JP2002017683A - Non-contact type tomometer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a non-contact type tomometer capable of obtaining measurement values with high reliability, even if there are differences in a corneal thickness or a corneal hardness, by reducing the affection by the differences. SOLUTION: The tomometer is provided with a fluid blowing means for blowing a compressed fluid toward the cornea of an examined eye, a cornea deformation detection means for detecting the deformation of the cornea caused by the compressed fluid from the blowing means, a pressure detection means for detecting a pressure value of the compressed fluid blown against the cornea, an operating means for determining an intraocular pressure value based on the detection results by the cornea deformation detection means and the pressure detection means, a time determination means for determining a time from the start of cornea deformation to a prescribed deformed state, and a correction means for correcting the intraocular pressure value determined by the operating means based on the determined time by the time determination means.

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 used in ophthalmic clinics and the like.

[0002]

2. Description of the Related Art There is known a non-contact tonometer which injects a compressed fluid such as air toward a cornea to be examined, detects that the cornea has undergone a predetermined deformation, and measures an intraocular pressure value.

[0003]

However, in the above-mentioned prior art, there is a problem that the influence of the corneal thickness and corneal hardness is not taken into consideration, so that an accurate intraocular pressure value cannot be measured.

The present invention has been made in view of the above-mentioned problems of the prior art,
It is an object of the present invention to provide a non-contact tonometer capable of reducing the influence of a difference in corneal thickness and corneal hardness even when there is a difference in the corneal thickness and corneal hardness and obtaining a highly reliable measurement value.

[0005]

Means for Solving the Problems In order to solve the above problems, the present invention is characterized by having the following configuration.

(1) Fluid ejecting means for injecting a compressed fluid toward the cornea to be examined, corneal deformation detecting means for detecting a state of deformation of the cornea by the compressed fluid from the fluid ejecting means,
Pressure detecting means for detecting the pressure of the compressed fluid injected into the cornea; calculating means for obtaining an intraocular pressure value based on the detection results of the corneal deformation detecting means and the pressure detecting means; and deformation of the cornea due to the injection of the compressed fluid A time measuring unit for obtaining a time from a start to a change to a predetermined deformation state, and a correcting unit for correcting an intraocular pressure value obtained by the calculating unit based on the time measured by the time measuring unit. Features.

(2) The correction means (1) is characterized in that a correction value corresponding to the time measured by the time measurement means is obtained for each intraocular pressure value obtained by the calculation means.

[0008]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a view showing a fluid ejection mechanism and a control mechanism of the non-contact tonometer according to the present invention, and FIG. 2 is a view showing a schematic configuration of an optical system.

[Fluid Injection Mechanism] Fluid pressure is generated by being compressed in the air compression chamber 11 by pressing the air in the cylinder 1 with the piston 2 driven by the solenoid 3. The compressed air is ejected toward the cornea of the eye E through the nozzle 6.

Reference numeral 7 denotes a transparent glass plate which holds the nozzle 6 and transmits observation light and alignment light. The glass plate 7 serves as a side wall of the air compression chamber 11.
Reference numeral 9 denotes a transparent glass plate provided on the back surface of the nozzle 6, which constitutes a rear wall of the air compression chamber 11, and transmits observation light and alignment light. Behind the glass plate 9, an optical system for observation and alignment described later is arranged.
Reference numeral 12 denotes a pressure sensor that detects the pressure of the air compression chamber 11.

[Optical system] In FIG.
The image of the eye to be inspected illuminated by the beam splitter 3
1. An image is formed on the CCD camera 35 via the objective lens 32 and the filter 34. The filter 34 transmits light from the light source 30 and the light source 40 for alignment, and has a characteristic of being impermeable to light from an LED 50 for detecting corneal deformation described later. CC
The image formed on the D camera 35 is displayed on a television monitor 36. OL indicates the optical axis of the observation optical system, and the nozzle 6
Axis.

Numeral 40 denotes an infrared LED for alignment. The infrared light projected through the projection lens 41 is reflected by the beam splitter 31 and projected on the eye E from the illumination. The corneal bright spot formed on the cornea of the subject's eye by the LED 40 is transmitted through the beam splitter 31 to the filter 34 to C.
An image is formed on the CD camera 35 and used for alignment.

