JP4834445B2 - Tonometry device - Google Patents

Description

  The present invention relates to an intraocular pressure for injecting air into the cornea of a subject eye, optically detecting deformation of the subject eye cornea, and measuring intraocular pressure of the subject eye based on air pressure when detecting applanation of the subject eye cornea The present invention relates to a measuring device.

  In a non-contact tonometer, an air flow is discharged from the air injection nozzle to the eye cornea to deform the eye cornea, and when the eye cornea is deformed into a predetermined shape, that is, the eye cornea is applanated. The detected timing is optically detected, and the intraocular pressure is measured based on the pressure of the air flow at that time. Such a basic configuration is shown, for example, in Patent Document 1 below.

  In this type of apparatus, during measurement of the normal eye to be inspected, a single peak-shaped detection waveform (for example, Fig. 2b of Patent Document 1) is obtained by the light receiving element, and the peak timing detected from such a detection waveform is obtained. It is possible to calculate the intraocular pressure based on this. However, in actual measurement, the waveform is often disturbed due to various factors such as eye movement, alignment instability, tears, and blinking (for example, FIG. 2c of Patent Document 1). In many cases, the detected waveform including the disturbance has a plurality of peaks.

Usually, this type of device is configured to guarantee the accuracy of the entire measurement by detecting abnormal peaks (such as blinking and eye movement) by detecting the waveform peak above a certain intensity of the detection waveform obtained from the light receiving element. However, if the peak of the optical detection waveform does not exceed a certain intensity, a measurement error occurs and remeasurement is required.
JP-A-1-153137 JP-A-2-283349

  In consideration of the measurement error as described above, there is also proposed a configuration in which measurement is performed by changing the air pressure range of the air injected to the eye to be examined when the measurement error occurs (Patent Document 2). However, in the configuration in which the injection air pressure is changed in this way, for example, when the control is changed so that a stronger air pressure is applied, the burden on the subject is heavy, and there is a risk of anxiety and fear. If possible, it is preferable that measurement can be performed with a predetermined minimum injection air pressure.

  Therefore, if the injection air pressure is not changed, the measurement gain setting of the light receiving / measuring system that detects applanation of the eye cornea is taken into account, that is, the gain of the detection signal obtained from the light receiving element and its waveform peak are detected. It is conceivable to set the relative relationship of the thresholds for this purpose accordingly. However, with a single measurement gain setting, it is very difficult to accommodate all measurement situations.

  The measurement gain, that is, the relative relationship between the gain of the detection signal obtained from the light receiving element and the threshold value is almost the same regardless of whether the gain of the detection signal is changed or the threshold value is changed. However, if the threshold value is lowered, the condition is bad, for example, abnormalities of the cornea and tear film, blinking, and eye movements can be measured. There is a high possibility that detection will be performed even during anomalous measurement, resulting in poor measurement accuracy and variable values.

  In addition, if the method of increasing the sensitivity of the light receiving element is obtained to obtain the same effect as lowering the threshold value, it becomes more susceptible to external noise, etc., or normal when measuring high intraocular pressure. Despite being measured, there is also a risk that the signal overflows and the correct value cannot be obtained.

  On the other hand, if the threshold value is increased so that the measured value is stable, that is, the conditions for detecting applanation are strict, the measurement accuracy is guaranteed if the measurement is successful, but a measurement error always occurs depending on the eye to be examined. The situation that cannot be measured at all tends to occur.

  From the above considerations, it is preferable that the measurement gain, that is, the relative relationship between the gain of the detection signal obtained from the light receiving element and the threshold value, can be controlled dynamically and automatically according to the measurement situation. It is done.

  An object of the present invention is to solve the above-mentioned problems and dynamically and automatically control a measurement gain of a light receiving system for detecting deformation of an eye cornea according to a measurement situation, thereby imposing a heavy burden on the subject. It is to be able to perform intraocular pressure measurement accurately and reliably.

