Intraocular pressure measuring apparatus

In the non-contact intraocular pressure measuring apparatus for measuring the intraocular pressure of the eye to be examined for a suitable measurement time, after alignment of the apparatus main body with the eye to be examined is performed, the time required for charging the condenser is calculated based on current supply time for the rotary solenoid at the time of the previous intraocular pressure measurement. When the calculated charging time elapses, the desired quantity of current is supplied from the condenser to the rotary solenoid, allowing the air supply unit to spray air to the cornea of the eye to be examined. The cornea is transfigured and flattened by the sprayed air. At the same time, intraocular pressure measuring light is illuminated from the intraocular pressure measuring optical system to the flattened cornea. The reflected light therefrom is detected to calculate intraocular pressure value of the eye to be examined.

BACKGROUD OF THE INVENTION 
1. Field of the invention 
The present invention relates to a non-contact type intraocular pressure 
measuring apparatus for measuring intraocular pressure of the eye to be 
examined after the apparatus main body is aligned with the eye to be 
examined. 
2. Description of Related Art 
In the conventional non-contact type intraocular pressure measuring 
apparatus, an alignment light is projected on the cornea of the eye to be 
examined, and then the reflected alignment light is received to align the 
optical axis of the apparatus optical system with that of the eyeball. 
After the apparatus main body is aligned with the eye to be examined to 
secure a desired working distance, air is sprayed toward the cornea from a 
spraying nozzle provided that the spraying direction corresponds to the 
optical axis of the apparatus optical system to transfigure the cornea of 
the eye to be examined. Concurrently with the air spraying, an intraocular 
pressure measuring light is irradiated to the cornea and then the 
reflected light from the transfigured cornea is received, thus enabling 
non-contact measurement of intraocular pressure of the eye to be examined. 
The working distance represents a distance between the top of the cornea 
of the eye to be examined and the tip of the spraying nozzle. 
In the above conventional type non-contact intraocular pressure measuring 
apparatus, a spraying nozzle is provided on the tip of an air supply unit 
having a cylinder with a piston, the piston is activated by a driving unit 
having solenoid. The solenoid is connected to a condenser which a charging 
circuit is connected to, and operated by current supplied from the 
condenser. The solenoid, thus operated by current supplied from the 
condenser that completes charging, activates a piston to cause a spraying 
nozzle to spray a fluid such as air to the cornea of the eye to be 
examined. 
In the conventional intraocular pressure measuring apparatus, however, the 
completion of charging of the condenser for current supply to solenoid is 
determined by the elapse of the predetermined long charging time (for 
instance, three seconds). This is because if the condenser is always to be 
charged at a constant charging time, a long charging time must be set, 
considering that there is a wide variation in discharging quantity of the 
condenser between low intraocular pressure measurement where a small 
quantity of air is sprayed to the cornea and high intraocular pressure 
measurement where a large quantity of air is sprayed to the cornea. Thus 
it takes long time to measure intraocular pressure, causing a big burden 
to an examinee. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide an intraocular pressure 
measuring apparatus which will save a wasteful charging time of the 
condenser and shorten an intraocular pressure measurement time, and thus 
reduce a burden to the examiner or the examinee, in such a way that 
charging time of the condenser adapted to activate a driving unit for 
driving an air supply unit for spraying air to the cornea of the eye to be 
examined to execute non-contact intraocular pressure measurement to the 
eye will be properly set according to the current supply time to the 
driving unit and the intraocular pressure value obtained by the 
intraocular pressure measurement. 
To solve the above problems, the intraocular pressure measuring apparatus 
of the present invention is characterized in that an intraocular pressure 
measuring apparatus comprises spraying means for spraying a fluid to a 
cornea of an eye to be examined, pressure calculating means for 
calculating a pressure of the fluid in the spraying means, cornea 
transfiguration detecting means for detecting a transfiguration state of 
the cornea by the fluid sprayed from the spraying means, intraocular 
pressure value calculating means for calculating an intraocular pressure 
value of the eye to be examined in accordance with results of the pressure 
calculating means and the cornea transfiguration detecting means, 
disabling means for disabling the spraying means for a desired time, and 
control means for changing an operating time of the disabling means. 
