JPS5854927A - Method and 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 a method and apparatus for ophthalmological measurement, particularly corneal topography of an eye to be examined. It is also used to measure direction, as well as for cross-scanning.

Conventional ophthalmometers and keratometers project an index onto the cornea of the eye being examined, observe the size of the corneal reflection using a microscope, and move optical members such as prisms.
The corneal refractive power was determined from the amount of movement.

However, this method has a major problem in that it takes time to measure and errors occur due to movement of the subject's eye.

By the way, since the cornea generally does not have a uniform curvature in each meridian direction, the corneal reflection image has an elliptical shape, but in order to identify this ellipse, conventionally, by measuring the maximum value in each of the three meridian directions. known to ask. This takes advantage of the fact that when the center of the cornea is regarded as a toric surface, the change in the corneal curvature in the meridian direction can be regarded as sinusoidal. However, in the measurement in three meridian directions, it is necessary to increase the alignment accuracy, that is, to make the measurement optical axis and the optical axis of the eye to be examined closely coincide.

The present invention does not increase alignment accuracy as described above,
There is also a new device that can measure the corneal shape of the eye being examined in a short period of time. ! An object of the present invention is to provide a method and a measuring device. The purpose of this is to detect the corneal reflection 1 using at least 3 iJ one-dimensional image sensor installed at a predetermined position, and to use 5 of the detected 6 points of intersection position coordinates to form a corneal reflection image. This is achieved by calculating the ellipse shape of .

Hereinafter, the present invention will be described in detail using the accompanying drawings.

1 and 12 are a vertical sectional view and a cross sectional view, respectively, of a first embodiment of the apparatus of the present invention. A ring-shaped slit 1 has a narrow opening in each meridian direction, and is illuminated by a ring-shaped strobe 2.

Here, the ring-shaped strobe 2 has a light emitting section that extends in the circumferential direction around the measurement optical axis. 3 is Dona.

This collimating lens has a refractive power in an arbitrary meridian direction, but has no refractive power in a direction perpendicular to the meridian direction, that is, in the circumferential direction.

The ring-shaped slit 1 is arranged at a distance from the collimating lens 3 by its focal length.

As a result, the Idetomo light from the collimating lens 3 is converted into parallel light within the cross section in the meridian direction and illuminates the corneal area of the eye to be examined. Note that a projection index other than the ring-shaped slit may be used. 1/ is the ring-shaped slit 10 cornea I! During the reflection by c, the reflected light from the cornea lc is reflected toward the projection lens 5 as if it were emitted from the reflection*1/, and the light flux that passed through the projection lens 5 passes through the aperture plate 4 to form a one-dimensional image. It is connected as 1' onto the detection surface of sensor 9 (hereinafter referred to as sensor).

As shown in FIG. 3, the diaphragm plate 4 has 95 circular apertures deviated from the optical axis, and is positioned near the focal point of the optical axis direction projection lens 5 so that it can be separated into five beams. provided. The light beams passing through the five circular apertures are guided to five sensors 9 by a wedge prism 7, which will be described later.

What should be noted here is that as shown in Figure 4, each measurement meridian direction (y direction) from the optical axis is orthogonal to the corresponding aperture center direction (one direction) when viewed from the optical axis direction. That's true. That is, in the measurement meridian direction, the optical system constitutes a telecentric system. As a result, the light *h passing through the center of the five circular openings in each measurement meridian direction becomes a light ray that is reflected so that the cornea E0 is also parallel to the optical axis. The reason why the aperture aperture is not placed on the optical axis is to separate the beams that should be deflected to each sensor! Since the centers of each aperture are offset from the optical axis, the system is telecentric in only one direction, that is, the y direction, and is non-telecentric in the X direction perpendicular to this. However, when measuring in the y direction, A one-way telescopic system is useful in the sense of eliminating directional magnification errors. In other words, the five apertures shown above create a telecentric system in each corresponding meridian direction, and the distance from the eye to be examined (working distance)
Even if deviates slightly from the optimum value, the image will be blurred, but the size of me will not change and there will be no measurement error. , *The prism 7 is for deflecting the light beam passing through each aperture of the aperture plate 4 to the corresponding one-dimensional image sensor 9. By passing through this wedge prism 7, the light beam passes through the projection lens 5 of the corneal reflex lens 1'. The projected skin l' is separated into ss'm.

The wedge prism 7 is arranged so that the direction in which the light beam is deflected is perpendicular to the detection direction of the sensor 9, as shown in FIG. This is a rounding that minimizes the chromatic aberration caused by the prism on the sensor 9 and makes it a telecentric optical system within the cross section in the meridian direction that includes the measurement point as described above.

As shown in FIG. 5, the wedge prism 7 has five prisms pasted radially so that the periphery becomes thicker.

