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Lecture Correcting Astigmatism With RGP

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Lecture Correcting Astigmatism With RGP Powered By Docstoc
					                                                                        4/11/2010




                            301
       Rigid Gas Permeable
        Lenses Correction
            Clarke Newman, OD, PC




      Please no cameras or recorders during the class presentation.
      You will be asked to leave the room if request is not followed.




Correcting Astigmatism With
Rigid Gas Permeable Lenses
                           Presented
                              By
     Clarke D. Newman, OD, FAAO
                       April 10, 2010
                      OptoWest 2010
                     Indian Wells, CA
                    COPE #: 26617-CL




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                                                                                                                        4/11/2010




Disclaimer
I have no financial interest in any of the products, or companies,
   that will be presented in this lecture. I am, however, on the
Advisory Boards for Inspire Pharmaceuticals and Abbott Medical       Introduction
      Optics, and I lecture for Bausch + Lomb and Addition
                           Technologies.

              I may discuss “FDA Off-Label” uses




                                                                     What’s the Point
“As you advance the scope of
                                                                      To Correct Residual Astigmatic Errors That
optometry, don’t leave a vacuum.                                       Degrade the Quality of the Patient’s Vision
S
Someone will fill it.”                                                    Physiological Residual Astigmatism (P.R.A.)
                                                                          Induced Residual Astigmatism (I.R.A.)
                                          -Dr. Irv Borish             To Correct Poor Physiological Alignment




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How Often Do We Need Toric
R.G.P.'s?
 If the Average Eye Care Practitioner Prescribes RGP
  Lenses 9% of the Time, (Give-Or-Take), AND
 About 30% of Those Patients Have Clinically Significant
  Physiologic Residual Astigmatism, AND
 Another 5%-10% Could Use Some Form of Toricity on the
  Posterior Lens Surface to Improve Physiology And / Or
  Comfort, THEN
 5% (Uh, That’s One-in-Twenty) of Your Patients Should
  Be Wearing Some Form of Toric RGP Lens in One, Or
  Both, of Their Eyes.
 However, the number of patients in your practice that are
  candidates for RGP toric lens correction is about 30 %!!!




A QUICK NOTE ABOUT KERATOCONUS




                                                                     3
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                                                    Let’s J Say Th We Need ‘Em
                                                    L ’ Just S That W N d ‘E




The Questions Stay the Same, But
the Answers Change                                  The DAC Six Axis Lathe
 The New Lathes Allow the Practitioner to Design    Can Produce Aspheric Toric Lenses
  and Produce Exact and Complex Lens                 Can Produce Lenses With Base Curves and Peripheral
                                                      Curves Sets That Have Different Amounts of Toricity
                                       y g
  Geometries That Were Not Possible Only Eight
                                                      Can P d      T i Anterior L ti l Z         F
                                                     C Produce Toric A t i Lenticular Zones For a
  Years Ago                                           Constant Edge Thickness
 One Can Also Reproduce These Lens Designs          Non-Orthogonal Lenses For Irregular Astigmatism
  With a High Degree of Fidelity                     Lenses Are So Fine That They Require Only Ten
                                                      Seconds of Polishing
                                                     Produces Toric Lenses Without Induced Prism
                                                     Slab-Off Lens Orientation Control




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                           The Corneal Surface
                                               Central Toricity
                                               Peripheral Toricity
    C       S
The Corneal Surface




Central Corneal Toricity   Peripheral Corneal Toricity




                                                                             5
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The Problem With The
Keratometer
 Assumes The Cornea Is Round                                  Using the Corneal Topographer
 Assumes Orthogonality
                                                                      g G
                                                               to Design RGP Lenses
 Measures A Small Area
 Measures Only Four Points
 Assumes A Compensation For Corneal Back
    Surface When Calculating Diopters Of Curvature




Using the Topographer to Design
                                                               What Is The Point Of
RGP Lenses
   Using the Diopter of Curvature Plots
                                                               Topography?
       Axial (Sagittal) Map
                                                                Provide A More Complete Approximation Of The
       Tangential (Instantaneous, Meridional) Map
                                                                 Corneal Surface
   Refractive (Power) Map: Best For Estimating the Cornea’s
    Contribution The Total Refractive Astigmatism
    C ib i to Th T l R f i A i                i                 Corneal Topography Is A Standard Of Care
   The Other Useful Plots                                      These Instruments Are Relatively Cheap
       Numerical View                                           These Instruments Can Be Profitable
       Keratometry View
                                                                Patients Love Your Toys!
   Contact Lens Design Modules
       Lens Design
       Fluorescein Pattern Simulation




