WO2017027494A1

WO2017027494A1 - Intraocular pressure measurement through a closed eyelid

Info

Publication number: WO2017027494A1
Application number: PCT/US2016/046119
Authority: WO
Inventors: G. B. Kirby Meacham
Original assignee: Barron Precision Instruments, Llc
Priority date: 2015-08-10
Filing date: 2016-08-09
Publication date: 2017-02-16

Abstract

The present invention is directed to a method, device and system for measuring intraocular pressure in the human eye to through the closed eyelid to avoid direct contact with the cornea. Closed eye measurement allows the measurement to be made outside a clinical setting, even by the patients themselves, since it reduces user skill requirements, eliminates the need for anesthetic eye drops, and simplifies infection control. A probe with a concave face is pressed against the closed eyelid, producing hydrostatic pressure in the eyelid tissue that balances the intraocular pressure through the corneal membrane. The concave face incorporates a spatial array of multiple contact pressure sensors that generate a time sequence of eyelid tissue contact pressure data sets at the sensor locations. A selection algorithm and a measurement algorithm provide results shown by audible or visual signals.

Description

INTRAOCULAR PRESSURE MEASUREMENT THROUGH A CLOSED EYELID

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional application Serial No.

62/202,972 filed August 10, 2015, the disclosure of which is hereby incorporated in its entirety by reference herein.

TECHNICAL FIELD

[0002] The present invention is directed to a method, device and system for measuring intraocular pressure in the human eye to detect glaucoma and monitor the efficacy of treatment. In particular, the device and method measure the intraocular pressure through the closed eyelid to avoid direct contact with the cornea, allowing the measurement to be made outside a clinical setting, even by the patients themselves.

BACKGROUND

[0003] Normal intraocular pressure in the human eye is between 10 and 20 millimeters of mercury above ambient atmospheric pressure, and values above this range can result in glaucoma. Glaucoma is a progressive and irreversible deterioration of the optic nerve, and may result in serious loss of vision. Medications and surgical treatments to reduce intraocular pressure are well known and effective in slowing or stopping the progression of glaucoma, and clinical measurement of intraocular pressure is used to screen for elevated pressure and monitor the treatment.

[0004] Prior art intraocular pressure measurements are typically made by a mechanical member contacting the corneal membrane of the open eye and measuring its force-deflection characteristics of to infer the pressure of the aqueous humor, the fluid contained by the cornea. These open-eye methods are effective, but are generally limited to a clinical setting by several factors. First, the cornea is very sensitive to touch, and anesthetic eye drops are necessary to numb the eye prior to the procedure. Second, the person making the measurement must be trained in the use of the device to avoid the possibility of injury. Finally, infection control steps are needed to avoid transmitting microorganisms to the eye from the environment or between patients. Self- measurement or large scale screening using relatively untrained personnel are not practical with devices using direct corneal contact.

[0005] The physical properties and geometry of the human eye and eyelid are important elements in this invention. When the eyes are closed and the gaze is straight ahead, the cornea is entirely or almost entirely covered by the upper eyelid, with the lashes and contact area between the upper and lower eyelids beneath the cornea. The eyelid tissue over the cornea in this condition is therefore relatively thin and uniform, and behaves as a very soft elastomer or gel in the sense that it is a "contained fluid". As a "contained fluid" it will conform to contacting surfaces, transmit static pressures, and yet not flow out of a confined pressurized gap beyond a limited amount related to its elastic properties.

SUMMARY

[0006] The present invention is directed to devices and methods for making intraocular pressure measurements through the closed eyelid to eliminate the need for anesthetic eye drops and to minimize the skill required to avoid injury and control infection while getting valid pressure measurements. It is further directed to making self-measurements practical.

[0007] The device of the invention comprises a probe with a concave face that is gently pressed against the closed eyelid over the cornea. The concave face has a diameter, e.g., 10 millimeters, approximately equal to the corneal diameter and a spherical radius, e.g., 11 millimeters, approximately equal to the spherical radius of the closed eyelid over the cornea. A number, e.g., 7, of contact pressure sensors are arrayed on the concave face such that they measure the contact pressure distribution of the probe against the eyelid. Preferably the array comprises a central sensor ringed by a regularly spaced ring of sensors, but other arrangements are possible. The device optionally incorporates a concentric sleeve surrounding the probe that contacts the eyelid at a larger diameter, e.g., 20 millimeters, to assist the user in centering the probe on the eyeball and the cornea.