In the present invention, in order to solve the above-described problem, air is jetted to the cornea of the eye to be examined, the deformation of the eye cornea is optically detected, and the pressure of the eye to be examined is detected based on the air pressure when the applanation of the eye cornea is detected. In an intraocular pressure measurement device that performs intraocular pressure measurement, a gain of a detection signal obtained from a light receiving element of a light receiving system that detects applanation of a subject's eye cornea is compared with the detection signal in order to detect applanation of the subject's eye cornea. that the intraocular pressure measurement means for performing the intraocular pressure measurement using the measurement gain determined by the relative relationship of the threshold, then attempt to tonometry to the intraocular pressure measurement means using a certain measure gain, said sample line measurement errors When a plurality of times fails, a configuration is adopted in which the control gain is increased by a predetermined difference to cause the intraocular pressure measurement means to try the intraocular pressure measurement .

  According to the above configuration, when the intraocular pressure measurement by the intraocular pressure measurement unit results in a measurement error, the measurement gain is changed so that the intraocular pressure measurement unit performs the intraocular pressure measurement. Excellent effect of measuring intraocular pressure accurately and reliably without imposing a heavy burden on the subject by dynamically and automatically controlling the measurement gain of the light-receiving system that detects deformation. There is.

  Further, when the intraocular pressure measurement means is made to try the intraocular pressure measurement and the trial fails a plurality of times due to a measurement error, the second measurement mode using the second measurement gain larger than the first measurement gain is entered, or Even if a trial of intraocular pressure measurement is accidentally unsuccessful due to conditions such as blinking of the eye to be examined, the intraocular pressure measurement means is made to try the intraocular pressure measurement by increasing the measurement gain by a predetermined difference. Thus, it is possible to improve the probability that the intraocular pressure measurement can be successfully performed without changing the injection air pressure and the measurement gain.

  Hereinafter, as an example of the best mode for carrying out the present invention, an embodiment relating to a non-contact intraocular pressure measuring device will be described.

  FIG. 1 shows a configuration of an intraocular pressure measuring device as an embodiment of an ophthalmologic apparatus employing the present invention, and FIG. 2 shows a configuration of a control system of the apparatus of FIG.

  In FIG. 1, illumination light sources 10 and 11 for illuminating the anterior segment are provided, and the cornea of the eye E is illuminated by these light sources. In addition, an alignment light source 12 is provided to detect the position (X, Y direction) of the eye to be measured with respect to the intraocular pressure measuring device, and the light flux from this light source is projected onto the half mirror 14 via the lens 13. Thereafter, the light is reflected by the half mirror and projected onto the eye to be examined.

  The light beam of the light source 12 reflected by the cornea of the eye to be examined passes through the half mirror 14 and is relayed by the lens 15, passes through the half mirrors 16 and 17, enters the lens 18, passes through the filter 19, and is coupled onto the CCD camera 20. Imaged. This filter 19 is for passing the wavelengths from the light sources 10, 11, 12 and cutting other wavelengths.

  A signal from the CCD camera 20 is input to the CPU 131 of FIG. 2, and alignment in the X and Y directions is determined by a known alignment determination calculation executed by the CPU 131. When the alignment is achieved, the CPU 131 displays the alignment via the monitor 134.

  The reflected light of the light beam from the alignment light source 12 passes through the half mirror 14 and the lens 15, is reflected by the half mirror 16, and is guided to the applanation light sensor 24 through the lens 23. The alignment light source 12 is controlled to be turned on by the CPU 131 and also serves as a light source for measuring intraocular pressure.

  The intraocular pressure measuring device of FIG. 1 is provided with an air pressurizing means (not shown) for blowing an air flow to the eye cornea to be examined. The air pressurizing means changes the pressure with respect to the eye E with time. The cornea of the eye E is deformed by receiving this air flow, and the amount of light received by the applanation light sensor 24 changes.

  The air pressure discharged from the nozzle 22 is detected by the pressure sensor 132 of FIG. The air pressure detection value of the pressure sensor 132 is input to the CPU 131 via an A / D converter (not shown).

  The optical system leading to the alignment light source 12 and the applanation light sensor 24 is arranged so that the applanation light sensor 24 generates the maximum output when the cornea of the eye to be examined is applanated by the air flow. Based on the air pressure detection value obtained from the sensor 132, the CPU 131 calculates an intraocular pressure value and displays it on the monitor 134 (or prints on the printer 135).