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A Few Definitions
 CVK- Computerized Video Keratography (Corneal
  Topography)
 Line Of Sight- A line connecting the point of fixation
                                  p p           y
  with the center of the entrance pupil of the eye
 Visual Axis- The axis connecting the point of fixation to
  the fovea that passes through the nodal point of the eye
 VK Axis- An axis connecting the point of fixation of the
  topographer to the center of curvature of the cornea




A Few Definitions                                                     Conic Sections
                                                                         Value- The rate of departure from circularity
   Apex-
       The point on the cornea with the greatest elevation from the
                                                                                                  value = 0
       pupil (The most anterior point of the cornea)
       The point on the cornea with the greatest curvature
   Vertex Point- A point tangential and normal to the point
    on the cornea intersected by the VK Axis                                                      Circle




                                                                                                                                 7
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Conic Sections                   The Oblate and Prolate Ellipse


                        –1.0
            value = > 0 –1 0 <




              Ellipse                  Oblate                   Prolate




Conic Sections                   Conic Sections


                      10
              value = 1.0                                 10
                                                value = > 1.0




             Parabola                           Hyperbola




                                                                                 8
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Conic Sections

                                                                                        Line of Sight
                                                                         Vertex Point

                    value = Infinity                        Outline f th
                                                            O tli of the
                                                            Entrance Pupil



                                                                                           APEX



                       Plane




Best-Fit Sphere                                 Best-Fit Sphere
 A Model Surface Of A Single Curvature That
  Most Closely Aligns With The Most Number Of
  Measured Points On The Corneal Surface




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Orthogonal vs. Non-Orthogonal
 Begin To Think In Hemi (Semi)-Meridians
 Orthogonality Is Diagnostic For Spectacle Blur




The Axial Map                                            The Axial Plot
                                  Diopters of
                                   Curvature
                                  Not Accurate in the
                                   Periphery
                                  Most Reproducible
                                  Not Best for Local,
                                   Sharp Changes in
                                   Curvature




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                                                 The Tangential Plot
The Tangential Map
                      Diopters of
                       Curvature
                      Most Accurate in the
                       Periphery
                      Less Reproducible
                      Best for Local,
                       Sharp Changes in
                       Curvature




The Refractive Map                               The Photokeratoscopic View
                      Diopters of Power
                      Best Describes the
                       Refractive Contribution
                       of the Corneal Surface
                      Not Accurate in the
                       Periphery Due to
                       Spherical Aberration




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The Numerical View             The Keratometry View




The “Contact Lens Multi-Vue”   The Contact Lens Modules




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Pentacam® Four Map Selectable   Pentacam® Tangential Curvature




Pentacam® Sagittal Curvature    Pentacam® Front Elevation




                                                                       13
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Pentacam® Equivalent K-     Pentacam® Corneal Thickness
Reading Power               Plot




Pentacam® Topometric Plot   Pentacam® Len Fitting Module




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                                                            The Contact Lens Modules?
The Contact Lens Modules?
                                                             Use the Corneal Topographer in a Qualitative Manner
 The Research Shows That These Modules Improve the          Don’t Rely on the Contact Lens Modules Too Carefully
  Success of the Neophyte Practitioner                       As a Rule, the Simulated Keratometric Data Is Fairly
 Only Two of the Programs Allow the Practitioner to          Accurate. However, For the Toric Cornea, Measure
  Position The Lens on the Eye                                Your Own Keratometry and Correlate the Data to the
                                                              Topographer
 Only One Allows the Practitioner to Rock the Lens
                                                             The Simulated Fluorescein Patterns Are Fairly
 None of Them Really Allow the Practitioner to               Accurate—Use This Module to “Trial” Successively
  Manipulate the Front Surface                                Steeper Base Curve Radii For Keratoconic FDACL
                                                              Designs
                                                             Remember, the Goal Is to Get Accurate Data in a
                                                              Manner That Improves Your Efficiency




