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
  • A61B3/165—Non-contacting 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
  • A61B3/0008—Apparatus for testing the eyes; Instruments for examining the eyes provided with illuminating means
• • 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
  • A61B3/107—Objective types, i.e. instruments for examining the eyes independent of the patients' perceptions or reactions for determining the shape or measuring the curvature of the cornea

Definitions

• Embodiments of the invention generally relate to methods and apparatus for measuring characteristics of a deformable object through changes in the surface of the object during a deformation interval. More particularly, embodiments of the invention relate to the measurement of physical and biomechanical characteristics of a live cornea.
• the measurement of the surface characteristics of an object can reveal much information about the physical and mechanical properties of the object. If the surface of the object is defo ⁇ nable in response to an applied force, measurement of the changes in characteristics of the surface may provide further useful information.
• a particularly interesting, exemplary object is the cornea of a human eye.
• the widespread interest in understanding the physical, biomechanical, optical and all other characteristics of the eye is obviously motivated.
• different theories have been presented about the structural and dynamic properties of the eye, particularly the cornea. Earlier theories modeling the cornea as a solid structure have more recently given way to understanding the cornea as a layered, biodynamically responsive structure that to this day is not completely understood.
• topographical characteristics of the cornea include corneal curvature and surface elevation with respect to a reference surface, as well as others known in the art.
• Corneal topography measuring devices are alternatively referred to as topographers, keratographers or keratometers (a topographer is a generic term referring to an apparatus for measuring the topographical characteristics of an object surface, while keratographer and keratometer more specifically refer to measurements of the cornea).
• topographers is a generic term referring to an apparatus for measuring the topographical characteristics of an object surface, while keratographer and keratometer more specifically refer to measurements of the cornea.
• Different devices use different measuring principles to determine various topographical characteristics of the cornea. For example, some devices use Placido-based reflective image analysis.
• Placido-based devices can measure curvature parameters of the cornea but typically lack the capability to directly measure surface elevation.
• the Orbscan ® anterior segment analyzer (Bausch & Lomb Incorporated) is a topography characteristic measuring device that utilizes a scanning optical slit. Device software provides for direct measurement of surface elevation and corneal thickness as well as surface curvature.
• Another commercial device developed by Par Technology Corporation is known as the PAR CTSTM Corneal Topography
• the PAR imaging system utilizes a raster photography method.
• the PAR CTS imaging system projects a known grid geometry onto the anterior corneal surface that is viewed by a camera from an offset axis.
• Other topography characteristic measuring techniques include confocal microscopy, optical coherence tomography, ultrasound, optical interferometry and others, all of which are well known in the art.
• confocal microscopy While the measurement of various topographical characteristics of the cornea provide a wealth of information about vision and the effects of corneal shape on visual performance, corneal topography by itself cannot reveal the physical and biomechanical properties of the cornea necessary for a thorough understanding of its structure and function.
• Tonometers for measuring intraocular pressure (IOP) where originally developed as contact-type instruments, meaning that a portion of the instrument is brought into contact with the cornea during the measurement procedure.
• IOP intraocular pressure
• a well known instrument of this type is the Goldmann applanation tonometer (GAT) originally developed in the 1950s.
• GAT measures the force required to flatten ("applanate") a known area of the cornea, and is used today as a standard against which other types of tonometers are compared to assess measurement accuracy.
• the Reichert Ocular Response Analyzer utilizes a dynamic bidirectional applanation process to measure a cornea tissue property called corneal hysteresis.
• corneal hysteresis refers to the difference in pressure values of the air pulse at the inward moving applanation point and the outward moving applanation point during a measurement interval (inward moving refers to an initial convex corneal shape moving to a flattened condition, while the outward applanation point refers to the post air pulse concave corneal surface moving towards the
• corneal hysteresis appears to be a repeatable measurement, it may provide a metric that is useful for identifying and categorizing various conditions of the cornea. For example, measurement of corneal hysteresis is alleged to aid in identifying and classifying conditions such as corneal ectasia and Fuch's Dystrophy, and as helping in the diagnosis and management of glaucoma. Differences in hysteresis measurements for different corneal conditions may better inform about the biomechanical and biodynamical properties of the cornea.
