Abstract:
A portable non-contact tonometer ( 2 ) for measuring Intra-Ocular Pressure (IOP) of subject&#39;s eye is presented. In its preferred embodiment tonometer ( 2 ) is designed to be operated by the subject himself. It is housed in a hand-held case ( 4 ) which contains compressed air source ( 40 ), eye alignment detectors ( 12, 14 ), cornea applanation detector system ( 8, 10 ), a pressure sensor ( 32 ) and optical system for presenting gaze target ( 48 ). 
     The animated gaze target ( 48 ) advantageously draws subject&#39;s attention to itself and keeps his eye ( 62 ) in alignment long enough for the measurement to take place, while optionally displaying system status and operating instructions. An audio annunciation system ( 16 ) guides the subject in the operation of the tonometer and prepares him for the actual procedure. The timing of the air puff is randomized to prevent subject&#39;s conditioning. The overall operation of the tonometer is controlled by a built-in microprocessor ( 50 ) system. 
     In one of the tonometer embodiments ( 2 B) a 3-D map of cornea is computed and a technique to compute the IOP derived from the difference of 3-D corneal maps before and during the air puff application is disclosed.

Description:
FIELD OF INVENTION 
       [0001]    This invention relates in general to tonometers, and in particular to portable tonometers which can be easily moved and utilized in various positions by subjects themselves or by operators. 
       BACKGROUND OF INVENTION 
       [0002]    Measurement of intra-ocular pressure (IOP) is an important procedure in diagnosing various diseases and abnormalities of the eye as well as monitoring status of ophthalmic therapies and procedures. 
         [0003]    IOP is measured by a device called tonometer. Traditional stationary tonometers are used only in an ophthalmologist&#39;s office environment and only in a vertical position. There are two basic types of tonometers: the Goldmann-type which has been a universally recognized standard instrument which relies on the direct contact with a subject&#39;s cornea, and contact-less tonometers which use a puff of air to achieve flattening or “applanation” of the cornea and then compute the IOP as a function of the air pressure required for such corneal applanation. 
         [0004]    Contact tonometers require anesthesia of subject&#39;s cornea and carry a potential risk of transmitting eye infection from one subject to another and also a potential damage to the cornea itself if the device is not applied correctly or is improperly calibrated or maintained. 
         [0005]    Both of these types of tonometers are quite large and heavy, up to 40 lbs (18 kg) as is in case of the Topcon CT-80 computerized tonometer made by Latham &amp; Philips Ophthalmic Products, Inc. They are therefore consigned to medical offices. They also generally operate only in vertical position and require subjects to be cooperative while a measurement is performed. One non-contact tonometer, Pulsair EasyEye by Keeler, Inc. has a movable measuring head connected to a stationary base, which limits the range of its deployment and utility. 
         [0006]    Another type is a contact tonometer which measures IOP by compressing the subject&#39;s cornea through the eyelid. One such tonometer made by the Tonopen, Inc. is portable but requires considerable skill for its use to achieve repeatable and reliable readings. The same can be said for the Diaton tonometer marketed by BiCom, Inc. These tonometers require several readings to be taken and then averaged due to the variability of the measurement process. 
         [0007]    Measurement of IOP in different subject&#39;s positions sometimes results in differing readings, so some medical practitioners suggest measuring it at several different positions. 
         [0008]    Uncooperative subjects such as small children have to be sedated in order to perform an IOP measurement. In case of the elderly or in an emergency room setting there&#39;s also a need to measure IOP when the subject is prone. 
         [0009]    It has been recommended for some cases for the IOP measurements to be performed more or less continuously, as IOP displays diurnal variation which may not be adequately captured and evaluated when a patient has to visit a medical office for an IOP measurement. 
         [0010]    It is desirable, therefore to have a means to measure, store and transmit IOP readings remotely, possibly several times a day, without a visit to the doctor&#39;s office, while at the same time providing information to the patient. 
