Classifications

• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
  • A61B3/16—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for measuring intraocular pressure, e.g. tonometers
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
• • A—HUMAN NECESSITIES
  • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
  • A61B—DIAGNOSIS; SURGERY; IDENTIFICATION
  • A61B3/00—Apparatus for testing the eyes; Instruments for examining the eyes
  • A61B3/10—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions
  • A61B3/14—Arrangements specially adapted for eye photography

Definitions

• This invention relates to an applanation tonometer for providing a measurement of the intraocular fluid pressure (lOP) inside the eye of a human or animal patient
• the applanation tonometer herein disclosed has means responsive to both the contac force of the tonometer against the cornea and the touch contact area of the tonometer with he cornea so that paired force and area data is collected, whereby KIP can b accurately measured with minimal dwell time on the cornea and discomfort to the patient.
• a tonometer is & non-invasive instrument which has heretofor been used to measure pressure or tension in human or veterinary tissues, to the human body, intraocular ⁇ pressure in the eye (IOP) is measured to provide basic information for the diagnosis and treatment of glaucoma and. related eye disease.
• IOP intraocular ⁇ pressure in the eye
• IOP is determined by a calculation of the contact force applied by a tip of the GAT against the cornea divided by area of contact. That is, determining IOP with the GAT relies upon the contact tip covering an applanation area to a feed diameter of 3.06 rnm. The applied force necessar to reach fee requisite applanation area is adjusted manually by the healthcare physician or technician.
• the moving parts of the GAT may jam which can interfere with the effectiveness of the IOP testing.
• the relatively long dwell time required for the contact tip to press correctly against the cornea and the need to apply a topical anesthesia as a result thereof may increase patient discomfort and tissue safel concerns.
• an applanation tonometer with no moving parts is disclosed according to the preferred embodiment to pro vide an accurate measurement of the intraocular fluid pressure (IOP) inside a human or animal eye in order to make information available for the diagnosis and treatment of glaucoma and other ocular healt issues.
• the applanation tonometer includes a prism assembly at a prox ml end thereof, a laser module at a distal end, and an intermediate beam splitter module between the prism assembly and the laser module.
• the prism assembly of the applanation tonometer includes a conical prism that tapers to a (e.g., circular) contact tip.
• the contact tip has an ideal diameter of be ween 1 to 8 mm.
• Lying opposite the contact tip of the prism is a piezo element that is responsive to the force generated as the contact tip is pressed against the cornea while approaching, during and following cornea saturation and full applanation.
• a light ring having a light absorbing center, a !igbt-absorbkg outside area, and a !ight-hansmitting area between the h ' ght-absorbing center and outside area is located behind the contact tip of the prism to allow incoming and outgoing light beams to be transmitted inwardly through and outwardly .fern the prism, fw3 ⁇ 4)7j
• the laser module of the applanation tonometer includes a source of light (e.g., a lase or an LED) that supplies incoming light beams to the prism of the prism assembly by way of a collimator, the beam splitter module and the light ring of the prism assembly.
• the beam splitter module includes a photo diode and an internal reflective surface thai is aligned to reflect to the photo diode outgoing light beams that are reflected internally through the prism before, during and after full applanation.
• the intensity of the light detected by the photo diode is dependent upon the area of the cornea that is covered by the contact tip as the prism is pressed against the eye, fi3 ⁇ 43 ⁇ 4 ) 8] As the applanation tonometer is moved towards the eye and the contact tip of the prism is pressed against the cornea to achieve applanation, some of the light is deeo pkxl from the incoming light beams that are transmitted inwardly through the prism.
• the incoming light which is decoupled is iransmited through the contact tip of the prism and lost into the eye.
• the decoupling is a result of manufactemg the conical prism so that the incoming light beams which are transmitted from the light source of the laser module through the prism are reflected internally to the contact tip of the prism so as to make an angle of between 20 to 27 degrees with a tapered wall of the prists.
• the remaining light which is ⁇ decoupled is reflected internally by sad outwardly from the prists through the light ring of the prism assembly and off the reflective surface of the beam splitter assembly to be detected by the photo diode.