08] While any suitable pressure sensor capable of measuring in the range of 0 through

, 40 millimeters of mercury that meets the size requirements of the probe may be used to implement the invention, it has been demonstrated that commercially available microelectromechanical systems (MEMS) piezo resistive sensors fabricated on silicon wafers meet the size and functional requirements. The sensors may be covered with a thin layer of soft elastomer gel that transmits the eyelid pressure to the sensor while protecting the sensor and presenting a smooth surface to the eyelid. Either differential or absolute pressure sensors may be used, since the sensors may be zeroed in software for each measurement.

[0009] While not wishing to be bound by theory, the probe and sensor array are believed to respond to intraocular pressure through the eyelid through hydrostatic pressure transfer in an elastic media in a manner analogous to measuring blood pressure in an artery surrounded by soft tissue using a blood pressure cuff. Prior to probe contact, the cornea is a thin spherical membrane tensioned by the internal aqueous humor pressure and supported at the circular edge by the relatively stiff sclera. When the hydrostatic pressure applied to the eyelid by the probe equals the internal pressure, the corneal membrane tension equals zero and the eyelid pressure is equal to the internal pressure and may be measured by the probe sensors. When the probe is pressed further, the slack corneal membrane deflects inward at nearly constant pressure. If the probe geometry is such that the center sensor is closer to the cornea than the surrounding sensors, the measured center pressure will rise first, followed by the surrounding measured pressures. When all the sensors measure similar values, the measured values are essentially equal to the intraocular pressure. If the probe is pressed too far, the surrounding sensors will measure higher pressures because the edge of the cornea has relatively stiff mechanical support from the sclera compared to the mechanically unsupported center. Also, if the probe is tipped or off-center, there will be significant variation in the surrounding sensor values. It is therefore possible to determine when the sensor array contacting the eyelid is measuring the true intraocular pressure by considering the pressure distribution among the sensors in the array and only selecting "good" sets of sensor pressure values.

[0010] The device further comprises means for energizing the contact pressure sensors, acquiring the instantaneous pressure reading of each sensor, computation resources to process the pressure readings in real time, e.g., 50 times per second, and display means to present the results.

Optionally it includes visual indicators such as blinking lights or audible indicators such as beeps to let the user when the device is making "good" measurements, indicate the end of the test, and warn against "too hard" pressure of the probe against the eye. [0011] The method of the invention comprises pressing the concave probe gently against the closed eyelid approximately concentric with the cornea, acquiring contact pressure reading data sets from the sensor array at a rate of e.g., 50 datasets per second, analyzing each data set in real time to determine if it is "good", calculating an intraocular pressure from each "good" data set, and averaging these calculated values to determine and report an intraocular pressure result when specified conditions such as acquiring a certain number of "good" readings are met, and indicating that the measurement is successful or must be repeated.

[0012] In general, a "good" data set meets a set of criteria such as the following:

[0013] A minimum average value greater than e.g., 5 millimeters of mercury that indicates the probe is in contact with the eyelid;

[0014] Sensor to sensor pressure variation within a prescribed maximum fraction of the average value, e.g., 0.6, as a measure of alignment of the probe with the cornea; and

[0015] Edge pressures lower than the central pressure, indicating the probe is not pressed too hard by the user.

[0016] The probe orientation and force must be in a relatively narrow range for all the criteria to be met simultaneously, and a hand-held probe produces pressure traces with substantial variations. In practice only a fraction of the datasets yield a "good" result while most are discarded, and there is some variation in the "good" results. It is believed, and experiments indicate, that an average of a number of "good" values provides accurate and repeatable results.

[0017] At least two valid approaches may be used for calculating the pressure value reported for a "good" data set. The center value may be used, since it is removed from edge effects and may better reflect the aqueous humor pressure transmitted through the cornea and the eyelid. Alternatively, a simple average or weighted average may reduce noise and also give a valid result. The best algorithm may vary from user to user, and may optionally be a selectable device feature. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The appended claims set forth those novel features that characterize the invention.

