JP3560746B2 - Eye refractive power measuring device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an eye refractive power measuring device that objectively measures the refractive power of an eye to be examined.
[0002]
[Prior art]
As an eye refractive power measurement device, a slit-shaped light beam is scanned and projected onto the fundus of the eye to be examined, and the light reflected from the fundus of the eye to be examined due to the projection of the slit light beam sandwiches the optical axis at a position substantially conjugate with the cornea to be examined. In order to obtain the refractive power of the eye to be inspected based on detection by two pairs of light receiving elements symmetrically arranged as described above. The measurement result of this type of apparatus is based on three parameters of S (spherical power), C (astigmatic power), and A (astigmatic axis angle), assuming that the refractive power of the eye to be examined is symmetric about the cornea. The operation is output.
[0003]
[Problems to be solved by the invention]
However, the refractive power of the eye is not always symmetrical about the center of the cornea, and many eyes have irregular astigmatism. With an irregular astigmatic eye, the results of S, C, and A obtained when the subject's eye looks at the center of the fixation target inside the apparatus and when looking at a position other than that are different. As a typical example of the irregular astigmatism, in the case of keratoconus, the values of S, C, and A may be completely unreliable.
[0004]
In recent corneal surgery using an excimer laser, which has been spotlighted as a method of correcting refractive errors, the surface of the cornea is excised and its curvature is changed. However, if the axis is misaligned during the operation, the symmetry of the cornea is broken. .
[0005]
In the eye to be examined in which the symmetry of the refractive power is not secured, the measurement results of S, C, and A often become inaccurate. In this case, it takes a long time for the eyeglass prescription and the like by the subjective test to be performed subsequently, and the eye to be inspected may be tired and an incorrect prescription value may be output.
[0006]
The present invention has been made in view of the above-described drawbacks of the conventional apparatus, and provides an eye-refractive-power measuring apparatus that can obtain an eye refractive power based on a more accurate phase difference method and that can easily detect the presence or absence of irregular astigmatism. The technical issues.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the present invention is characterized by having the following configuration.
[0008]
(1) A slit light projection optical system that scans a slit-like light beam in at least two directions , and a slit light beam reflected by the fundus of the eye to be examined is symmetrically arranged with a light axis interposed at a position substantially conjugate with the cornea of the eye to be examined. A detection optical system for detecting with two or more pairs of light receiving elements, and an eye refractive power measuring device that obtains the refractive power of the eye to be inspected based on a phase difference signal output between the light receiving elements, wherein the scanning direction of the slit light beam is Except for a pair of light receiving elements for measuring a corresponding refractive power in the meridian direction, a center detecting means for detecting a corneal center in the measured meridian direction based on a phase difference signal output of at least another pair of light receiving elements. It is characterized by having.
[0009]
(2) A slit light projection optical system that scans a slit-like light beam in at least two directions , and a slit light beam reflected by the fundus of the eye to be examined is symmetrically arranged at a position substantially conjugate with the cornea of the eye with the optical axis interposed therebetween. A detection optical system for detecting with two or more pairs of light receiving elements, and an eye refractive power measuring device that obtains the refractive power of the eye to be inspected based on a phase difference signal output between the light receiving elements, wherein the scanning direction of the slit light beam is A corneal center of the eye to be inspected in the measured meridian direction is detected based on a phase difference signal output of at least another pair of light receiving elements excluding a pair of light receiving elements for measuring a corresponding refractive power in the meridian direction. Based on the center detecting means and the detected corneal center and the measured output signals of the light receiving elements arranged in the meridian direction, the refractive power in the measured meridian direction at the corneal site corresponding to each light receiving element position To Refracting power calculating means for calculating the corneal center of the eye to be examined as a center.
[0013]
【Example】
An embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic layout diagram of an optical system of an apparatus according to an embodiment. The optical system is roughly classified into a slit projection optical system, a slit detection optical system, a fixation target optical system, and an observation optical system.