         [0011]    It is also desirable to have a portable tonometer which can be easily transported and used at subject&#39;s home, a tonometer which would be also easy to use both by non-specialist personnel and subjects themselves. 
         [0012]    It is also desirable for a tonometer to operate in any position and be usable with pediatric and geriatric patients and other ‘difficult’ subjects, like those encountered in veterinary practice, without anesthesia or constraints. 
       OBJECTIVES OF THE INVENTION 
       [0013]    Thus, it is an objective of instant invention to provide a portable tonometer which can be easily carried by or to the subject. 
         [0014]    Another objective of instant invention is to provide a tonometer which is easy to use, so it can be operated by subject himself, in a home environment rather than by a medical specialist in a medical office. 
         [0015]    Yet another objective of instant invention is to provide a tonometer that can be used with pediatric subjects with minimum preparation of the subject or operator training. 
         [0016]    Another objective of instant invention is to provide a tonometer which can be used in any position. 
         [0017]    Another objective of instant invention is to provide a tonometer which will cause minimized discomfort to the subject during the measurement. 
         [0018]    Yet another objective of instant invention is to provide a tonometer that is relatively inexpensive. 
         [0019]    Another objective of instant invention is to provide a tonometer which can store and transfer IOP readings to remote devices and locations. 
       SUMMARY OF THE INVENTION 
       [0020]    In accordance with the present invention a self-contained hand-held tonometer is introduced. It is small, lightweight and is preferably battery-operated. The tonometer can be operated by subject himself or an operator. The tonometer operation is essentially automatic and starts upon subject&#39;s or operator&#39;s turning it on. The tonometer has an internal compressed air generator, either in the form of an electrical pump similar to the ones found in portable blood pressure monitors, or a spring-loaded or electrically actuated plunger moving within a cylinder. 
         [0021]    The tonometer employs an internal electronic target display device which is capable of displaying still or moving target image or images along with system information to help align the eye along the optical axis of the tonometer. Such a display can be based on a liquid crystal (LCD), light-emitting diodes (LED&#39;s) or other display technologies. In addition, tonometer contains an automatic eye alignment detection subsystem, a pressure sensor, an air puff trigger mechanism, and a corneal applanation detection subsystem. 
         [0022]    As an option, the tonometer also has an audio annunciation subsystem to guide user in tonometer operation and also to help acquire and maintain the gaze of the pediatric subjects. 
         [0023]    The tonometer contains as an option a deployable forehead rest assembly which further assists with the proper alignment of the subject&#39;s eye with respect to the tonometer. 
         [0024]    During tonometer operation the subject is urged to look at the target and as soon as his eye is aligned with the optical axis of the device and is at the proper distance, a puff of air is released towards the subject&#39;s cornea to achieve its applanation. The timing of air pulse is randomized to minimize a chance of subject&#39;s conditioning. The eye alignment detection system consists of one or more optical emitter-detector pairs. A gaze target imaging system limits the field of view of the target display to facilitate proper alignment of the subject&#39;s eye. The overall operation of the tonometer is controlled by a built-in microprocessor system. 
         [0025]    A variation of the tonometer contains a viewing port and a system status display for an operator-assisted operation. 
         [0026]    A yet another variation of the tonometer contains a small video camera pointed toward the subject&#39;s eye and a display on the obverse side of the tonometer case. The camera captures the position of the subject&#39;s eye which is then shown on the display with optional alignment marks and alignment instructions derived from eye alignment detection system and generated by a microprocessor system. This feature is useful when the tonometer is operated by a person other than the subject himself. 
         [0027]    The use of imaging camera enables precision optical techniques to be utilized to measure the degree of corneal applanation. In alternative tonometer embodiment, a reference geometric pattern such as concentric rings or a rectangular grid are projected onto the cornea. The 3-D corneal shape is then calculated from the resulting image, and from the change of the corneal shape in response to an air puff the degree of corneal applanation is computed. 