• the output of the piezo element and the photo diode provide force and area data pairs which can be displayed, stored and processed either at the site of the test or remotely to provide a measurement of 1 ⁇ .
• FIG. 1 is a perspective view of as applanation tonometer for measuring ktraocuiar pressure according so a prefered embodiment of fee present invention:
• FIG . 2 is aa exploded view of the applanation tonometer of FIG. 1 ; fOOil)
• FIG. 3 shows the applanation tonometer illustrating the paths therethrough of incoming and interaaJ!y-refieeted outgoing light beams;
• FIG. 4 shows a light ring through which the incoming and reflected light beams of FIG. 3 axe transmitted
• FIG. 5 illustrates the paths of the incoming and reflected light beams with respect to a prism of the applanation tonometer when a contact tip of the prism is spaced .from the patient's eye;
• 0014] PIG. 6 illustrates the paths of the incoming and reflected light beams wife respect to th prism when the contact tip thereof is moved into contact with the cornea of the eye to achieve applanation;
• FIG, ? shows linear representations of the output voltage responses of a piezo element and a photo diode of the applanation tonometer prior to, during and following applanation
• FIG. 8 is a block diagram which is illustrative of means for displaying, storing and processing force/area data derived from the outputs of the piezo element and photo diode of the applanation tonometer.
• FIGs. 1 and 2 of the drawings there is shown a preferred embodiment for an applanation tonometer 1 with no moving parts that is adapted to provide healthcare professionals with a measuremen of the intraocular fluid pressure inside the eye of a patient to aid in the diagnosis of glaucoma and other ocular health issues such as scleral rigidity.
• the applanation tonometer 1 includes a prism assembly 3 at a proximal end thereof a laser module 5 at & distal end, and an intermediate beam splitter module 7 lying therebetween.
• the prism assembly 3, beam splitter module 7 and laser module 5 are axiaiiy aligned with one another.
• the prism assembly 3 of the applanation tonometer 1 includes a conical prism 9 (best shown in FIGs. 4 and 5) that is manufactured from glass, acrylic or other suitable ligk- transmitting material.
• the proximal end of the prism 9 is ground flat to create a circular contact tip 10 to be moved into contact with the cornea of the eye of a patient fox a urpose that will be explained, is greater detail hereinafter.
• the circular contact tip 10 of prism 9 has ideal diameter of 1-8 mm depending upon the pressure testing application for which the tonometer is employed.
• the prism assembly 3 includes an outer shell 12 that surrounds and supports the prism 9.
• a pair of retainer rings 14 and 16 are located in front of the outer shell : 2 to hold the prism 9 in axial alignment with the beam splitter module 7.
• a retainer ring 18 is located behind the outer shell 12 to surround and provide additional support for the prism 9.
• the prism assembly 3 also includes a. piezo ring 1 which surrounds a force-responsive (e.g., piezo) element (designated 44 in FIG. 3).
• Retainer rings 28 and 30 surround and support opposite ends of laser module 5.
• the laser module 5 also has an alignment ring 32 and 34 at each end thereof lying inside and adjacent one of the retainer rings 1% and 30 to provide self-centering of the laser module with respect to the beam splitter module 7 and the prism assembly 3.
• Wire potts 36 and 38 are formed in the alignment rings 32 and 34 through which electrical wires (not shown) are connected to the piezo element and the photo diode carried by the intermediate beam splitter module 7.
• the laser module 5 ideally provides parallel laser light, beams to the prism 9 of the prism assembly 3 to be internally reflected by the prists 9 first to the beam splitter module ? and then to the photo diode of the beam splitter module 7,
• FIG. 3 of the drawings shows additional details of the prism assembly 3, laser module 5 and intermediate beam splitter module ? of the applanation tonometer 1 previously described while referring to FIGs. 1 and 2,
• the conical prism 9 of the prism assembly 3 is shown extending outwardly from the proximal end of the applanation tonometer so that the contact tip 10 can be briefly pressed against and apply pressure to the patient's cornea to achieve applanation.