[0014]
Reference numeral 1 denotes a slit projection optical system. Reference numeral 2 denotes a slit illumination light source that emits infrared light, and 3 denotes a mirror. Reference numeral 4 denotes a cylindrical rotating sector which is rotated by a motor 5 at a constant speed in a constant direction. 2, a plurality of slit openings 4a and 4b having two different inclination angles are provided on the side surface of the rotating sector-4. The slit opening 4a is provided so as to have an inclination angle of 45 degrees with respect to the rotation direction of the rotating sector-4, and the slit opening 4b has an inclination angle of 135 degrees with respect to the rotation direction so as to be orthogonal to the opening 4a. It is provided in. Reference numeral 6 denotes a projection lens, and the light source 2 is located at a position conjugate with the vicinity of the cornea of the subject's eye with respect to the projection lens 6. 7 is a limiting aperture, and 8 and 9 are beam splitters.
[0015]
The infrared light emitted from the light source 2 is reflected by the mirror 3 to illuminate the slit opening 4a or 4b of the rotating sector-4. The slit light beam scanned by the rotation of the rotating sector-4 is reflected by the beam splitter 8 after passing through the projection lens 6 and the limiting aperture 7. Thereafter, the light passes through the beam splitter 9 and is condensed near the cornea of the eye E, and then projected onto the fundus. Since the rotating sector-4 has slit openings with different inclination angles, the sensor 20 detects which angle of the slit light beam is projected.
[0016]
Reference numeral 10 denotes a slit detection optical system, which includes a light receiving lens 11, a stop 13, and a light receiving unit 14 on the optical axis L1. The diaphragm 13 is arranged at a focal position on the rear side of the light receiving lens 11, and the light receiving unit 14 is arranged at a position substantially conjugate with the cornea of the eye to be examined with respect to the light receiving lens 11. The light receiving section 14 has four light receiving elements 15a to 15d on its light receiving surface as shown in FIG. The light receiving elements 15a and 15b are provided symmetrically about the optical axis L1, and similarly, the light receiving elements 15c and 15d are provided symmetrically about the optical axis L1. The two pairs of light receiving elements are arranged so that the scanning direction of the slit light beam on the fundus of the eye to be inspected projected by the slit apertures 4a and 4b having two kinds of inclination angles (the slit light beam on the fundus is in the longitudinal direction of the slit) (Scans in orthogonal directions). In the apparatus according to the embodiment, when the slit light beam is scanned by the slit opening 4a on the fundus of the eye to be examined having no astigmatism, which corresponds to the direction orthogonal to the longitudinal direction of the slit received on the light receiving unit 14. A pair of light receiving elements 15a and 15b are arranged in the same manner, and when the slit light beam is also scanned by the slit opening 4b, the pair of light receiving elements 15a and 15b correspond to a direction orthogonal to the longitudinal direction of the slit received on the light receiving section 14. 15c and 15d are arranged.
[0017]
Reference numeral 30 denotes a fixation target optical system. 31 is a light source, 32 is a fixation target, and 33 is a light projecting lens. The light projecting lens 33 foggs the eye to be examined by moving in the optical axis direction. Numeral 34 denotes a beam splitter for making the fixation target optical system and the observation optical system coaxial. The light source 31 illuminates the fixation target 32, and the light beam from the fixation target 32 passes through the light projecting lens 33 and the beam splitter 34, is reflected by the beam splitter 9, and travels toward the eye E to be examined. E fixes the fixation target 32.
[0018]
Reference numeral 35 denotes an observation optical system. The anterior segment image of the eye E to be inspected illuminated by the illumination light source 36 is imaged on the imaging element surface of the CCD camera 38 by the photographing lens 37 via the beam splitters 9 and 34, and is displayed on the TV monitor 39. .
