberration with the Shack-Hartmann wavefront sensor will be described below.
FIG. 7 is a flowchart for obtaining the wavefront.
The measuring unit 600 obtains the position of the point image from the Hartmann image (step S91). The measuring unit 600 reads each point image (position) from the memory 800 and obtains a correspondence between the reference positions (step S93). Next, the measuring unit 600 obtains point image position deviations Δx and Δy from the correspondence between the point image position and the reference position (step S95). Next, the measurement unit 600 analyzes the wavefront aberration by obtaining the wavefront W (X, Y) from the position (X, Y) of the reference point and the deviations Δx, Δy as described below (step S97). ).

Next, wavefront aberration analysis will be described. Therefore, a method for calculating the Zernike coefficient c _i ^2j-i from a generally known Zernike polynomial will be described. The Zernike coefficient c _i ^2j-i is important for grasping the optical characteristics of the eye 100 to be measured based on the inclination angle of the light beam obtained by the CCD through the Hartmann plate by each light receiving unit (Hartmann sensor), for example. Parameter.
The wavefront aberration W (X, Y) of the eye 100 to be measured is expressed by the following expression using the Zernike coefficient c _i ^2j−i and the Zernike polynomial Z _i ^2j−i .

ただし、（Ｘ，Ｙ）はハルトマン板の縦横の座標である。
また、波面収差Ｗ（Ｘ，Ｙ）は、ＣＣＤの縦横の座標を（ｘ、ｙ）、ハルトマン板とＣＣＤの距離（ハルトマン板のマイクロレンズの焦点距離）をｆ、ＣＣＤで受光される点像の移動距離を（Δｘ、Δｙ）とすると、次式の関係が成り立つ。

However, (X, Y) are the vertical and horizontal coordinates of the Hartmann plate.
The wavefront aberration W (X, Y) is expressed by (x, y) in the vertical and horizontal coordinates of the CCD, f in the distance between the Hartmann plate and the CCD (focal length of the micro lens on the Hartmann plate), and a point image received by the CCD. If the movement distance is (Δx, Δy), the following relationship is established.

ここで、ゼルニケ多項式Ｚ_ｉ ^２ｊ−ｉは、次式で表される。
具体的には、図１１に、（ｒ，ｔ）座標のゼルニケ多項式の図、及び、図１２に、（ｘ，ｙ）座標のゼルニケ多項式の図をそれぞれ示す。

Here, the Zernike polynomial Z _i ^2j−i is expressed by the following equation.
Specifically, FIG. 11 shows a Zernike polynomial of (r, t) coordinates, and FIG. 12 shows a Zernike polynomial of (x, y) coordinates.

The Zernike coefficients c _i ^2j−i can be obtained with specific values by minimizing the square error represented by the following equation.

Where W (X, Y): wavefront aberration, (X, Y): Hartmann plate coordinates, (Δx, Δy): distance of movement of the point image received by the CCD, f: distance between the Hartmann plate and the CCD.

The calculation unit 600 calculates Zernike coefficients c _i ^2j−i and uses them to obtain eye optical characteristics such as spherical aberration, coma aberration, and astigmatism. In addition, the calculation unit 600 calculates the aberration amount RMS _i ^2j−i using the Zernike coefficient c _i ^{2j−i according} to the following equation.

3. Calibration 3.1 Calibration of the Hartmann Plate Lenslet Array FIG. 8 is an explanatory diagram showing how to calibrate the lenslet array and determine the reference points.
The intensity sensor 60-1 indicates an intensity measurement CCD placed at the position of the pupil. The intensity sensor 60-1 placed at the position of the pupil includes a CCD 61. The CCD 61 corresponds to the calibration light source system 60-2 and corresponds to the center of the small lens and the center of gravity of the light beam. The calibration light source system 60-2 is a light source system installed on the Hartmann sensor side. The calibration light source system 60-2 includes a point light source 62 and a pinhole 63. The calibration light source system 60-2 is installed in a state where the CCD of the Hartmann sensor is removed and only the lenslet array is left. In this measurement, it is desirable that the same wavelength as that of the light source 1 is selected. As the point light source, a combination of a halogen lamp, an interference filter, and a pinhole can be used.