• a flange 40 surrounds the rear of the prism 9 so as to hold a light ring 42 (i.e., a light baffle) in coaxial alignment with the prism 9 so that the prism 9 and light ring 42 will press against the pkzo element 44 as the contact tip 10 of the prism 9 is pressed against the cornea.
• the piezo element 44 is manufactured from a metal- doped ceramic disc or the like that is mounted on an electrical substrate or shim and, as will be known to those skilled in the art, is adapted to generate an electrical output voltage signal that is indicative of a change in force as the contact tip 10 of prism 9 is pressed against the patient's cornea during testing.
• the piezo element 44 has a light-transmitting hole 45 through its center to enable light generated by the laser module 5 to reach the prism assembly 3, Because the piezo element 44 is conventional, the details thereof will not be described.
• the light ring 42 is preferably a disk (i.e., an optically-pure substrate) manufactured from a lightweight optically-transparent material.
• the dot 46 is sized and shaped to match the diameter of the circular contact, area 10 of the prism 9, Thus., the diameter of dot 46 is ideally between 1 to S mm,
• An optieslly-traaspareat ring-shaped area 48 of the light ring 42 surrounds the optically-opaque dot 46.
• the size of the optically-transparent ring-shaped area 48 will depend upon the size and internal angles of the prism 9.
• a light absorbing ring-shaped area 50 surrounds the optically-transparent ring-shaped area 48 of light ring 42.
• the light- absorbing area 50 can be.
• both incoming light transmitted from the laser module 5 to the prism 9 and outgoing light internally reflected by the prism 9 to the beam splitter mod le 7 will pass through the optically-transparent ring-shaped area 48 of light ring
• the applanation tonometer 1 also includes a pair of conventional light beam expanders and/or collimators 54 and 56 thai are located between the prism assembly 3 and the beam splitter module 7 so as to lie in the paths of the incoming light aansmftted from the laser module 5 and the outgoing light reflected from the prism 9.
• the light beam expanders and collimators 54 and 56 are adapted to focus and absorb stray light and thereby reduce spurious light transmissions in cases where the incoming light from the source is not transmitted as parallel beams.
• a combination of expanders and collimators may be used for different applications,
• the beam splitter module ? of the applanation tonometer 1 includes a conventional beam splitter having an internal reflecting surface 58.
• incoming parallel light beams 60 being transmitted from the laser module 5 pass through the beam splitter to the prism 9 of the prism assembly 3.
• the outgoing parallel light beams 62 which are reflected internally by prism 9 are tr nsmitted to and reflected by the reflecting sur&ee 58 of the beam splitter module 7 to the photo diode $4 that is retained within the opening (designated 26 in FiGs. I and 2) of module ?.
• fee incoming and outgoing light beams 60 and 62 are shown traveling in separate paths. However, as will be explained when referring to FiGs. 5 and 6, the incoming and outgoing light beams travel along identical paths between the beam splitter module 7 and the prism assembly 3.
• the expanders'colismators 66 and 68 may be identical to those designated 54 and 56 between the prism assembly 3 and beam splitter module ?.
• the light beam expanders and collimators 66 and 68 also control the incoming l ght and further ensure that parallel light beams 60 will pass through the beam splitter module 7 to the prism assembly 3. n this regard, it may be appreciated that the pairs of light beam expanders/colJimators 54, 56 and 66, 68 located at opposite ends of the beam splitter module 7 cooperate to form a well-known light management assembly.
• the laser module 5 is preferabl a Class II laser (e.g., a laser diode).
• any other suitable light sou ce e.g., as LED
• incoming parallel-aligned laser light beams generated by the laser module 5 are supplied through the light ring 42 to the prism 9 by way of the beam splitter module 7 and the light beam expander/collirnator assemblies at opposite ends of the beam splitter module,
• feat converging or diverging light (as opposed to parallel light beams) may also be supplied to the prism 9.
• PIG, 5 shows the prism assembly 3 prior to the contact tip 10 of the prism 9 being moved into contact with and applying pressure against the patient'.: cornea. That is to s , there is initially a space or air gap 74 between the contact tip 10 at the proximal end of prism 9 and the eye, in FIG, 6, the prism assembly 3 is relocated towards the eye so that the contact tip 10 of prism 9 is moved into contact with and presses against the cornea.