An Example of What I’m Talking
About…                                                      The Patient’s Original Lens
   Manifest Refraction:
       O.S.: - 3.00 / - 5.00 X 161
   Measured Keratometry:
       43.75 (7.71   )         47.37 (7.12   )
       43 75 (7 71 mm) @ 162 / 47 37 (7 12 mm) @ 072
   Horizontal Visible Iris Diameter (H.V.I.D.):
       11.50 mm
   Trial Lens Used:
       Overall Lens Diameter (O.A.D.)=           9.60 mm
       Posterior Optic Zone Diameter (P.O.Z.)=   8.00 mm
       Base Curve Radius (B.C.R.)=                7.71 mm




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How About Fluorescein   How About Fluorescein
Simulation?             Simulation?




How About Fluorescein   How About Fluorescein
Simulation?             Simulation?




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How About Fluorescein
Simulation?

                                                    The Posterior Lens Surface:
                                                      G       y
                                                    A Geometry Problem




The Posterior Lens Surface:
A Geometry Problem                                  When Not To Use A Toric Base
 Base Curve Radius Selection                       When the Central Corneal Toricity Is Less Than
    Spherical Iso-Curve Base (Iso-Sphere)            Two Diopters
     – With Spherical Or Aspherical Periphery                                    p             y
                                                    Beware When There Is No Peripheral Toricity
    Aspherical Iso-Curve (Iso-Asphere)
     – With Spherical Or Aspherical Periphery
    Toric Curve (Either Spherical Or Aspherical)
     – Iso-Curve Base / Toric Periphery
     – Toric Base / Iso-Curve Periphery
     – Toric Base / Toric Periphery




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Question: “Why Does an Aspheric Lens Work
Better on a Toric Cornea Than a Spherical
Lens?”                                           Using an Iso-Asphere

 It Is Not Urban Myth
 An Aspheric Lens Has Two Different Radii at
  Any Point That Is Non-Apical
 HUH!?!




Using an Iso-Asphere                             Using an Iso-Asphere
                                   Posterior
                                 Apical Radius




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Using an Iso-Asphere   Using an Iso-Asphere
                                                Tangential Radius




Sagittal Radius        Sagittal Radius




Using an Iso-Asphere   Using an Iso-Asphere
                                          Apical Point




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Using an Iso-Asphere                                     Using an Iso-Asphere
                                 Apical Point
                                                          Because the Benefit of the Tangential and the Sagittal
                                           Non-Apical      Radii Are Only Present When the Lens Decenters, AND
                                             Point
                                                          One Always Wants Vertical Decentration, and Never
                                                           Horizontal Decentration, THEN
                                                          Using an Iso-Asphere to Mask Corneal Toricity Only
                                                           Works on a With-The-Rule Cornea
                                                          Use an Iso-Asphere on Corneas With Less Than Two
                                                           Diopters of Corneal Toricity




Toric Curve Alignment                                    Toric Curve Alignment
 Saddle Alignment                                        Saddle Alignment
    Both Principle Meridians Are Aligned                      Both Principle Meridians Are Aligned
 Low Toric Simulation                                    Low Toric Simulation
    One Principle Meridian Is Aligned and the Other Is        One Principle Meridian Is Aligned and the Other Is
    Flatter Than the Corneal Curvature                        Flatter Than the Corneal Curvature
    “You Fit the Flattest Corneal Meridian ‘On K’, and        “You Fit the Flattest Corneal Meridian ‘On K’, and
    the Steeper Corneal Meridian Flatter Than ‘K’”            the Steeper Corneal Meridian Flatter Than ‘K’”




                                                                                                                          20
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Question: “What Is the Best Corneal                      Question: “What Is the Best Corneal
Topography For Aligning an Iso-Spherical RGP             Topography For Aligning an Iso-Spherical RGP
Lens?”                                                   Lens?”
1.   A Spherical Cornea                                  1.    A Spherical Cornea
2.   A With-The-Rule Cornea With 0.50 D of Corneal       2.    A With-The-Rule Cornea With 0.50 D of Corneal
     Toricity                                                  Toricity
3.     With-The-Rule C           1 00    fC
     A With Th R l Cornea With 1.00 D of Corneall        3.      With-The-Rule C
                                                               A With Th R l Cornea With 1.00 D of Corneall
                                                                                           1 00    fC
     Toricity                                                  Toricity
4.   An Against-The-Rule Cornea With 0.50 D of Corneal   4.    An Against-The-Rule Cornea With 0.50 D of Corneal
     Toricity                                                  Toricity
5.   An Against-The-Rule Cornea With 1.00 D of Corneal   5.    An Against-The-Rule Cornea With 1.00 D of Corneal
     Toricity                                                  Toricity
6.   None of the Above                                   6.    None of the Above