In Figure 1, 8 is a cylindrical lens that forms an image of the aperture of the diaphragm plate 4 onto the detection surface of each sensor 9a to 9C. information can be obtained by focusing the light on the sensor 9. This cylindrical lens 8 does not have a refractive power in the detection direction of the center and the center, but has a refractive power in a direction perpendicular to this, and five cylindrical lenses are provided in the KsF- row in the detection direction of each sensor, corresponding to each sensor 9a to 9e. .

As the sensor, a position detecting element such as a position detector or a position detector may be used in addition to an image pickup element such as MO8, COD, etc.

FIG. 6(A) is a layout diagram of the sensor, and corneal projection @x'
The relative relationships between a to 1'c and sensors 9a to 9c are shown. Regarding the sensor 9a, the sensor 9a is oriented parallel to the measurement meridian direction (y direction), that is, orthogonal to the direction connecting the corresponding aperture aperture center and the optical axis (X direction), toward the center of the pre-projection I'm. '1 at one point. The other sensors 9b to 9c are similarly provided in parallel to the corresponding measurement meridian direction.

However, the arrangement position of each sensor is not limited to this, and it is possible to use it at any specified position.

By detecting the position as described above, the coordinates of the corresponding five points A, B, C, D, and R as shown in FIG. is found.

In addition, in order to perform alignment and working distance adjustment while observing as shown in FIG. The anterior segment of the eye is illuminated by a light emitting diode 12 so that one image can be seen.

FIG. 7 is an explanatory diagram for calculating the corneal curvature radius R from the elliptical shape of the corneal reflection 11'.

However, if the present invention is used, even if the optical axis of the eye to be examined and the measurement optical axis are misaligned,
The coordinates of the intersection of the points can be extracted and the shape of the corneal reflection image 1' can be calculated from this, and there is no need to increase the alignment accuracy compared to the conventional measurement of the maximum dimension in the three meridian directions.

FIG. 8 is a block diagram showing one embodiment of the measurement process for this equipped dragon.

The corneal reflection yJ1' is separately projected onto the sensors 9a to 9e, and its brightness is stored in the sensor.

@8 In Figure 8, first, the channel selection signal 33 selects the analog multiplexer 22 to channel a, and the senna successive signal 32a is added to the sensor drive circuit 20aK.
Sensor 9! The analog signal 31 corresponding to brightness stored in the memory is taken out, amplified by 21M, passed through an analog multiplexer 22, converted to a digital signal 25 by a sample hold 23 and an analog/digital converter 24, and stored in the read/write memory 28. Ru. Similarly Sen? 9b~94
1 information is also channel selection signal 33 and sensor readout signal 3
2b to 32e are sequentially switched to perform analog-to-digital conversion,
It is stored in the read/write memory 28. Note that 27 is a read-only memory.Based on this information, the sensor 9
The microcomputer 26 calculates which position on m-9e is the brightest and sets the optical axis of the corneal reflection image 1' in FIG. 6(B) as the origin and 1. Ninety-five x and y coordinates are obtained.

Now let these coordinates be Xa - Xe and Ya - Ye.

By moving and rotating, "/a; + '/"/b' =
Make it into the shape of 1.

From this, determine the major axis and minor axis of the ellipse and calculate the nine rotation angles to calculate the corneal radius of curvature, fracture power, and degree of astigmatism.

Calculate the astigmatism axis and print it on the numerical display 29 or printer 3.
The result is output to 0. Note that 31 is a strobe drive circuit;
32 is a ring-shaped strobe, 34 is information from a sensor A
This is the signal after /D conversion. The measurement time in the example of -11,8+yA is such that the corneal reflection l is
equal to the time stored in Since this is due to the light emission from the ring strobe 2, it takes several milliseconds. As described above, according to the present invention, the corneal shape can be measured in a short time.

FIG. 9 is an illustration of another embodiment in which a semi-transparent mirror is used to separate the friction.

The optical path is divided into three by the semi-transparent * 13b and 13C.

That is, the light beam from the corneal reflection image 1' is transmitted through the projection lens 5.
After passing through the aperture plate 4' and the prism 7', the light passes through the semi-transparent mirrors xac and 13b to the sensor 9a.

In addition, the sensor 9b is transmitted through the semi-transparent mirror 13c, and is transmitted through the semi-transparent mirror 13c.
It is reflected by the semi-transparent mirror 13C and goes towards the i9 sensor 9c. Here, on the aperture plate 4'.

Opening 4/ in one meridian direction shown in FIG.
, 4/b are provided, and the light beams passing through each aperture are deflected in the same meridian direction by the corresponding prisms 7'a, 7'bK.

The sensors 9a*, 9b, 9C are provided in parallel to each other, as shown in FIG. 11, for example, and extract five points out of the six intersection points detected by the separated corneal reflection images. ζThus, even if the optical axis of the eye to be examined and the measurement optical axis are misaligned, the coordinates of the five points of intersection can be extracted, and measurement can be performed even if the alignment accuracy is poor.

Here, calculation of the shape of the corneal reflection image 1' will be described.

As shown in FIG. 12(A), the prism 7
When the amount of deflection caused by
) Y satisfies the following formula.

h+for=y+n From this, points AI and Bl shown in FIG. 12(B).