         [0028]    In a yet another variation the tonometer contains internal memory to store IOP readings with a real-time clock function to reference them and an output capability to transmit IOP readings and preferably its self-diagnostic and/or calibration information to a remote devices such as computers, printers or PDAs (personal digital assistants). Such capability can be realized through a wired connection such as a USB or an Ethernet port, or wireless such as radio frequency or infra-red light. These data transmission methods are well known in their respective arts. 
       PRIOR ART 
       [0029]    Prior art contains several contact-less tonometers, some of which are portable. Most of the tonometers of the prior art are designed to be operated by a person other than the subject and require extensive training prior to operation. In contrast, the present tonometer is expressly designed to be operated by subjects themselves, except in some special cases such as the elderly, special patients (immobile, psychiatric, etc.), and children. 
         [0030]    The U.S. Pat. No. 6,623,429 to Percival at al. described a hand-held tonometer designed to be used by a trained operator. 
         [0031]    None of the prior art tonometers has a moving, animated or picture-like target display to help align subject&#39;s eye. 
         [0032]    None of the prior art has an audio subsystem to facilitate operation, measurement and to ease subject&#39;s possible anxiety. 
         [0033]    Likewise, none of the prior art teaches an imaging system restricting the field of view of the alignment target to facilitate alignment. 
         [0034]    None of the prior art has a randomized air pulse timing. 
         [0035]    Also, none of the prior art teaches a technique to compute the IOP derived from the difference of 3-D corneal maps before and after the air puff application. 
       OBJECTS AND ADVANTAGES 
       [0036]    In contrast to the prior art mentioned hereinabove, the present invention provides a simplified alignment to the subject&#39;s eye, which enables operation of the tonometer by subjects themselves, or in case of pediatric subjects, greatly simplifying the procedure, so that even an inexperienced operator, such as child&#39;s parent can easily measure subject&#39;s IOP. 
         [0037]    In addition, the operation of the tonometer is for the most part automatic, further simplifying its operation. 
         [0038]    The animated target advantageously draws subject&#39;s attention and thus aligns his eye, while optionally displaying system status and operating instructions. In addition, the audio annunciation system guides the subject in the operation of the tonometer and prepares him for the actual procedure. 
         [0039]    For pediatric subjects the audio annunciation system calms them prior to the measurement, encourages them to look at the target image and praises them after the measurement is complete. Preferably animated images of the popular cartoon characters or objects are displayed to draw subject&#39;s attention and to fixate his gaze in proper alignment and for sufficient time for a reliable measurement to be taken. For example, an animated image of a dragon puffing smoke can be displayed in preparation for the air puff of the tonometer. The subject&#39;s anxiety is diminished as the procedure is presented as a type of play. This additionally reduces the so-called ‘squint-squeeze’-induced IOP measurement error. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0040]      FIG. 1  is a perspective view of the preferred embodiment of the present invention. 
           [0041]      FIGS. 1A and 1B  are perspective views of the back of the two embodiments of the present invention. 
           [0042]      FIG. 1C  is cross section of forehead rest assembly. 
           [0043]      FIG. 1D  is a side member of forehead rest assembly. 
           [0044]      FIG. 2  is a partial sectional view along cross sectional line A-A of the  FIG. 1 . 
           [0045]      FIG. 3  is a sectional view similar to the embodiment in  FIG. 2  but featuring alternative compressed air system 
           [0046]      FIG. 4  is a partial sectional view along cross sectional line C-C of the  FIG. 1   
           [0047]      FIG. 5  is a partial sectional view along cross sectional line B-B of the  FIG. 1  omitting some elements for clarity. 
           [0048]      FIG. 6  is a simplified schematic of the optical train for the subject&#39;s eye observation by operator in  FIG. 5   
           [0049]      FIG. 7  is a simplified schematic of the optical train for the alignment target imaging for viewing by subject in  FIG. 5 . 
           [0050]      FIG. 8  is a simplified schematic of the optical train for the system status display for operator in  FIG. 5 . 
