JPH0358728B2 - - Google Patents

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is a non-contact method that deforms the cornea by spraying compressed fluid onto the eye to be examined, and measures the intraocular pressure of the eye to be examined based on the deformed state. This relates to a type tonometer.

[Prior Art] Conventionally, in this type of non-contact tonometer, compressed air is usually used as the compressed fluid. As described above, a piston driven by a solenoid gradually compresses the air in the cylinder, and this compressed air is injected into the cornea of the eye through a nozzle to measure the time it takes for the cornea to become applanated. After measuring, the power to the solenoid is turned off. However, even after the power is turned off, the piston further compresses the air inside the cylinder due to inertia, so even after measurement, unnecessary compressed air is injected into the cornea of the subject's eye, causing an extra shock to the subject. It has the disadvantage of giving.

In addition, this type of non-contact tonometer has a maximum measurement range of about 100 mmHg in order to be able to measure even severely elevated intraocular pressure. Therefore, the compressed air for applanating the cornea must be injected with sufficient strength, and the output torque of the solenoid that drives the piston is also set high in advance. However, when measuring low intraocular pressure, if the solenoid is driven at the same pressure setting, the inertial force will naturally increase, resulting in injecting compressed fluid at a pressure higher than necessary onto the cornea, causing excessive discomfort to the patient. It turns out.

[Object of the Invention] In order to improve the drawbacks of the conventional example, the object of the present invention is to enable the measurement range to be set in multiple stages, and for example, for a patient's eye with low intraocular pressure, the measurement range can be set at a maximum of about 50 mmHg in the full range. An object of the present invention is to provide a non-contact tonometer that can soften the impact on a subject as much as possible by producing compressed fluid necessary for measuring intraocular pressure.

[Summary of the invention] The gist of the present invention for achieving the above object is as follows:
A non-contact tonometer comprising: a fluid ejection mechanism that compresses fluid in a cylinder with a piston and injects the compressed fluid to the cornea of an eye to be examined; and a corneal deformation detection means that detects a predetermined deformation of the cornea due to the compressed fluid. This non-contact tonometer is characterized by being able to set the maximum pressure in multiple stages.

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

FIG. 1 shows the fluid ejection mechanism and optical system of a non-contact tonometer according to the present invention. The fluid ejection mechanism compresses air in a cylinder 1 by entering a piston 3 driven by a solenoid 2. This compressed air is blown onto the cornea Ec of the eye E through the nozzle 4. Further, windows 5 and 6 made of transparent material are provided in a portion corresponding to the optical path L of the compression chamber, and the nozzle 4 is connected to the window 5.
is attached to the center of the On the optical path L behind the window 6, half mirrors 8 and 9 are obliquely installed following the objective lens 7, and furthermore, an imaging lens 10,
Television cameras 11 are arranged in sequence, and the outputs of the television cameras 11 are connected to a television monitor 12. On the optical axis on the reflection side of the half mirror 8, there is an infrared light source 1 for alignment of infrared light emitting diodes, etc.
3 and a lens 14 are arranged, and a lens 15 and an SPD 16 are arranged on the optical axis on the opposite side of the half mirror 9. This SPD 16 is arranged so that the amount of incident light is maximized when the cornea Ec is in an applanation state. Further, a plurality of light emitting elements 17 for extraocular illumination are arranged around the window 5.

First, the examiner sees the eye image Ea to be examined, which is formed on the television camera 11 through the windows 5 and 6, the objective lens 7, and the imaging lens 10, and the eye image Ea, which is emitted from the infrared light source 13 and reflected by the cornea Ec. Alignment is performed by observing the light source image 13a on the television monitor 12,
When this alignment is completed, the solenoid 2 is energized automatically or manually. Therefore, as mentioned above, the piston 3 is driven by the solenoid 2,
The air in the cylinder 1 is compressed and injected from the nozzle 4 onto the cornea Ec, and the cornea Ec begins to deform. and,
When the cornea Ec is in an applanation state, the amount of light incident on the SPD 16 becomes maximum, so the intraocular pressure is determined by measuring the time until the output of the SPD 16 reaches its peak.