First, the CCD 61 is placed as an intensity sensor at the pupil position, and the calibration light source system 60-2 is installed on the Hartmann sensor side. The measurement unit 600 controls the light source 62 with the control unit 610 to irradiate the CCD 61 with a light beam, and the CCD 61 measures the intensity of light from the light source 62. Thereby, the relationship between the small lens of the Hartmann plate and the position on the pupil is obtained. That is, the absolute position of the reference point on the pupil is obtained in the analysis of the Hartmann sensor.
Although the number of small lenses of the lenslet array constituting the Hartmann plate is usually several tens to several hundreds, it is not necessary to measure all of them in actual calibration. Since the lenslet array is used with accurate position accuracy, such as BOE made using semiconductor manufacturing technology, calibration data is taken with several lenslet arrays and affine transformation is performed. The conversion process parameters such as are determined by the least square method or the like.
The affine transformation is used to relate the position of the lenslet array and the position of the pupil. The affine transformation is expressed by the following equation.
x ′ = A _L1 x + B _L1 y + C _L1
y ′ = A _L2 x + B _L2 y + C _L2
The following lenslet array calibration parameters are stored in a memory (storage device).
A _L1 , B _L1 , C _L1
A _L2 , B _L2 , C _L2

3.2 Calibration of CCD placement error FIG. 9 is an explanatory diagram for calibration of CCD placement error of each Shack-Hartmann sensor.
FIG. 9 (a) shows a point image obtained when measuring a non-aberrated model eye with a CCD, and FIG. 9 (b) shows the CCD of the first light receiving unit 21-1 to the fourth light receiving unit 21-4. The point images obtained in are shown respectively. In FIG. 9B, it is necessary to obtain affine transformation parameters with four CCDs. The point image position determined from the absolute position of the reference point obtained previously is shown. Although it is not always in order as shown in the figure, it is shown in this way for simplicity of illustration.
In general, a CCD is assembled with good accuracy as an optical instrument. However, there are cases where the optical axis is slightly rotated, so-called tilting occurs, or the position is displaced in a plane perpendicular to the optical axis. This is a small amount, but as shown in the figure (the figure is exaggerated), the point images that can be observed with each CCD when the non-aberration model eye is measured are moved or distorted. There may be. For example, in FIG. 9A, only distortion and position movement due to the lenslet array are added, and distortion and positional deviation due to the CCD are added on the CCD in FIG. 9B.

The point image on the CCD shown in FIG. 9A and the position of the CCD obtained by the previous measurement shown in FIG. 9B and the arrangement of the point image when there is no rotation error (reference point). There is a one-to-one correspondence between them. The measurement unit 600 makes this correspondence and approximates the relationship between the arrays of two point images by affine transformation expressed by the following equation.
x ′ = A _C1 x + B _C1 y + D _C1
y ′ = A _C2 x + B _C2 y + D _C2
The following calibration parameters for the CCD are stored in a memory (storage device) 800.
A _C1 , B _C1 , D _C1
A _C2 , B _C2 , D _C2
Next, FIG. 10 shows a flowchart for obtaining the position calibration of the apparatus using a model lens having no aberration.
The measuring unit 600 places and measures a model eye whose aberration is known in advance at the position of the eye 100 to be examined (step S71). Next, the measurement unit 600 captures images of the aberration-free model eyes from the four units of the first light receiving unit 21-1 to the fourth light receiving unit 21-4 (step S73). The measurement unit 600 reads out the images taken from the four light receiving units, and obtains a relational expression of the positional relationship between the pixels of the four CCDs from the place where the taken images overlap (step S75). Here, for example, the measurement unit 600 approximates the positional relationship between two point images by affine transformation as described above, and obtains a calibration parameter. Calibration parameters are calculated from the relational expression obtained in step S75 and stored in the memory 800 (step S77).

4). Modified Example 4.1 Configuration for Shifting by Half Pixel FIG. 13 is an explanatory diagram showing a configuration for shifting a plurality of light receiving units (CCD) by half a pixel. In the example of this figure, the arrangement of the CCDa of any one light receiving unit and the CCDb of any other light receiving unit is shown.
Examples of the shape of one pixel of the CCD include a square and a rectangle. In the case of a rectangle, the amount of information per unit length on the long side is smaller than that on the short side. Therefore, in this modification, the two CCDs are arranged so as to be shifted by half a pixel on the long side. In addition, you may shift by a half pixel to the short side. As a result, the amount of information on the long side can be increased, and highly accurate measurement is possible. For example, if the CCDa of the first light receiving unit is arranged so that the optical axis coincides with the center of the pixel at the center, the CCDb of the second light receiving unit is the boundary between the pixel at the center and the adjacent pixel. So that the optical axes coincide with each other. Or you may arrange | position reversely.
As described above, the CCDa and the CCDb are arranged so as to be shifted from each other by half a pixel, and the measurement unit 600 measures the aberration with higher accuracy based on the output from the CCDa and the CCDb than on the output from one light receiving unit. Can be configured.

  The present invention can be widely applied to ophthalmic measuring devices, surgical devices, and the like.