           [0051]      FIG. 9  is a partial sectional view similar to one in  FIG. 5  but featuring alternative embodiment of  FIG. 1B . 
           [0052]      FIG. 10  is a simplified partial schematic of the optical system for viewing of the alignment target by subject in tonometer embodiment on  FIG. 1B . 
           [0053]      FIG. 11  is a simplified partial schematic of the optical system for imaging of the subject&#39;s eye for the camera in tonometer embodiment on  FIG. 1B . 
           [0054]      FIG. 12  is a partial sectional view similar to one in  FIG. 5  but featuring alternative tonometer embodiment with cornea 3-D shape measurement feature. 
           [0055]      FIG. 13  is a simplified partial schematic of the optical system for viewing of the alignment target by subject in tonometer embodiment on  FIG. 12 . 
           [0056]      FIG. 14  is a simplified partial schematic of the optical system for the cornea shape target projection and subject&#39;s eye imaging in embodiment on  FIG. 12 . 
           [0057]      FIG. 15  is a sample display of the gaze target, eye alignment and system status. 
           [0058]      FIG. 16  is a sample of the system status, eye alignment display and system status including superimposed image of subject&#39;s eye. 
           [0059]      FIG. 17  is tonometer system&#39;s simplified operational sequence diagram. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0060]    In the foregoing description like components are referenced by the like numerals. 
         [0061]    Optical elements and subsystems are presented in simplified form to convey their overall function, such as imaging, collimation, etc. The actual construction and layout of the optical systems and lens elements themselves may differ from their representation and will be governed by the physical optical design considerations. For example, additional folding mirrors and beamsplitters may have to be utilized in order to conform the design within physical constraints of the overall tonometer system, lens elements themselves may have to contain several groups to adapt to system&#39;s physical size constraints and control optical aberrations. 
         [0062]    The preferred embodiment  2  of the present invention is shown on  FIG. 1 . Tonometer  2  is housed in housing  4 . Referring to  FIG. 2 , tonometer is controlled by a microprocessor  50  and is powered by an internal power source  52 , which can be rechargeable or non-rechargeable battery. The back of the tonometer is shown on  FIG. 1A , with the operator observation port  26 , data port  15 , optional auxiliary display  23 , and mode selection buttons  17  visible. 
         [0063]    The IOP measurement operation is initiated when subject himself or an operator presses the power button  22  which starts tonometer microprocessor system, and then selects the mode of tonometer operation, such as the measurement to be self-conducted by the subject, pediatric, audio enunciation, gaze target selection, etc. via buttons  17 . For instance, for the self-conducted measurement, gaze target  48  includes in addition to the central gaze target system status and alignment information on its periphery. For pediatric use, selection of animated targets can be offered along with a selection of audio accompaniment and/or narration. 
         [0064]    Upon the signal from button  22  microprocessor  50  initiates the measurement sequence and controls it to completion. 
       Pressurization of Air Source 
       [0065]    Referring to  FIG. 2 , microprocessor  50  communicates with and controls system components via bus  51 . Under microprocessor  50  control air pump  40  compresses air via a one-way valve  37  in accumulator chamber  36  whose outlet is held closed by electrically-activated valve  34 . The air pressure in chamber  36  is monitored by pressure switch  33  which is activated when pressure reaches a pre-determined value. The pump  40  is then stopped and the system status updated accordingly. 
         [0066]    Alternatively, as shown on  FIG. 3  electrical air pump can be substituted by a manually operated plunger  56  which compresses air in the chamber  54  which communicates via a one-way valve  37  with accumulator chamber  36 . Subject or operator pumps up the air by depressing knob  58  connected to plunger  56 . Plunger  56  is returned to its initial position by spring  60 . Pressure in chamber  36  is monitored by pressure switch  33  which communicates with microprocessor  50  which in turn generates corresponding notification via an audio signal and/or system status display update when the operating air pressure is achieved. 