However, the invention itself, as well as further objects and advantages thereof, will best be understood by reference to the following detailed description of preferred embodiments. In the accompanying drawings like reference characters identify like elements throughout the various figures:

[0019] FIGURE 1 A is a sectional side elevation of an intraocular pressure measuring device approaching the closed eyelid;

[0020] FIGURE IB is a similar view showing the device pressed against the closed eyelid in the measuring position;

[0021] FIGURE 2A through FIGURE 2D contain four sectional side elevation details of the intraocular pressure measuring device in contact with the eyelid illustrating different contact pressure distributions;

[0022] FIGURE 3 contains multiple views of a probe according to the invention wherein the

MEMS pressure sensors measure differential pressure;

[0023] FIGURE 4 contains multiple views of a probe according to the invention wherein the

MEMS pressure sensors measure absolute pressure; and

[0024] FIGURE 5 is a block diagram illustrating an exemplary system embodying the invention.

DETAILED DESCRIPTION

[0025] As required, detailed embodiments of the present invention are disclosed herein; however, it is to be understood that the disclosed embodiments are merely exemplary of the invention that may be embodied in various and alternative forms. The figures are not necessarily to scale; some features may be exaggerated or minimized to show details of particular components.

Therefore, specific structural and functional details disclosed herein are not to be interpreted as limiting, but merely as a representative basis for teaching one skilled in the art to variously employ the present invention.

[0026] Upon examination of the following detailed description the novel features of the present invention will become apparent to those of ordinary skill in the art or can be learned by practice of the present invention. It should be understood that the detailed description of the invention and the specific examples presented, while indicating certain embodiments of the present invention, are provided for illustration purposes only. Various changes and modifications within the spirit and scope of the invention will become apparent to those of ordinary skill in the art upon examination of the following detailed description of the invention and claims that follow.

[0027] Figure 1A shows a generic intraocular pressure measuring device 100 according to the invention and a patient eye 101 prior to the probe 102 contacting the closed upper eyelid 103, and Figure IB shows it in the measuring position contacting and pressing against the eyelid. The probe 102 has a concave face 104 that is gently pressed against the closed eyelid 103 over the cornea

105. The concave face 104 has a diameter, e.g., 10 millimeters, approximately equal to the corneal diameter and a spherical radius, e.g., 11 millimeters, approximately equal to the spherical radius of the closed compressed eyelid 103 over the cornea 105. A number, e.g., 7, of contact pressure sensors 106 are arrayed in the concave face 104 such that they measure the contact pressure distribution of the probe 102 against the eyelid 103. Preferably the array comprises a central sensor

106 A ringed by a regularly spaced ring of six sensors 106B, but other arrangements are possible.

The device optionally incorporates a concentric sleeve 107 surrounding the probe that contacts the eyelid 103 at a larger diameter, e.g., 20 millimeters, to assist the user in centering the probe on the eyeball 108 and the cornea 105. The device also may include a support body 109 that connects the concentric sleeve 107 to the probe 102 through an adjustable connection such as the screw thread connection 110. An elastomer seal ring 111 may be included to allow adjustment of the sleeve 107 while excluding contaminants from the device and permitting application of liquid cleaning and disinfecting solutions. The device and the system further comprises (not shown) means for energizing the contact pressure sensors, acquiring the instantaneous pressure reading of each sensor, computation resources to process the pressure readings in real time, e.g., 50 times per second, and display means to present the results. Optionally it includes visual indicators such as blinking lights or audible indicators such as beeps to let the user whether the device is making "good" measurements, indicate the end of the test, and warn against excessive pressure of the probe against the eye that result in "too hard" readings.