If you know the coordinates of C1, you can calculate A2°B2.
The coordinates of C2 are known. Note that the relative coordinates of Al, Bl, and C1 can be read by a one-dimensional sensor. This intersection A1. B
l, C1, M2. B2. By extracting and calculating arbitrary five points out of the six points of C2, the above-mentioned ellipse equation is revised. Note that the sensors 9a to 9C can be set in any positional relationship without being provided parallel to each other.

9. If the size of the sensor can be made larger, as shown in $1311, one corneal reflection 1' can be detected as it is without separating it with a prism, and 5 out of 6 intersection points can be extracted to measure the corneal shape. It is possible to do.

Note that in the present invention, accuracy can also be confirmed using the sixth point. Calculation of the elliptical shape can also be performed by visual observation rather than by electrical automatic calculation.

As described above, according to the present invention, the corneal shape can be measured in a short time by five-point detection, there is no need to increase alignment accuracy, and measurement errors due to eye movement can be prevented.
It also makes it easier to measure elderly people and children who cannot maintain a stable line of sight.

[Brief explanation of the drawing]

@ Figures 1 and 2 are a vertical cross-sectional view and a cross-sectional view of the first embodiment of the device of the present invention. Figure 3 is a diagram of the drawing plate. @Figure 4 is a one-way telecenter) An explanatory diagram of the IJ hook system. FIG. 5 is an explanatory diagram of the prism. FIG. 6(A) is a relative view of the sensor and the corneal projection. FIG. 6(B) is an explanatory diagram of the measurement position of the corresponding corneal reflection. FIG. 7 is an explanatory diagram of corneal curvature radius calculation. Figure 8 shows a block diagram of a signal processing system. FIG. 9 is a diagram of a second embodiment of the device of the present invention. FIG. 10 is a diagram of the aperture plate. FIG. 11 is a relative view of the sensor and the corneal projection. FIGS. 12(A) and 12(B) are explanatory diagrams of elliptic shape calculation. Figure 1g13 is a diagram of a third embodiment of the apparatus of the present invention. In the figure. 1 is a ring-shaped aperture, 1' is a corneal reflection, 2 is a ring-shaped strobe 3 is a donut-shaped collimating lens 4, 4' is an aperture plate 5 is a projection lens 6 is a dichroic mirror 7 is a wedge prism 8 is a cylindrical lens The one-dimensional image sensor 9 is a relay lens 11#i camera tube. Applicant: Canon Co., Ltd. Representative: Marushima -- Figure 1

Claims (1)

[Scope of Claims] (1) A method of projecting a predetermined index onto the cornea of the eye to be examined and measuring the shape of the cornea from the shape of the reflected image of the target by the cornea, the method comprising determining the position coordinates of at least five points of the corneal reflected image. A corneal shape measuring method characterized by determining the corneal shape by calculating a general formula for the elliptical shape of the detected corneal reflection image. (2) In an apparatus for projecting a predetermined index onto the cornea of a subject's eye and measuring the shape of the cornea from the shape of an image reflected by the cornea of the index, a separation means for separating a light beam from the reflected image into at least five parts; and at least three one-dimensional position detection means for detecting the one-dimensional position detection means, and a storage optical system for projecting the corneal reflected image onto the detection surface of the one-dimensional detection means, and at least one of the five points to be detected. , a corneal shape measuring device characterized in that the shape of a corneal reflection source is determined using five points. (3) The cornea according to claim 2, wherein the self-separating means includes an aperture means that separates the light beam into at least five light beams, and a light beam deflection means that deflects the separated light beam to a corresponding one-dimensional position detection means. Shape measuring device. (4) The corneal shape measuring device according to claim 3, wherein the corneal reflected light passing through each aperture center position of the aperture means is parallel to the measurement optical axis. (5) The aperture means is provided in the optical axis direction at the focal point position of the converging optical system, and each aperture center position is deviated from the optical axis in a plane perpendicular to the optical axis. Corneal topography measurement device. (6) The corneal shape measuring device according to claim 5, wherein the detection direction of the -dimensional position detecting means is orthogonal to the direction connecting the corresponding aperture center and the optical axis. (71i!m The predetermined index has a ring-shaped light emitting part, and the corneal shape measuring device according to claim 2, in which parallel light is incident on the cornea of the eye to be examined within a measurement plane including the optical axis. 8) The corneal shape measuring device according to claim 2, which has a cylindrical lens having no refractive power in the detection direction of the detection means, in the middle of the -dimensional position detection means in the optical path. 9. The corneal shape measuring device according to claim 8, wherein the cylindrical lens has an aperture of diaphragm 9 as a one-dimensional position detecting means. A corneal shape measuring device. aυ The corneal shape measuring device according to claim 10, wherein the three -dimensional position detecting means are provided in parallel to each other. The corneal shape measuring device according to claim 2, which guides the light flux of 1 to the observation optical system.