Abstract:
An intraocular pressure is measured by an apparatus, which includes a probe supported in the case, one coil ( 50 ) around the probe for giving the probe a specific velocity in order to bring the probe in contact with the surface of the eye, and another coil ( 60 ) for performing measurement and setting functions, and a device for processing and displaying the measurement data and for controlling operations. The probe is formed of a non-magnetic front part and a back part. Magnetization is induced into the back part of the probe by one or more coils before the probe ( 4 ) is put into movement against the eye for the measurement.

Description:
PRIOR APPLICATION 
       [0001]    This is a US national phase patent application that claims priority from Chinese patent application no. 200610172996.X, filed 30 Nov. 2006. 
       TECHNICAL FIELD 
       [0002]    The present invention relates to a method for measuring intraocular pressure. 
       BACKGROUND ART AND SUMMARY OF THE INVENTION 
       [0003]    Intraocular pressure (IOP) is the fluid pressure inside the eye. It may become elevated due to anatomical problems, inflammation of the eye, genetic factors, as a side-effect from medication, or during exercise. If the IOP is elevated, it can cause pressure within the eye to increase and damage the optic nerve. Since abnormal pressures usually don&#39;t cause symptoms, it&#39;s very important to have the pressure checked regularly. 
         [0004]    The intraocular pressure is generally measured with a special instrument called a tonometer, which is placed on the surface of the cornea measuring its elasticity using various methods (Goldmann tonometer, Schibtz tonometer, etc.). Two of the most commonly used principles for measuring intraocular pressure are the measurement of the force required to applanate a certain area of the surface of the eye, or the measurement of the diameter of the area that is applanated by a known force. These methods require the patient&#39;s co-operation and cannot be applied without general anaesthesia to small children, persons suffering from dementia, or animals. 
         [0005]    Methods, such as those presented in the U.S. Pat. Nos. 5,148,807, 5,279,300, and 5,299,573, in which the surface of the cornea is not touched, the intraocular pressure being measured instead with the aid of a water or air jet, or various kinds of waves, have also been developed. These methods are technically complex and thus expensive. Meters operating on the air-jet principle are widely used by opticians, but their cost has prevented them from being more extensively used by general practitioners. 
         [0006]    U.S. Pat. No. 5,176,139 discloses a method, in which a freely-falling ball is dropped onto the eyelid and the height of the ball&#39;s rebound is measured. 
         [0007]    The Finnish patent 109269 presents an apparatus, which is based on the fact that a probe is forwarded with a certain speed to contact the surface of the eye, wherefrom it will rebound. The movement of the probe can be a basis for the calculation of the intraocular pressure. Such apparatuses are also presented in WO publication 03/105680, US patent application 2005/0137473 and U.S. Pat. No. 6,093,147 of the applicant. 
         [0008]    U.S. Pat. No. 6,093,147 comprises such an apparatus for measuring intraocular pressure. The apparatus comprises a probe, which is propelled at a constant velocity to impact the eye and includes means for continuously determining the velocity of the probe. The velocity is used to derive the intraocular pressure. The probe is propelled by means of a coil and a permanent magnet, whereby a current flowing through the coil causes a repelling force in the magnet. A similar device is presented in US patent application 2005/0137473 and WO publication 03/105680. 
         [0009]    The problem in connection with many of these last mentioned apparatuses of prior art is, however, that the speed of the probe is not high enough for proper measurements. 
         [0010]    The object of the invention is therefore primarily to achieve a sufficient speed for the probe in an apparatus, which is based on the fact that a probe is forwarded with a certain speed to contact the surface of the eye, wherefrom it will rebound. 
         [0011]    The method of the invention is used for measuring intraocular pressure by means of an apparatus, which includes a probe supported in a case, one coil around the probe for giving the probe a specific velocity in order to bring it in contact with the surface of the eye, and another coil for performing measurement and setting functions, means for processing and displaying the measurement data and means for controlling operations. The probe is formed of a non-magnetic front part and a back part. The method is mainly characterized by inducing magnetization into the back part of the probe by means of one or more coils before the probe is put into movement against the eye for the measurement. 