[0028] While not wishing to be bound by theory, the probe and sensor array are believed to respond to intraocular pressure through the eyelid through hydrostatic pressure transfer in an elastic media in a manner analogous to measuring blood pressure in an artery surrounded by soft tissue using a blood pressure cuff. Prior to probe 102, contact with the upper eyelid 103, the cornea 105 is a thin spherical section membrane tensioned by the internal aqueous humor intraocular pressure 200 as shown in Figure 2 A. Figure 2B illustrates a "good" reading with the probe 102 lightly compressing the eyelid 103 against the cornea 105. When the hydrostatic pressure 20 IB applied to the eyelid 103 by the probe equals the internal pressure 200, the differential pressure across the cornea 105 vanishes, the corneal membrane tension equals zero, and the eyelid pressure is substantially equal to the internal pressure 200 and may be measured by one or more of the probe sensors 106A and 106B. When the probe 102 is pressed further, the slack corneal membrane 105 deflects inward at a nearly constant contact pressure 201. If the probe 102 geometry is such that the center sensor 106A is closer to the cornea 105 than the surrounding sensors 106B, the measured center pressure will rise first, followed by the surrounding measured pressures. When all the sensors measure similar values, the measured values are essentially equal to the intraocular pressure. If the probe 102 is tipped or off-center relative to the cornea 105 as shown in Figure 2C, there will be significant variation in the surrounding sensor 106 B pressure values in the contact pressure distribution 201C. If the probe 102 is pressed too far as shown in Fig 2D, the surrounding sensors 106B will measure higher pressures than the center sensor 106 A values in the contact pressure distribution 20 ID because the edge of the cornea 105 has relatively stiff mechanical support from the sclera 202 compared to the mechanically unsupported center.

[0029] It is therefore possible to determine when the sensors 106 A and 106B contacting the eyelid are measuring eyelid hydrostatic pressure 201 value close to the true intraocular pressure 200 by considering the pressure distribution among the sensors in the array and only selecting "good" data sets that meet specified criteria such as the following example:

[0030] A minimum average value of all the sensors 106A and 106B greater than e.g., 5 millimeters of mercury that indicates the probe 102 is in contact with the eyelid 103; [0031] Sensor to sensor pressure variation within a prescribed maximum fraction of the average value, e.g., 0.6, as a measure of alignment of the probe 102 with the cornea 106; and

[0032] Edge pressures measured by sensors 106B lower than the central pressure measured by sensor 106A, indicating the probe 102 is not pressed too hard by the user.

[0033] It will be obvious to those skilled in the art that different numerical values for these criteria and different computational schemes can lead to comparable results. The inventive principle is that the pattern of variations between the measured pressure values may be analyzed to evaluate whether or not the probe alignment and force against the eyelid will result in a valid measurement of the intraocular pressure.

[0034] The orientation and force applied by the user to the probe 102 must be in a relatively narrow range to meet all the criteria simultaneously, and a hand-held probe produces pressure traces with substantial variations. In practice, only a fraction of the datasets yield a "good" result, and most are discarded. There is also some variation in the "good" results, but it is believed and experiments indicate that an average of the "good" values provides accurate and repeatable results. Experiments also indicate that the concentric sleeve 107 shown in Figure 1A and Figure IB appears to assist in centering the probe 102 by pressing through the upper eyelid 103 and the lower eyelid 204 to bear against the sclera 202 of the eyeball 108. It also appears to assist the user in applying controlled and steady pressure to the probe 102 compared to the probe alone, and is believed to increase the fraction of the measurements resulting in "good" values. Real time audible and visual indicators of "good" readings and "too hard" readings appear to be very useful in guiding the user in adjusting the alignment and the force applied to the device 100 and the patient's eye 101.

[0035] At least two valid approaches may be used for calculating the pressure value reported for a "good" data set. The center value measured by sensor 106A may be used, since it is removed from edge effects and may better reflect the pressure of the aqueous humor 200 transmitted through the cornea 105 and the upper eyelid 103. Alternatively, a simple average or weighted average may reduce noise and give a valid result. The best algorithm may vary from user to user, and may optionally be a selectable device feature. [0036] Figure 3A and Figure 3B show an exemplary implementation of the invention that has been built and tested as a proof of principle functional model. The pressure sensors 300 are Allsensors MEMS piezoresistive DIE-L30G with a range of +/-30 inches of water {+1-56 millimeters of mercury). The sensors are differential, with the diaphragm front faces 301 contacting a thin layer of silicone rubber gel 302 forming the concave face 104 of the probe 102 and rear faces of the diaphragms 301 vented to atmosphere through holes 303 in the rear of the sensor dies 300. The sensor dies sit in cylindrical pockets in a die carrier 304, and are held in place by a retainer shell 305. The retainer has portholes 306 positioned to expose the sensor diaphragms 301 to the silicone rubber 302. The silicone rubber has been shown to transfer contact pressure from the probe contact face 104 to the sensor diaphragms 301 with negligible losses. As shown in more detail in Figure 3B, electrical connections to the pressure sensor dies 300 are made through flex circuits 307 that are joined to the front faces of the dies using known flip chip techniques. These techniques provide electrical contact between the die contact pads and the conductive traces 308 of the flex circuits as well as an adhesive mechanical bond. The flex circuits 307 include soldering pads 309 at the opposite ends for connection to a cable leading to the power supply and signal conditioning and analysis modules that interface with the sensors (not shown). They also include an opening 310 at the sensor end to expose the diaphragm 301 to the pressure transmitted by the silicone rubber 302.