• outgoing parallel- aligned laser light beams 78 are reflected off the tapered outer wall 79 and outwardly from the prism 9, around and through the optically-transparent area 48 of the light ring 42, and through the center hole 45 of piezo element 44 for receipt by the photo diode 64 by way of the reflective surface 58 of the be m splitter module 7 of FIG. 3, it is to be understood that the inward and outward light transmission through the optica] ly ⁇ tran3 ⁇ 4p rent area 48 of light ring 42 and the prism. 9 occurs cirenmfere ialiy (i.e., around a fell 360 degrees) with respeci to the light ring. Therefore, incoming and outgoing light direction arrows illustrated in FIGs.
• both the incoming and reflected light beams 76 and 78 pass around and through the optically-transparent area 48 of the light ring 42 along identical paths.
• the conical prism 9 should be manufactured so that the slope of its tapered oarer wall 79 is between 20 to 27 degrees with respect to its longitudinal axis, whereby the incoming parallel-aligned light beams 76 will be reflected off the tapered outer wall 79 and towards (or from) the contact tip 10 so as to make an identical angle 80 of between 20 to 2? degrees with respect to tapered wall 79,
• the conical prism 9 is moved towards the patient's eye until the air gap (74 of FIG. 5) is eliminated and the contact tip 10 of prism 9 lies in fall contact (i.e., applanation) against the cornea regardless of the pushing pressure being applied-
• the incoming parallel-aligned laser beams 76 are once again transmitted from the laser module 5, around and through the optically-transparent area 48 of the light ring 42, through the piezo element (44 of FIG, 3), and inwardly through the prism 9 to be reflected at the angle 80 off the tapered outer wall 79 of the prism 9 to the contact tip 10 against the cornea.
• the applanation tonometer 1 moves towards saturation (i.e., full contact with the cornea)
• some of the light beams 82 will be decoupled from the incoming light beams 76 that are reflected at the tapered prism wall 79 to the contact tip 10 of prism 9.
• the decoupled light beams 82 escape the prism to be absorbed by the patient ' s eye and are not returned to the photo diode 64.
• the intensity of the outgoing light beams (?8 of FIG, 5 and 84 of FIG. 6) internally reflected by the prism 9 to the photo diode 64 prior to, during and after applanation, is inversely proportional to the area of touch contact between the contact tip 10 of prism.9 and the opposing surface of the patient's cornea.
• the amount of internal reflection by the prism 9 decreases as the contact tip 10 progressively applanates the cornea thus producing a differential signal.
• the differential light signal is paired with a differential force signal, information will be available to accurately calculate IOP. in this same regard, it may be appreciated that the decoupled light beams 82 which escape the prism 9 to be absorbed by the eye also depend upon the area of touch contact between contact tip 10 and the cornea,
• FIG. 7 of the drawings shows graphical ⁇ i.e., linear) representations of the voltage responses of the piezo element 44 and the photo diode 64 of the applanation tonometer 1 of FiGs, 1-3 as the prism 9 of prism assembly 3 is moved towards, into contact with, and away from the cornea of the patients eye. It is to be understood that the responses of the piezo element 44 and the photo diode 64 could also be indicated by resistance rather thau voltage.
• the first (bottom most) of the linear representations illustrates the output voltage signal of the iezo element 44 as the pushing force is first increased to achieve Ml applanation and subsequently diminished following cornea saturation
• a flat baseline voltage 88 is initially set when the prism 9 is spaced from the eye by the air gap 74 shown in FIG. 5 and so pressure is applied to the cornea.
• the COB tact pressure will increase so that the voltage 90 generated by the iez electric element 44 correspondingly a d continuously increases until a .maximum voltage 92 is generated at the apex of touch contact.
• the poshing force (voltage 94) necessary to Initially saturate the patient's eye and achieve fell applanation is typically less than the maximum pushing • force (voltage 92).
