JPS62106749A - Ultrasonic probe for measuring thickness 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 [Industrial Application Field] The present invention relates to an ultrasonic probe for measuring corneal thickness that measures corneal thickness and its distribution using ultrasonic waves.

[Prior Art] Corneal thickness measurement has been used to monitor corneal function, but recently it has been used in a surgery called radial keratotomy to convert a myopic eye into an emmetropic eye by changing the curvature of the cornea. In this surgery, since there is a risk of damaging the cornea in the radial direction, it is important to adjust the length of the scalpel blade, and there is a growing need for accurate measurement of corneal thickness and its distribution.

Methods for measuring corneal thickness are broadly divided into optical methods and ultrasound methods. Optical methods can generally measure accurately, but the operation is complicated and correction is required. . On the other hand, methods using ultrasonic waves are becoming widespread because they are easy to handle and provide measurement data with sufficient accuracy to withstand use.

The probe of an ultrasonic device that is popular for measuring ocular biomembranes includes a single transducer with a diameter of about 1 mm.
In order to determine the thickness distribution of the cornea, this probe is moved over the cornea and measured. For this reason, the identification of the measurement position may be inaccurate, and since the tip of the probe that contacts the cornea is small compared to the corneal diameter, unexpected force may be applied during movement or during measurement, causing damage to the cornea. There are some disadvantages, such as the risk of

[Object of the Invention] An object of the present invention is to provide an ultrasonic probe for corneal thickness measurement that eliminates the above-mentioned drawbacks and can measure corneal thickness and its distribution easily, safely, and accurately. It is in.

[Summary of the Invention] The gist of the present invention to achieve the above-mentioned object is to provide a plurality of superconducting layers on at least one radial line on a plurality of arcuate layers formed approximately concentrically with the center of curvature of the cornea. This is an ultrasonic probe for corneal thickness measurement characterized by having a sonic transducer arranged therein.

[Embodiments of the invention] The present invention will be explained in detail based on illustrated embodiments.

FIG. 1 is a cross-sectional view of a probe shaped like a surgical contact lens. An acoustic matching layer 2.3 with a radius of curvature R is provided inside an outer frame 1 formed in a tapered shape. A delay layer 4 is provided. On the surface of the matching layer 3, for example, five ultrasonic transducers 5a to 5e are arranged along a diameter of 1-41L as shown in FIG. '79 backing layer 6
is provided on the upper layer. In addition, the vibrators 5a to 5e
The output is connected to an external electrical device via a lead wire 7 and a connector 8.

The delay layer 4 reflects the ultrasound from the cornea and the ultrasound transducer 5.
It is for separating the drive pulses a to 5e, and is made of, for example, acrylic, which has almost the same acoustic impedance as a living body. Acoustic matching box? , 3 is a layer with a thickness of 0/4 for matching the acoustic impedance of the ultrasonic transducers 5a to 5e and that of the delay layer 4, where 0 is the wavelength of the ultrasonic wave, and ZOlZl and Z2 are the intermediate layers, respectively. Assuming the acoustic impedance of (ZO) and the layers (Zl, Z2) that sandwich it, ZO = (Zl・Z2)'/2
It is made of materials that satisfy the following relationship.

The ultrasonic transducers 5a to 5e have frequencies of 10 to 20
a piezoelectric element 7 having a thickness of 1/2 that vibrates at a thickness of MHz;
For example, it is a vapor deposited film based on a piezoelectric film such as pVDF or a piezoelectric material such as CdS, which is crystallized by heat treatment. When using PVDF, the matching layer 2.3
However, when using a CdS film, the matching layer 2.3 becomes important because the acoustic impedance is about one order of magnitude different from that of a living body. In this case, good results can be obtained if epoxy is used as the matching layer 2 and 5i02 is used as the matching layer 3.

Although the electrodes of the ultrasonic transducers 5a to 5e are not shown in FIG. 1, if the lead wires 7 are arranged as shown in FIG. Vibrator 5a~
Individual electrodes may be provided on the backing layer 6 side of 5e.