[0037] Figure 4A and Figure 4B show a second exemplary implementation of the invention using absolute rather than differential MEMS pressure sensor dies in the probe 102. The absolute pressure sensors 400 in the illustration are Amphenol NovaSensor MEMS piezoresistive P-330 dies with a range of 450 to 1050 millimeters of mercury or -310 to +290 millimeters of mercury relative to 760 millimeters of mercury standard atmospheric pressure. The sensors 400 are bonded to a flex circuit 401. The contact pads 402A-402D on the sensor are connected to flex circuit traces 403 A- 403 C on the flex circuit 401 by gold wire bonds 404A-404D using known wire bonding techniques. As shown in Figure 4B, the sensor die 400 comprises a silicon body 404 with a evacuated cavity 405 closed by a piezoresistive sensing membrane 406. The piezoresistive elements of the membrane change resistance with changes in pressure between the media outside of the membrane and the vacuum in the cavity 405. The power supply and signal conditioning and analysis modules (not shown) that interface with the sensors 400 through the flex circuit traces 403 measure the resistance change to determine the absolute pressure of the media outside the sensor 400. Each of the sensors 400 is positioned in a separate pocket 407 in the probe head body 408 by the flex circuits 401 such that they are just below the surface of a silicone rubber gel layer 409 (shown cutaway) that forms the concave contact face 104. The flex circuits 401 each pass from the rear of the probe head body 408 into the pockets through conduit openings 410, and may be connected to the conduit walls by a bond 411 to fix their positions and resist stresses on the flex circuits during and after addition of the silicone rubber layer 409. Rubber layer 409 is preferably added as a catalyzed liquid and cured in place so that it makes intimate contact with the probe head body 408, the sensor dies 400, and the portions of the flex circuits 401 within the head pockets 407, and at least a portion of the conduit openings 410.

[0038] In the absolute pressure sensor embodiment of Figure 4, the sensor dies 400 measure the absolute hydrostatic pressure of the silicone rubber layer 409 in the vicinity of the sensor die, thereby measuring the absolute hydrostatic pressure of the adjoining tissue of the eyelid 103, thus enabling the measurement of intraocular pressure as described in reference to Figure 2. Since changes in weather and altitude change the absolute ambient pressure, it is necessary to subtract the absolute pressure sensor readings prior to pressing the probe 102 against the eyelid 103 from the subsequent readings to obtain correct hydrostatic pressure readings relative to atmospheric pressure as required for intraocular pressure readings. This may be done automatically in software during instrument startup.

[0039] Figure 5 is a block diagram illustrating a complete intraocular pressure measurement system employing the probe 100 and the measurement method described in reference to Figure 2. The sensor power supply 500 provides a controlled excitation voltage to the sensors in probe 100. The resulting analog pressure signals are converted to digital pressure data by the analog/digital converter 501 a rate of e.g., 50 conversions per second per sensor and passed on to the computation and control module 502. The user interface module 503 accepts user commands, provides real time visual and/or audible guidance to the user during the measurement, and displays the measurement results and other data. The measurement guidance to the user includes but is not limited to "good" measurement, pressing too hard, and measurement complete. The user commands include but are not limited to instrument on/off, start test, abort test, user identification, and left or right eye identification. The other data includes but is not limited to a need to retest, a history of prior test results, and the quality of the measurement based on the variability of the "good" results averaged for the final value.

[0040] The system operation follows the following sequence:

[0041] The user turns the system on through the user interface 503, starting the computation and control module 502 and energizing the sensor power supply. The initial pre-contact measurements from probe 100 are digitized by analog/digital converter 501 and stored in the computation and control module 502 to provide zero-correction values for subsequent pressure data values.