Reference numeral 50 denotes an LED for detecting corneal deformation.
The light emitted from the ED 50 is converted into a substantially parallel light beam by the collimator lens 51 and projected onto the cornea of the eye to be examined. The light reflected by the cornea passes through a light-receiving lens 52, a filter 53 having a characteristic of being impermeable to light from the light source 30 and the light source 40,
The light is reflected by the beam splitter 54, passes through a pinhole plate 55, and is received by a photodetector 56. The optical system for detecting corneal deformation is arranged so that the amount of light received by the photodetector 56 becomes maximum when the cornea of the eye to be examined is flattened.

The optical system for detecting the corneal deformation also serves as a part of the optical system for detecting the working distance. The light passing through the beam splitter 54 is incident on the one-dimensional detecting element 57 and is operated based on the output signal. The distance is detected.

[Control System] In FIG. 1, reference numeral 20 denotes a control circuit for controlling the entire apparatus. An output signal from the pressure sensor 12 and an output signal from the photodetector 56 are converted into an applanation detection signal processing circuit 21 and a signal. It is input to the control circuit 20 via the detection processing circuit 22. The control circuit 20 obtains intraocular pressure by performing predetermined arithmetic processing based on each input output signal. The measurement result is displayed and output on the television monitor 36. 23
Is a drive circuit for driving the solenoid 3. Reference numeral 24 denotes a memory, which stores data of a temporal change in pressure detected by the pressure sensor 12 and temporal output signal data from the photodetector 56. In addition, the memory 24 stores an intraocular pressure correction table which stores intraocular pressure correction data due to the influence of the corneal thickness and hardness.

The operation of calculating the intraocular pressure in the apparatus having the above configuration will be mainly described. The examiner uses the television monitor 36
Observe the anterior segment image and alignment bright spot displayed on the
Performs vertical and horizontal alignment adjustments. In addition, since the guidance distance is displayed on the television monitor 36 based on the position information sent from the one-dimensional detection element 57, the working distance direction is displayed.
The alignment is adjusted according to this.

After the alignment is completed, when the examiner presses the measurement start switch (or the control circuit 20 automatically issues a measurement start signal based on a detection signal from the alignment optical system), the control circuit 20 sends the signal via the drive circuit 23. To drive the solenoid 3. The piston 2 compresses the air in the cylinder 1 and blows the compressed air from the nozzle 6 onto the cornea of the eye. The cornea is gradually deformed by blowing compressed air,
The maximum amount of corneal reflected light of the LED 50 is incident on the photodetector 56 when the cornea reaches a flat state. Output signals from the pressure sensor 12 and the light detector 56 are sequentially processed and stored in the memory 24 with time.

FIG. 3 shows a pressure signal P from the pressure sensor 12.
FIG. 6 is a graph showing a time-dependent change graph of the corneal reflected light amount signal Qs by the photodetector 56. When the light amount signal Qs reaches a pressure value that deforms the corneal surface, the light amount signal Qs increases as the pressure signal Ps increases. The control circuit 20 stores the pressure signal Ps and the light amount signal Qs in the memory 24 at a predetermined sampling time interval from the start to the end of the blowing of the compressed air. When the blowing of the compressed air is completed, the time tb, which has the same time width before and after the time ta when the maximum value Qmax is obtained from the sampled light amount signal Qs, is taken as a reference.
tc, the value of the pressure signal Ps is extracted, and the average pressure value Pav
Find (t). An intraocular pressure value PE is calculated from the average pressure value Pav (t) by a predetermined intraocular pressure conversion formula.
(T) is calculated.

Conventionally, the intraocular pressure value PE (t) obtained in this way is used as a measurement result of the eye to be examined. However, since this is a value that does not consider the thickness and hardness of the cornea, the calculated value will be different if the thickness and hardness of the cornea are different even though the true intraocular pressure is the same . FIG. 4 shows a temporal change graph of the corneal reflection light quantity signal Qs1 when the cornea is soft, the corneal reflection light quantity signal Qs2 obtained when the intraocular pressure is equal, and the cornea is thick and hard, and the pressure signal Ps. FIG. Here, the average pressure value Pav at the time of applanation obtained from the light amount signal Qs2 of the thicker and harder cornea.
(T2) is the average pressure value Pav (t1) of the soft side of the cornea.
This is a higher value than.