  Further, the optical system of FIG. 1 is provided with a light source 30 for performing alignment in the optical axis direction of the eye to be examined and the apparatus, and a light beam from this light source is projected onto the eye to be examined through a lens 31. Reflected light from the eye to be examined is received by a two-divided sensor 34 including sensors 34 a and 34 b through a filter 32 and a lens 33. The filter 32 transmits the wavelength of the light beam from the light source 30 and cuts the wavelengths of other light sources. Further, by calculating the outputs of the sensors 34a and 34b of the two-divided sensor 34, the alignment determination in the optical axis direction between the eye to be examined and the apparatus is performed based on the principle of triangulation.

  Specifically, the sensors 34a and 34b are arranged so as to have the same amount of received light when the cornea of the eye to be examined and the distance in the optical axis direction of the apparatus are appropriately adjusted, and the output voltage of each sensor 34a and 34b. Va and Vb are converted into digital signals via an A / D converter (not shown), and then input to the CPU 131. The CPU 131 checks the balanced state of the output voltages Va and Vb of the sensors 34a and 34b. The suitability of the alignment state in the optical axis direction between the eye to be examined and the apparatus is determined. The fixation lamp 26 is a light source for the patient to gaze to make the patient immobile with respect to the apparatus.

  The control system of FIG. 2 is configured by connecting each member described in FIG. 1 (using the same reference numerals as described above) to the system bus of the CPU 131. The output of the applanation light sensor 24 is input to the CPU 131 via the sensor control circuit 133. The sensor control circuit 133 changes the amplification factor of the detection signal output from the applanation light sensor 24 in order to change the measurement gain based on the control of the CPU 131 in the control described later.

  The CPU 131 is connected to a monitor 134 for displaying the measurement operation state and the measurement result, and a printer 135 for outputting the measurement result. The CPU 131 controls lighting / extinguishing (or light quantity) of the light sources 10, 11, 12.

  In the intraocular pressure measurement, the CPU 131 calculates the intraocular pressure value based on the air pressure detection value obtained from the pressure sensor 132 at the timing when the output of the applanation light sensor 24 reaches the maximum (peak).

  The measurement control procedure described later is stored in, for example, the ROM 136 as a control program for the CPU 131.

  Next, the operation in the above configuration will be described with reference to FIG. 3 to 5 show the flow of the measurement control procedure in the intraocular pressure measurement device of FIG.

  The measurement control procedure in FIG. 3 is substantially the same as a known basic intraocular pressure measurement control procedure using a single measurement gain V. In this embodiment, the measurement gain means the relative relationship between the gain of the detection signal output from the light receiving element for detecting the applanation light, that is, the applanation light sensor 24, and the threshold value. Even if the amplification factor is changed or the threshold value is changed, an equivalent result can be obtained.

  However, in the following, for the sake of simplicity, it is assumed that the measurement gain is changed by the sensor control circuit 133 changing the amplification factor of the detection signal output from the applanation light sensor 24 under the control of the CPU 131. Of course, it is easy for those skilled in the art to modify the embodiment shown below to change the measurement gain by changing the threshold value.

  In step S31 of FIG. 3, measurement mode 1 is set, and here, the measurement mode input by the examiner via an operation panel (not shown) or the like is selected. In step S32, the measurement gain V used in the measurement mode 1 is selected. For example, the measurement gain V can be set to two types, H (high) and L (low).

  Here, assuming that the conditions of the light amount of the applanation light sensor 24 and the air pressure discharged from the nozzle 22 are the same, the measurement gain V of H (high) is detected by the sensor control circuit 133 and output from the applanation light sensor 24. In a state where the signal amplification factor is increased (see FIG. 6), the L (low) measurement gain V is a state where the sensor control circuit 133 reduces the amplification factor of the detection signal output from the applanation light sensor 24 (see FIG. 7). ) (Same below).

  Similar to the known intraocular pressure measurement device, after aligning the device and the eye to be examined, the CPU 131 injects air from the nozzle 22 in step S33 and outputs a detection signal of the applanation light sensor 24 via the sensor control circuit 133. The applanation of the eye to be examined is detected by monitoring. For the applanation timing of the eye to be examined, when the detection signal of the applanation light sensor 24 exceeds the applanation detection level (threshold) T as shown in FIG. 6, for example, the peak timing is detected as the applanation timing. To do.

  If the applanation of the eye to be examined can be detected in step S33, the air pressure detection value is acquired from the pressure sensor 132 at that time in step S34, and the CPU 131 calculates the intraocular pressure value based on the air pressure detection value obtained in step S35. In step S36, the image is displayed on the monitor 134 (or printed by the printer 135).