Figure 2a is a graph showing how the air in the cylinder 1 is compressed over time;
The horizontal axis represents time t, and the vertical axis represents internal pressure P of the cylinder 1. On the other hand, Fig. 2b shows
It represents the state of the output I of the SPD16, and the time t is the second
The scale is aligned with figure a. Generally, when the solenoid 2 is energized at a certain point, the air inside the cylinder 1 is gradually compressed, or the pressure increases, as shown by curve A in Figure 2a, and when the internal pressure reaches P0 at time ta, the corneal Ec becomes In a flat state, the output of the SPD 16 reaches a peak as shown by C in FIG. 2b. In this system, a relational expression between the time from a certain point until the cornea Ec becomes applanated and the intraocular pressure is prepared in advance, and the intraocular pressure of the eye E to be examined is determined from the time ta.

As shown in Fig. 2a, after time ta has elapsed, solenoid 2 is de-energized to prevent excess compressed air from being applied. As described above, the air in the cylinder 1 is further compressed as shown by the solid line due to the inertial force of , and the excess compressed air is injected onto the cornea Ec. Curve A in Figure 2a is
In the case of the conventional example where the measurement range is increased to a maximum value of 100 mmHg, if the torque given to solenoid 2 is set small in advance as shown in curve B, it will take ta until the same internal pressure of P0 is reached.
Although it requires a longer time tb, the above-mentioned inertial force becomes significantly smaller.

Therefore, it is possible to measure the eye E to be examined, which can be in an applanation state at the internal pressure P0, using either curve A or B in Fig. 2a, but it is better to use the latter curve B. This is desirable because the impact can be reduced. When measuring low intraocular pressure, curve B in Figure 1a is used, and when measuring high intraocular pressure, curve A is used.If these can be switched, the test eye E It can reduce the extra impact on the However, it is necessary to prepare, for example, two types of relational expressions of time versus intraocular pressure corresponding to curves A and B.

FIG. 3 shows an example of a control circuit for controlling the torque of the solenoid 2, in which a charging resistor 21 and an electrolytic capacitor 2 are used to supply DC power for the solenoid 2.
2 is provided, a MOS type field effect transistor 2
The current I flowing to the solenoid 2 is increased or decreased by switching between the two source resistors 24a and 24b. In FIG. 3, 25 is a switch for switching the source resistors 24a and 24b, 26 is a gate resistor of the transistor 23, and 27 is a switch for switching the source resistors 24a and 24b.
shows a surge absorbing diode and a constant voltage circuit that provides a pulsed gate voltage of 28.

In the case of FIG. 3, the electrolytic capacitor 22 is charged from the applied voltage Vi through the charging resistor 21, and the current I flowing through the solenoid 2 is controlled in accordance with the source resistor 24a or 24b selected by the switch 25. It is possible.

FIG. 4 illustrates the relationship between the magnetomotive force N·I of the solenoid 2 and the output torque T, where N represents the number of turns of the coil and I represents the energizing current. If the current I flowing through solenoid 2 is increased from I0 to I1,
The torque T also increases from T0 to T1, and the driving force of the piston 3 in FIG. 1 increases. Therefore, compressed air with a higher compression rate can be created in the cylinder 1, and can also be used for measuring ocular pressure.

In addition, as a means to change the driving torque of the solenoid 2, a voltage Vi applied to the solenoid 2 is used.
It is also possible to adopt a method of selecting , or a method of controlling the overall electrical energy by selecting the capacitance of the solenoid charging capacitor 22 .

FIG. 5 shows another embodiment of the present invention, in which a pressure sensor 18 for directly measuring the internal pressure of the cylinder 1 shown in FIG. 1 is provided, and the other configurations are exactly the same as in FIG. 1. In this Figure 1, the second
As mentioned above, in order to measure the times ta and tb in the figure and calculate the intraocular pressure from the relationship between time and intraocular pressure, two separate relational expressions for both curves A and B must be prepared. be. On the other hand, the fifth
In the embodiment shown in the figure, the internal pressure is directly measured by the pressure sensor 18, and the intraocular pressure can be determined from the relationship between this internal pressure P0 and the intraocular pressure, so one relational expression common to both curves A and B is used. It becomes possible to use

Figure 6 shows RL as the source resistance of the field effect transistor that controls the current I flowing to the solenoid 2.
This example shows a system that has two resistance switching means, RH and RH, and allows the device itself to automatically perform this switching. In addition, 30 is a control circuit shown in FIG. 3, 31 is an analog switch, 32 is an amplifier, 33 is an A/D converter, 34 is an MPU,
35 indicates a reset switch.