[0042] The subsequent corrected pressure measurements at each time point are evaluated using the method described in reference to Figure 2 to determine if it is a "good" reading. "Good" readings are indicated to the user by an audible and/or visual means, and warnings that the user is pressing the probe too hard are indicated by a distinctly different audible and/or visual means. The "good" results counted and the results are averaged, while the other readings are discarded.

[0043] A measurement is successfully completed when a criterion such as accumulating a given number of "good" readings, e.g., 50 is met. More complex criteria that consider factors such as the variability between the "good" values as well as the number are possible and considered to be within the scope of the invention. Success is indicated to the user by a distinct audible and/or visual means, and the result is displayed and optionally stored.

[0044] The measurement is aborted when it goes on too long, e.g., 10 seconds, without obtaining enough "good" readings to form a successful measurement. Consistent failure to obtain good measurements may require refinement of the user's technique or adjustment of the concentric sleeve 107 surrounding the probe 100 to better match the patient's eye.

[0045] A new measurement is started by the user through the user interface module 503, causing the computation and control module 502 to perform actions including storing the prior reading, resetting the routine that counts, averages and displays "good" values, and updating the zero-correction values. The user may also have the opportunity to identity the patient and indicate left or right eye. [0046] The system is turned off when measurements are complete through the user interface module 503. Stored data are maintained using known means.

[0047] The physical arrangement and interconnection means of the modules shown in Figure

5 may vary without departing from this invention. One variation is to include the entire system within a hand-held device. This option is expected to be most suitable for a user measuring intraocular pressure of another individual, since they can use both audible and visual features of the user interface module 503. Visual features are less useable for a user who is self-testing, and a user interface module separate from the probe 102 may be more easily viewed by the open eye. Connection may be made by known cable or wireless techniques, and at least a portion of the control and computation module 502 may be physically incorporated within the separate user interface module 503. Optionally, a device such as a smartphone or personal computer with a suitable software application may be used to perform the functions of the user interface module 503 and at least most of the functions of the control and computation module 502. It will be obvious to those skilled in the art that a number of such permutations and combinations are within the scope of the invention. Each wirelessly connected physical portion of the system will require its own power source.

[0048] Figure 1 through Figure 5 and the accompanying description are primarily intended to illustrate the conceptual features of the invention, and it will be obvious to those skilled in the art that a number of equivalent functional elements and construction details may be used to implement the concept. The general proportions and scale of the device 100, however, are depicted in the drawings to be compatible with the human eye and to depict practical implementations of the invention.

[0049] The mathematical term "average" as used in the preceding specification and the claims that follow encompasses a simple average, a weighted average or other known means of aggregating two or more values into a single value. [0050] While exemplary embodiments are described above, it is not intended that these embodiments describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention. Additionally, the features of various implementing embodiments may be combined to form further embodiments of the invention.

Claims

WHAT IS CLAIMED IS:

1. A method for measuring the intraocular pressure in a closed eye through the eyelid comprising:

pressing a concave surface against the eyelid such that it applies pressure to the cornea through the eyelid to counteract the aqueous humor pressure causing tension in the corneal membrane;

measuring the contact pressure of the eyelid against the concave surface at each of a plurality of locations at the concave surface substantially simultaneously at one or more time points;

analyzing the set of pressure measurements taken at a given time point using a first algorithm to determine if the spatial distribution of this set of pressure measurements at the concave surfaces meets criteria indicating that these measured pressures applied to the eyelid substantially counteract and balance the aqueous humor pressure and form a valid measurement data set; and

calculating the aqueous humor intraocular pressure from the valid data measurement set using a second algorithm if the criteria of the first algorithm are met; otherwise

disregarding the measurement data from this time point.

2. The method of claim 1 wherein the first algorithm compares the differential pressures between measurement locations with high pressure and measurement locations with low pressure with a criterion setting a maximum allowable pressure variation.

3. The method of claim 2 wherein the criterion setting a maximum allowable pressure variation between locations with high pressure and measurement locations with low pressure is a differential pressure between said locations.

4. The method of claim 2 wherein the criterion setting a maximum allowable pressure difference between locations with high pressure and measurement locations with low pressure is a differential pressure fraction comprising a differential pressure divided by a pressure representative of the measured pressure range.

