JPH08572A - Non-contact tonometer - Google Patents

Abstract

PURPOSE:To measure an intraocular pressure value by eliminating influence on optically detected output by the difference in reflected light quantity generated from the cornea of an eye to be inspected. CONSTITUTION:Reflected light from an anterior eye part by a light source 13 is image-formed on a video camera 8, and the anterior eye image Pf is displayed on a television monitor 19. The reflected light from the cornea Ec irradiated by the light source 10 is similarly image-formed on the television camera 8, and is displayed on the television monitor 19 as a light source image 10a. When alignment is completed by unifying those images, a rotary solenoid 17 is driven, and the air in a compression chamber 14 is compressed, and the cornea Ec is deformed by spraying the air on the cornea Ec from a nozzle 1. When the cornea Ec is deformed to a prescribed shape, the output of a light receiving sensor 12 is maximized, and it is transmitted to an MPU 22 via a nonlinear amplifier circuit 23, and the internal pressure of the compression chamber 14 is detected by a pressure sensor 18, then, it is converted to the intraocular pressure value.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-contact tonometer which blows compressed air onto an eye to be inspected to deform the cornea and measures the intraocular pressure of the eye depending on the deformed state.

[0002]

2. Description of the Related Art Conventionally, in this type of non-contact tonometer, compressed air is blown onto the cornea of an eye to be examined, detection light is projected from the light source to the cornea, and reflected light reflected from the cornea is received to receive light. The applanation of the cornea is detected from the amount of received light. In this case, generally, the light amount of the light source that projects the detection light and the sensitivity of the light receiving means are constant, but this is premised on that the amount of reflected light of the cornea does not change from person to person.

Further, as disclosed in Japanese Patent Publication No. 104242/1989, there is known a method of controlling the light quantity of a light source for projecting detection light based on the quantity of light reflected by the cornea due to the alignment detection light.

[0004]

However, in reality, there are individual differences in the amount of light reflected by the cornea, and the difference reaches several times. Therefore, if the sensitivity of the light receiving means is adjusted to an eye with a large amount of reflected light, detection will be difficult with an eye with a small amount of reflected light. Conversely, if the sensitivity is adjusted to an eye with a small amount of reflected light, the output of the light receiving means will saturate and the pressure will decrease. There is a problem that it becomes difficult to detect the flat surface and the measurement accuracy is lowered.

Further, the method disclosed in Japanese Patent Publication No. 1-104242 requires a device such as an AD converter and a DA converter and a control means for controlling them, which complicates the structure of the device. There is a point.

It is an object of the present invention to provide a simple non-contact tonometer for measuring the intraocular pressure with high accuracy by eliminating the influence of the difference in the amount of reflected light generated by the cornea of the subject's eye.

[0007]

To achieve the above object, a non-contact tonometer according to the present invention comprises a projection optical system for projecting a light beam onto the cornea of an eye to be inspected, and a light detection for detecting a light beam reflected from the cornea. Means and a signal processing control system for processing the output of the light detecting means by a non-linear means.

[0008]

In the non-contact tonometer having the above-mentioned structure, the projection optical system projects a light flux onto the cornea of the eye to be examined, the light detecting means detects the reflected light flux from the cornea, and the signal processing control system detects the light flux from the light detecting means. Non-linear processing is performed on the output of to measure the intraocular pressure.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail based on the illustrated embodiments. FIG. 1 shows a configuration diagram of the present embodiment. A nozzle 1 is arranged on an optical path L in front of an eye E to be inspected, and the nozzle 1 is attached to a central portion of a perforated window 2 formed of a transparent member. . A transparent window 3 made of a transparent member, an objective lens 4, half mirrors 5 and 6, an imaging lens 7, and a television camera 8 are sequentially arranged along the optical path L behind the nozzle 1. A light source 1 for projecting a light flux onto a cornea Ec, which includes a lens 9, an infrared light emitting diode, etc., on the light path on the incident side of the half mirror 5.
0 is arranged, and the lens 1 is provided on the reflection side of the half mirror 6.
1, the light receiving sensor 12 is arranged, the light receiving sensor 12
Is set so that the incident light amount exhibits the maximum value when the cornea Ec is applanated. Around the perforated window 2, a plurality of light emitting elements 13 for external eye illumination are provided.

A cylinder 15 is formed below the partial compression chamber 14 surrounded by the perforated window 2 and the transparent window 3. A piston 16 is fitted and inserted in the cylinder 15, and the piston 16
Is connected to the rotary solenoid 17. A pressure sensor 18 for detecting the internal pressure is attached to the compression chamber 14.

The output of the TV camera 8 is the TV monitor 19
The output of the pressure sensor 18 is connected to the amplifier 2
0, an A / D converter 21 is connected to an MPU (microprocessor unit) 22, and an output of the light receiving sensor 12 is an MPU via a non-linear amplifier 23 and an A / D converter 21.
It is connected to 22. The output of the MPU 22 is connected to the rotary solenoid 17 and the memory 24,
The output of the measurement switch 25 is connected to the MPU 22.

The reflected light from the anterior segment Ef illuminated by the light source 13 is imaged on the television camera 8 through the perforated window 2, the transparent window 3, the objective lens 4, the half mirrors 5 and 6, and the imaging lens 7. Then, it is displayed on the television monitor 19 as the anterior eye image Pf.