The Goal of a Low Toric                                  A Quick Word About Oblique
Simulation                                               Corneal Toricity
 The Goal of a Low Toric Simulation Is To                Use a Saddle Alignment
  Simulate a With-The-Rule Cornea With 1.00 D of          Low Toric Simulation Doesn’t Work Well, and
  Corneal Toricityy                                           They Work Less Well As the Corneal Toricity
 One Needs to Think In Terms of the “Horizontal”             Increases
  and the “Vertical” Meridians, Not In Terms of the
  “Flattest” and the “Steepest” Meridians




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The Nuts and Bolts of Designing a
Toric Posterior Surface                                The “Contact Lens Multi-Vue”
 Perform a World-Class Refraction, and Measure Your
  Vertex Distance For a Change!
 Take Careful Keratometry Readings
 Do Corneal Topography and Print the “Contact Lens
  Multi-Vue”




                                                       The Nuts and Bolts of Designing a
Pentacam® Four Map Selectable                          Toric Posterior Surface
                                                        Perform a World-Class Refraction, and Measure Your
                                                         Vertex Distance For a Change!
                                                        Take Careful Keratometry Readings
                                                                                              Contact
                                                        Do Corneal Topography and Print the “Contact Lens
                                                         View”
                                                        Note the “Anatomic Measurements”
                                                            Horizontal Visible Iris Diameter (H.V.I.D.)
                                                            Vertical Visible Aperture (V.V.A.)
                                                            Superior and Inferior Lid Station
                                                            Photopic and Scotopic Pupillary Diameters
                                                            Note the Lid Tension As: Flaccid, Average, Tight, Or Asian




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The Anatomic Measurements   The Anatomic Measurements




                                       Horizontal
                                       Visible Iris
                                        Diameter




The Anatomic Measurements   The Anatomic Measurements

                                                      Vertical
                                                       Visible
                                                      Aperture




           H.V.I.D.




                                                                   23
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The Anatomic Measurements              The Anatomic Measurements


                            V.V.A.                                      Inferior
                                                                          Lid
                                                                        Station




The Anatomic Measurements              The Anatomic Measurements

                            Superior
                               Lid
                             Station




                                                Scotopic and Photopic
                                                 Pupillary Diameters




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Remember Our Example                                   One Last Look At the Example
   Manifest Refraction:
                                                       Patient
       O.S.: - 3.00 / - 5.00 X 161
   Measured Keratometry:
       43.75 (7.71 mm) @ 162 / 47.37 (7.12 mm) @ 072
                                    (H.V.I.D.):
    Horizontal Visible Iris Diameter (H V I D ):
       11.50 mm
   Visible Vertical Aperture (V.V.A.):
       9.00 mm
   Superior & Inferior Lid Stations:
       Superior: + 1.50 mm & Inferior: +1.00 mm
   Photopic & Scotopic Pupillary Diameter:
       Photopic: 3.50 mm & Scotopic: 5.50 mm




Calculated Residual                                    Calculated Residual
Astigmatism                                            Astigmatism
 I’m Not a Real Fan of Doing This Calculation          The Calculated Residual Astigmatism (CRA) Is
  Because It Isn’t That Accurate, But Sometimes It       Equal to the Total Refractive Astigmatism (TRA)
  Can Shed Some Light on the Case
                     g                                   Minus the Corneal Toricity (∆ K)
 The Calculated Residual Astigmatism Becomes
                                                                        CRA = TRA - ∆ K
  More Accurate For Higher Astigmatic Errors As         For Example,
  More of the Total Refractive Astigmatism Is                         TRA = - 5.00 D x 161
  Corneal                                                            (-) ∆ K = 3.62 D x 162
                                                                      CRA = 1.37 D x 161




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What Numbers to Pick                                                              What Numbers to Pick

