Abstract:
A tonometer includes a chamber containing a fluid medium and having a contact tip for contacting an eye surface, the contact tip having a flexible surface stretched by the fluid medium, a pressure sensor detecting a pressure variation of the fluid medium, a detecting mechanism determining whether the tonometer is correctly placed against the eye surface, and a processing circuit configured to treat electrical a signal received from the detecting mechanism.

Description:
FIELD OF THE INVENTION  
       [0001]     The present invention generally relates to tonometry measurements, and more particularly to the construction of a tonometer apparatus that can obtain accurate and precise measurement data of the intraoccular pressure.  
       DESCRIPTION OF THE RELATED ART  
       [0002]     Glaucoma is a disorder that arises when the fluid pressure within an eye, usually called intraoccular pressure, increases to levels that the eye cannot withstand. The result is blindness if such pressure increase is not detected early. Glaucoma can be detected and evaluated via measuring the eye&#39;s fluid pressure with a tonometer apparatus.  
         [0003]     The general principle of a conventional tonometer applies a force against the eye to depress or flatten its surface, and then measures the amount of force necessary to produce the flattening or depressing. Conventional tonometers can be divided in two types: contact type tonometers and non-contact type tonometers. The mechanism of a conventional non-contact tonometer usually includes applying a puff of compressed air of known volume and pressure against the eye surface, and then detecting via sensor devices the time necessary to achieve a predetermined amount of deformation of the eye surface by application of the air puff. Though the non-contact tonometer can prevent problems such as extraneous pressure on the eye or transmission of disease by contact, it is expensive and requires a skilled manipulation by the operator.  
         [0004]     On the other hand, a conventional contact tonometer generally includes a probe end that applies a pressure by contact with the eye surface, and sensor devices that sense movement of the probe end in response to a counterforce produced by the intraoccular pressure. U.S. Pat. Nos. 4,951,671 and 5,165,409 issued to Coan, the disclosure of which is incorporated herein by reference, describe an example of contact tonometer. These two patents describe a contact tonometer which probe end is constructed from a movable shaft slidably mouted to the tonometer housing. When in pressing contact against the eye surface, the probe end slides rearward to deform a membrane of an air chamber and accordingly compresses the air inside the air chamber. An air pressure sensor detects the air pressure variation, which reflects the intraoccular pressure.  
         [0005]     The aforementioned contact tonometer of the prior art has some disadvantages. For example, the movement of the probe end produces mechanical frictions that interfere with the measurement data obtained from the pressure sensor. Another disadvantage is that the conventional contact tonometer is incapable of giving an information with respect to the pressing force applied by the operator to urge the probe end against the eye surface; this pressing force may vary each time a measurement is taken, which can result in an imprecision of the obtained measurement data.  
         [0006]     Therefore, there is presently a need for a tonometer apparatus that can provide accurate measurement data and inform the operator whether the tonometer is adequately positioned for measurement so that imprecision due to inadequate placement of the tonometer is prevented.  
       SUMMARY OF THE INVENTION  
       [0007]     In one embodiment, a tonometer apparatus according to the invention comprises a chamber containing a fluid medium and having a contact tip provided with a flexible surface stretched by the fluid medium, a pressure sensor configured to sense a pressure variation of the fluid medium in response to a pressing action exerted by an operator to press the contact tip against an eye surface, a detecting mechanism configured to determine whether the tonometer is correctly placed against the eye surface, and a processing circuit configured to treat electrical signals received from the detecting mechanism and the pressure sensor. In some embodiments, the chamber and the contact tip are formed in a single body. In some embodiments, the chamber includes a flexible portion that resiliently contracts when the contact tip is pressed against the eye surface.  
         [0008]     In some embodiments, the detector mechanism includes a movable member configured to slide in a first direction in response to a pressing action exerted by the operator in a second direction to press the contact tip against the eye surface, and a position detector configured to determine whether the movable member sliding in the first direction goes beyond a reference position.  
         [0009]     In some embodiments, the position detector includes a light-emitting device and a light-sensing device configured to detect whether light emitted from the light-emitting device travels through a portion of the movable member. In some embodiments, the position detector includes a plurality of springs placed apart from one another, so that a sliding movement of the movable member beyond a predetermined position in the first direction causes a contact between at least two springs indicating that the tonometer is not in the reference position.  
         [0010]     In some implementations, the processing circuit emits an error signal in response to a signal from the position detector indicating the movable member has gone beyond the reference position. In variant implementations, the processing circuit obtains measurement data from the pressure sensor when the movable member is at the reference position. In other variations, the processing circuit emits an error signal in response to a signal from the position detector indicating the movable member has left the reference measurement position.  