       Alignment 
       [0067]    As shown on  FIGS. 1 ,  1 A and  1 B prior to measurement an optional forehead rest assembly  6  which is normally stored in housing  4  is folded out. The use of the forehead rest helps to position tonometer at proper distance to subject&#39;s eye by steadying tonometer, but it is not mandatory, since the proper distance is automatically indexed when the subject brings the gaze target into focus. 
         [0068]      FIG. 1C  shows forehead rest assembly  6  which consists of an essentially U-shaped main member  7  which interacts with two side members  9   a  and  9   b  which are spring loaded and can retract into the side sections of the main member  7 . Side members  9   a  and  9   b  are biased by springs  11   a  and  11   b  respectively. The travel of side members  9   a  and  9   b  is limited by internal stops  11   c  and  11   d  in the main member  7 . As shown on  FIG. 10  side members  9   a  and  9   b  have transverse openings  9   c  and  9   d  respectively which enable forehead rest assembly  6  to pivot for storage around corresponding pins (not shown) in housing  4 . 
         [0069]    The subject himself or an operator positions tonometer  2  so rest  6  is against subject&#39;s forehead  61  opposite one of his eyes  62  as shown on  FIG. 5 . 
         [0070]    Referring to  FIGS. 2 ,  5  and  7  gaze target  48  is turned on and is imaged for observation by the subject via lens element  46 , beamsplitter BS and lens system elements  20  and  64 . The combined effect of these lens systems is to provide a narrow-angle view of target  48  which necessitates proper alignment of the subject&#39;s eye in order for him to see the target well. The optical design of these lens systems ensures a sufficient depth of field so that subject&#39;s eye is able to accommodate the shift in the position of the tonometer when it is moved to and from subject&#39;s eye for proper distance for measurement. 
         [0071]    Target  48  is preferably a small electronic display, which is preferably a back-lighted liquid crystal (LCD), and can be monochromatic or color. Alternatively, target  48  can be of a light-emitting type, such as light-emitting diodes (LED), plasma, or electroluminescent. The preliminary eye alignment is achieved by animating or moving the target image to attract and hold subject&#39;s attention, and bring him to gaze at the target along the optical axis of the target imaging system which by design coincides with the optical axis of the tonometer. 
         [0072]    Referring to  FIG. 7  when tonometer operation is selected for conduct by the subject himself, target  48  includes in addition to the central gaze target, a system status and alignment information. An example of such target display is shown on  FIG. 15 . Central gaze target  90  is represented as a crosshair, but can be any image, stationary or animated, suitable for acquiring and retaining subject&#39;s attention. Alignment indicators  80  display alignment of subject&#39;s eye with respect to tonometer optical axis and show the needed correction when re-alignment is needed by changing their color like  80   a , shape, blinking or a message similar to  80   b . Focus status is indicated by message  88  and status indicators  88   a ,  88   b , and  88   c . When tonometer is out of focus, message  88  and corresponding status indicator  88   a  or  88   b  may be made to blink, change color or shape. Simultaneously, audio instructions for alignment and/or sounds accompanying any central target  48  animation can be produced by audio enunciator  16  under control of microprocessor  50 . System status indicators such as air supply readiness  82 , overall system readiness  84  and battery charge level  86  are included in the display. 
         [0073]    For operator-assisted measurement, subject&#39;s eye  62  is illuminated for viewing by light sources  13  positioned around lens element  20 . 
         [0074]    Referring to  FIGS. 5 and 6  operator  70  observes subject&#39;s eye  62  via lens system elements  20 ,  64 , beamsplitter BS and lens system elements  66  and  68 . 