                         LENS PERAMETER SELECTION CHART                                                    LENS PERAMETER SELECTION CHART

  H.V.I.D.   10.00 mm      10.50 mm        11.00 mm       11.50 mm    12.00 mm      H.V.I.D.   10.00 mm      10.50 mm        11.00 mm       11.50 mm    12.00 mm
  O.A.D.     8.50 mm       8.80 mm          9.20 mm       9.60 mm     10.00 mm      O.A.D.     8.50 mm       8.80 mm          9.20 mm       9.60 mm     10.00 mm
  P.O.Z.     7.10 mm       7.40 mm          7.70 mm       8.00 mm     8.40 mm       P.O.Z.     7.10 mm       7.40 mm          7.70 mm       8.00 mm     8.40 mm
  A.O.Z.     7.50 mm       7.80 mm          8.10 mm       8.40 mm     8.80 mm       A.O.Z.     7.50 mm       7.80 mm          8.10 mm       8.40 mm     8.80 mm
HORIZONTAL    On K         0.25 Flat        0.50 Flat     0.75 Flat   1.00 Flat   HORIZONTAL    On K         0.25 Flat        0.50 Flat     0.75 Flat   1.00 Flat
FIT FACTOR                                                                        FIT FACTOR
 VERTICAL    1.00 Flat     1.25 Flat        1.50 Flat     1.75 Flat   2.00 Flat    VERTICAL    1.00 Flat     1.25 Flat        1.50 Flat     1.75 Flat   2.00 Flat
FIT FACTOR                                                                        FIT FACTOR




What Numbers to Pick                                                              What Numbers to Pick

                         LENS PERAMETER SELECTION CHART                                                    LENS PERAMETER SELECTION CHART

  H.V.I.D.   10.00 mm      10.50 mm        11.00 mm       11.50 mm    12.00 mm      H.V.I.D.   10.00 mm      10.50 mm        11.00 mm       11.50 mm    12.00 mm
  O.A.D.     8.50 mm       8.80 mm          9.20 mm       9.60 mm     10.00 mm      O.A.D.     8.50 mm       8.80 mm          9.20 mm       9.60 mm     10.00 mm
  P.O.Z.     7.10 mm       7.40 mm          7.70 mm       8.00 mm     8.40 mm       P.O.Z.     7.10 mm       7.40 mm          7.70 mm       8.00 mm     8.40 mm
  A.O.Z.     7.50 mm       7.80 mm          8.10 mm       8.40 mm     8.80 mm       A.O.Z.     7.50 mm       7.80 mm          8.10 mm       8.40 mm     8.80 mm
HORIZONTAL    On K         0.25 Flat        0.50 Flat     0.75 Flat   1.00 Flat   HORIZONTAL    On K         0.25 Flat        0.50 Flat     0.75 Flat   1.00 Flat
FIT FACTOR                                                                        FIT FACTOR
 VERTICAL    1.00 Flat     1.25 Flat        1.50 Flat     1.75 Flat   2.00 Flat    VERTICAL    1.00 Flat     1.25 Flat        1.50 Flat     1.75 Flat   2.00 Flat
FIT FACTOR                                                                        FIT FACTOR




                                                                                                                                                                          26
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Calculating the Base Curves and                                   Calculating the Base Curves and
Powers                                                            Powers
 Determine the “Horizontal Keratometric Value”                    Determine the “Vertical Keratometric Value”
 Subtract Algebraically the Horizontal Fit Factor and Convert     Subtract Algebraically the Vertical Fit Factor and Convert to
  to Millimeters of Radius For the Final Contact Lens               Millimeters of Radius For the Final Contact Lens
  Prescription                                                      Prescription
   f     Spectacle Axis Is Horizontal, Then the Power in the
 If the S                                                           f     Spectacle Axis Is Vertical, Then the Power in the
                                                                   If the S
  Horizontal Meridian Is the Vertex Corrected Sphere Power          Vertical Meridian Is the Vertex Corrected Sphere Power
 If the Spectacle Axis Is Vertical, Then the Power in the         If the Spectacle Axis Is Horizontal, Then the Power in the
  Horizontal Meridian Is the Vertex Corrected Sphere +              Vertical Meridian Is the Vertex Corrected Sphere + Cylinder
  Cylinder Power                                                    Power
 Add Algebraically the Horizontal Fit Factor to the Horizontal    Add Algebraically the Vertical Fit Factor to the Vertical
  Meridian Power                                                    Meridian Power