In the above intraocular pressure measuring apparatus, the present 
invention is characterized in that the control means changes the operating 
time of the disabling means in accordance with a current supply time to 
the spraying means. 
Also, in the above intraocular pressure measuring apparatus, the present 
invention is characterized in that the apparatus further comprises 
alignment means for automatically aligning a main body of the intraocular 
pressure measuring apparatus with the eye to be examined, and wherein the 
control means controls the alignment means according to operation of the 
spraying means. 
Also, in the above intraocular pressure measuring apparatus, the present 
invention is characterized in that the apparatus further comprises switch 
means for switching a spraying pressure of the fluid to the cornea, and 
wherein the control means controls an operating time of the disabling 
means in accordance with the spraying pressure of the fluid switched by 
the switch means. 
Also, in the above intraocular pressure measuring apparatus of the present 
invention is characterized in that the control means changes an operating 
time of the disabling means in accordance with the intraocular pressure 
value calculated by the intraocular pressure value calculating means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The intraocular pressure measuring apparatus of the present invention will 
be described by using the drawings. 
(Embodiment 1) 
FIG. 1 shows a view of the structure of an intraocular pressure measuring 
apparatus according to the first embodiment of the present invention. As 
shown in FIG. 1, the intraocular pressure measuring apparatus has a 
spraying nozzle 10, an air supply unit 11, a rotary solenoid 12, an 
applanation sensor 13, A/D (analogue/digital) converters 14 and 15, a 
pressure sensor 16, a control circuit 17, a current supply unit 18, an 
intraocular pressure measuring optical system 19, a memory unit 20, an 
image processing circuit 21, a display unit 22, a control panel 23, and a 
printer apparatus 24. 
The air supply unit 11 is constructed by a cylinder 11a and a piston 11b. 
The piston 11b activated by the rotary solenoid 12 compresses air within 
the cylinder 11a to spray air to the cornea C of the eye E to be examined 
of an examinee through the spraying nozzle 10. 
The intraocular pressure measuring optical system 19 irradiates intraocular 
pressure measuring light to the cornea C of the eye E to be examined to 
measure intraocular pressure of the examinee at the same time when air is 
sprayed from the air supply unit 11 toward the cornea C. 
The applanation sensor 13 electrically detects, as an applanation signal, 
the reflected light from the cornea C that is transfigured and flattened 
by air sprayed to the cornea C of the eye E to be examined through the 
spraying nozzle 10. The applanation signal detected by the applanation 
sensor 13 is converted into digital signals by the A/D converter 14, and 
the digital signals are output to the control circuit 17. 
The pressure sensor 16 is provided in the cylinder 11a of the air supply 
unit 11 and electrically detects the air pressure in the cylinder 11a as a 
pressure signal. The pressure signal detected by the pressure sensor 16 is 
converted into digital signals by the A/D converter 15, and the digital 
signals are output to the control circuit 17. 
The control circuit 17 is constructed by a CPU (Central Processing Unit) 
17a, a program memory 17b, and a timer 17c. The CPU 17a controls the whole 
of the intraocular pressure measuring apparatus according to various 
control/processing programs stored in the program memory 17b. The CPU 17a 
also calculates values of intraocular pressure of the eye E to be examined 
based on applanation signals detected by the applanation sensor 13 and 
pressure signals detected by the pressure sensor 16. The timer 17c is used 
to measure current supply time to the rotary solenoid 12 at the time of 
non-contact intraocular pressure measurement for an examinee. 
The current supply unit 18 is constructed by a condenser 18a, a charging 
circuit 18b; and a switch 18c. The condenser 18a is charged by the 
charging circuit 18b, and starts to discharge when the switch 18c is 
turned on by control of the CPU 17a. Accordingly, the rotary solenoid 12 
is activated with current supplied from the condenser 18a. 
The memory unit 20 stores data representing current supply time to the 
rotary solenoid 12 at the time of intraocular pressure measurement for an 
examinee. 
The front portion image of the eye E to be examined obtained by the 
alignment optical system (as described later) is image-processed by the 
image processing circuit 21 and displayed on the display unit 22. 
