JPH08299282A - Device which accurately measures pressure plane in order to measure eye pressure - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately determine an applanation surface by providing a second receiver for monitoring purity of an end surface of a prism, positioning a light separating element between a light source within a bundle of light beams transferred from the light source and the prism, and conveying the separated light beams to the second receiver in the form of contrast beams. SOLUTION: Light beams emitted from a light source 1 are penetrated into a prism 5 through a lens 9, and light beams emitted from the prism 5 are focused on a receiver 6 by a lens 10. The receiver 6 outputs a basic light intensity value due to an operating condition of a tonometer in a condition that the prism 5 does not touch an eye. A measuring value of the light intensity outputs a light intensity value due to a volume of applanation surface value in a condition that the prism 5 touches the eye. A second receiver 8 outputting a contrast value is positioned adjacently to the receiver 6, and light beams emitted to the second receiver 8 are directly divided by a light separating element 2 from a bundle of light beams emitted from the light source 1 and and deflected by a mirror 7 to penetrate onto the receiver 8.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses an tonometer, and more particularly, an automatic applanation tonometer to measure an intraocular pressure.
ationsflaeche) relating to a device for accurately measuring.

[0002]

2. Description of the Related Art In an automatic tonometer, an effective pressing force and an applanation area are detected in an applanation process in order to measure an intraocular pressure. In many cases, the applanation area is optically detected by various methods.

One of the principles of optically measuring the applanation area is to measure a reflected light beam which is lost in total reflection at the contact pressure body or the end surface of the pressure body when the end surface of the pressure body is brought into contact with the cornea. And the amount of ray loss is proportional to the size of the pressure plane.

[0004] For example, a solution of this kind is disclosed in German Patent No. 3,931,630. Here, a measuring body in the form of a prism is used. The prism has at least one inclined side surface. The light flux incident from the bottom surface of the prism is reflected toward the end surface on the inclined side surface of the prism to form total reflection on the end surface of the prism extending parallel to the bottom surface (air is used as an external medium). When the end surface of the prism is in contact with the eye, the light beam incident on the pressure plane formed on the end surface is refracted and emitted from the prism. As a result, the light intensity of the entire light flux reflected on the end face and incident on the receiver is reduced.

In order to accurately measure the applanation area, no deposits should be present on the end face of the pressure body before the measurement. However, deposits remain on the end face of the pressurizing body after contact with the eye, and the deposits need to be removed by special cleaning. It is desirable to always readjust the initial value (light intensity value I ₀ ) of the measurement light beam when the adhered matter is removed. But,
This process causes a substantial measurement error because the light intensity itself does not show a sufficiently constant value.

The largest cause of the error is the temperature dependence of the light source and the receiver. Temperature drift within the normal fluctuation range at room temperature in the range of 15-30 ° C. leads to a ± 8% fluctuation of I ₀ when using light emitting diodes.

Another source of error is the replacement of the pressurizer, which is required to sterilize the pressurizer. Due to the low permissible positional tolerance, a slight misalignment of the pressure body that occurs when the pressure body is replaced can easily cause a large decrease in light intensity.

The present invention has been made in view of the above-mentioned circumstances, and an object thereof is to provide an apparatus for accurately measuring an applanation area for performing intraocular pressure measurement using a tonometer. .

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to accurately measure a pressure plane to measure intraocular pressure using an tonometer equipped with a light source, a prism as a pressurizing body, a receiver and an evaluation unit. The prism has an end face that forms a pressure plane on the surface of the eye, and the light flux propagated from the light source is totally reflected at the contact with the air on the end face, and the total reflection is when the eye comes into contact with the eye. The light rays that are partially eliminated and reflected at the end face are propagated on the receiver and are converted in the same receiver, the light intensity change caused by the reduced total reflection by the evaluation unit placed further in the direction of the light ray propagation. A device having means for calculating the area of the pressure plane from the first receiver comprises a second receiver for monitoring the cleanliness of the end faces of the prism, the second receiver comprising the first receiver.
A light-splitting element, which is arranged adjacent to the receiver of the light source, detects the contrast value, and is in the light beam propagated from the light source, and between the light source and the prism. The ray is propagated as a reference beam onto the second receiver, and the evaluation unit comprises means for forming a reference value ratio from the basic light intensity value of the first receiver and the reference value of the second receiver, Has a storage means for storing the determined normal value and a subtracter for calculating an error value from the ratio of the normal value and the measured reference value, and an error value below the allowable error value is used as a precondition for starting the applanation measurement process. It is realized by a device characterized by being performed.

