JPH06335454A - Apparatus for measuring thickness of cornea - Google Patents

Abstract

PURPOSE:To heighten a positional accuracy in an measuring apparatus provided with a means for detecting an echo of ultrasonic beam irradiated on an eye ball to be examined, with a means for judging that the central axis of a probe and the central axis of the crystalline lens of an eye to be examined have substantially coincided. by comparison of the echo strengths. CONSTITUTION:This measuring apparatus for accurately measuring the thickness of a cornea and the distribution thereof before an operation to correct eye refraction comprises: a plurality of radially arranged ultrasonic vibrators 3 (3a-3g) in a housing 2; and a contact terminal 4 as a sonic medium. In measuring the end surface 4a of the contact terminal 4 is brought into contact with the surface of the cornea C through a liquid such as tears, in which state an ultrasonic beam is oscillated from the ultrasonic vibrators 3 to detect the echoes on the cornea C and the surface of the crystalline lens L. At this time, by comparing the echo strengths of the central vibrator 3a and the vibrators 3 surrounding it, it is judged that the central axis of a probe 1 and the central axis of the crystalline lens L have substantially coincided, and thereafter the measurement of the thickness of the cornear is performed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a corneal thickness measuring device. More specifically, it relates to a corneal thickness measuring device for measuring the thickness of the cornea and its distribution by ultrasonic waves.

[0002]

2. Description of the Related Art In recent years, in the field of ophthalmology, a surgical operation for correcting myopic eyes called radial keratotomy, in which an incision of a predetermined shape and depth is made on the surface of the cornea, is becoming popular as an eye refractive correction operation. Furthermore, recently, surgery is being performed to correct myopia by automatic removal of the corneal surface by excimer laser. At that time, by accurately measuring the corneal thickness and the thickness distribution immediately before the operation, it becomes possible to adjust the knife blade length or the laser irradiation power based on the measurement result.

Conventional corneal thickness measuring devices include an optical type and an ultrasonic type. Since the optical type is non-contact with the cornea, alignment operation such as positioning and focusing of the measuring device with respect to the eyeball to be operated. However, the correction is necessary due to the difference in the curvature of the cornea. On the other hand, the ultrasonic type is a type that makes contact with the cornea, but it is widely used because alignment is easy. What is generally used as an ultrasonic type is a probe to which one ultrasonic transducer is attached.

Recently, a probe (multipoint probe) having a plurality of ultrasonic transducers for measuring the corneal thickness distribution at one time has been proposed. For example, Japanese Patent Laid-Open No. 62-1067
No. 50 and Japanese Patent Application Laid-Open No. 2-261438.

[0005]

However, in the case of a probe to which one ultrasonic transducer is attached, the probe is moved over the cornea to measure the thickness of the cornea and its distribution. However, the measurement points are strictly determined as a guide, and the accuracy of position accuracy is lacking.

In the probe disclosed in Japanese Unexamined Patent Publication (Kokai) No. 62-106750, a fixation lamp is arranged at the center of the multipoint probe or symmetrically with the center so that the subject can fix the eye. The center of the cornea and the center of the probe are made to coincide with each other. However, the examiner cannot confirm whether or not the examinee is gazing and the position accuracy is not guaranteed.

The probe disclosed in Japanese Patent Laid-Open No. 2-261438 does not have a mechanism for alignment with the central axis of the cornea. Further, since the curvature of the contact concave surface with the cornea of the probe does not easily match the curvature of the cornea, it is extremely difficult to align the central axis of the cornea with the central axis of the contact concave surface.

If the alignment is inaccurate in this way,
The front surface of the cornea cannot be irradiated with the ultrasonic beam in the normal direction, and the corneal thickness cannot be accurately measured. Moreover, since the contactor must be repeatedly moved on the cornea for alignment, there is a risk that the eyeball to be inspected may be damaged.