5. The method of claim 4 wherein the pressure representative of the measured pressure range is an average of the pressure at two or more of the measurement locations.

6. The method of claim 4 wherein the pressure representative of the measured pressure range is the pressure at one of the measurement locations.

7. The method of claim 1 wherein the first algorithm compares the differential pressure variation between a group of one or more measurement locations central to the concave surface and a pressure representative of the measured pressure range, with criteria setting upper and lower limits on this differential pressure variation.

8. The method of claim 7 wherein the criteria setting upper and lower limits on the differential pressure variation comprise differential pressure limits.

9. The method of claim 7 wherein the criterion setting upper and lower limits are differential pressure fractions comprising the differential pressure variation divided by a pressure representative of the measured pressure range.

10. The method of claim 7 wherein the pressure representative of the measured pressure range is an average of the pressure at one or more of the measurement locations, wherein at least one of these measurement locations is central to the concave surface.

11. The method of claim 7 wherein the pressure representative of the measured pressure range is an average of the pressure at one or more of the measurement locations, wherein none of these measurement locations is central to the concave surface.

12. The method of claim 1 wherein the second algorithm calculates the intraocular pressure by averaging the pressure measurements at one or more locations central to the concave surface.

13. The method of claim 1 wherein the second algorithm calculates the intraocular pressure by averaging one or more pressure measurements, wherein at least one of the locations is not central to the concave surface.

14. An apparatus for measuring the intraocular pressure in a closed eye through the eyelid comprising:

a probe having a concave surface with a diameter approximately equal to the diameter of the cornea and a spherical radius approximately equal to the spherical radius of the cornea plus the thickness of the closed eyelid;

the concave surface incorporating a plurality of pressure sensors at a plurality of surface locations disposed to measure contact pressure with the closed eyelid; and

control and data acquisition means enabling substantially simultaneous measurement of the contact pressure of the eyelid against the concave surface at one or more time points employing the plurality of pressure sensors.

15. An apparatus according to claim 14 further comprising a body carrying the probe.

16. An apparatus according to claim 14 further comprising a concentric sleeve surrounding the probe dimensioned to center the probe on the eyeball.

17. An apparatus according to claim 16 wherein the concentric sleeve is axially adjustable relative to the probe.

18. An apparatus according to claim 14 wherein the plurality of pressure sensors comprise differential pressure sensors measuring the pressure contacting the concave probe face relative to the ambient atmospheric pressure, thereby allowing contact pressure measurement relative to atmospheric pressure at a single time point.

19. An apparatus according to claim 18 wherein contact pressure is transmitted from the surface of the concave probe face to the active pressure sensor element through an intermediate substance comprising an elastic gel.

20. An apparatus according to claim 14 wherein the plurality of pressure sensors comprise absolute pressure sensors measuring the pressure contacting the concave probe face relative to a vacuum, thereby allowing determination of contact pressure relative to atmospheric pressure by calculating the difference between an absolute pressure measurement during contact and a reference measurement made prior to contact.

21. An apparatus according to claim 20 wherein contact pressure is transmitted from the surface of the concave probe face to the active pressure sensor element through an intermediate substance comprising an elastic gel.

22 A system for measuring the intraocular pressure in a closed eye through the eyelid comprising interconnected functional modules:

an eyelid-contacting probe comprising contact pressure sensors, analog data transmission means, power transmission means, and supporting mechanical structures;

a sensor power supply;

an analog to digital signal converter;

a computation and control unit;

a user interface; and

and interconnection means transferring data, control signals and power between the various modules.

23. A system for measuring the intraocular pressure in a closed eye through the eyelid according to claim 22 wherein the functional modules are combined in one assembly.

24. A system for measuring the intraocular pressure in a closed eye through the eyelid according to claim 22 wherein the functional modules are divided between two or more assemblies linked by known interconnect means including but not limited to conductive wires or wireless data links.

25. A system for measuring the intraocular pressure in a closed eye through the eyelid according to claim 24 wherein one of the assemblies includes the eyelid contacting probe functional module and a separate assembly includes the user interface functional module.

26. A system for measuring the intraocular pressure in a closed eye through the eyelid according to claim 25 wherein the assembly including the interface functional module is a multifunctional communication and data processing device of a class including but not limited to personal computers and smartphones.