         [0012]    It is important that the speed of the probe when it is forwarded towards the eye is high enough for proper measurements. For this purpose, the magnetic properties of the back part of the probe have to be appropriate, i.e. the magnetization level of the magnetic part of the probe has to be high enough. 
         [0013]    In the invention, a magnetization or a strengthening of the magnetization can be performed in several steps until a sufficient magnetization level for the probe is achieved. The measurement of the intraocular pressure itself then takes place before the magnetization has disappeared, usually it is performed shortly thereafter. In some embodiments, the time until the measurement has to be performed after the magnetization step is known and tested or calculated in advance. In practice, however, the magnetization is easy to carry out by means of the invention, and the performing of the magnetization is not a problem and being done usually before each measurement. In this way, the invention solves the problem of insufficient speeds of the probe due to low magnetization of the probe and each measurement gives a more accurate result than the methods of prior art. 
         [0014]    The apparatus used in the invention is connected to a case component of a suitable material inside which all the components essential for the measurement are fitted. An adjustable support is needed in order to adjust the distance from which a probe impacts the eye being measured. The result of the measurement can be shown on a display and control component and an operating switch, when pressured, releases the probe towards the eye. 
         [0015]    The method of the invention is simple, economical, and precise and the intraocular pressure can be measured in patients incapable of co-operating, and who can be restrained only momentarily. 
         [0016]    In the following the invention is presented in detail by means of an example to which the invention is not restricted. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]      FIG. 1  is a general view of an embodiment of the apparatus of the invention; 
           [0018]      FIG. 2  shows a vertical cross-section of the above, rotated to an angle of 90 degrees to the above; and 
           [0019]      FIG. 3  is a more detailed view of the part of  FIG. 1 , in which the probe is launched towards the eye. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    Thus,  FIG. 1  presents, as stated above, one practical embodiment of an apparatus applying the invention, while  FIG. 2  shows a cross-section of it. These two figures can be used together to illustrate the general principle and construction. 
         [0021]    The apparatus is formed of a case component  1  made of a suitable material, inside of which all the components essential for the measurement are fitted. 
         [0022]    In this embodiment, the case or body component  1  is essentially elongated and includes at its upper end a forehead support  2 , which is intended to adjust the distance from which the probe  4  impacts the eye being measured. The forehead support  2  is specifically adjustable, e.g. by means of a wheel  3 , which can be rotated manually. 
         [0023]    The apparatus further includes a display and control component  5 , which is e.g. a liquid-crystal panel, in which the measurement result is displayed and related control buttons etc. Reference number  6  is the operating switch, which when pressed, releases the probe  3  towards the eye. 
         [0024]    The operating power can be taken from dry cells or batteries  7 , while the apparatus additionally can have a socket  8 , to which an external recharging device or power supply can be connected. The narrowing  10  make the apparatus comfortable to use. 
         [0025]    The electronics of the apparatus are assembled on a circuit board. 
         [0026]      FIG. 3  shows the part related to the launch of the probe  4 , the recording of the measurement and other operations. 
         [0027]    The probe  4  is supported and located in the case  1  (shown in  FIG. 1 ).  FIG. 3  shows two coils  50 ,  60  of the solenoid type around the probe  4 , the front one of which is intended to provide the probe  4  with a specific velocity for impacting against the eye when the intra ocular pressure of the eye is measured and being oriented accordingly. In  FIG. 3 , the back coil  60  is to provide a movement of the probe  4  in an opposite direction when activated with a voltage. 