The present invention has been made in order to solve the above-mentioned problems, and utilizes an ultrasonic transducer provided in an ultrasonic probe of a corneal thickness measuring apparatus to measure a crystalline lens of an eye to be inspected. By detecting the front and / or back echoes and comparing the strength of the echoes, it is automatically detected that the central axis of the cornea and the central axis of the probe match, and in the case of multi-point type At the same time, it is an object of the present invention to provide a corneal thickness measuring device capable of scanning the transducer group and measuring the thickness and distribution of the cornea with high positional accuracy.

[0010]

A corneal thickness measuring apparatus according to the present invention is an apparatus for measuring corneal thickness, which includes an ultrasonic transducer and has means for detecting an echo of an ultrasonic beam applied to an eye to be inspected. By comparing the intensities of the echoes of the irradiated ultrasonic beam on the anterior surface and / or posterior surface of the lens, it is determined that the central axis of the probe and the central axis of the crystalline lens of the eye to be inspected are substantially coincident with each other. It is characterized by having means for.

The measuring device comprises a plurality of the ultrasonic transducers arranged radially from the center of the probe, and the ultrasonic transducers arranged at the center of the probe irradiate the ultrasonic transducers. By comparing the intensity of the echo of the ultrasonic beam emitted and the intensity of the echo of the ultrasonic beam emitted from the surrounding ultrasonic transducer, the central axis of the probe and the central axis of the crystalline lens of the eye to be examined are compared. Has a means for determining that they substantially match, or the pre-measuring device is provided with at least one ultrasonic transducer located at the center of the probe,
By comparing the intensity of the echo of the ultrasonic beam emitted from the ultrasonic transducer with the intensity of a preset echo, the central axis of the probe and the central axis of the crystalline lens of the eye to be inspected are substantially It preferably comprises means for determining a match.

Further, when the comparison means determines that the central axis of the probe and the central axis of the crystalline lens of the eye to be inspected are substantially coincident by comparing the echo intensities, the cornea is automatically set. Preferably, the measurement of the corneal thickness is started from the intensity of the echo on the front surface and the rear surface of the.

In addition, it is more preferable to include means for displaying the coincidence between the central axis of the probe and the central axis of the crystalline lens of the eye to be inspected.

[0014]

[Function] The front and rear surfaces of the crystalline lens have a substantially constant curvature (that is, a part of a substantially perfect spherical surface), and the central axes of both are naturally coincident. Therefore, the center of the crystalline lens should be detected. Is easy. Moreover, the central axis of the crystalline lens and the central axis of the cornea coincide with each other. Therefore, the present inventors have created a measuring device that can easily and accurately detect the center of the cornea by detecting the central axis of the crystalline lens based on the position of the crystalline lens.

The central axis of the crystalline lens can be determined by the intensities of the crystalline front surface echo and / or the posterior surface echo generated by the transducer arranged at the center of the probe. This is because the echo of the ultrasonic beam incident in the normal direction of the surface to be inspected becomes the strongest. Therefore, for example, in a probe in which a plurality of transducers are radially arranged, the determination can be made by comparing the transducers arranged in the center of the probe with the strengths arranged in the periphery thereof. In this way, the central position of the cornea can be objectively determined by utilizing one or more lens echoes of the probe. As a result, the corneal thickness and its distribution can be measured extremely accurately.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, a corneal thickness measuring device of the present invention (hereinafter simply referred to as a measuring device) will be described with reference to the accompanying drawings.

FIG. 1 is a longitudinal sectional view showing an embodiment of the probe in the measuring apparatus of the present invention, FIG. 2 is a front view of the probe of FIG. 1, and FIG. 3 is a measurement relating to the embodiment of the present invention. FIG. 4 is a block diagram schematically showing the device, and FIG. 4 is an explanatory diagram showing an echo display that can be detected by the probe shown in FIG.