Let’s Use Our Example…                                            Let’s Use Our Example…
 Manifest Refraction:                                             Manifest Refraction:
       O.S.: - 3.00 / - 5.00 X 161                                       O.S.: - 3.00 / - 5.00 X 161
                     y
 Measured Keratometry:                                                                y
                                                                   Measured Keratometry:
       43.75 (7.71 mm) @ 162 / 47.37 (7.12 mm) @ 072                     43.75 (7.71 mm) @ 162 / 47.37 (7.12 mm) @ 072
 Horizontal Base Curve & Power:                                   Vertical Base Curve & Power:
       43.75 (7.71 mm) @ 162 & - 3.00 D                                  47.37 (7.12 mm) @ 072 & - 8.00 D (- 7.25)
 Apply the Horizontal Fit Factor (0.75 D)                         Apply the Vertical Fit Factor (1.75 D)
       43.00 (7.84 mm) & - 2.25 D                                        45.62 (7.39 mm) & - 5.50 D




                                                                                                                                          27
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Let’s Use Our Example…                                  The Patient’s Original Lens
   Manifest Refraction:
       O.S.: - 3.00 / - 5.00 X 161
   Measured Keratometry:
       43.75 (7.71   )         47.37 (7.12   )
       43 75 (7 71 mm) @ 162 / 47 37 (7 12 mm) @ 072
   Final Contact Lens Prescription:
       9.60 mm Overall Diameter (O.A.D.)
       8.00 mm Posterior Optic Zone Diameter (P.O.Z.)
       7.84 mm / - 2.25 D
       7.39 mm / - 5.50 D
            Specify “Back Vertex Drum Readings”




The New Lens


                                                        The Future?
                                                              The Future is the Spline Curve




                                                                                                     28
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Spline Curves                                                           Peripheral Curves
 A Mathematical Expression of a Curve That Varies In                    Iso-Spherical Peripheral Curves
  Three Dimensions Instead of Two
                                                                         Iso-Aspherical Peripheral Curves
 Created By Using a Center Point, Polar Coordinates,
  and Point Magnitudes                                                   Toric Peripheral Curves

 The First Baby Step Towards Spline Curve Lenses Are                          Spherical
  Now Becoming Available                                                       Aspherical
     The ESSential™ Multifocal Lens
     Practically Every Third Generation or Newer Progressive
     Addition Spectacle Lens
     Quadrant Specific Lenses Like a QuadraKoneTM




Words to Live By                                                        Peripheral Curves
                                                                           Iso-Curve Base Curve / Toric Peripheral Curve
                                                                              Use When the Base Curve Alignment of an Iso-Sphere or
  “Always Design Rigid Contact Lenses So                                      and Iso-Asphere Is Proper, But the Peripheral Alignment
 That You Can Solve Problems By Removing                                                                       Meridian,
                                                                              Shows Excessive Bearing In One Meridian While Showing
                 Plastic”                                                     Excessive Clearance In the Other Meridian
                                                                           Toric Base Curve / Iso-Curve Peripheral Curve
                        -Dr. Irv Borish to an impressionable 4th year         Some Like These Curves In Saddle Alignments and Low
                        Optometry student one rainy day in 1986               Toric Situations, But I Think That That Is Old Thinking




                                                                                                                                              29
                                                              4/11/2010




  Peripheral Curves              Peripheral Curves

                      P.O.Z.                         P.O.Z.




With a Toric Base                With an Iso-
Curve and a Toric              Curve Base Curve
Peripheral Curve               and an Iso-Curve
       Set                     Peripheral Curve
                                      Set




  Peripheral Curves              Peripheral Curves

                      P.O.Z.                         P.O.Z.