The light flux from the light source 10 is applied to the cornea Ec through the lens 9, the half mirror 5, the objective lens 4, the transparent window 3 and the perforated window 2, and the reflected light returns to the reverse optical path, and the half mirror 5 is illuminated. , 6 through the imaging lens 7 to be imaged on the television camera 8 and displayed on the television monitor 19 as a light source image 10a. The examiner performs alignment while observing the screen of the television monitor 19.

After the alignment is completed, the time shown in FIG.
In To, the rotary solenoid 17 is rotated automatically or manually by operating the measurement switch 25, and the piston 16 enters along the inner wall of the cylinder 15 and the compression chamber 1
Compress the air in 4. This air is blown onto the cornea Ec of the eye E from the tip of the nozzle 1, and the cornea Ec starts to deform. At this time, if the vertical axis in FIG. 2 is the pressure P in the compression chamber 14 and the horizontal axis is the elapsed time T, the pressure in the compression chamber 14 detected by the pressure sensor 18 rises, as shown by the dotted line Pr in FIG. Shows a locus.

When the cornea Ec reaches the applanation state, the amount of light incident on the light receiving sensor 12 becomes maximum, and the light receiving sensor 1
The output after amplification of 2 shows the peak value Ph as shown by the solid line in FIG. The pressure value Pt of the compression chamber 14 at this time Tp is detected by the pressure sensor 18, and the intraocular pressure value is calculated by a conversion formula prepared in advance.

Normally, the output of the light receiving sensor 12 is amplified by a linear amplifier circuit. In the linear amplifier circuit, when the amount of light reflected by the cornea Ec is small, the peak value Ph becomes small as shown in FIG. Problems and reduced resolution occur. Also,
On the contrary, when the reflected light amount of the cornea Ec is large, the peak value Ph is saturated as shown in FIG. 4 and the measurement accuracy is deteriorated.

In the present embodiment, the output of the light receiving sensor 12 is amplified by the non-linear amplifier 23, and the non-linear amplifier 23 has the amplification factor A and the received light amount L which are inversely proportional to each other as shown in FIG. 5, and the peak value Ph of the received light amount L. The smaller the gain, the larger the amplification factor, and the larger the peak value Ph, the smaller the amplification factor. As shown in FIG. 6, the peak value Ph can be adjusted to a level that does not affect the measurement accuracy. Become.

FIG. 7 is a circuit diagram showing the case where the non-linear amplifier 23 is a logarithmic amplifier circuit. As a result, the output from the light receiving sensor 12 is input from the input terminal I, is non-linearly amplified, and is output from the output terminal O. Regardless of the size of the light flux reflected by the cornea of the examiner, it is possible to always perform accurate intraocular pressure measurement.

FIG. 8 is a circuit diagram showing the case where the non-linear amplifier 23 is a polygonal function non-linear circuit. Similarly, highly accurate intraocular pressure measurement can be performed without being affected by the detection output of the reflected light beam by the cornea.

Further, FIG. 9 is a circuit configuration diagram in the case where the nonlinear amplifier 23 is an automatic gain control circuit having a nonlinear circuit. As in the case described above, the corneal reflected light amount is nonlinearly processed to obtain a highly accurate intraocular pressure. A measurement can be made.

[0021]

As described above, in the non-contact tonometer according to the present invention, the output of the light detecting means for detecting the reflected light beam from the cornea of the eye to be inspected is processed by the non-linear means so that the amount of the reflected light is small or large. Eliminates the influence of the light detection output due to
The intraocular pressure value can always be measured with high accuracy.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a present embodiment.

FIG. 2 is a graph of outputs of a pressure sensor and a light receiving sensor.

FIG. 3 is a graph diagram when the amount of light reflected from the cornea is small.

FIG. 4 is a graph when the amount of light reflected from the cornea is large.

FIG. 5 is a graph showing characteristics of a non-linear amplifier circuit.

FIG. 6 is a graph of outputs of the pressure sensor and the light receiving sensor according to the present embodiment.

FIG. 7 is a circuit configuration diagram of a logarithmic amplifier circuit.

FIG. 8 is a circuit configuration diagram of a polygonal line function nonlinear circuit.

FIG. 9 is a circuit configuration diagram of an automatic gain control circuit.

[Explanation of symbols]

 1 Nozzle 8 Television Camera 10, 13 Light Source 12 Light-Reception Sensor 17 Rotary Solenoid 18 Pressure Sensor 19 Television Monitor 22 MPU 23 Nonlinear Amplifier 25 Measurement Switch

Claims (4)

[Claims] 1. A projection optical system for projecting a light beam onto a cornea of an eye to be inspected, a light detecting means for detecting a light beam reflected from the cornea, and a signal processing control system for processing an output of the light detecting means by a non-linear means. A non-contact tonometer characterized by having. 2. The non-contact tonometer according to claim 1, wherein the non-linear means is a logarithmic circuit. 3. The non-contact tonometer according to claim 1, wherein the non-linear means is a broken line circuit. 4. The non-contact tonometer according to claim 1, wherein the non-linear means is an automatic gain control circuit.