         [0075]    Referring to  FIGS. 5 and 8  system status including alignment information and guidance are displayed via system status display  44  which is made available for viewing by operator  70  via imaging sub-system consisting of lens element  42 , beamsplitter BS and lens system elements  66  and  68 . To facilitate operator&#39;s convenience, this and other system information is superimposed onto the image of subject&#39;s eye viewed by operator by the action of beamsplitter BS. An example of information display is shown on  FIG. 16 . In addition to the elements presented on  FIG. 15  for the self-conducted measurement, the display  44  contains an image  92  of subject&#39;s eye  62  to assist with alignment process. Gaze target  90  representation can also be a combination of what subject sees and an additional superimposed alignment aid for the operator. For example, target  48  which is visible to the subject can be replicated in display  44  visible to the operator, but displayed dimmed or of different color, with an overlay of a simpler alignment aid. This enables operator to monitor the target visible to the subject. This is advantageous for pediatric subjects when an operator may want to comment on what a child sees to guide him through the procedure. 
         [0076]    Simultaneously, audio instructions and/or sounds accompanying target  48  animation can be produced by audio enunciator  16  under control of microprocessor  50 . 
         [0077]    The subject himself or operator then advances tonometer closer to the subject&#39;s eye by compressing forehead rest assembly  6  until the system determines that a proper focus is reached and commences the measurement. As mentioned earlier, using forehead rest is not mandatory, since the proper distance is automatically indexed when the gaze target is in focus for the subject. 
         [0078]    Referring to  FIGS. 2 ,  5  and  6  subject&#39;s eye alignment, including proper focus position is verified by microprocessor  50  via alignment sensors  12  and  14 . These sensors each consist of the light source—detector pair known in the art and measure reflectance of the subject&#39;s eye. 
       IOP Measurement 
       [0079]    As the subject&#39;s eye alignment, and air supply readiness are confirmed microprocessor  50  turns on the applanation detection system and, after a short random time interval opens valve  34  which releases compressed air from chamber  36  via plenum  30  to orifice  28  in lens systems  20  and  64  and ultimately toward subject&#39;s eye  62 . Random time delay, while optional, improves the accuracy of the measurement by minimizing subject&#39;s squinting and other potential involuntary actions by making the exact air pulse timing unknown and preventing subject&#39;s conditioning to it. After the release of the air pulse, applanation detection ensues. 
         [0080]    Referring to  FIGS. 1 ,  2  and  4 , subject&#39;s eye  62  is illuminated by applanation light probe source  8 . Upon reflection from the cornea the light is detected by applanation detector system  10  which is preferably equipped with light collecting optical elements and an internal pinhole in front of a light sensor element which together comprise a corneal applanation detection mechanism well known in the art. As cornea flattens (“applanates”) under the action of the air pulse, it reflects the light probe beam differently which is detected by the system. 
         [0081]    Pressure sensor  32  measures air pressure inside plenum  30  while corneal applanation detection takes place. As soon as applanation is detected by light source  8 —detector system  10  combination, output of sensor  32  is read by microprocessor  50  and the IOP value is subsequently calculated. The IOP value can then be displayed in several different ways, such as on the system status display  44 , onto the target display  48 , via an audio announcement by audio enunciator  16 , a combination thereof, an auxiliary display  23 , a bargraph type LED or LCD display, or discrete LEDs of different colors corresponding to the IOP value measured. 
         [0082]    All alignment and applanation detection light sources preferably emit infra-red light invisible to the subject, so as not to distract him or cause discomfort. The eye illumination sources  13  and target  48  illumination source in this embodiment preferably emit visible light. IOP measurement data generated by microprocessor  50  can be transferred to other devices via a wired data port  15  or wirelessly via a wireless transceiver  55 . The present preferred technology for the wired port is USB, while for the wireless port it is IEEE 802.11 also known as WiFi, or BlueTooth. All these data transport mechanisms are well known in their respective arts. 
       Additional Embodiments 
       [0083]    In the foregoing description like components are labeled with like numerals. 
         [0084]    An alternate tonometer embodiment  2 A is shown on  FIGS. 1B ,  9 ,  10  and  11 . In this embodiment operator&#39;s direct observation of the subject&#39;s eye and the corresponding optical system are replaced with internal electronic camera  74  with its corresponding imaging system and display  24 . 