  With an Iso-                 With a Toric Base
Curve Base Curve                Curve and an
   and a Toric                    Iso-Curve
Peripheral Curve               Peripheral Curve
       Set                            Set




                                                                    30
                                                                                                   4/11/2010




                                        The Front Toric Lens
                                         Indicated When the Patient Has Significant (1.00 D, Or
The Anterior Lens Surface:                More) Physiological Residual Astigmatism (P.R.A.), and
   Op
An Optics Problem                         the Corneal Toricity Is Less than Two Diopters
                                         Use Larger Lens Diameters (0.4 mm Larger Than
                                          Normal)
                                         Decenter the Posterior Optic Zone (P.O.Z.) Superiorly
                                          0.5 mm
                                         Whenever Possible, Use a Periballasted Lens Design




The Periballast                         The Periballast
                             Original                                                 Original
                              Minus                                                    Minus
                             Carrier                                                  Carrier


              Optic Zone                                        Optic Zone




             Ballast Zone
                                        Finished               Ballast Zone
                                          Lens
                                        Diameter




                                                                                                         31
                                                                                4/11/2010




The Periballast             The Periballast
                             There Is No Induced Vertical Prism
                             There Is No Power Change Due to Thickness
                                              0.25          0.1
                              Changes (About 0 25 D Per 0 1 mm Thickness
              Optic Zone      Change
                             With an Additional, Inferior, Offset Lenticular
                              Zone, a Constant Edge Thickness Is Achieved
Finished     Ballast Zone    Disadvantage: Inadequate Rotational Stability
  Lens
Diameter




The Periballast             The Periballast



              Optic Zone                         Optic Zone




                                                                         Offset
Finished     Ballast Zone
                            Finished             Ballast Zone          Lenticular
  Lens                        Lens                                       Zone
Diameter                    Diameter




                                                                                      32
                                                                                                                 4/11/2010




  Ballasts and Periballasts:
  Other Considerations                                                    Placing a Prism Ballast
   During a Blink, the Lower Lid Action Is to Move Nasally
    Which Causes the Bottom of the Lens to Rotate
    Nasally, THERFORE
   One Needs to Order the Prism Rotated Nasally (About
    10 ° - 15 °)
   Order About 2.0 Prism Diopters
         More For Higher Minus Lenses (- 4.00 D and Above)              Cylinder
         Less For Plus Lenses                                             Axis
         Decrease Prism For Materials of Higher Specific Gravities       (161)
         and Increase Prism For Materials of Lower Specific Gravities




  Placing a Prism Ballast                                                 Placing a Prism Ballast
                                               Prism Axis                                           Prism Axis

                                                 (090)                                                (085)




Cylinder                                                                Cylinder
  Axis                                                                    Axis
 (161)                                                                   (161)




                                                                                                                       33
                                                                                                  4/11/2010




  Ballasts and Periballasts:
  Other Considerations                                       Lens Truncation
                                                                                Prism Axis
   Truncate As a Last Resort                                                     (090)
         Truncating a Minus Lens Decreases the Prism
         Truncating a Plus Increases the Prism
         Rotate the Truncation 10° Nasally For the Same
         Reason That One Would Rotate a Prism
                                                           Cylinder
                                                             Axis
                                                            (161)




  Lens Truncation                                            Lens Truncation
                                        Prism Axis                              Prism Axis
                                          (090)                                   (090)




Cylinder                                                   Cylinder
  Axis                                                       Axis         10o
 (161)                                                      (161)
                                              Truncation                             Truncation
                                                 Line                                   Line




                                                                                                        34
                                                                                                                    4/11/2010




The Toric Base / Spherical Front
Lens (Base Toric Or Back Toric)                                Induced Residual Astigmatism
 Useful Only When the T.R.A. Is Roughly One-Third              Because the Index of Refraction of the Tear Film
  Greater Than the ∆ K (Varies With the Lens Material Index)     Is Different From the Index of Refraction of the
 Don’t Worry About When to Use a Back Toric Lens                                      ,
                                                                 R.G.P. Lens Material, a Toroidal Posterior
  When One Elects to Use a Toric Back Surface, Design            Surface Will Induce a Significant Amount of
  In the Manner Previously Described and the Powers
                                                                 Cylinder That Must Be Factored Into the Lens
  Take Care of Themselves
                                                                 Power
 However, One Should Remember that Toric Back
  Surfaces Induce Residual Astigmatism (I.R.A.)                 This Induced Cylinder Varies Greatly With the
                                                                 Index of Refraction of the RGP Lens Material