  The applanation detection in step S33 continues for a certain time (for example, several tens of milliseconds) after the air injection until the applanation of the eye to be detected can be detected. That is, if applanation cannot be detected in step S33, the elapse of a fixed time is determined using a timer (not shown) in step S37, and if the fixed time has not elapsed, the process loops to step S33. During this time, the air pressure of the nozzle 22 is controlled to increase gradually. If the applanation detection in step S33 continues to fail and a fixed time elapses in step S37, it is determined that the intraocular pressure measurement has failed (step S38), and error information is displayed on the monitor 134 (or printed by the printer 135) in step S39. .

  According to the basic control procedure described above (substantially the same as the conventional one), when the examiner selects one measurement gain (for example, H or L) and starts measurement, the measurement gain is measured for a certain period of time. However, during this time, the measurement situation in which the output of the applanation light sensor 24 does not reach the applanation detection level T continues as shown in FIG. 7 or FIG. 8, and if the applanation of the cornea cannot be detected, the measurement ends in error. Become. In this case, if the measurement gain can be increased and measurement can be performed, the setting must be performed and the measurement operation must be performed again.

  However, even if the measurement failed in the control as shown in FIG. 3, the measurement gain setting itself was appropriate, but there were many blinks of the eye to be inspected during the fixed measurement time detected in step S37. There is also a possible cause. In such a case, increasing the measurement gain may not always lead to a good result. For example, in a measurement situation in which a detection waveform with many peaks is obtained as shown in FIG. 8, even if the measurement gain is increased and the detection waveform greatly exceeds the applanation detection level T as shown in FIG. There is a high probability that the peak timing will be detected.

  That is, as shown in FIG. 3, it may not be sufficient to simply perform one set (times) of measurement for a fixed time and determine the success / failure.

  Therefore, in this embodiment, the measurement procedure as shown in FIG. 4 is also mounted in the intraocular pressure measurement device. In the procedure of FIG. 4, the measurement mode 1 using the measurement gain L (low) is tried for a predetermined number of measurement sets, and if that fails, the procedure proceeds to the measurement mode 2 using the measurement gain H (high). The measurement set is tried a predetermined number of times. In one set of measurement modes, the air pressure of the nozzle 22 is reset so as to change from the initial value every time.

  In step S41 of FIG. 4, measurement mode 1 using the measurement gain L (low) is selected. This mode selection is not performed by the examiner's setting operation, but is performed as one of the initialization processes of the measurement procedure of FIG. In step S41, a counter N for trying a plurality of sets of one measurement mode is initialized to zero.

  In step S42, as will be described later, it is determined whether or not the number of trials indicated by the counter N counted up every time one measurement mode fails has reached a prescribed number n (for example, n = 1 to about 3). judge. If the counter N is smaller than n, the process proceeds to step S43. If the counter N is greater than n and smaller than 2n, the process proceeds to step S45. If the counter N is larger than 2n, the process proceeds to step S56.

  That is, while the counter N is smaller than n, the measurement mode 1 using the measurement gain L (low) is selected in steps S43 and S44, and when the counter N becomes n or more, the measurement gain H (high) is set in steps S45 and S46. Measurement mode 2 to be used is selected.

  In step S47, the air pressure from the nozzle 22 is started after controlling the initial air pressure to be a predetermined value by, for example, initializing the position of the piston, the air is injected from the nozzle 22, and the applanation of the eye to be examined is performed. Start detection. In step S48, the applanation of the eye to be examined is detected by monitoring the detection signal of the applanation light sensor 24 via the sensor control circuit 133.

  Steps S49 to S51 in FIG. 4 are the same as steps S34 to S36 in FIG. That is, if the applanation of the eye to be examined can be detected in step S48, the air pressure detection value is acquired from the pressure sensor 132 at that time in step S49, and the CPU 131 calculates the intraocular pressure value based on the air pressure detection value obtained in step S50. The calculated value is displayed on the monitor 134 (or printed by the printer 135) in step S51.