The backing layer 6 is for applying damping to the transducers 5a to 5e and promoting absorption of ultrasonic waves, and is made of a material such as epoxy mixed with rubber, which has high ultrasonic absorption and mechanical strength. A material with high adhesive strength is preferable.

Now, the matching layer 2.3 and the delay layer 4 are spherical with the center being O, and the innermost layer, the delay layer 4, is brought into contact with the angle IQ. The emitted ultrasound waves are directly incident on the cornea. Furthermore, although the radius of curvature of a normal cornea is distributed between 6 mm and 9 mm, the radius of curvature of the inner surface 4a of the delay layer 4 is selected to be 7.4 to 7.8 mm, which is the average value of the distribution of the radius of curvature of the cornea. Then, the deviation of the radius of curvature will be minimized, and the pressing force required to fit the retardation layer 4 to the cornea will be minimized.

In operation, sterilized distilled water is dropped onto the inner surface 4a of the delay layer 4, brought into contact with the cornea, and a 0.3
It transmits and receives pulsed ultrasonic waves of approximately 1000 nm, and calculates the thickness from the return time and searches for the thinnest point, the apex of the cornea. After determining the apex of the cornea, under the control of a control device (not shown), waves are transmitted and received sequentially to the transducers 5b, 5a, 5d, and 5e, and the thickness at a fixed position on the same radial line is determined, thereby determining the corneal thickness. Distribution is required.

Here, when the cornea and the delay layer 4 are not in close contact at the periphery or the center, the memorized vibrator 5C at the center
The magnitude of the received signal at
The magnitudes of the received signals at e are compared, and if the difference exceeds a permissible range, a warning is displayed by sound or light. When the examiner applies pressure to the probe in response to this warning, the cornea can be brought into close contact with the inner surface 4a of the delay layer 4 due to the elasticity caused by the intraocular pressure.

As the ultrasonic transducers 5a to 5e, five elements are shown arranged on one radius line in FIG. Just repeat.

Further, as shown in FIG. 3, a large number of ultrasonic transducers may be arranged across a multiradial line.

For the purpose of radial keratotomy, what is required is an 8-radial line A shown in Figure 3 with a center and diameter of 4 mm or more,
B, . . . , the thickness on H.

When the ultrasonic transducers 5 in the second row are arranged radially in four rows from the inside including the center as shown in FIG. It is considered optimal that the diameter d is 4 mm and the array diameter of the fourth row of vibrators 5 is 8 to 9 mm. The number of rows of 50 transducers depends on the diameter of the transducer 5 and the spread of the ultrasonic beam due to the frequency, and is determined by the S/N ratio and resolution. It is desirable to increase the number of columns of 5. If the number of rows is increased, there is a problem that the wave transmitting/receiving circuit that drives each vibrator 5 becomes larger. However, the vibrators 5 are subdivided into groups within the range that crosstalk does not occur in receiving waves, and the transmitting waves are divided into groups. If a driving method is adopted in which the wave reception is selected for each vibrator 5 using a switch or the like, the size can be reduced.

[Effects of the Invention] As explained above, the ultrasonic probe for corneal thickness measurement according to the present invention has a plurality of ultrasonic transducers arranged in at least one radial direction, so it can be easily, safely, and accurately measured. It becomes possible to measure corneal thickness and its distribution.

[Brief explanation of drawings]

The drawings show an embodiment of the ultrasonic probe for measuring corneal thickness according to the present invention, and FIG. 1 is a cross-sectional view thereof, and FIGS. 2 and 3 are layout diagrams of an ultrasonic transducer. 1 is an outer frame, 2 and 3 are acoustic matching layers, 4 is a delay layer, 5 is a vibrator, 6 is a bar, a king layer, 7 is a lead wire, and 8 is a connector.

Claims (1)

[Claims] 1. A corneal thickness characterized in that a plurality of ultrasonic transducers are arranged on at least one radial line on a plurality of arcuate layers formed substantially concentrically with the center of curvature of the cornea. Ultrasonic probe for measurement. 2. The plurality of layers consist of an acoustic matching layer and a delay layer, and the radius of curvature of the inner surface of the innermost delay layer is 7.4 to 7.8 m.
The ultrasonic probe for corneal thickness measurement according to claim 1, wherein m is defined as m.