In FIG. 1A, 1 is a probe,
An ultrasonic transducer 3 and a contact terminal 4 are arranged in the housing 2. C is the cornea to be examined, and L is the lens. The contact terminal 3 is an acoustic medium such as PMMA.
Alternatively, a material having excellent ultrasonic characteristics such as polydimethylpentene is used. Ultrasonic transducers 3a, 3b, 3c, 3d,
3e, 3f, and 3g are arranged on the rear end surface of the contact terminal 4 having a spherical surface. Actually, as shown in FIG. 2, twenty-one ultrasonic transducers 3 are radially arranged, but only the seven ultrasonic transducers 3 are shown in this cross-sectional view (FIG. 1). The contact end surface (spherical concave surface having substantially the same curvature as the cornea) 4a of the contact terminal 4 is brought into contact with the surface of the cornea C via a liquid such as tears. In this state, an ultrasonic beam is oscillated from the ultrasonic transducer 3 to detect an echo on the surface of the cornea C or the lens L.

FIG. 1 (b) shows a crystalline lens L and a cornea C formed by a vibrator 3a located at the center of the probe 1 shown in FIG. 1 (a).
Shows the echo signal at. m is the front of the cornea, n
Is the posterior surface of the cornea, p is the anterior surface of the lens, and q is the echo on the posterior surface of the lens. The horizontal axis is the distance converted from the time difference,
The vertical axis schematically indicates the echo intensity. The front surface and the rear surface of the crystalline lens L each have a substantially constant curvature.
The ultrasonic echo has the strongest echoes on the front and rear surfaces of the crystalline lens when the ultrasonic beam is incident on the surface of the crystalline lens L in the normal direction. At that time, the central axis of the probe 1 coincides with the central axis of the crystalline lens. You can see that

Even if the point with the strongest echo is not searched for, the echoes p and q from the front and rear surfaces of the lens in FIG. You may make a judgment. With such a configuration, even if only a single ultrasonic transducer (which should be arranged at the center of the probe 1) is provided, alignment can be performed. It should be noted that Vs is a threshold value obtained by statistically processing echo values obtained in advance for a large number of eyeballs.

FIG. 2 is a layout view of the ultrasonic transducer 3 in the probe 1 of FIG. In this embodiment, 21 ultrasonic transducers for measuring the corneal thickness are radially arranged. Among them, one ultrasonic transducer 3a arranged at the center of the probe 1 and the other two transducers 3b and 3c arranged symmetrically with respect to 3a and the other ultrasonic transducer 3a symmetrically with respect to 3a. The arranged vibrators 3h and 3i are used for alignment. That is, the center vibrator 3a is aligned with a position that is considered to be the center of the crystalline lens (cornea), and the vibrators 3a, 3b, 3c, 3h, 3i are driven by the drive circuit 5 as shown in FIG.
Are sequentially driven, the detection circuit 6 detects echoes on the front surface and / or the rear surface of the lens L, and the comparison circuit 7 causes echoes of the ultrasonic beams by the ultrasonic transducers 3a, 3b, 3c, 3h, 3i to The strength) is compared and judged.

At this time, for example, as shown in FIG. 4, the echo by the central ultrasonic transducer 3a is shown in FIG. 4A, and the echoes by the surrounding ultrasonic transducers 3b, 3c, 3h, 3i are respectively shown in FIG. 4 (b), the probe 1 is the cornea C
It is judged that the position was accurately aligned with the center of.

This is because the echo is the strongest for the ultrasonic beam incident on the reflecting surface in the normal direction.

In FIG. 4, m is an echo of the anterior surface of the cornea, n
Is the echo of the posterior surface of the cornea, p is the echo of the anterior surface of the lens, and q is the echo of the posterior surface of the lens.

However, as described above, the plurality of ultrasonic transducers 3a, 3b, 3c, 3h, and 3i are concentric with the spherical center of the cornea when the contactor 4 is brought into contact with the eye to be inspected. Since it is arranged on a spherical surface, the echoes from the cornea C have almost the same intensity, and it is difficult to judge the central axis. Therefore, the echoes from the lens L are compared. It is possible to determine the difference in the intensity of the echo from the front surface of the crystalline lens L, but the echo from the rear surface of the crystalline lens L greatly differs depending on the incident position of the ultrasonic beam. If used together, the comparison becomes easier. This is because the curvature of the spherical surface on which the plurality of ultrasonic transducers are arranged and the curvature of the rear surface of the lens L are opposite to each other.