  On the other hand, if the applanation of the eye to be examined cannot be detected in step S48, the process proceeds to step S52. Steps S52 to S54 are the same as steps S37 to S39 in FIG. That is, if applanation cannot be detected in step S48, the elapse of a fixed time is determined using a timer (not shown) in step S52, and if the fixed time has not elapsed, the process loops to step S48. During this time, the air pressure of the nozzle 22 is controlled to increase gradually. If the applanation detection in step S48 continues to fail and a fixed time elapses in step S52, it is determined that the intraocular pressure measurement has failed (step S53), and error information is displayed on the monitor 134 (or printed by the printer 135) in step S54. .

  In FIG. 4, following step S54, the process is not ended here, but the counter N for counting the number of trials is incremented by 1, and the process returns to step S42.

  On the other hand, in step S42, the counter N becomes 2n or more, that is, the measurement mode 1 using the measurement gain L (low) is tried n times, and this fails, and the measurement mode 2 using the measurement gain H (high) is also used. If it has failed n times, error information is displayed on the monitor 134 (or printed by the printer 135) in step S56, and the measurement is terminated.

  As described above, even if the measurement mode 1 using the measurement gain L (low) fails, the process of FIG. 4 does not change to the measurement mode 2 using the measurement gain H (high) immediately until it fails n times. Do not migrate. In addition, the measurement mode 2 using the measurement gain H (high) is not immediately terminated unless it fails n times.

  Therefore, even if, for example, a certain trial in the measurement mode 1 using the measurement gain L (low) or the measurement mode 2 using the measurement gain H (high) happens to be unsuccessful, It may be possible to make the measurement successful in a trial. For example, even if the measurement situation is as shown in FIG. 7 in a certain trial, if the measurement situation as shown in FIG. 9 can be formed in the next trial under the same injection air pressure and measurement gain conditions, the injection air pressure and the measurement gain can be changed. Intraocular pressure measurement can be successful.

  That is, by the control as shown in FIG. 4, even if a certain measurement mode fails, the same injection air pressure and the same injection air pressure and the next measurement mode in which the measurement gain is immediately increased or the measurement process ends in error are not caused. The possibility that the intraocular pressure measurement succeeds in the next trial under the condition of the measurement gain can be increased.

  FIG. 4 shows a configuration in which intraocular pressure measurement is performed using measurement mode 1 using measurement gain L (low) and measurement mode 2 using measurement gain H (high). The structure performed by the process like this is also conceivable. Many parts of FIG. 5 are similar to those of FIG. 4, and in FIG. 5, the same step numbers are used for the same or similar parts to FIG.

  In the measurement procedure of FIG. 5, n measurement sets are tried at a certain measurement gain V. When n measurement set attempts fail, the measurement gain is increased by the difference ΔV and the next n measurement sets are repeated. To measure intraocular pressure. The measurement gain can be increased by increasing the amplification factor of the detection signal output from the applanation light sensor 24, for example.

  In FIG. 5, in step S41, a counter N for trying a plurality of sets of one measurement mode is initialized to 0, and a measurement gain V is initialized to V0. This initial value V0 may be a value equivalent to, for example, the measurement gain L (low) described in FIG.

  In step S42, it is determined whether or not the remainder obtained by dividing the value of the counter N by a predetermined value of n (number of times of measurement set) has become 0 (% is an operator indicating a remainder calculation). Since the counter N is counted up every time one measurement set fails as described later, it can be checked whether or not a certain measurement set has already been tried n times by the determination in step S42. If step S42 is affirmative, that is, if a certain measurement set has already been tried n times, the process proceeds to step S43. If step S42 is negative, that is, if a certain measurement set has not yet been tried n times, the process proceeds to step S44.

  If a certain measurement set has already been tried n times, it is determined in step S43 whether or not the measurement gain V has reached a predetermined maximum value (upper limit value) Vmax, and the measurement gain V is still at the maximum value (upper limit value). If it is confirmed that Vmax has not been reached, the measurement gain difference ΔV is added to the current measurement gain V in step S46 to set a new measurement gain V used in the next measurement set, and the process proceeds to step S47.

  On the other hand, if step S42 is negative, that is, if a certain measurement set has not yet been tried n times, in step S44, the current measurement gain V is set as a new measurement gain V used in the next measurement set (measurement gain). Does not change).

  In step S47, air injection from the nozzle 22 is started after controlling the initial air pressure to be a predetermined value by, for example, initializing the position of the piston, and then the measurement set of this time is performed from step S48 onward. To do. Steps S48 to S56 are the same as those in FIG. 4, and detailed description thereof is omitted here.