The beam splitting element includes a semi-transparent mirror, which is preferably a dielectric beam splitting film formed on a glass plate. The splitting ratio of light rays by the semi-transparent mirror is preferably 1: 1. The deflecting mirror, which is in the form of a concave mirror, is preferably arranged further ahead of the semi-transparent mirror in the ray propagation direction in order to focus the ray on the second receiver.

When using a diverging light source, such as a light emitting diode, an annular diaphragm with a mirror coating can be effectively used as the beam splitting element, the annular diaphragm being in the central aperture of the annular diaphragm within a beam of limited rays. Allows to be propagated through to the prism unimpeded. The mirror coating on the diaphragm is effectively formed as a concave mirror that focuses the split rays onto a second receiver.

A third possibility of realizing the beam splitting element is that of an optical fiber conductor whose one end is arranged in the peripheral region of the light beam emitted from the light source and whose other end is arranged on the second receiver. Includes use. The fiber optic conductor is preferably formed as a fiber ring arranged around the periphery of the light beam emitted from the light source.

The second receiver preferably has the same structure as the first receiver and is obtained from the same production batch. The evaluation unit preferably comprises further means for suppressing the effects of temporary fluctuations in the light intensity of the light source. In this case, it is preferable to convert the measured light intensity value formed by the pressure plane into a ratio to the measured reference value.

A substantial error in the tonometer when measuring the applanation area is caused by the deposit on the pressure body and the alignment error of the pressure body. Furthermore, changes in the temperature of the light source and the receiver also affect the tonometer error. It is impossible to effectively separate these errors. As a result, control channels (Kontrollkanals) are provided according to the present invention. The control channel first compensates for temperature effects, allowing the detection and assessment of error-causing external influences (pressure body surface deposits and pressure body misalignment). In this case, the criterion for preventing the start of measurement (erroneous measurement) when the error exceeds the tolerance is applied to the external factor.

By using the device of the present invention, the accuracy of the applanation area measurement can be improved and the reproducibility of the measurement can be improved.
This is effective for improving the accuracy when measuring the intraocular pressure using the tonometer, and further enables automation of the intraocular pressure measurement independent of the user's experience. Furthermore, the second consequence is that the temperature dependence in the applanation area measurement is substantially compensated.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The device according to the basic embodiment of the invention shown in FIG. 1 comprises a light source 1, a beam-splitting element 2 and a pressurizing body 5 for total reflection at its end face forming the contact surface with the eye. Two lenses 9, 10 and two receivers 6,
8 is provided.

The light source 1 is preferably a light emitting diode
It Light rays emitted from the light source 1 should pass through the lens 9.
Then, it becomes a parallel light beam, and is further incident on the pressure body. Base
The special trapezoidal prism 5 is used as a pressure body
That is effective. The medium facing the end face of the prism 5
In the case of air, the total reflection of parallel rays is inside the prism 5.
Will be realized. After this ray exits prism 5,
Is focused on the receiver 6 by the lens 10
It The receiver 6 has a state in which the prism 5 is not in contact with the eyes.
In this state, an electrical signal based on the usage status of the tonometer
And basic light intensity value I ₀Is output. Furthermore, the receiver 6
When the prism 5 is in contact with the eye, the applanation area is large.
Light intensity measurement value I_MIs output. Control value I_K
The second receiver 8 which outputs
It is arranged. The two receivers 6 and 8 have
Are considered to have the same sensitivity in positions adjacent to
Use optical receivers from the same production batch
Is effective.

The light beam incident on the second receiver 8 is directly split by the light beam splitting element 2 from the light beam emitted from the light source 1, and is further deflected by the mirror 8 so as to be incident on the receiver 8. The beam splitting element 2 can be any one of a semi-transparent mirror, a beam splitting cube (Teilerwuerfel) and a glass plate with a dielectric beam splitting film. Furthermore, the beam splitting element 2 splits the light beam emitted from the light source 1 into a measuring beam 3 and a reference beam 4, preferably in a ratio of 1: 1.

The beam splitting element 2 can be arranged on the optical path of a divergent ray or a parallel ray emitted from the light source 1.
That is, the beam splitting element 2 may be arranged in front of the lens 9 as shown in FIG. 1 or may be arranged on the other side of the lens 9. It is advantageous to form the mirror 7 as a concave mirror in order to prevent light loss of the reference beam 4 caused by the expansion of the beam cross section which occurs when the beam splitting element 2 is arranged in the optical path of the diverging light beam.