Thus, it is extremely effective to detect the echo on the rear surface of the lens.

In this embodiment, the echo by the central ultrasonic transducer 3a and the remaining ultrasonic transducers 3b, 3c, 3 are used.
Although the alignment was performed by comparison with the echoes of h and 3i, the present invention is not limited to such alignment. For example, by statistically processing the lens echo values obtained from a large number of eyeballs,
The echo intensity threshold value (for example, V _H ) is set for the central ultrasonic transducer, and the echo intensity threshold value (slightly smaller than V _H is set for the remaining ultrasonic transducers (for example, V _H ). For example, by setting V _L ), when the echo by the central ultrasonic transducer becomes V _H or more and all the echoes by the remaining ultrasonic transducers become V _L or less, the probe 1 The central axis and the central axis of the lens L (that is, the cornea C
The comparison circuit may be set so as to determine that the center axis of the comparison circuit is the same.

As is common to all the above-mentioned embodiments, a mechanism is provided for scanning the probe 1 on the surface of the eye to be examined until the comparison circuit detects the coincidence of the central axes.
This scanning mechanism may be the same as the conventional one.

Further, as shown in FIG. 3, the comparison circuit 7
At the same time that the coincidence of the central axes is detected by, the display circuit 8 for displaying this (by buzzer or lighting) and the ultrasonic transducer group are driven to measure the thickness of the cornea and its distribution. It is configured to give a start signal to the measurement drive circuit 9.

[0030]

The measuring device of the present invention can easily and accurately use an ultrasonic transducer for measuring corneal thickness without having to rely on the conventional optical member or the action of the subject to fixate. The position of the probe can be adjusted and the eyeball to be inspected is not damaged.

[Brief description of drawings]

FIG. 1 is a vertical sectional view showing an embodiment of a probe in a measuring apparatus of the present invention.

FIG. 2 is a front view of the probe shown in FIG.

FIG. 3 is a block diagram showing an outline of a measuring apparatus according to an embodiment of the present invention.

4 is an explanatory diagram showing an echo display that can be detected by the probe of FIG. 1. FIG.

[Explanation of symbols]

 1 probe 2 housing 3 ultrasonic transducer 4 contact terminal C cornea L crystalline lens

Claims (5)

[Claims] 1. A corneal thickness measuring apparatus comprising an ultrasonic transducer and having means for detecting an echo of an ultrasonic beam applied to an eye to be inspected, the front surface of a crystalline lens of the applied ultrasonic beam and / or Corneal thickness measurement characterized by having means for determining that the central axis of the probe and the central axis of the crystalline lens of the eye to be inspected are substantially matched by comparing the intensity of the echo on the posterior surface of the crystalline lens. apparatus. 2. An ultrasonic beam radiated from an ultrasonic transducer arranged in the center of the probe, comprising a plurality of the ultrasonic transducers arranged radially from the center of the probe. By comparing the echo intensity of the ultrasonic wave with the echo intensity of the ultrasonic beam emitted from the surrounding ultrasonic transducer, it was found that the central axis of the probe and the central axis of the crystalline lens of the eye to be examined were substantially coincident. The corneal thickness measuring device according to claim 1, further comprising means for determining. 3. At least 1 located at the center of the probe
Equipped with an ultrasonic transducer, by comparing the intensity of the echo of the ultrasonic beam emitted from the ultrasonic oscillator with the preset intensity of the echo, the central axis of the probe The corneal thickness measuring apparatus according to claim 1, further comprising means for determining that the center axis of the crystalline lens of the eye to be inspected substantially coincides. 4. The cornea is automatically provided when the comparing means determines that the central axis of the probe and the central axis of the crystalline lens of the eye to be inspected are substantially coincident by comparing the echo intensities. The corneal thickness measuring apparatus according to claim 1, wherein the corneal thickness measuring apparatus is configured to start measuring the corneal thickness based on the intensity of echoes on the front surface and the rear surface. 5. The corneal thickness measuring apparatus according to claim 1, further comprising means for displaying the coincidence between the central axis of the probe and the central axis of the crystalline lens of the eye to be inspected.