JPS5977828A - Apparatus for measuring shape of cornea - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to ophthalmological instruments, particularly corneal topography devices. A keratometer that measures the shape of the cornea is generally used to measure the three elements of corneal curvature, degree of astigmatism, and astigmatic axis direction, but it is also used to inspect the base curve of contact lenses.

The measurement methods of conventional keratometers can be broadly divided into two methods. The first method is to project the test chart onto the cornea,
This is a so-called manual type in which the reflected image is observed and adjusted to a predetermined state, and the measured value is obtained from the amount of adjustment.

The second method is a so-called automatic method in which a chart is automatically projected and measurements are automatically made based on the positional relationship of the reflected image, etc., by only manually adjusting the position of the cornea.

However, the former method requires time to measure, and it is difficult for the subject's eye to remain stationary without movement for a long period of time, so errors are likely to occur in the measurement. Furthermore, the latter has movable parts and has disadvantages in durability due to wear, vibration, etc., and has disadvantages in that the device is large and expensive due to the structure of the mechanism.

In view of the above points, it is an object of the present invention to provide a corneal shape side determining device that can automatically measure, is small, inexpensive, and has no moving parts.

According to the present invention, since there are no moving parts, the measurement can be carried out instantaneously, the time required to fix the eye to be examined is short, and therefore the measurement accuracy is improved, and the device is miniaturized and the operability of the device is improved. .

The present invention will be explained in detail below. , FIG. 1 shows an embodiment of the device according to the invention. The light emitted from the light source 10 is passed through a wavelength division optical filter or a diffusion plate 11 prepared as necessary.
The light flux passes through a slit 20, which is a measurement index carved with a predetermined pattern, and becomes a predetermined beam-shaped light flux, which is further transmitted to a circular aperture 30.
The light beam is narrowed down to a light beam 35, and the light beam 35 is focused through a lens 40.
As a result, the light beam becomes a light beam parallel to the optical axis (the axis of the subject's eye), passes through the half mirror 50, is projected onto the subject's eye 60 at a predetermined position, and is reflected on the surface of the cornea 61. This reflected light passes through a lens 70 and enters a line sensor 80 such as a so-called COD. The light beam 65 reflected by the cornea 61 of the eye 60 to be examined changes its reflection angle due to the difference in the shape of the cornea 61, especially the curvature thereof, and therefore the position at which the light enters the line sensor 80 differs. The angle (reflection angle) θi between the reflected light 65 reflected by the cornea 61 and the optical axis and the light incident position r of the line sensor 80
Corresponds to fi1:1. Therefore, by knowing the position of light incident on the line sensor 80, the corneal curvature of the eye 600 to be examined can be determined.

The aforementioned half mirror 50 is used to enable the examiner to observe the anterior segment of the eye 60 to be examined and to facilitate positioning operations. That is, the light flux from the anterior segment of the eye is shown as a light flux 55, which is reflected downward in the drawing by the half mirror 50, passes through the half mirror 90, and is imaged by the lens 100 on the face surface (imaging surface) 111 of the television camera ilO. Ru. The image of the eye 60 captured by the television camera 110 is displayed on a separately prepared television monitor. Although the examiner can directly observe the eye 60 to be examined, using this television observation system makes it easier to
More accurate alignment operations are possible.

Next, the fixation method for the eye 60 to be examined will be explained. The light emitted from the slit 130 from the fixation lamp 120 is turned into nearly parallel light by the lens 140, reflected by the half mirror 90 and the half mirror 50, and projected onto the retina 60a by the cornea and crystalline lens of the eye 60 to be examined. By gazing at the light emitted from the fixation lamp, the subject can align the optical axis of the measurement optical system with the optical axis of his or her own eye, making it easier to fixate the eye.

FIG. 2 shows an example of the pattern of the measurement index 20, and FIG. 3 shows an example of the arrangement of the line sensor group 80 corresponding thereto. These are arranged on a plane perpendicular to the optical axis in FIG. In FIG. 2, the five holes 21 to 25 are at equal angles ψ. , equal radius t.

The light from these holes 21 to 25 is arranged in concentric circles (center //i optical axis in Figure 1), and the position detection direction is perpendicular to the circumferential direction as shown in Figure 3. It is input to line sensors 81 to 85. These line sensors 81
.about.85 are arranged in concentric circles (the center of which is the optical axis in FIG. 1) with equal angle ψi1 and equal radius t1. When jin ψ
0=ψi. Generally, the corneal shape is expressed by an elliptic equation, and the corneal shape characteristics can be expressed by finding each factor. To do this, we need to set five points at equal angles (ψ
0=ψ1=72°). But! 7. In order to easily obtain the corneal shape, instead of measuring the position at five points, it is also possible to approximate it by measuring the position at four points on the left, right, top and bottom, or at two points either on the left, right or top and bottom.