Diagram of an optical system that uses a half mirror as a mirror. Diagram of an optical system composed of sharp mirrors. An explanatory view about arrangement of four CCDs. 1 is a block diagram of an ophthalmic measuring apparatus. The figure which shows the effect by the reading time of CCD being shortened. The flowchart of a wavefront aberration measurement. The flowchart for calculating | requiring a wave front. Explanatory drawing about the calibration of a lenslet array and how to determine a reference point. Explanatory drawing about calibration of the arrangement | positioning error of CCD of each Shack-Hartmann sensor. The flowchart which calculates | requires position calibration of the apparatus using a non-aberration model eye. A diagram of the Zernike polynomial in (r, t) coordinates. A diagram of the Zernike polynomial in (x, y) coordinates. Explanatory drawing which shows the structure which shifts a some light-receiving part (CCD) by a half pixel.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 1st light source part 10 1st illumination optical system 11 Adjustment part 12 Beam splitter (B2)
20 1st light reception optical system 20 '2nd light reception optical system 21-1 1st light-receiving part (Hartmann sensor 1)
21-2 2nd light-receiving part (Hartmann sensor 2)
21-3 3rd light-receiving part (Hartmann sensor 3)
21-4 4th light-receiving part (Hartmann sensor 4)
22-24 Separate reflector (half mirror)
22-2 to 24-2 Separating reflector (Kirikaki mirror)
30 Anterior segment observation unit 31 Fifth light receiving unit 32 Reflector (B1)
40 anterior eye illumination unit 50 target optical unit 51 fixation target 52 reflecting mirror 60-1 intensity sensor 60-2 calibration light source system 61 intensity measurement CCD
62 Light source 63 Pinhole

Claims (10)

A light source unit that emits a light beam for illuminating the fundus;
An illumination optical system that illuminates the light flux from the light source unit as a substantially point image on the fundus of the eye to be measured;
It has a plurality of light receiving portions having a number of pixels smaller than the number of pixels satisfying the measurement accuracy required for the measurement area, and the light beams from the measurement target area are divided and received by the plurality of light receiving portions. Receiving optical system,
Based on the outputs from the plurality of light receiving units, a measuring unit that measures the aberration of the eye under measurement in the entire measurement area;
An ophthalmic measuring apparatus.   The light receiving optical system branches reflected light from the eye to be measured into a plurality of optical paths. In each optical path, the plurality of light receiving units are arranged eccentrically, and a part of the light flux from the measurement target area is further provided. The ophthalmic measuring apparatus according to claim 1, further comprising a separation reflection unit that separates a light beam so that the light can be divided and received in an overlapping state.   The light receiving optical system branches the reflected light from the eye to be measured into a plurality of optical paths, and in each optical path, the plurality of light receiving units are eccentrically arranged so as to divide and receive a light beam from the measurement target area. Furthermore, the division | segmentation reflection part which reflects partially is provided further, The ophthalmic measurement apparatus of Claim 1 characterized by the above-mentioned.   The plurality of light receiving units are arranged so as to be shifted from each other by an amount less than one pixel, and the measurement unit is based on the output from the plurality of light receiving units and more accurately than the output from one light receiving unit. The ophthalmic measurement apparatus according to claim 1, wherein the apparatus is configured to perform aberration measurement.   Prior to the measurement eye measurement, the measurement unit uses a non-moving target object such as a model eye as a measurement target, and uses conversion processing such as affine transformation from the outputs of the first and second light receiving units at that time. The ophthalmic measurement apparatus according to claim 1, wherein a calibration mode for obtaining a mutual positional relationship is executed.   2. The ophthalmologic according to claim 1, wherein the measurement unit is configured to combine the outputs from the plurality of light receiving units to form a composite image corresponding to a measurement area and then perform aberration measurement. Measuring device.   The measurement unit obtains a light receiving position of light from the fundus from each of the outputs from the plurality of light receiving units, performs wavefront aberration measurement from the obtained light receiving position, and then forms a composite image corresponding to the measurement area. The ophthalmic measuring apparatus according to claim 1, which is configured as described above.   The measurement unit calibrates the position of the point images of the plurality of images obtained by the plurality of light receiving units and combines them into a single image, and then obtains wavefront aberration based on the combined single image. The ophthalmic measurement apparatus according to claim 1.   The measurement unit obtains a plurality of wavefront aberrations for the plurality of images based on the plurality of images obtained by the plurality of light receiving units, and then calibrates the positions of the plurality of wavefront aberrations and combines them into one image. The ophthalmic measuring apparatus according to claim 1, wherein the measuring apparatus is ophthalmic. 10. The position calibration includes one or both of calibration of a lenslet array of a plurality of Hartmann plates with respect to the plurality of light receiving units and calibration of an arrangement error of the CCD of the plurality of light receiving units. The ophthalmic measuring apparatus as described.

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