         [0011]     The foregoing is a summary and shall not be construed to limit the scope of the claims. The operations and structures disclosed herein may be implemented in a number of ways, and such changes and modifications may be made without departing from this invention and its broader aspects. Other aspects, inventive features, and advantages of the invention, as defined solely by the claims, are described in the non-limiting detailed description set forth below. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1A  is a cross-sectional view of a tonometer apparatus according to an embodiment of the invention;  
         [0013]      FIG. 1B  is a cross-sectional view of a tonometer apparatus pushed against an eye surface to measure an intraoccular pressure according to an embodiment of the invention;  
         [0014]      FIG. 1C  is a cross-sectional view of a tonometer apparatus in an overpressure position according to an embodiment of the invention;  
         [0015]      FIG. 2  is a schematic view of a detector position implementation in a tonometer apparatus according to an embodiment of the invention;  
         [0016]      FIG. 3  is a circuit diagram illustrating an electric circuit implementation of a tonometer apparatus according to an embodiment of the invention; and  
         [0017]      FIG. 4  is a schematic view of a detector position implementation in a tonometer apparatus according to another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS  
       [0018]     This application describes a tonometer apparatus provided with a position detecting mechanism that can detect any overpressure of the contact tip of the tonometer against the eyeball surface.  
         [0019]      FIG. 1A  is a schematic view illustrating the construction of a tonometer apparatus according to an embodiment of the invention. Reference numeral  100  generally designates the tonometer apparatus. The tonometer  100  comprises a case  102  inside which is securely mounted a fluid chamber  104 . The fluid chamber  104  is formed in a single elongated hollow body that includes a flexible portion  106  arranged between two opposite ends. Any flexible materials such as elastic rubber may be adequate to form the fluid chamber  104 . A first end of the fluid chamber  104  forms a deformable contact tip  107  and a second end  108  of the fluid chamber  104  connects to a pressure sensor  110 . In this embodiment, the fluid chamber  104  includes an inner cavity filled with air, which is in contact with an inner side of the contact tip  107 . The contact tip  107  thus has a deformable contact surface that is stretched by the air contained within the fluid chamber  104 . The elongated body of the fluid chamber  104  lies through a guiding hole  109  of the case  102  and has its contact tip  107  protrude outward through a collar  120 . A sheath  105  which may be replaceable or cleanable may cover the contact tip  107  to ensure hygienic contact with the eye surface each time a measurement is taken.  
         [0020]     The pressure sensor  110  communicates with the inner cavity of the fluid chamber  104  via a chamber port  112 , and has a differential intake port  114  in contact with ambient air. The second end  108  of the fluid chamber  104  forms an elastic mouth that fits and seals over the chamber port  112 . The pressure sensor  110  compares the pressure within the fluid chamber  104  via the chamber port  112  with the external ambient pressure via the differential intake port  114 .  
         [0021]     Referring again to  FIG. 1A , the movable collar  120  is slidably mounted to an opening  118  of the case  102 , and terminates in a concave cup  122  having a central opening through which the contact tip  107  of the chamber  104  protrudes outwardly. A compressive spring  124  connects the collar  120  to the case  102 . The compressive spring  124  exerts a counterforce that causes the collar  120  to slide in a forward direction away from the case  102  once an opposite force pushing the collar  120  rearward toward the inside of the case  102  has been released. The collar  120  includes a rearward portion  126  through which is defined a slot  128 .  
         [0022]     A position detector  130  is mounted adjacent to the rearward portion  126  of the collar  120 . As shown in  FIG. 2 , the position detector  130  has a generally U-shaped body having a first arm  132  provided with a light-emitting diode  134  and a second arm  136  provided with a photo-sensor  138 . The rearward portion  126  of the collar  120  passes through a gap  139  between the two arms  132  and  136  so as to selectively obstruct a light path between the light-emitting diode  134  and the photo-sensor  138 . When the collar  120  slides to a position where the slot  128  is aligned with the light-emitting diode  134  and the photo-sensor  138 , light from the light-emitting diode  134  travels through the slot  128  and strikes on the photo-sensor  138 , which accordingly changes the voltage output of the photo-sensor  138 . Electric signals outputted from the pressure sensor  110  and the position detector  130  are respectively wired to a circuit board  140  fixedly secured to the case  102 .  
         [0023]      FIG. 3  is a schematic circuit diagram showing a processing circuit implementation of a tonometer apparatus according to an embodiment of the invention. Electric power from a power supply  166  is processed via a voltage and current regulator  164  to supply the electrical circuit with an operating voltage and current. Analog signal outputs from the pressure sensor  110  are converted to suitable digital signals via a converter circuit  152  and sent to a micro-controller  156  for processing. Obtained measurement data are shown on a display  158 . A reset circuit  160  is operated to reset the tonometer before each measurement operation. The position detector  130  sends an electric signal to the micro-controller  156  reflecting a position bias with respect to the reference measurement position. The micro-controller  156  includes an inner clock that counts a measurement time period, and determines the number of electric signal changes from the position detector  130  within one measurement time period to determine whether an erroneous manipulation has occurred.  