[0019]
Next, a method will be described in which the center of the cornea (or the center of the visual axis) is determined from the output signals of the light receiving elements 15a to 15d, and the refractive power at the cornea corresponding to each light receiving element with respect to the center of the cornea.
[0020]
Now, when the slit light beam by the slit opening 4a is scanned at a constant speed and the slit image reflected from the fundus traverses each of the light receiving elements 15a to 15d, its signal output waveform is shown in FIG. ~ (D) This is the case where the subject's eye is in a hyperopic or myopic state and has astigmatism.
[0021]
Now, assuming that the refractive power is symmetrical about the center of the cornea, it corresponds to the phase difference (time difference) between the output signal from the light receiving element 15a in FIG. 4A and the output signal from the light receiving element 14b in FIG. Thus, it is possible to obtain the refractive power between the corneal sites corresponding to the light receiving elements 15a and 15b. However, the refractive power is not always symmetric about the center of the cornea. Therefore, a method of obtaining the centers of the light receiving elements 15a and 15b from the signal outputs of the light receiving elements 15c and 15d located in the direction orthogonal to the light receiving elements 15a and 15b will be considered. Then, the refractive power corresponding to the corneal site corresponding to each position of the light receiving elements 15a and 15b is obtained. This makes it possible to evaluate the symmetry of the refractive power with respect to the center.
[0022]
Here, for the sake of simplicity, when the rise time of the optical voltage signal waveform generated in each light receiving element in accordance with the incidence of light is detected (ta, tb, tc, td in FIG. 4), the reference time t0 The center of the light receiving elements 15a and 15b is
(Tc + td) / 2
Can be obtained by Therefore, if the time from the corneal site corresponding to the light receiving element 15a to the corneal center is Ta, and the time from the corneal center to the corneal site corresponding to the light receiving element 15b is Tb,
Ta = [(tc + td) / 2-ta]
Tb = [tb− (tc + td) / 2]
By making the times Ta and Tb correspond to the refractive power, the refractive power between the center of the cornea and a predetermined corneal part can be obtained.
[0023]
Next, a case where the output signal from each light receiving element is binarized to detect the phase difference time will be described. When a certain threshold level is set for a signal output from each light receiving element and binarization processing is performed, if there is a light amount difference between each light receiving element, an error may occur in the detection of the phase difference time. This is likely to occur when the translucent body of the eye is turbid, such as a cataract eye. For example, FIG. 5 is a diagram showing an example of signal waveforms from the corneal site corresponding to the light receiving element 15b when the corneal site corresponding to the light receiving element 15b is heavily clouded with respect to the corneal site corresponding to the light receiving element 15a (FIG. In order to simplify the explanation, the light receiving timing is aligned). A waveform 65 indicates a signal waveform from the light receiving element 15a, and a waveform 66 indicates a signal waveform from the light receiving element 15b. The waveform amplitude of the light receiving element 15b is small due to turbidity. This analog waveform is shaped into a rectangular waveform at a certain threshold level 67 by a binarization process. However, when the amplitude changes, the rise times ta1 and tb1 from the reference time t0 when the rectangular waveform is shaped are changed. , Δt. Therefore, when there is a light quantity difference between the respective light receiving elements, the time difference of Δt becomes an error when converted into refractive power.
[0024]
Therefore, in consideration of the case where there is a light quantity difference between the respective light receiving elements, the center of the meridional direction to be measured (corneal center) and the refractive power with respect to the center take a time half the pulse width of the shaped rectangular waveform. To This can eliminate the influence of the amplitude difference at each light receiving element position. That is, in FIG. 5, the times ta1, ta2, tb1, and tb2 from the reference time t0 are measured, and the time ta3 or tb3 to the center may be obtained. ta3 and tb3 are respectively
ta3 = ta1 + ta2 / 2
tb3 = tb1 + tb2 / 2
It becomes. This means that accurate time can be obtained even if the threshold levels in the binarization processing corresponding to the respective light receiving elements are different.