The control panel 23 has a two-stage switch for switching the range of 
intraocular pressure (0 to 30 mmHg for low intraocular pressure and 0 to 
60 mmHg for high intraocular pressure), a print switch for printing the 
results of intraocular pressure measurement by the printer 24. At the time 
of intraocular pressure measurement for an examinee, an examiner pushes 
the two-stage switch to set the range of the intraocular pressure 
measurement. 
FIGS. 2 and 3 show views of structures of the alignment optical system for 
the intraocular pressure measuring apparatus according to the first 
embodiment of the present invention. As shown in FIGS. 2 and 3, the 
intraocular pressure measuring apparatus has a front portion observing 
optical system 100, a target projecting optical system 120, an 
XY-direction alignment detecting optical system 30, a Z-direction 
alignment illuminating optical system 50, a Z-direction alignment 
detecting optical system 70, and a fixation mark projecting optical system 
80. The X-direction and Y-directions represent an up-and-down direction 
and a right-and left direction to the face of an examinee, respectively. 
The Z-direction represents a vertical direction (forward and backward 
directions) to the face of the examinee. 
The front portion observing optical system 100 for observing the front 
portion of the eye E to be examined has a plurality of light sources 101 
provided on the rightward and leftward sides of the eye E to be examined, 
for illuminating the front portion of the eye E to be examined directly by 
infrared lights, half mirrors 102 and 104, an objective lens 103, and a 
CCD (charge coupled device) camera 106. The half mirrors 102 and 104, the 
objective lens 103 and the CCD camera 106 are arranged with an optical 
axis O. The front portion of the eye E to be examined is illuminated from 
the light sources 101. The reflected light from the front portion passes 
through the half mirror 102, the objective lens 103 and the half mirror 
104, and is led to the CCD camera 106, so that the front portion image is 
obtained. 
In the target projecting optical system 120, the alignment target light is 
projected on the cornea C of the eye E to be examined to align the main 
body of the intraocular pressure measuring apparatus with the eye E to be 
examined in XY-directions. The target projecting optical system 120 has a 
light source 121 for emitting infrared lights, a condenser lens 122, an 
aperture stop 123, a pinhole plate 124 for forming an alignment target, a 
dichroic mirror 125, a projection lens 126 disposed on an optical path to 
focus the light on the pinhole plate 124, and the half mirror 102. The 
infrared lights emitted from the light source 121 are converged by the 
condenser lens 122, passes the aperture stop 123 and is led to the pinhole 
plate 124. The light passed through the pinhole plate 124 is reflected by 
the dichroic mirror 125. At the projection lens 126 the light is rectified 
into parallel light flux and reflected by the half mirror 102, and then it 
is projected on the cornea C. 
In the XY-direction alignment detecting optical system 30, the alignment 
target light reflected from the cornea C of the eye E to be examined is 
received at an alignment detecting sensor 31 to detect the relative 
position in XY-directions between the apparatus main body and the eye E to 
be examined. The XY-direction detecting optical system 30 has the half 
mirrors 102 and 104, the objective lens 103, and the alignment detecting 
sensor 31. In the target projecting optical sys em 120, the alignment 
target light which is projected on and reflected from the cornea C 
transmits the half mirror 102 and is converged by the objective lens 103. 
The portion of light is reflected by the half mirror 104 and made incident 
on the alignment detecting sensor 31. The alignment detecting sensor 31 is 
constructed by a light receiving element such as a PSD (Position Sensitive 
Device) that can detect the position of the incident light. For example, a 
two-dimensional PSD is used. Two units of one-dimensional PSD can be used 
in combination. 
The XY-direction alignment detecting circuit 91a calculates the relative 
position in XY-directions between the apparatus main body and the eye E to 
be examined based on an output of the alignment detecting sensor 31 and 
outputs position information 131 to the control circuit 17. On the other 
hand, the light passing through the half mirror 104 is led to the CCD 
camera 106. Output information 132 of the CCD camera 106 is output to the 
control circuit 17, and the desired image processing is performed by the 
image processing circuit 21. By this image processing, the front portion 
image of the eye E to be examined and the alignment light spot image are 
displayed on the display unit 22. An examiner moves the apparatus main 
body in up-and-down and right-and-left directions (XY-directions) to 
position the alignment light spot image representing the position of the 
optical axis O of the apparatus optical system in an alignment area, so 
that the optical axis O of the apparatus optical system is aligned with 
the optical axis of the eyeball of the eye E to be examined. 