  As described above, in the measurement procedure of FIG. 5, n measurement sets are tried at a certain measurement gain V. If n measurement set attempts fail, the measurement gain is increased by the difference ΔV and the next n times. The intraocular pressure measurement is performed by repeating the measurement set.

  Here, in the measurement procedure of FIG. 5, for example, the measurement gain difference ΔV may be considered as the difference between the measurement gain L (low) and the measurement gain H (high) in FIG. 4 (in this case, the measurement gain control). Is equivalent to that of FIG. 4), but by setting the measurement gain difference ΔV to a value smaller than the difference between the measurement gain L (low) and the measurement gain H (high) in FIG. Can be controlled.

  Thereby, even if an attempt of a certain measurement set fails, it is possible to increase the possibility that the intraocular pressure measurement will succeed in the next measurement set by changing the measurement gain less. For example, even if a measurement set trial fails in a measurement situation where there are a plurality of signal peaks as shown in FIG. 8, the measurement gain is not greatly changed in the next measurement set, so a plurality of peaks as shown in FIG. For example, a measurement situation in which only the highest peak exceeds the applanation detection level T is formed instead of a measurement situation that exceeds the applanation detection level T, and the possibility that a better intraocular pressure measurement can be performed is increased. it can.

  It should be noted that the intraocular pressure measurement control procedures in FIGS. 3, 4 and 5 are not exclusive and can be implemented in one intraocular pressure measurement device without causing any contradiction. In particular, the intraocular pressure measurement control procedure in FIG. 3 can be implemented as a procedure in which a measurement mode using the measurement gain L (low) or a measurement mode using the measurement gain H (high) is tried once. .

  The present invention can be implemented in an intraocular pressure measurement device that optically detects the applanation of the eye cornea by injecting air into the cornea of the eye to be examined. The control program for carrying out the present invention can be supplied to the intraocular pressure measurement device via various storage media (ROM, CDROM, MO, etc.), and not only via the storage media but also via a network or the like. It can be supplied to an intraocular pressure measuring device and updated.

It is explanatory drawing which showed the structure of the intraocular pressure measuring apparatus which employ | adopted this invention. It is the block diagram which showed the structure of the control system of the intraocular pressure measuring apparatus of FIG. It is the flowchart figure which showed the intraocular pressure measurement control procedure in the intraocular pressure measuring apparatus of FIG. It is the flowchart figure which showed the different intraocular pressure measurement control procedure in the intraocular pressure measuring apparatus of FIG. It is the flowchart figure which showed the further different intraocular pressure measurement control procedure in the intraocular pressure measuring apparatus of FIG. It is explanatory drawing which showed the measurement condition in the intraocular pressure measuring apparatus of FIG. It is explanatory drawing which showed the measurement condition in the intraocular pressure measuring apparatus of FIG. It is explanatory drawing which showed the measurement condition in the intraocular pressure measuring apparatus of FIG. It is explanatory drawing which showed the measurement condition in the intraocular pressure measuring apparatus of FIG. It is explanatory drawing which showed the measurement condition in the intraocular pressure measuring apparatus of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 11 Light source for illumination 12 Light source for alignment 13 Lens 14 Half mirror 15 Lens 16, 17 Half mirror 18 Lens 19 Filter 20 CCD camera 24 Applanation light sensor 32 Filter 131 CPU
132 Pressure sensor 133 Sensor control circuit 134 Monitor 135 Printer 136 ROM

Claims (1)

In an intraocular pressure measuring device that injects air to the cornea of the subject eye, optically detects deformation of the subject eye cornea, and measures the intraocular pressure of the subject eye based on the air pressure when detecting the applanation of the subject eye cornea,
Measurement gain determined by a relative relationship between a gain of a detection signal obtained from a light receiving element of a light receiving system for detecting applanation of the eye cornea to be detected and a threshold value to be compared with the detection signal in order to detect applanation of the eye cornea of the eye to be examined An intraocular pressure measuring means for measuring the intraocular pressure using
Using the measurement gain, the tonometry means tries the tonometry, and when the attempt fails a plurality of times due to a measurement error, the tonometry is measured by increasing the measurement gain by a predetermined difference. An intraocular pressure measuring device having a control means for trying .

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