[0025]
FIG. 6 specifically shows such a time detecting method for each light receiving element. (A) shows a digital waveform of a measurement pulse serving as a reference. In this case, the timing at the first rise of the pulse waveform after binarization processing among the light receiving elements 15a to 15d is used as a reference. (B) to (e) show digital waveforms obtained from the four light receiving elements 15a to 15d, and t _A3 , t _B3 , t _C3 , and t _D3 are each a pulse width from a reference time (rising edge of a measurement pulse). It shows the time to the center. Therefore, when the directions of the light receiving elements 15a and 15b are set as the measurement meridian directions, the center (corneal center) is obtained by (t _C3 + t _D3 ) / 2, and the position of the light receiving element 15a up to the obtained center is obtained. the time difference _{T B} at the position of the light receiving element 15b the time difference _{T a,} and from the center,
_{T A = (t C3 + t} D3) / 2-t A3
_{T B = t B3 - (t} C3 + t D3) / 2
Is required. Then, this time difference can be made to correspond to the refractive power with respect to the center in the meridian direction.
[0026]
Similarly, assuming that the directions of the light receiving elements 15c and 15d are measurement meridian directions, their centers (corneal centers) are obtained based on digital waveforms from the light receiving elements 15a and 15b, and the positions of the light receiving elements 15c and 15d with respect to the centers. The time difference between the two is also determined.
[0027]
Next, the operation of the apparatus will be described with reference to the schematic block diagram of the signal processing system of FIG. The examiner performs alignment by moving the apparatus up, down, left and right and back and forth while observing the anterior eye image of the eye E illuminated by the illumination light source 36 with the TV monitor 39 (alignment is performed by using an index for positioning on the cornea). A well-known device that projects the image so that the corneal reflection luminescent spot and the reticle have a predetermined relationship can be used.) When the alignment is completed, a trigger signal is generated by a measurement start switch (not shown) to start the measurement.
[0028]
When the measurement is started, a slit light beam restricted by the slit opening 4a or 4b enters the eye through the pupil from the slit projection optical system 1, and scans and projects on the fundus. The light flux of the slit image reflected by the fundus and passing through the pupil is condensed by the light receiving lens 11 of the slit image detecting optical system 10 and reaches the light receiving unit 14 via the aperture 13. Here, if the subject's eye E is an emmetropic eye, a light voltage is generated in the light receiving elements 15a to 15d on the light receiving unit 14 at the same time when a light beam enters the eye. The image light moves so as to cross over the light receiving unit 14.
[0029]
With the movement of the light of the slit image on the light receiving section 14, a light voltage is output from each of the light receiving elements 15a to 15d (a time difference occurs in the light voltage). The output optical voltages are input to four amplifiers 40a to 40d and amplified, respectively, and subjected to voltage level shift processing by four level shift circuits 41a to 41d, respectively, and then binarized circuits 42a to 42d. By 42d, the digital signal is converted into a binary digital signal at a predetermined threshold level. Thereafter, each digital signal is input to the counter circuits 46a to 46d and the OR circuit 43, respectively. The OR circuit 43 sets the first rising edge in the binarization circuits 42a to 42d as the rising of the measurement pulse, and is input to the flip-flop 44 that follows. The flip-flop 44 includes a reference time (rising edge) at which measurement is started, and means a measurement time from completion of measuring pulses from all light receiving elements to reception of an Rset signal output from the control circuit 50. The measurement pulse signal is output to the counter circuits 46a to 46d.
[0030]
Each of the counter circuits 46a to 46d receives the pulse signal binarized by the binarization circuits 42a to 42d and the measurement pulse signal from the flip-flop 44, and receives the rising edge (= reference time) of the measurement pulse signal. And counts and holds the time until the pulse signal rises and the time of each pulse width. To explain this with reference to the example of FIG. 6, the time until the input of each pulse signal with respect to the reference time t0 is t _A1 (t _A1 = 0 in FIG. 6), t _B1 , t _C1 , t _D1 . The pulse width times are t _A2 , t _B2 , t _C2 , and t _D2 , respectively.
