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  • Understand the CorneaUnderstand the Pressure

    Corneal Biomechanics, Accurate IOP, and CCTin one Simple Instrument

  • One Device, Five ParametersIOPG - Goldmann Correlated IOPIOPCC - Corneal Compensated IOPCH - Corneal HysteresisCRF - Corneal Resistance FactorCCT - Central Corneal Thickness

  • ORA Technology Background

  • Measuring Pressure Goldmann Tonometry PrinciplesThe Goldmann Tonometer has long been considered the gold standard for measuring pressure. It is based upon the Imbert-Fick Law (W = P x A) where:- W is the force to applanate- P is Intra Ocular Pressure (IOP)- A is the area applanated

  • Measuring PressureGoldmann Tonometry Assumptions - Surface is dry - Volume is perfectly spherical - Surface is infinitely thin and perfectly flexible - Tear-film effect and corneal thickness effect cancel each other out

    Recognizing that corneal effects and surface tension are factors which influence the measurement; Goldmann selected a tonometer tip size of 3.06mm which he believed would nullify these effects based on a constant central corneal thickness of 525 microns

  • Measuring Pressure Goldmann Tonometry FlawsAccordingly, Goldmann tonometry cannot compensate for differences in corneal thickness, corneal elasticity, and many other parameters that influence tonometer readings. This applies to all other Goldmann-correlated tonometers! - Experimentation done on cadaver eyes - Not representative of live corneas - Variation in corneal thickness is significantly greater than assumed - Variations in corneal biomechanical properties unaccounted for

  • Non- Contact Tonometers- Invented by Dr. Bernie Grolman in the 1960s (American Optical)- To enable ODs in the USA to perform tonometry- Introduced in 1971 - Uses rapid air pulse technology- Easy to use- Strong Goldmann correlation- Objective: no operator bias- No anesthetic required - No risk of cross-contamination

  • NCT Traditional Method of Operation

  • Traditional NCT vs. GATIn conclusion, the current study shows that theXPERT vs GAT Sdiff (1.5 mmHg) is comparable tosingle GAT instrument repeatability, and far superiorto that of two GAT instrument repeatability/reliability.

  • Ocular Response AnalyzerMethod of Operation

  • Static vs. Dynamic MeasurementGoldmann tonometers make static measurements. That is they derive IOP from the force measured during a steady state applanation of the cornea.The Ocular Response Analyzer makes a dynamic measurement, monitoring the movement of the cornea in response to a rapid air impulse.

    The dynamic nature of the ORA measurement makes possible the capture of other useful data about the eye.

  • Visco-Elastic SystemAn Automotive Strut Assembly- Coil Spring: Static Resistance (Elasticity). strain(deformation) is directly proportional to stress (applied force), independent of the length of time or the rate at which the force is applied.- Shock Absorber: Viscous Resistance (Damping). The resistance to an applied force depends primarily on the speed at which the force is applied.

  • Method of Operation

  • Applanation Signal Plot

  • DefinitionsHysteresisThe phenomenon was identified, and the term coined, by Sir James Alfred Ewing in 1890.Hysteresis is a property of physical systems that do not instantly follow the forces applied to them, but react slowly, or do not return completely to their original state.Corneal HysteresisThe difference in the inward and outward pressure values obtained during the dynamic bi-directional applanation process employed in the Ocular Response Analyzer, as a result of viscous damping in the cornea.

  • Corneal Hysteresis:A New Ocular Parameter

  • Right/Left Eye Hysteresis

    Chart3

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    normals

    First NameMeasure DateEyeIOPgIOPccCRFCHEyeIOPgIOPccCRFCH

    AARON1/27/06 12:22L13.0015.808.108.60R14.0015.609.309.60

    AARON1/27/06 12:22L11.3013.908.009.00R14.3013.9010.9011.40

    abeer3/21/06 13:54L13.3014.809.209.70R15.0016.409.609.70

    abeer3/21/06 13:54L13.5015.808.609.00R15.3016.709.609.60

    ADRIANA1/3/06 15:45L12.3014.608.409.20R12.0013.509.009.90

    ADRIANA1/3/06 15:45L13.4015.308.909.40R13.3014.009.9010.50

    AKSHAY3/10/06 11:24L16.0021.706.405.50R12.8018.306.006.10

    AKSHAY3/10/06 11:24L17.4022.207.406.20R16.7021.507.306.30

    ALBERTO3/27/06 14:14L13.3016.308.108.40R12.8015.708.108.60

    ALBERTO3/27/06 14:14L13.7016.608.208.40R15.1019.707.106.60

    alexis3/21/06 14:15L8.208.109.5011.90R9.009.109.4011.60

    alexis3/21/06 14:15L8.907.0011.0013.50R11.2010.1010.9012.50

    ALICIA12/27/05 16:23L15.9015.1011.5011.50R17.7016.7012.0011.50

    ALICIA12/27/05 16:23L16.8018.409.709.20R17.7018.9010.209.40

    ALISA11/12/05 11:04L14.0015.109.7010.10R14.2015.609.409.70

    ALISA11/12/05 11:04L13.3013.7010.1010.80R17.9018.7010.609.80

    ANASTASIA1/24/06 13:33L14.1013.1011.3012.00R16.9014.3013.1013.10

    ANASTASIA1/24/06 13:33L15.7014.8011.5011.60R17.1014.8012.9012.80

    ANDREW11/15/05 18:47L14.8014.4011.0011.40R12.2010.1011.8013.20

    ANDREW11/15/05 18:47L15.4015.0011.1011.30R12.3010.6011.6012.90

    ANDREW11/15/05 18:47L18.9018.5011.8010.80R12.8011.0011.7012.90

    ANGELO2/21/06 17:25L11.6013.208.809.90R9.4012.307.409.00

    ANGELO2/21/06 17:25L10.8011.709.3010.70R10.3012.408.109.60

    ANNA12/3/05 10:27L11.2011.709.6011.00R12.5012.909.9010.90

    ANNA12/3/05 10:27L15.1015.9010.1010.20R13.8014.1010.2010.80

    anne4/13/06 11:21L8.7011.707.209.00R8.5010.807.709.70

    ANTHONY1/3/06 15:19L18.6017.0012.6011.90R17.5016.3012.1011.70

    ANTHONY1/3