In the Z-direction alignment illuminating optical system 50, a parallel 
light is irradiated from an oblique direction to the cornea C of the eye E 
to be examined to align the apparatus main body of the intraocular 
pressure measuring apparatus with the eye E to be examined in a 
Z-direction. The Z-directional alignment illuminating optical system 50 
has a light source 51 for emitting infrared light, a condenser lens 52, a 
slit plate 53, a dichroic mirror 44, an aperture stop 45 and an objective 
lens 46. Infrared light emitted from the light source 51 is converged by 
the condenser lens 52, and passes the slit plate 53. The transmitted light 
is reflected by the dichroic mirror 44, and passes the aperture stop 45 
and the objective lens 46. Then the transmitted light is irradiated on the 
cornea C of the eye E to be examined. 
In the Z-direction alignment detecting optical system 70, slit light 
illuminated from the illuminating optical system 50 is reflected by the 
cornea C. The reflected light is received at an alignment detecting sensor 
71 to detect a Z-directional position. The Z-direction alignment detecting 
optical system 70 has an objective lens 61, a dichroic mirror 62, and the 
alignment detecting sensor 71. The slit light reflected by the cornea C is 
converged by the objective lens 61, and then is led to the dichroic mirror 
62. Further, the light is reflected by dichroic mirror 62 and made 
incident upon the alignment detecting sensor 71. The alignment detecting 
sensor 71 is constructed by a light receiving element such as a line 
sensor (PSD) with which a distribution of the quantity of light can be 
detected. 
A Z-direction alignment detecting circuit 91b detects the peak position of 
the quantity of light based on the output of the alignment detecting 
sensor 71, so that the relative position in a Z-direction is detected. The 
position information 130 is output from the Z-directional alignment 
detecting circuit 91b to the control circuit 17. The information 
representing a working distance calculated based on this position 
information is displayed on the display unit 22 through the image 
processing circuit 21. 
The examiner moves the apparatus main body in the backward and forward 
direction (Z-direction) to the eye E to be examined by reference to the 
information representing the working distance so as to secure the desired 
working distance. The working distance is a distance between the top of 
the cornea C of the eye E to be examined and the tip of the spraying 
nozzle 10, which is set by the examiner and stored in the memory unit 20. 
The fixation mark projecting optical system 80 for projecting a fixation 
mark image on the eye E to be examined has a light source 81 for emitting 
visible light, a pinhole plate 82, the dichroic mirror 125, the projection 
lens 126, and the half mirror 102. visible light emitted from the light 
source 81 is reflected by the dichroic mirror 125, passes the pinhole 
plate 82, and is rectified into parallel light flux by projection lens 
126. The parallel light flux is reflected by the half mirror 102 and is 
projected on the eye E to be examined. The line of sight of the eye E to 
be examined is fixed by closely observing the fixation mark light as a 
fixation target. 
The operation of intraocular pressure measuring apparatus according to the 
first embodiment of the present invention will be described below. 
FIG. 4 is an intraocular pressure measurement control flow chart of the 
intraocular pressure measuring apparatus according to the first embodiment 
of the present invention. In step A1, after alignment is completed, the 
first intraocular pressure measurement is performed by the above known 
method. In this time, the timer 17c measures a current supply time to the 
rotary solenoid 12 (step A2). 
In step A3, time required for fully charging the condenser 18a is 
calculated in accordance with the current supply time measured by the 
timer 17c. 
The following description deals with relations of the current supply time 
and the time required for charging. 