[0031]
The time held by each counter circuit is output by a calling command signal (CSa to CSd) from the control circuit 50 and input to the control circuit 50 via the data bus 47. The control circuit 50 controls the time (t _A1 , t _B1 , t _C1 , t _D1 ) until the rise of each pulse signal with respect to the reference time in each light receiving element from each of the counter circuits 46a to 46d, and the time of the pulse width (t _A2). , T _B2 , t _C2 , t _D2 ) and the discrimination signal of the type of slit projection by the sensor 20, the time of the corneal center in the measurement meridian direction (scanning direction of the slit light beam) is obtained by the above-described method, and then the measurement is performed. The time difference (phase difference) from the center of the cornea of each of the pair of light receiving elements located in the meridian direction is obtained.
[0032]
When a time difference is obtained in this way, this is converted into refractive power. FIG. 8 shows a relationship between the time difference detected by the phase difference method and the refractive power. This relationship can be obtained, for example, by sampling by using a model eye whose refractive power value is known in advance, and storing the phase difference data to obtain a refractive power value corresponding to the time difference.
[0033]
Further, three parameters of S (spherical power), C (astigmatic power) and A (astigmatic axis angle) are obtained as follows. The value obtained from the phase difference between the output signals of the pair of light receiving elements 15a and 15b when the slit light beam is scanned by the slit opening 4a is obtained from D1, and the value obtained from the phase difference between the output signals of the other pair of light receiving elements 15c and 15d. Similarly, the value obtained is D2, the value obtained from the phase difference between the output signals of the pair of light receiving elements 15a and 15b when the slit light beam is scanned by the slit opening 4b is D3, and the other pair of light receiving elements 15c and If the value obtained from the phase difference of the output signal of 15d is D4,
D1 = S + Ccos ² θ
D2 = (C / 2) sin 2θ
D3 = − (C / 2) sin 2θ
D4 = S + Csin ² θ
Are satisfied, the values of S, C, and A (= θ) are obtained by arithmetically processing these relational expressions.
[0034]
The measurement results obtained as described above are displayed on the display unit 51. At this time, if there is a predetermined amount of difference in the refractive power in the measurement meridian direction with respect to the corneal center, it is displayed that there is irregular astigmatism. Further, the degree of the difference and the direction of the measurement meridian may be displayed.
[0035]
Further, when the measurement results are printed out from the printer 52, as shown in FIG. 9, in addition to the values of S, C, and A, as well as the center with respect to each measurement meridian direction (45-degree direction and 135-degree direction in the embodiment). The refractive power difference 70 at each measurement light receiving element position is displayed. If the difference is equal to or larger than a predetermined value (for example, ΔD> 0.5 diopter), a message display 71 indicating that there is irregular astigmatism and that it is better to prescribe a contact lens is displayed. With such a display, the examiner can be warned to carefully reconfirm the values of S, C, and A obtained from the apparatus in the subsequent optometry for the final prescription.
[0036]
In the above embodiments, the measurement in two meridian directions by two pairs of light receiving elements has been described. However, in order to further increase the measurement accuracy, the scanning direction of the slit light beam and the number of light receiving elements may be increased. For example, when measuring in three meridian directions, the rotating sector-4 is provided with slit openings 80a, 80b, and 80c having three types of inclination angles of 30 degrees, 90 degrees, and -30 degrees with respect to the rotation direction (FIG. 10). On the other hand, a pair of light receiving elements 81a and 81b, a pair of light receiving elements 81c and 81d, and a light receiving element 81e are provided on the light receiving portion 14 such that the optical axis is symmetrical at every 60 degrees so as to correspond to the directions of the three types of slit openings. , 81f (see FIG. 11). In this case, when the direction of the slit opening (scanning direction of the slit light beam on the fundus of the eye to be inspected) corresponds to the direction of the light receiving elements 81a and 81b, a pair of light receiving elements 81c and 81d or a pair of light receiving elements excluding this direction. From the phase difference when light crosses the elements 81e and 81f (or the average phase difference between them), the center of the slit light beam in the scanning direction can be obtained by the above-described method, and the light is received in each meridian direction with respect to the center. Refractive power at the cornea position corresponding to the element can be obtained.