The arrangement relationship at this time is shown in FIG. The four line sensors 81' to 84' are arranged at an equal angle ψi' (=90°),
Concentric circles with equal radius ti'! 7. Correspondingly, the hole positions of the 7-roar measurement indicators 20 are also arranged in four concentric circles at an angle of 90°. Using only two points, either left or right or top and bottom, is also effective in realizing a low-cost and simple keratometer.

Extremely speaking, it is possible to use only one point in a simpler manner, and conversely, it is necessary to have more than five points in order to obtain a more accurate keratometer.

Note that the line sensor 80 is a one-dimensional COD sensor that outputs the position of the received small and medium luminous flux as an electrical signal.
If so, its position can be found from the temporal relationship of the electrical signals.In addition, in a line sensor that has individual photodiodes arranged in a straight line with their light-receiving surfaces, an electrical surge is detected by the photodiode that receives the light. The positional relationship can be obtained from this.

Next, we will discuss how to find the radius of curvature. The radius of corneal curvature of the human eye is said to be approximately in the range of 6.5 fl to 9.5 fi. The standard root degree is 7.6, and here we assume 7.
．． The line sensor 80 is arranged as shown in FIG. 5 using 6 vm as a reference for the radius of corneal curvature.

In this case, the reflection optical axis 66 at the reference cornea 62 is the projection optical axis 5.
The angle made with 6 is 00, and it is perpendicular to the line sensor 80.
The intersection point is the reference point 0, and the distance PO between the corneal reflection point P and the reference point 0 at this time is R.

shall be. Further, the distance between the parallel projection light 57 and the projection source axis 56 is assumed to be D.

Now, when measuring the cornea PA of the eye to be examined, the angle formed by the reflected light 65 with the projection optical axis 56 is θ11, the position where the light enters the line sensor 80 QA#i When there is a distance of xi from the base point O, r6 is the corneal Assuming the curvature at point P, the following equation holds true.

Re = R6to (θi-θO) ・・・・・・
...(1) From equations (1) and (2), the radius of corneal curvature at point P of the eye to be examined r6'fi (8) In the equation, DsR□ is determined by the structure of the keratometer, and πi is the electrical signal of the line sensor 80. Therefore, the radius of corneal curvature r( at point P is calculated.

Although the lens 70 is inserted between the eye to be examined and the line sensor in FIG. 1, it will be understood from the above that the configuration shown in FIG. 5 is basically sufficient. However, this lens has the following effects. That is, on the reference cornea 62, on the so-called measurement optical axis between the point P to be measured and the base point 0 of the line sensor 80, a lens 70 having a predetermined magnification and a focal length such that the image of the point P is formed on the base point O is inserted. This allows the use of a line sensor 80 that is shorter in the longitudinal direction. Furthermore, even if the position of the eye to be examined moves, especially in the direction of the projection optical axis, the point to be measured P
.

P' is imaged at point Q on the line sensor 80. That is, a one-dimensional CCD sensor with a fine structure can be used as a line sensor, and the device can be downsized. In addition, operations such as positioning as a keratometer become easier, which in other words improves measurement accuracy.

In this way, a predetermined number (for example, 5) of line sensors 8
0 at a predetermined position as shown in FIG. 3, for example, and the radius of curvature ri, to r of the cornea at the measurement point corresponding to each sensor 81 to 85 can be determined.

Or each base point O5-0 of each line sensor 81-85
．． Distance from z4. It is also possible to find πi and solve the following elliptic equation.

az+bl/+cZ+dY+eZm/=O---...(4
) In the elliptic equation (4), x, 1/ is town, and ~z is also.

It is obvious that the variable &r'Q+e+do 6 can be obtained by substituting these into equation (4). Therefore, as shown in FIG. 7, the short axis of the corneal surface of the eye to be examined, that is, the toric surface
The long axis and its axial angle are calculated based on the shape of the corneal reflection image, and thereby a desired radius of curvature in the meridian direction can be obtained.

It goes without saying that the corneal refractive power can be calculated from the corneal radius of curvature.

Next, other embodiments of the present invention will be explained.

An example of a projected pattern is shown in Fig. 2, but a one-dimensional CCD that can be used as a line sensor generally has a structure in which each light receiving cell is elongated in the horizontal direction, as shown in an enlarged view of Fig. 8. . A large number of light receiving cells 2 having a uniform structure and uniform characteristics and having a size of several tens of micrometers perform photoelectric conversion in an optically and electrically insulating substrate 200.
11-216 are arranged in a straight line.