• corneal hysteresis measurement is credited for presenting a complete characterization of the cornea's biomechanical state, it is believed to have additional potential uses in screening refractive surgery candidates as well as predicting and controlling surgical outcomes.
• the interested reader is directed to the aforementioned website address for further information provided by the manufacturer.
• Embodiments of the invention are generally directed to apparatus and methods for measuring a deformation characteristic of a deformable target surface. It is to be understood that the measurement principles of the invention may be applied to a large variety of organic (e.g., human, animal or plant tissue) and inorganic materials having a surface that can be deformed by an applied non-contact force. The surface may be light diffusing and non-transparent or non-diffusing and transparent. Apparatus suitable for measuring the surface topography characteristics of a deformable target surface during or over a deformation interval, that incorporate a component which can supply a non-contact force that deforms the target surface over the deformation interval, are considered to be within the scope of the claimed invention.
• organic e.g., human, animal or plant tissue
• inorganic materials having a surface that can be deformed by an applied non-contact force.
• the surface may be light diffusing and non-transparent or non-diffusing and transparent.
• an embodiment of the invention is directed to a device for measuring a deformation characteristic of a deformable target surface that includes a topographer and a non- contact target surface deformer that is operationally integrated with the topographer and is located along a first operational axis of the device.
• the topographer includes a high speed camera located along a second, operational axis of the device.
• a suitable camera or detector is required to capture sequential images or still images of specific deformation events during the deformation interval.
• the device also includes an optical system including a grid object and a light source for projecting a grid image, aligned along a third, operational axis of the device.
• at least one of the second and third axes are offset from the first axis. More particularly, all of the axes are directionally independent.
• the topographer advantageously is a computer-assisted videokeratography-based topographer (referred to herein as a corneal topographer).
• the corneal topographer is a modified PAR CTS imaging device.
• the non-contact target surface deformer is an air pressure pulse-based apparatus.
• the non-contact target surface deformer is a non-contact tonometer.
• a device including a topographer for making a topography characteristic measurement of the target surface and a non-contact force producing component apparatus is provided.
• the target surface to be measured is suitably positioned with respect to the device.
• the target surface subjected to the force and experiences responsive deformation over a deformation interval.
• a plurality of topography characteristic measurements are made during the deformation interval.
• Exemplary topography characteristic measurements may include, but are not limited to, surface curvature, surface elevation, surface indentation, surface deformation symmetry, surface deformation shape, surface deformation area, surface deformation hysteresis and elasticity, viscosity and pressure.
• An illustrative and particularly advantageous embodiment of the invention is directed to a device for measuring a deformation characteristic of a cornea.
• the device comprises a corneal topographer and a non-contact tonometer that is operationally integrated with the corneal topographer.
• the corneal topographer is a rasterstereography-based topographer. More particularly, the corneal topographer is a modified PAR CTS imaging device. [0013] Use of the aforementioned device enables a method for measuring a deformation characteristic of the cornea. In addition to the measurable deformation characteristics listed above, dioptric power, intraocular pressure, corneal hysteresis, corneal elasticity, corneal viscosity and various known corneal topography characteristics can be measured.
• FIG. 1 is a schematic plan view of a device according to an embodiment of the invention.
• FIG. 2 A is a schematic force diagram of a cornea at a first moment of applanation
• FIG. 2B is a schematic force diagram of a cornea at a second moment of applanation
• FIG. 3 is a graph showing applanation detection and plenum pressure signals for a deformation characteristic measurement according to an embodiment of the invention
• FIG. 4 is a top view of a projected PAR CTS grid on a simulated cornea before air puff deformation of the corneal surface
• FIG. 5 is a top view of a projected PAR CTS grid on a simulated cornea after an air puff deformation of the corneal surface
• FIG. 6 is a schematic side view of corneal indentation corresponding to the deformation shown in FIG. 5;
• FIG. 7 is a schematic side view of corneal indentation showing a narrower, deeper corneal indentation that that shown in FIG. 6.
• An embodiment of the invention is generally directed to a device for measuring a deformation characteristic of a deformable target surface.