FIG. 5 is a diagram of a pressure signal representing output of the 
pressure sensor 16, an applanation signal representing output of the 
applanation sensor 13, current supply/stop to the rotary solenoid 12, 
charging/discharging time of the condenser 18a, intraocular pressure 
enabling time, and intraocular pressure disabling time in the intraocular 
pressure measuring apparatus according to the first embodiment of the 
present invention. In FIG. 5, the pressure signal represents the output 
signal of the pressure sensor 16 that detects air pressure in the cylinder 
11a as an electric signal when air is sprayed from the spraying nozzle 10 
to the cornea C of the eye E to be examined, while the applanation signal 
represents the output signal of the applanation sensor 13 that detects as 
an electric signal, the intraocular pressure measuring light reflected 
from the cornea C at the same time when the cornea C is transfigured and 
flattened by air sprayed from the spraying nozzle 10. 
The applanation signal, the output signal of the applanation sensor 13, and 
the pressure signal, the output signal of the pressure sensor 16 are 
respectively converted into digital signals by the A/D converters 14 and 
15, and then output to the CPU 17a of the control circuit 17. The CPU 17a 
calculates the intraocular pressure value based on the applanation signal 
and the pressure signal using the desired formula. 
After confirming the applanation signal, the CPU 17a turns off the switch 
18c to stop the current supply to the solenoid 12. Therefore, the 
operation of the solenoid 12 is stopped, and the air spraying operation of 
the air supply unit 11 is stopped, so that air pressure in the piston 11b 
is lowered. 
The higher the intraocular pressure of the eye E to be examined is, later 
the applanation signal appears after air spray. That is, if the 
intraocular pressure of the eye E to be examined is higher, since more air 
must be sprayed from the air supply unit 11 to flatten the cornea C of the 
eye E to be examined, it will take longer time to supply more current to 
the solenoid 12. Thus, since the discharging time H of the condenser 18a 
as energy source becomes longer, the charging time T of the condenser 18a 
also becomes longer. 
The CPU 17a determines the discharging level of the condenser 18a by 
confirming the current supply time to the solenoid 12. Based on the 
determination result, the time required for charging the condenser 18a can 
be calculated. 
In step A4, it is determined whether or not the time required for charging 
the condenser 18a elapses as calculated in step A3 after the discharging 
of the condenser 18a. Since the charging time is measured by the timer 
17c, the read-out charging time is compared with the required charging 
time calculated in step A3. Thus, it can be determined whether or not it 
is possible to start the next intraocular pressure measurement. If the 
sufficient time does not elapse, the intraocular pressure measurement is 
not started. 
On the other hand, when the time required for charging the condenser 18a 
elapses as calculated in step A4, since the condenser 18a is fully 
charged, it is possible to execute intraocular pressure measurement. 
Accordingly, in step A5, the switch 18c is turned on. Therefore, the 
desired quantity of current is supplied from the condenser 18a to the 
solenoid 12 to activate the solenoid 12. By the activated solenoid 12, the 
piston 11b of the air supply unit 11 is operated to compress air in the 
cylinder 11a and spray the compressed air to the cornea C of the eye E to 
be examined through the spraying nozzle 10. Further, air pressure in the 
cylinder 11a (chronological pressure change) is detected as a pressure 
signal by the pressure sensor 16. Thus, in the first embodiment of the 
present invention, since the time required for charging the condenser 18a 
is calculated, it is possible to eliminate a wasteful waiting time in 
intraocular pressure measurement. 
In step A6, the intraocular pressure measuring light is irradiated toward 
the cornea C of the eye E to be examined from the intraocular pressure 
measuring optical system 19. Thus, the light reflected from the cornea C 
that is transfigured and flattened by the sprayed air is detected as an 
applanation signal by the applanation sensor 13. The intraocular pressure 
value of the eye E to be examined is calculated using the desired formula 
in accordance with the pressure signal detected by the pressure sensor 16 
and the applanation signal detected by the applanation sensor 13. 
In step A7, the current supply time to the solenoid 12 at the time of 
current intraocular pressure measurement (second intraocular pressure 
measurement) is measured by the timer 17c. The data representing the 
measured current supply time is stored in the memory unit 20. The data is 
used for the third intraocular pressure measurement that is performed 
next. By the control operation as described above, when the three 
intraocular pressure measurements are completed, the average value of the 
three measurement values are printed by the printer 24. 