• the pieso element 44 will sense a continuously decreasing force and. generate a corresponding smaller voltage 96 as the prism 9 is subsequently moved away from the patient ' s eye and the contact pressure feereagainsi is ultimately eliminated so that another Hat baseline voltage 98 indicative of no force is generated.
• the other (i.e., top roost) of the linear representations of FIG. 7 represents the output voltage of the photo diode 64 depending upon the area of touch contact between the contact rip 10 of the prism 9 and the patient's cornea and the corresponding amount of incoming laser light that is transmitted inwardly through prism 9 and decoupled at the contact tip. That is to say, increasing the size of the touch ares results in greater decoupling and less light being reflected outwardly through the prism to the photo diode 64, fOQ36f More particularly, a flat baseline voltage 100 is initially set when the prism 9 is spaced from the eye by the air gap (74 of FIG .
• a steady voltage 108 (between voltage points 106 and 1 10) is generated by the photo diode 64 ch that the area of the cornea covered by the contact tip 10 remains constant regardless of a pressure increase and the corresponding increase in voltage 92' generated by the piezo element 44.
• FIG. S of the drawings shows a microprocessor 120 tor use at a test site Co receive the output sigaals generated by the piezo element 44 and photo diode 64 of FIG. 3.
• a suitable microprocessor having an integrated data acquisition system to be used with the applanation tonometer I to provide a measurement of IOP is either one of Part Nos. LM12458 or L 12B458 manufactured by National Semiconductor Corporation, Such a microprocessor 120 provides the advantage of combining a Mly-dverential self- calibrating 13-bit analog-to-digital converter with a sample-and-hoid feature. Programmable data acquisition times and conversion rates are available by .means of infernal clock-driven timers.
• the microprocessor is capable of operating from a 5 volt DC (e.g., battery) power supply 122.
• the microprocessor 120 can be programmed to display its determination of IOP at an onboard display such as., for example, an LCD display 124.
• the microprocessor 120 can also control light indicators in order to rovide the teat adm nistrator with an instantaneous measurement whether the patient's IOP test results represent a passing or failing pressure.
• the IOP measurements may be internally computed by the microprocessor 120 at the test site.
• the computations may be stored in. an onboard memory 126.
• the computations can be roads and/or analyzed (and displayed) by a well-known remote handheld device such as an iPhone, iPad, tablet, and the like.
• a wireless data transmitter 328 communicates with the remote handheld device over a wireless path.
• IOP is determined, by a calculation of contact force divided by the area of touch contact represented by the output voltage signal pairs (such as 94 and 106 of FIG. 7 ⁇ generated by the piezo element. 44 and the photo diode 64,
• the paired force and area measurements can be acquired at greater than 5000 cps. Measurement mean and variance are calculated after only a single touch, although multiple touch data acquisition may be employed.
• Tissue rigidity may be inferred by analyzing a broad range of force-area pairs between the increasing voltages 90 and 102 of FIG. 7 as applanation is achieved.
• a table look-up operation can also be performed on the basis of a no nogram-derived reference of IOP compiled from clinical or laboratory acquired testing measurements taken from a population of human and animal eyes.
• the applanation tonometer 1 herein disclosed is m improvement over the Go mann device by allowing for fast and objective are and force measurements with minimal touch, contact with the underlying tissue.
• a short dwell time typically less than 100 msec
• obviates the need in most cases for a topical anesthesia so as to reduce patient safety concerns.
• With the elimination of moving parts, a jam-free, stable and self-calibrating test environment is available.
• the applanation tonometer 1 has been described in its preferred application for measuring IQP inside an eye.
• the tonometer may be extended to include obtaining pressure measurements in botanical tissues, biologically- solid, fluid or air-filled human or animal organs such as blood vessel, stomach, bladder, lung, finger or ankle, and flexible hydrostatic bodies.
• the tonometer can also be used in product and packa ge manufacturing by measuring the pressure of any light-absorbing surface associated therewit to predict a fissure or rupture and thereby ensure production quality, shelf-life durability .and packaging integrity.

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• Life Sciences & Earth Sciences (AREA)
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• Ophthalmology & Optometry (AREA)
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• 2011
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