         [0024]     Referring to  FIGS. 1A through 1C , the operation of the tonometer apparatus now is described in accordance with an embodiment of the invention. To measure the intraoccular pressure of the eyeball, the contact tip  107  is brought in contact with the eye surface. Then, as the operator moves the tonometer apparatus  100  toward the eye to press the contact tip  107  against the eye surface along a pressing axis of the tonometer, the fluid chamber  104  resiliently retracts rearward by deformation of its flexible portion  106  while the eye surface inwardly deforms. Since the contact tip  107  has a deformable contact surface stretched by the air filled in the chamber  104 , damaging contacts to the eye surface are prevented when the operator presses the contact tip  107  against the eye surface.  
         [0025]     Referring to  FIG. 1B , as the tonometer apparatus  100  moves forward, the cup  122  in turn is urged in contact with the eye surface. Accordingly, the collar  120  slides rearward and compresses the spring  124 . When the slot  128  becomes aligned with the position detector  130 , the micro-controller  156  detects a change in the output of the photo-sensor  138 , which changes from a first voltage level to a second voltage level. The micro-controller  156  accordingly sends a signal to the audio-signal generator  162  to trigger a beep sound informing the operator to hold the reached position for measurement over a time period of about 3 seconds, for example. The micro-controller  156  then obtains measurement data of the intraoccular pressure from the pressure sensor  110 . Once the measurement time period lapses, the micro-controller  156  drives the audio-signal generator  162  to emit a second beep sound to inform the operator that the tonometer can be released.  
         [0026]     Referring to  FIG. 1C , if the slot  128  after being aligned with the position detector  130  slides further rearward along with the rearward movement of the collar  120  before the time period of measurement lapses, the micro-controller  156  detects two voltage level changes from the output of the photo-sensor  138  and accordingly emits two successive beep sounds to inform the operator that an erroneous manipulation of the tonometer  100  has occurred and that the measurement has to be restarted. In the configuration of  FIG. 1C , the erroneous manipulation is due to an excessive pressure applied by the operator while pressing the tonometer against the eye surface, which results in a rearward course of the collar  120  that goes beyond the reference measurement position defined by the position detector  130 .  
         [0027]     On the other hand, if the slot  128  after being aligned with the position detector  130  moves forward and prematurely leaves the reference measurement position before the time period of measurement lapses, the micro-controller  156  also detects two voltage level changes from the output of the photo-sensor  138  and triggers the emission of an error signal. This erroneous manipulation typically corresponds to a premature release of the tonometer by the user during the measurement operation, which causes the collar  120  to slide forward and leave the reference measurement position before the measurement time period lapses.  
         [0028]     By defining a reference measurement position along the pressing axis of the tonometer, the operator obtains consistent and reliable intraoccular pressure data because each measurement is obtained with respect to a same reference measurement position of the tonometer. Measurement errors due to a pressing force varying each time a measurement is taken thus are eliminated. In addition, because the contact surface of the contact tip  107  achieves a flexible and deformable interface between the air inside the air chamber and the eye surface, the air pressure sensed by the pressure sensor  110  accurately reflects the intraoccular pressure, and imprecision due to mechanical frictions between movable component parts of the tonometer is eliminated.  
         [0029]      FIG. 4  is a schematic view of a variant mechanism of the position detector implemented in a tonometer apparatus according to another embodiment of the invention. For the sake of simplification, only the mechanism of the position detector is illustrated in  FIG. 4 . The other parts of the tonometer not illustrated are similar to the embodiments shown in  FIGS. 1A through 1C .  
         [0030]     In the embodiment shown in  FIG. 4 , the position detector  230  includes a first spring  232  securely fixed to the rearward portion  126  of the collar, and second and third springs  234 ,  236  assembled within the case of the tonometer. When the rearward portion  126  of the collar slides rearward in the arrow direction under pressure against the eye surface, the first spring  232  comes in electrical contact with the second spring  234  via contact pad  238   a  to trigger the measurement. In other words, the reference measurement position is reached when the first and second springs  232 ,  234  are in electrical contact with each other. If the portion  126  slides further rearward, the second spring  234  in turn is pushed by the portion  126  via the first spring  232  to come in electrical contact with the third spring  236  via contact pad  238   b , which accordingly produces a position error signal.  
         [0031]     Though two examples have been illustrated, a person skilled in the art of tonometry technique would readily appreciate that many variations of the position detector can be implemented. For example, in another variation not illustrated, the position detector may be implemented through a pressure sensor configured to sense an external force exerted by the operator during pressing of the tonometer toward the eye surface. When the sensed external force exceeds a preset value, the micro-controller can issue an alert signal informing the operator that an excessive pressing action is exerted against the eye surface.  
         [0032]     In other variations, the fluid chamber may contain fluid elements other than air chosen with respect to their density so as to provide a pressure variation that adequately reflects the intraoccular pressure during measurement.  
         [0033]     Realizations in accordance with the present invention therefore have been described in the context of particular embodiments. These embodiments are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, plural instances may be provided for components described herein as a single instance. Structures and functionality presented as discrete components in the exemplary configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of the invention as defined in the claims that follow.