In the case of an intraocular pressure measuring apparatus with a automatic 
alignment adjusting function, the automatic alignment adjustment is not 
performed during the intraocular pressure measurement disabling period. 
This is because it is not possible to measure intraocular pressure if the 
automatic alignment adjustment is performed. Accordingly, in the 
intraocular pressure measuring apparatus with the automatic alignment 
adjustment function, during a charging period of the condenser 18a, the 
automatic alignment adjustment is not disabled to avoid wasteful operation 
to the apparatus. Therefore, it is possible to save power consumption in 
the intraocular pressure measuring apparatus, thereby to shorten 
intraocular pressure measurement time. 
However, the intraocular pressure measuring apparatus can be designed in 
such a manner that before the completion of charging of the condenser 18a 
the automatic alignment adjustment starts, and completes immediately 
before or immediately after the completion of charging of the condenser 
18a. For example, assuming that the charging completion time t2 of the 
condenser 18a is calculated based on the time required for charging the 
condenser 18a as calculated in step A3. Then, considering the average time 
Tave required for the automatic alignment adjust ent, an automatic 
alignment driving unit (not shown) is unlock d-at time (t2 minus Tave), 
Tave earlier than time t2, to start automatic alignment adjustment. Thus, 
it is possible to further shorten the intraocular pressure measurement 
time. 
(Embodiment 2) 
In the intraocular pressure measuring apparatus according to a second 
embodiment of the present invention, the discharging quantity of the 
condenser 18a is determined according to the measured intraocular pressure 
value of the eye E to be examined. Based on the determination result, the 
time required for charging the condenser 18a is calculated. The higher the 
intraocular pressure value of the eye E to be examined is, the more the 
spraying air to the cornea C is required. It is necessary to extend the 
current supply time to the solenoid 12 accordingly. 
It is possible to use a table stored in advance in the memory unit 20 
instead of making calculation to determine the discharging quantity of the 
condenser 18a. The table has data wherein the intraocular pressure value 
of the eye E to be examined and the discharging quantity (current 
quantity) of the condenser 18a are in pairs. 
(Embodiment 3) 
In the intraocular pressure measuring apparatus according to a third 
embodiment of the present invention, the discharging quantity of the 
condenser 18a is determined by detecting the maximum value of the pressure 
signal by the pressure sensor 16 without calculating the intraocular 
pressure value of the eye E to be examined. Based on the determination 
result, the charging time required for the condenser 18a is calculated. 
The discharging quantity of the condenser 18a may be determined by using 
the table stored in advance in the memory unit 20 instead of making the 
calculation. The table has for example, data wherein the maximum value of 
the pressure signal and the discharging quantity (current quantity) of the 
condenser 18a are in pairs. 
(Embodiment 4) 
In the intraocular pressure measuring apparatus with a switching function 
for the measurement range of high intraocular pressure and low intraocular 
pressure, according to a fourth embodiment of the present invention, the 
intraocular pressure measurement disabling time is set in a two-stage 
according to the intraocular pressure measurement range to the examinee. 
Thus, it is possible to reduce the load to the CPU 17a and shorten the 
processing time of the CPU 17a. 
(Embodiment 5) 
The intraocular pressure measuring apparatus according to a fifth 
embodiment of the present invention has both of function as noted in the 
above embodiment and charging voltage detection function for the condenser 
18a. Thus, it is possible to grasp the intraocular pressure measurement 
disabling time securely and to deal with possible degradation of the 
condenser 18a. In this case, the method for detecting a charging voltage 
of the condenser 18a can be simplified. 
Whether or not the condenser 18a is completely charged is determined by 
detecting the charging voltage of the condenser 18a using an electric 
circuit (not shown) such as an operational amplifier and a comparator. 
As described above, according to the present invention, it is possible to 
adequately set an intraocular pressure measurement disabling time suitable 
to charge the condenser used as energy source for spraying air in 
intraocular pressure measurement, so that a wasteful intraocular pressure 
measurement can be avoided and intraocular pressure measurement time can 
be shortened. Thus, it is possible to considerably reduce the burden to 
the examiner and the examinee.