[0037]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain the refractive power at the corneal site in the meridian direction with respect to the corneal center. Therefore, the presence or absence of irregular astigmatism can be easily found, and the examiner can be alerted in the subsequent optometry for eyeglass prescription and the like.
[Brief description of the drawings]
FIG. 1 is a diagram showing a schematic arrangement of an optical system of an apparatus according to an embodiment.
FIG. 2 is a development view of a slit opening provided on a side surface of the rotating sector.
FIG. 3 is a diagram illustrating an arrangement of four light receiving elements included in a light receiving unit.
FIG. 4 is a diagram showing an example of signal output waveforms from four light receiving elements with respect to a reference time t0.
FIG. 5 is a diagram showing an example of signal waveforms from the corneal site corresponding to the light receiving element 15b when turbidity of the corneal site corresponding to the light receiving element 15b is larger than that of the corneal site corresponding to the light receiving element 15a.
FIG. 6 is a diagram showing a detection method of the binarization processing of the present invention for each light receiving element.
FIG. 7 is a schematic block diagram of a signal processing system of the device according to the embodiment.
FIG. 8 is a diagram illustrating a relationship between a time difference detected by a phase difference method and a refractive power.
FIG. 9 is a diagram illustrating an example of print output by the apparatus according to the embodiment.
FIG. 10 is a diagram showing an example of the arrangement of slit openings provided on the side surface of a rotating sector when measurement is performed in three meridian directions.
FIG. 11 is a diagram illustrating an example of the arrangement of light receiving elements when measurement is performed in three meridian directions.
[Explanation of symbols]
1 Slit projection optical systems 4a, 4b Slit aperture 10 Slit detection optical systems 15a to 15d Light receiving elements 46a to 46d Counter circuit 50 Control circuit

Claims (2)

A slit light projection optical system that scans a slit-like light beam in at least two directions , and a pair of slit light beams that are reflected by the fundus of the eye to be examined and are symmetrically disposed at positions substantially conjugate with the cornea of the eye with the optical axis interposed therebetween. A detection optical system for detecting by the above light receiving element, an eye refractive power measuring device for obtaining the refractive power of the eye to be inspected based on the phase difference signal output between the light receiving elements, wherein the meridian corresponding to the scanning direction of the slit light beam Excluding a pair of light receiving elements for measuring refractive power in the direction , including a center detecting means for detecting a corneal center in a measured meridian direction based on a phase difference signal output of at least another pair of light receiving elements. Characteristic eye refractive power measurement device. A slit light projection optical system that scans a slit-like light beam in at least two directions , and a pair of slit light beams that are reflected by the fundus of the eye to be examined and are symmetrically disposed at positions substantially conjugate with the cornea of the eye with the optical axis interposed therebetween. A detection optical system for detecting by the above light receiving element, an eye refractive power measuring device for obtaining the refractive power of the eye to be inspected based on the phase difference signal output between the light receiving elements, wherein the meridian corresponding to the scanning direction of the slit light beam excluding the light receiving element of a pair of measuring the refractive power of the direction, based on the phase difference signal output of at least one other pair of light receiving elements, the center detecting means for detecting the corneal center of the eye in the measured meridian direction If, subject's eye based on the respective output signals of the detected corneal center and the measured meridian direction arranged light receiving elements, the refractive power measurement meridian direction corneal portions corresponding to each of the light receiving element position Eye refractive power measuring apparatus characterized by comprising: a power calculating means for calculating around the corneal center, a.

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