FIG. 2 shows another way of splitting the light rays to form a reference beam 4. In this embodiment, since the light beam emitted from the light emitting diode has a relatively large divergence, the fact that the peripheral regions of the light beam are not parallel due to the lens 9 is used in all cases. This relatively large peripheral area is slightly inclined (up to 4
The target beam 4 using the annular diaphragm 11
Are effectively used to form Focusing means are required due to the relatively large divergence of the light rays. The focusing means may be realized by using a beam deflecting mirror 7 in the form of a concave mirror as shown in FIG. 1, or the diaphragm 11 itself may be formed as a concave mirror and the light beam on a receiver 8 aligned with the diaphragm 11. This can be achieved by directly focusing on.

The device shown in FIG. 2 has the same basic structure as the device shown in FIG. However, in FIG. 2 the applanation of the eye on the end face of the prism 5 is shown. The receiver 6 outputs the basic light intensity value I ₀ (the output signal is shown by a broken line) before contact with the eye, while the light intensity measurement value I _M is formed based on the surface flattened at the time of contact with the eye. Record the variation of the light rays. FIG. 1 shows the state in which the eye is not applanated and shows the subsequent detection of the light intensity measurement I _M (broken line).

The structure shown in FIG. 3 is based on the structure shown in FIG. Here, the means of optical splitting of the rays to form the reference value I _K is modified. Optical splitting of the light beam is performed by the fiber optic conductor 12. The optical fiber conductor 12 guides a light beam from the peripheral edge of the light beam emitted from the divergent light source 1 toward the second receiver 8. In order to achieve this, the optical fiber conductor 12 effectively has a fiber bundle arranged respectively concentrically around the measuring beam 3 in a holder 13, which is preferably made of cast plastic, and also has a basic light intensity. Ensure that the values I ₀ and I _K are approximately the same.

The converted receiver signal is evaluated in an evaluation unit (not shown). The evaluation unit according to the invention comprises means for forming a reference value ratio (Kontrollwertquotienten) from the basic light intensity value I ₀ and the reference value I _K, storage means for storing the normal value thus formed, normal value and measured reference. And a subtractor that calculates an error value from the value ratio.

The target value ratio I ₀ / I _K is calculated to indicate the cleanliness of the prism 5. Fluctuations in the light intensity of the light source 1 are detected by the second receiver 8 at least through the radially extending luminous flux (Strahlenkegels) emitted from the light source 1.

Next, the light intensity of the light source (control value I _K ) is the light intensity (basic light intensity value I ₀ ) measured on the first receiver 6 during idle operation of the tonometer (without contact with the eye). Is converted to the ratio. This guarantees the elimination of variations in light intensity due to temperature changes, since the effects of temperature changes on the basic light intensity I ₀ and the reference value I _K are equal to each other. Since the receivers 6 and 8 are arranged adjacent to each other, it is guaranteed on the receivers 6 and 8 that the fluctuation of the light intensity due to the temperature change is prevented.

By this basic standardization or scaling, the contrast value ratio I ₀ / I _K indicates the measured value of the optical state of the prism 5 including the cleanliness of the end surface of the prism 5 and the arrangement position. Since the prism 5 is frequently removed and replaced in order to perform sterilization, the measurement value indicating the position of the prism 5 is particularly important.

For the purpose of objectively examining the error value found in the measurement of the applanation area, the standard value of the control value ratio (I
₀ / I _K ) _Norm is measured and stored in the prism 5 at optimal clean and aligned conditions. The actual value of the contrast value ratio (I ₀ / I _K ) _actual is detected immediately before each measurement of the applanation area of the eye. The evaluation unit then calculates the difference between the standard value and the measured value of the control value ratio, and further compares the difference with a predetermined tolerance. The applanation step is started only when the difference is below the tolerance (T) as shown in the following equation. (I ₀ / I _K ) _Norm − (I ₀ / I _K ) _actual <T This guarantees a sensitive inspection of the optical conditions in the prism 5 and automatically blocks false measurements of the pressure plane. By performing at least one of cleaning and readjustment of the prism 5, the cause of the error can be accurately eliminated, and further, it can be evaluated by a new inspection measurement (Kontrollmessung). The applanation process is then automatically started when the tolerances are maintained.