         [0028]    Different embodiments are possible with respect to the arrangement of the coils and the direction of the applied voltage in order to achieve desired movement directions for the probe. In the arrangement, the (mutual) orientation and distance of the coil(s), the number and size of the coils, the positions of the coils with respect to part  42 , the length of the probe, and the direction of the current caused by the applied voltage can be varied. 
         [0029]    When the ends of the back part  42  of the probe are inside the respective two coils a sin  FIG. 3  and both coils are directed in the same direction, the coils provides opposite directions for the movement of the probe since one of the coils are around the positive pole of the magnetic back part and the other coil around the negative pole. 
         [0030]    In one embodiment the orientation of the two coils are the same, giving the probe a movement in opposite directions since 
         [0031]    An inner tube  105  is held in place by an inner sleeve  104 , which lies around the probe and is secured by means of a separate plug  103  particularly equipped with a screw attachment. The inner tube  105  and the inner sleeve  104  can be changed, because extraneous material collected over time might disturb the measurement. 
         [0032]    In this embodiment, the probe  4  is formed of a non-magnetic front part  41  and a magnetic or a magnetizable rear shaft part  42 . The material of the shaft part  42  is chosen from paramagnetic or ferromagnetic materials. Steel is an example of a ferromagnetic material. The front part is preferably of plastic of technical and cost reasons. There is, preferably a shoulder, wherein the front part joins the shaft and is made to rest on the edges of the opening of the inner sleeve  104 , through which the shaft  42  runs. 
         [0033]    The front part  41  is in such a ratio to the magnetic shaft that the shaft extends for a certain distance inside the coil  50 , e.g. half into the coil, counting from its front. 
         [0034]    A voltage fed to the front coil  50  induces a pushing force in the probe, causing it to move towards the eye (actually in the direction where the eye is intended to be). 
         [0035]    The two coil arrangement of  FIG. 3  is used as an example, in which one of the coils  50  (the front coil in  FIG. 3 ) is used for moving the probe in one direction while the other coil  60  (the rear coil in  FIG. 3 ) is used to measure the movement of the probe  4 . After the measurement, the measuring coil  60  is also used for moving the probe  4  in the opposite direction back to the original position for the next measurement or it is changed to another probe  4 . Another number of coils could, however, be used as well. For example, an arrangement with three coils could have one coil for moving the probe forward, another coil for measuring the movement of the probe and a third coil for moving it backwards. Also the orientation of the coils could be varied in different embodiments, as was already mentioned before. E.g. the orientations of the coils in  FIG. 3  could be the opposite and consequently, the operations mentioned above and below would be vice versa. 
         [0036]    The probe is formed of a front part  41  of a non-magnetic material such as e.g. plastics and of a back part  42 , which is of a paramagnetic or ferromagnetic material. The joint between parts  41  and  42  is located preferably somewhere inside the front coil  50 , e.g. approximately in the middle of the coil. 
         [0037]    The two parts  41  and  42  of the probe can also be separate pieces, so that the front part  41  is disposable (for example, plastic) and the back part  42  is located inside the device and acts like a holder for the front part. In such an arrangement, the back part is kept from falling out of the device by some internal mechanical construction. The part can be changed by opening part  20 . 
         [0038]    Part  20  is a plug or a nut by the aid of which the above described components are fastened to the case of the apparatus. An inner sleeve  30  can be replaceable after e.g. the measurement or several measurements have been performed. 
         [0039]    It is important that the speed of the probe when it is forwarded towards the eye is high enough for proper measurements. For this purpose, the magnetic properties of the back part  42  of the probe  4  have to be appropriate, i.e. the magnetization level of the magnetic part of the probe has to be high enough. 
         [0040]    Thus, according to the method of the invention the applicants have discovered that the coils, in addition to being used for moving the probe for the measurements, also can be used for magnetization of the back part of the probe  4  and also for strengthening the magnetization of the back part, when it is made of a paramagnetic material and/or it already has been magnetized in some extent in earlier magnetization steps. 