When using such a line sensor, measurement index 2
The projection pattern of 0 is as shown in Figure 9.
21 to 225 or a ring-shaped slit (321) as shown in FIG. 10 are effective.

In particular, the ring-shaped slit 321 in FIG.
The feature is that the positioning work in the angular direction with respect to 0 is extremely easy.

Projection pattern slits are generally produced by depositing an opaque film on a transparent glass plate, etching an opaque metal thin film, etc. FIG. 10 also shows supports 331 and 332 necessary for the latter manufacturing method.

Next, in FIG. 11, the projection pattern 21 of FIG.
FIG. 2 shows an example in which the projected patterns 221 and 321 in FIGS. 9 and 10 are respectively received by the line sensor 80 as shown in FIG.

Further, the electrical signal waveform of the line sensor 80 in this example is shown in FIG.

That is, the waveform of the output amplifier 401 of the line sensor 80 is driven by the clocks φ, to φ4. The horizontal axis shows time [2
The vertical axis is the clock voltage and the output amplifier voltage or current waveform. In this example, the maximum peak occurs at timing 2130, and this is used as position information.

Next, we will add an explanation of the measurement light source. In FIG. 1, one light source lamp 10 and a filter or diffuser plate 11 are used. A plurality of light source lamps 10 may be used to increase the amount of light depending on the pattern shape of the slits 20. Furthermore, the lamp itself may be an incandescent lamp, a light emitting diode, or a laser with good directivity, without any hindrance to forming the keratometer according to the present invention. If the measurement light is visible light, the eye stability will be impaired if it is too bright for the eye to be examined, so for example, a wavelength division filter that passes only infrared light, which is invisible to the eye, is inserted. Further, the diffuser plate is used to reduce the directivity of the lamp 10, and is particularly effective when only one lamp is used. The filter mentioned above. Achieving both and diffusion in one would reduce costs.

As explained above, the realization of the automatic keratometer with a movable part according to the present invention not only makes the device more compact, but also makes assembly and adjustment of the device extremely easy. The measurement accuracy has been improved as a result. Note that the projection pattern of the measurement index is not limited to the one described in the example, but may be of any shape (for example, square, triangle, etc.), and the optical position detection element may be one-dimensional CCD or two-dimensional.
A dimensional CCD, position detector, etc. can be used.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing an embodiment of the corneal shape measuring device according to the present invention, Fig. 2 is a projection pattern arrangement diagram, Figs. 3 and 4 are arrangement diagrams for the line sensor, and Figs. 5 and 6. is an explanatory diagram of the measurement system, Figure 7 is a diagram showing the relationship between the corneal reflection image and the sensor, Figure 8 is a diagram showing line sensor ÷ light receiving section, and Figures 9 and 10 are examples of different projection patterns. Figures 11 and 12 are diagrams of projection patterns projected onto the line sensor operator; Figure 13 is a diagram of the output waveforms of the line sensor and electric circuit; Eye to be examined 61 is cornea 80 is line sensor 110 #″i
Derepi camera 120H fixation light 130V slit. Applicant: Quinon Co., Ltd. J11! Miss Marushima −

Claims (1)

[Scope of Claims] 1. A light source, measurement index means for converting the light emitted from the light source into a predetermined beam-like light flux, means for projecting the beam-like light flux onto the subject's eye so as to be parallel to the optical axis; A corneal shape measuring device characterized by having a light position detecting means for receiving light reflected by the cornea of a subject's eye of a beam-like light flux. 2. The corneal shape measuring device according to claim 1, wherein the optical position detection means is a line sensor. 3. The corneal shape measuring device according to claim 1, further comprising an imaging lens between the cornea of the eye to be examined and the optical position detection means. 4. The corneal shape measuring device according to claim 1, wherein the measurement index means is provided with a plurality of apertures. 5. The aperture is provided in a circumferential shape centered on the optical axis,
The corneal shape measuring device according to claim 4, wherein the corneal shape measuring device has a slit shape in which the longitudinal direction is the circumferential direction. 6. The corneal shape measuring device according to claim 4, wherein the aperture has a spot shape provided in a circumferential shape centered on the optical axis. 7. The corneal shape measuring device according to claim I@1, wherein the measurement index means is provided with a ring-shaped opening. 8. The corneal shape measuring device according to claim 5, 6, or 7, wherein the detection direction of the optical position detection means is perpendicular to the circumferential direction of the aperture. 9. Claim 1, wherein the optical position detection means has at least five position detection parts in a circumferential shape centered on the optical axis.
The corneal topography measuring device described in Section 1.