The correction of the intraocular pressure value in consideration of the thickness and hardness of the cornea will be described. As shown in FIG. 4, when the intraocular pressure is equal, the cornea starts to deform when the spray pressure exceeds the intraocular pressure, regardless of the thickness and hardness of the cornea. That is,
The rising time points (time) of the light quantity signals Qs1 and Qs2 are substantially the same time point tx. However, the elastic force of the cornea itself affects the corneal deformation during the time from the start of the corneal deformation to the flattened state (the time when the light amount signal Qs is maximized). For this reason, ΔT2 on the light amount signal Qs2 side where the cornea is thick and hard is longer than ΔT1 on the light amount signal Qs1 side (time from the start of corneal deformation to the flat state). Therefore, by comparing the time from the start of corneal deformation to the flattened state with respect to each measured intraocular pressure value, it is possible to correct the fluctuation of the intraocular pressure value affected by the corneal thickness and hardness.

The procedure for correcting the intraocular pressure will be described with reference to the flowchart shown in FIG. As described above, the control circuit 20 calculates the average pressure value Pav (t) based on the time when the maximum value Qmax of the light amount signal Qs is obtained, and calculates the converted intraocular pressure value PE (t) from this. I do. In addition, the time ΔT from the rising point of the light amount signal Qs obtained at a predetermined sampling time interval, that is, the corneal deformation start point to the flat state (the maximum value Qmax of the light amount signal Qs) is obtained. Next, the time ΔT is compared with the lower limit value T1 and the upper limit value T2 of the correction range for the measured intraocular pressure value PE (t), and it is determined whether correction is necessary. The lower limit value T1 and the upper limit value T2 of the correction range are stored in the memory 24 in advance in association with the intraocular pressure value. The time ΔT is equal to the lower limit T1 to the upper limit T
If it is in the range of 2, no correction is required, and the measured intraocular pressure value PE
(T) is the measurement result as it is.

On the other hand, the time ΔT is between the lower limit value T1 and the upper limit value T2.
If it is out of the range, a correction calculation is performed. The measured intraocular pressure value PE (t) as shown in FIG.
And a table of correction values Ph (ΔT, t) that match the combination of time ΔT and time ΔT are stored in advance.
The correction value is obtained from this table. Then, the corrected intraocular pressure value PE ′ (t) is calculated by the calculation of PE ′ (t) = PE (t) + Ph (ΔT, t) and displayed on the monitor 36.

The table of the correction values Ph is, for example,
The relationship between the measurement result of manometry, which measures the intraocular pressure by placing a needle directly in the eye, and the intraocular pressure values PE (t) and ΔT obtained by the above-described measurement with the same subject's eye was determined by clinical experiments. It can be created by performing on the eyes.

[0024]

As described above, according to the present invention, even if there is a difference in corneal thickness and corneal hardness, the influence is reduced,
Highly reliable measurement results can be obtained.

[Brief description of the drawings]

FIG. 1 is a view showing a fluid mechanism of a non-contact tonometer according to the present invention and a control mechanism thereof.

FIG. 2 is a diagram showing a schematic configuration of an optical system.

FIG. 3 is a diagram illustrating a time-series change of a light amount signal and a pressure signal.

FIG. 4 is a diagram showing a time series change of a light amount signal and a pressure signal of a soft cornea eye and a thick and hard eye.

FIG. 5 is a diagram showing a flowchart of intraocular pressure correction.

FIG. 6 is a diagram showing a table for obtaining an intraocular pressure correction value from a combination of a measured intraocular pressure value and a rise time until flattening.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cylinder 2 Piston 3 Solenoid 12 Pressure sensor 20 Control circuit 21 Pressure signal processing circuit 22 Signal detection processing circuit 23 Drive circuit 24 Memory 50 LED 56 Photodetector

Claims (2)

[Claims] 1. A fluid ejecting means for ejecting a compressed fluid toward a cornea to be examined, a corneal deformation detecting means for detecting a state of deformation of the cornea caused by the compressed fluid from the fluid ejecting means, and a compressed fluid ejected to the cornea. Pressure detection means for detecting the pressure of
Calculating means for obtaining an intraocular pressure value based on the detection results of the corneal deformation detecting means and pressure detecting means; and time measuring means for obtaining a time from the start of the deformation of the cornea due to the injection of the compressed fluid to a change to a predetermined deformation state. A non-contact tonometer comprising: a correction unit configured to correct an intraocular pressure value obtained by the calculation unit based on a time measured by the time measurement unit. 2. The non-contact tonometer according to claim 1, wherein the correction means obtains a correction value corresponding to the measurement time by the time measurement means for each of the intraocular pressure values obtained by the calculation means.