Here, the relationship between the two source resistances RL and RH is
Assume that RH>RL and that the source resistance is set to RH and the intraocular pressure is measured. In this case, if the result of A/D conversion of the output from the pressure sensor 18 that detects the internal pressure inside the cylinder 1 by the A/D converter 33 exceeds the measurement range, the MPU 34
immediately controls the analog switch 31 to automatically switch the source resistance RH to RL so that more current flows through the solenoid 2.

On the other hand, if the result obtained when the source resistance is set to RL is within the range that can be measured even with the source resistance RH, the source resistance is automatically set to RH in the same way by a command from the MPU 34. From next time onwards, avoid applying unnecessary shock to the eye E to be examined. Further, by turning on the reset switch 35, it is possible to arbitrarily select the setting state of the analog switch 31.

The set pressure is not only the pressure information mentioned above, but also
It may be switched depending on the time required for the previous measurement or the obtained intraocular pressure value.

[Effects of the Invention] As explained above, the non-contact tonometer according to the present invention divides the measurement range into several levels and switches between them, so that measurement can be performed in a measurement range that matches the intraocular pressure of the eye to be examined. This has the effect of not giving unnecessary shock to the eye to be examined.

[Brief explanation of drawings]

The drawings show an embodiment of a non-contact tonometer according to the present invention, and FIG. 1 is a configuration diagram of a fluid ejection mechanism and an optical system;
Figure 2a is a graph of cylinder air pressure versus time;
b is a graph of SPD output versus time, Fig. 3 is a configuration diagram of a circuit that controls the current flowing to the solenoid, Fig. 4 is a diagram of the relationship between magnetomotive force and torque of the solenoid, and Fig. 5 is a diagram of another example. Block diagram, FIG. 6 is a block diagram of an embodiment incorporating an automatic switching circuit. 1 is a cylinder, 2 is a solenoid, 3 is a piston, 4 is a nozzle, 7 is an objective lens, 8 and 9 are half mirrors, 10 is an imaging lens, 11 is a television camera, 12 is a television monitor, 16 is an SPD, 18
21 is a pressure sensor, 21 is a charging resistor, 22 is an electrolytic capacitor, 23 is a field effect transistor, 24a,
24b, RL, and RH are source resistances, 30 is an automatic circuit, 33 is an A/D converter, and 34 is an MPU.

Claims (1)

[Scope of Claims] 1. A non-contact type having a fluid ejection mechanism that compresses fluid in a cylinder with a piston and ejects it to the cornea of the eye to be examined, and a corneal deformation detection means that detects a predetermined deformation of the cornea due to the compressed fluid. A non-contact tonometer, characterized in that the maximum pressure of the compressed fluid can be set in multiple stages. 2. The non-contact tonometer according to claim 1, wherein the pressure of the compressed fluid is detected by a pressure sensor, and the intraocular pressure is determined from the output of the pressure sensor. 3. The non-contact tonometer according to claim 1, wherein the means for controlling the maximum pressure of the compressed fluid is to change the current applied to a solenoid that drives the piston. 4. The non-contact tonometer according to claim 1, wherein the means for controlling the maximum pressure of the compressed fluid is to change the voltage applied to a solenoid that drives the piston. 5. The non-contact type eye according to claim 1, wherein the means for controlling the maximum pressure of the compressed fluid is to change the capacitance of a capacitor that supplies energy applied to a solenoid that drives the piston. Pressure gauge. 6. The non-contact tonometer according to claim 1, wherein the maximum pressure of the compressed fluid required for the next measurement is selected in accordance with the measured intraocular pressure information.