         [0085]    Referring to  FIGS. 9 and 10  subject  61  with his eye  62  views gaze target  48  via an optical system consisting of imaging lens element  46 , beamsplitter BS and lens system elements  20  and  64 . 
         [0086]    Referring to  FIGS. 9 and 11  subject&#39;s eye  62  is illuminated by illuminators  13  while its precise alignment to the tonometer optical axis is monitored by alignment detectors  12  and  14 . Subject&#39;s eye  62  is imaged via beamsplitter BS, turning mirror M and imaging lens  72  onto camera  74 . The output of camera  74  and any additional information, such as alignment status and guidance, system status and the resulting IOP value are then displayed on display  24 . 
         [0087]    It is also possible to detect corneal applanation with this camera by illuminating the eye with one or more narrow beam light sources and capturing their reflection(s) from the cornea. 
         [0088]    Another tonometer embodiment  2 B based a cornea shape calculation function is shown schematically on  FIG. 12 . In this embodiment optical element  47  images target  49  onto subject&#39;s eye  62  via beamsplitters BS 1  and BS 2 . Target  49  is made to display a cornea test pattern consisting of concentric light and dark rings, which is well known in the art for cornea shape measurement. Alternatively, a rectangular grid-, a multiple dot-, or other patterns can be displayed. Target  49  is preferably a back-lighted LCD, with its illumination source preferably infra-red, rather than visible, or it can be a static transmission mask with a backlight source. The image of this pattern on subject&#39;s cornea is conveyed to camera  74  via lens system elements  20  and  64 , beamsplitter BS 1 , turning mirror M and imaging lens  72 . Illuminators  13  can be temporarily turned off for the camera to acquire image of only the test pattern on the cornea. The resulting image output from the camera is then captured by image processor  53  which can be a stand-alone device or an internal implementation of microprocessor  50  or camera  74  itself. By processing the image, a 3-dimensional map of the cornea is generated. If target  49  illuminator is made to emit infra- red light rather than visible, beamsplitter BS 2  can be replaced by a dichroic mirror. If eye illuminator sources  13  are also infra-red, camera  74  has to be sensitive only to infrared light. 
         [0089]    The cornea shape measurement feature can be used to measure the IOP without the need for a dedicated cornea applanation detection system. According to this method, cornea shape is measured at least twice: just before, and also during the air pulse, and the differences between the two computed shapes are compared and correlated to the air pressure. Several shape measurements can be made during the duration of the air pulse for better data correlation. Due to high sensitivity of this method very small cornea shape change can be detected, thus requiring a much weaker air pulse pressure. As a result, the measurement can be made more comfortable for subjects. Also, by correlating localized cornea shape changes versus air pressure, additional cornea qualities can be measured as well, such as cornea elasticity versus air pressure, and also distribution of elastic non-uniformities throughout cornea which may indicate underlying localized cornea defects. Thus, non-uniform thinning of the cornea, such as in keratoconus and other corneal diseases can be detected. 
         [0090]    Additionally, an interferometric or Moire technique can also be utilized for comparing the cornea shape before and during the air puff and subsequently analyzing them. These methods, also being quite sensitive, would require a lower air puff pressure needed to deform the cornea with the corresponding decrease in patient discomfort. 
         [0091]    For all embodiments of the instant invention alternative air compression methods can be utilized, such as solenoid- or spring-activated plungers. Solenoids can be of linear- or rotational types which are well known the art. With such solenoids used for an air drive, accumulation chamber can be eliminated. The drawbacks in using solenoids are their relatively slow activation speed, high power surge requirements, and potential for increased operational noise. Spring-loaded plungers are also known in the art, but require electronic trigger. 
         [0092]    Although descriptions provided above contain many specific details, they should not be construed as limiting the scope of the present invention. Thus, the scope of this invention should be determined from the appended claims and their legal equivalents.