The basic light intensity value I ₀ (before applanation) of the light intensity measurement value I _M (eye contact) is substantially eliminated in order to substantially eliminate the influence of a temporary fluctuation caused by the light source 1 when measuring the applanation area. The measured value represented by the following mathematical formula is effectively used as the light intensity measured value for calculating the applanation area in place of the ratio to. I _N = I _M / I _K where I _N is the standardized light intensity measurement (normierten
Intensitaetsmesswert).

The transition of the values of the applanation area is obtained as a result of the transition of the ratio of the values of I _M and I _K obtained simultaneously. This broadens the applanation area measurement from all substantial sources of error in optical surface measurements.

[0030]

As described above in detail, according to the present invention, the excellent effect that the applanation area can be accurately measured in the intraocular pressure measurement using the tonometer is exhibited.

[Brief description of drawings]

FIG. 1 is a side view showing the basic embodiment of the optical part of the device of the present invention.

FIG. 2 is a side view showing an effective mode of the optical portion of the present invention.

FIG. 3 is a side view showing a second effective aspect of the optical portion of the present invention.

[Explanation of symbols]

1 ... Light source, 2 ... Ray splitting element, 4 ... Control beam,
5 ... prism, 6 ... first receiver, 7 ... mirror, 8 ... second receiver, 11 ... annular diaphragm, 12 ... optical fiber conductor, I ₀ ... basic light intensity, I _K ... control value.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Norbert Klose Greichenday, Federal Republic of Germany − 07616 Siedrunk 4 (72) Inventor Peter Voigt, Jena Day, Federal Republic of Germany − 07747 Hans Berger-Strasse 20 (72) Inventor Klaus Muir Federal Republic of Germany Jenaday-07607 Adolf-Geier-Strasse 3

Claims (9)

[Claims] 1. A device for accurately measuring a pressure plane to measure intraocular pressure using an tonometer equipped with a light source, a prism as a pressurizing body, a receiver, and an evaluation unit, wherein the prism is Has an end face forming a pressure plane on the surface,
At the end face, the light beam propagated from the light source is totally reflected at the contact with the air, the total reflection is partially canceled when contacting with the eye, and the light beam reflected at the end face is propagated on the receiver, and A device having means for calculating the area of the pressure plane from the change in light intensity caused by the reduced total reflection in the evaluation unit, which is converted in the same receiver and is arranged further forward in the light beam propagation direction, A second receiver (8) is provided for monitoring the cleanliness of the end face, said second receiver (8) being arranged adjacent to the first receiver (6) and also having a reference value (I _K ). Detecting and in the light beam propagated from the light source (1) and between the light source (1) and the prism (5), a beam splitting element (2) is arranged, whereby And being propagated to rays the control beam (4) as a second receiver (8) above, wherein the evaluation unit first basic light intensity value of the receiver (6) (I ₀₎ and a second receiver (8) Means for forming a reference value ratio from the reference value (I _K ), storage means for storing a normal value formed thereby, and a subtracter for calculating an error value from the normal value and the actually measured reference value ratio Has and
A device characterized in that an error value below the permissible error value is used as a precondition for starting the applanation measuring process. 2. Device according to claim 1, characterized in that the beam splitting element (2) is a semi-transparent mirror. 3. The apparatus according to claim 2, wherein the semi-transparent mirror is a dielectric beam splitting film arranged on a glass plate and splitting the light intensity at a ratio of 1: 1. 4. A mirror (7) for deflecting the split light beam toward a second receiver (8) is arranged further forward in the light beam propagation direction from the light beam splitting element (2). 4. Device according to claim 3, characterized in that the mirror (7) is preferably a concave mirror. 5. The ray-splitting element (2) is an annular diaphragm (11) with a mirror coating when using a divergent light source, which is preferably a light emitting diode, the annular diaphragm (11) being defocused. 2. Device according to claim 1, characterized in that it can be propagated in the light bundle through the central opening of the annular diaphragm (11) to the prism (5) unhindered. 6. Device according to claim 5, characterized in that the mirror coating of the diaphragm (11) is formed as a concave mirror which focuses the split rays onto a second receiver (8). 7. The light splitting element (2) according to claim 1, characterized in that it is an optical fiber conductor (12) arranged at the periphery of the light bundle and extending to a second receiver (8). apparatus. 8. Device according to claim 7, characterized in that the optical fiber conductor (12) is formed as a fiber ring arranged at the periphery of the luminous flux of the light source (1). 9. Device according to claim 1, characterized in that the second receiver (8) has the same structure as the first receiver (6) and is obtained from the same production batch.