         [0041]    Several embodiments are possible to perform the invention, e.g. only one of the coils can be used for the magnetization or two or more coils can be used for the magnetization. 
         [0042]    When only one coil is used for the magnetization, it is preferably the one causing a movement for the probe backwards from the eye in order to hinder the probe to move forward. It could be possible to use the other coil instead but then the movement of the probe forwards should preferably be prevented during the magnetization (such as with some holding mechanism) or by means of an oppositely directed coil during the magnetization or very shortly after the same. Otherwise the coil would cause an unnecessary movement of the probe and it could e.g. fall out from the device. 
         [0043]    In such an embodiment, wherein both the coils are used for the magnetization, a DC voltage is led to the front coil  5  as well as to the back coil  6  at least once for a short period before the probe  4  is put into movement against the eye. In this way the magnetization of the part  42  of the probe gets the highest magnetization possible. The direction of the magnetic field caused by the current in both coils  5  and  6  is such that they strengthen their mutual effect on magnetization. A microprocessor is used to control the switches feeding the voltage to the coils. 
         [0044]    The voltage supplied depends of different factors, such as the material of the probe. 
         [0045]    According to the invention, the magnetization phase might be effected several times before the probe  4  is shot towards the eye. When both coils are activated, the probe  4  does not move away from its original position. From outside, a certain trembling of the probe head can possibly be observed since when applying voltage for a short period to the front coil (in  FIG. 3  the one moving the probe towards the eye) it actually moves a very short distance forwards but is quickly moving backwards again when the voltage is directed to the back coil instead. 
         [0046]    Thus, magnetization of the back part  42  is performed by switching a short duration DC voltage into the coil(s)  50  and/or  60  at least once in turns by switching fast enough so as to hinder the probe  4  to move forwards when magnetizing coil  50 . The duration of each voltage feeding is e.g. in the order of 10-50 ms. In a certain embodiment the magnetization of the back part  42  is performed by switching a short duration DC voltage into the coils  50 ,  60  as several consecutive steps in turns. 
         [0047]    When the magnetization is ready and the probe is wanted to be put into movement towards the eye, which should take place before the magnetization level has decreased too much, voltage is fed only to the front coil  50  thus avoiding the holding effect of the back coil  60 . As the probe has a sufficiently high magnetization level, the speed of the probe is steady and enough for any measurement. The apparatus of the invention is constructed in such a way that when it is switched on, magnetization of the probe  4  takes place automatically. During the automatic magnetization, one of the coils can be used for measuring the movement of the probe and thus used for automatic detection of the presence of the probe (or the magnetization level). If the probe is not present, the device instructs the user to load the probe. 
         [0048]    Thus, the operation of the whole apparatus after magnetization takes place (simplified for illustrative purposes) so that power (a voltage) is supplied to the front coil  50  causing the probe to start moving and to impact the eye. When the probe  4  impacts the eye, the motion of the probe  4  is changed. The probe  4  rebounds as a result of contact with the eye and the movement backwards, takes place in a manner depending on the intraocular pressure. The movement of the probe is recorded by means of the rear coil  60  and processed by the same microprocessor as was used to control the switches feeding the voltage to the coils. The result is displayed by the display device  5 . In practice, the rear coil detects the speed of the probe continuously. The measurement results of the continuous motion of the probe are used to derive the intraocular pressure. The intraocular pressure is calculated from the motion parameters of the probe. 
         [0049]    The rear coil can be activated immediately after rebound from the eye for moving the probe back to the starting position. 
         [0050]    As has clearly been demonstrated by the above, the method according to the invention has properties, by means of which ease of use, accuracy, and reliability can be improved and maintained. Many variations are possible while remaining within the scope of the inventive idea and the accompanying claims. 
         [0051]    While the present invention has been described in accordance with preferred compositions and embodiments, it is to be understood that certain substitutions and alterations may be made thereto without departing from the spirit and scope of the following claims.