• An exemplary embodiment of the invention is directed to a device 10, as shown in Figure 1, for measuring a deformation characteristic of a live cornea.
• the device 10 includes a corneal topographer 20 and a non-contact tonometer 30 that are operationally and physically integrated components of the device.
• the corneal topographer 20 of the device shown in Figure 1 is a rasterstereography-based topographer that is modeled after a PAR CTS corneal topography system. Such a system is disclosed in US Patent Nos. 4,995,716 and 5,159,361, the disclosures of which are incorporated herein by reference to the fullest allowable extent as though fully set forth in their entireties.
• the corneal topographer 20 includes a high speed camera/detector 32 located along a second, operational axis 76 of the device 10 and an optical system 42, including a grid object 44 and a light source 45, for projecting a grid image, aligned along a third, operational axis 78 of the device 10.
• the target object in this case the cornea 87 of an eye 88, is located along a central device axis 82 in a measurement plane illustrated by dotted line 98.
• Various lenses and filters that are components of the PAR CTS corneal topographer 20 are not shown.
• the exemplary device 10 also includes a non-contact tonometer 52 located along a first operational axis 72. Axis 72 and axis 82 are coplanar.
• non-contact tonometer 52 is a Reichert Ocular Response Analyzer, a description of which is set forth in aforementioned U.S. Patent Nos. 6,419,631 and 6,875,175.
• measurement begins with generation of a metered air pulse directed at the cornea.
• the impulse energy imparted to the cornea by the air pulse reversibly deforms the cornea from its original state of convexity through a first state of applanation, Pi, to a state of concavity. As the air pulse decays
• FIGS. 2A and 2B are simplified diagrams showing the forces acting on a cornea C at the moment (ti) of first applanation ( Figure 2A) and second (t 2 ) applanation ( Figure 2B) during the measurement interval, while ignoring dynamic effects.
• F represents the inwardly directed force of an incident air pulse
• F 2 represents the force required to bend the corneal tissue itself
• F 3 represents the outwardly directed force attributed to intra-ocular pressure.
• the corneal topographer 20 can conveniently be triggered off of event Pi at time t !; event P 2 at time t 2 ,, at peak plenum pressure and/or at any predetermined trigger points over the defo ⁇ nation interval T to obtain a plurality of deformation characteristic measurements.
• the PAR CTS system modified to incorporate a high speed camera/detector as the corneal topographer 20 in device 10 is advantageous because the off-set axes 76, 78 of the camera 32 and optical system 42 provide for a centralized location of the tonometer 52.
• a Placido-based topographer may not allow the tonometer to be centrally located, other topography characteristic measuring apparatus may provide a suitable physical arrangement to be used in device 10.
• Figures 4 and 5 show simulated PAR CTS grid images before and after, respectively, an air puff deformation of a corneal surface.
• Figure 6 illustrates a wide, shallow corneal indentation corresponding to that in Figure 5.
• Figure 7 shows a narrower and deeper corneal indentation than that shown in Figure 6. The figures illustrate that softer or stiffer corneas may respond differently to an applied deformation force.
• Various deformation characteristics can be measured with the device embodiment described above.
• the magnitude, the symmetry or asymmetry, the shape and the area of the surface deformation could be measured during the deformation interval, as well as applanation depth, corneal curvature, elevation, hysteresis, corneal elasticity and viscosity, and IOP.

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• 2006
  • 2006-10-31 CA CA2621719A patent/CA2621719C/en not_active Expired - Fee Related
  • 2006-10-31 CN CN2006800407098A patent/CN101299957B/zh not_active Expired - Fee Related
  • 2006-10-31 BR BRPI0618066-3A patent/BRPI0618066A2/pt not_active Application Discontinuation
  • 2006-10-31 WO PCT/US2006/060381 patent/WO2007053826A2/en not_active Ceased
  • 2006-10-31 JP JP2008539140A patent/JP5498699B2/ja not_active Expired - Fee Related
  • 2006-10-31 EP EP06839630.8A patent/EP1942787B1/en not_active Ceased
  • 2006-10-31 US US12/091,307 patent/US9364148B2/en not_active Expired - Fee Related

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