Induced Residual Astigmatism                                   Induced Residual Astigmatism
(Continued)                                                    (Examples)
 The Index of Refraction of P.M.M.A. Is 1.49 (This             I Won’t Bore You With Formulas, But
    Index Represents a High Water Mark)
                                                                A Lens With an Index of 1.49 Induces 0.4563 X
           g
 A Mid-Range Index Would Be 1.45 (e.g., Fluoroperm
                                  ( g          p                 Δ K of the Lens (The “Rule of One-Half )
                                                                                       Rule One-Half”)
    30™, Fluoroperm 92™, Fluorex 700™, OP-7™)
                                                                A Lens With an Index of 1.45 Induces 0.3377 X
 A Low Index of Refraction Would Be 1.42 (e.g.,
    Boston EO™, Boston RXD™)                                     Δ K of the Lens (About One-Third)
 The Index of Boston XOTM Is 1.415 (This Index                 A Lens With an Index of 1.42 Induces 0.2785 X
    Represents a Low Water Mark)                                 Δ K of the Lens (About One-Quarter)




                                                                                                                          35
                                                                                                                4/11/2010




Induced Residual Astigmatism                        The Power of the Lens In Air
(Examples)                                          (Examples)
 Therefore, Boston EO™ Induces One-Half the         I Won’t Bore You With Formulas, But
  Residual Astigmatism That P.M.M.A. Induces!        A Lens With an Index of 1.49 Induces 1.4563 X
                                       Different,
 The Power of the Lens In Air Is Also Different      Δ K of the Lens (The “Rule of One and One-Half”)
                                                                            Rule            One-Half )
  and It Is Also Index Dependent                     A Lens With an Index of 1.45 Induces 1.3377 X
                                                      Δ K of the Lens (About One and One-Third)
                                                     A Lens With an Index of 1.42 Induces 1.2785 X
                                                      Δ K of the Lens (About One and One-Quarter)




                                                    The Spherical Power Effect (SPE)
Bitoric RGP Lenses                                  Bitoric RGP Lens
 The Spherical Power Effect (SPE) Bitoric RGP         Indicated When an Iso-Curve Lens Demonstrates Poor
                                                        Physiological Alignment and There Is No Physiological
  Lens                                                  Residual Astigmatism, In Other Words
 The Cylinder Power Effect (CPE) Bitoric RGP             The TRA = Δ K OrK,
  Lens                                                    There Is No CRA, Or
                                                          All of the Astigmatism Is on the Anterior Cornea
 The Crossed-Cylinder Effect (CCE) Bitoric RGP
                                                     There Is a Compensating Plus Cylinder on the Anterior
  Lens                                                Surface That Corrects For The Minus Cylinder Induced
                                                      By the Posterior Surface
                                                     Lens Behaves Optically Just Like a Iso-Curve Lens
                                                     Great Concept For a Toric Trial Set




                                                                                                                      36
                                                                                                                           4/11/2010




The Spherical Power Effect (SPE)                       The Cylinder Power Effect (CPE)
Bitoric RGP Lens                                       Bitoric RGP Lens
 Because an SPE Bitoric Lens Does Not Induce a         Indicated When an Iso-Curve Lens
  Cylinder, the Power of the Cylinder In Air Is            Demonstrates Poor Physiological Alignment and
   q
  Equal to the Δ K                                                    g           y     g
                                                           There Is Significant Physiological Residual
 A Large Proportion of the Bitoric Lens                   Astigmatism
  Candidates Can Wear an SPE Lens, and That
  Proportion Increases As the Residual
  Astigmatism Increases




Remember Our Example                                   The Crossed Cylinder Effect (CCE)
   Manifest Refraction:
                                                       Bitoric Lens
       O.S.: - 3.00 / - 5.00 X 161                        Indicated When an Iso-Curve Lens Demonstrates Poor
                                                           Physiological Alignment, and There Is a Significant Amount of
   Measured Keratometry:                                  Physiological Residual Astigmatism Present, AND the Principal
       43.75 (7.71 mm) @ 162 / 47.37 (7.12 mm) @ 072       Power Meridians and the Principal Curvature Meridians Are
   C l l t d Residuall Astigmatism:
    Calculated R id A ti        ti                         Significantly Misaligned (Us all 15° or More)
                                                                                    (Usually
                                                          There Is a Step-By-Step Guide to Prescribing These Lenses and
                 T.R.A. = - 5.00 D x 161
                                                           Determining the Power In Air In the Handout
                  (-) ∆ K = 3.62 D x 162                  Absolutely Use an SPE Bitoric Trial Set
                  C.R.A. = 1.37 D x 161                   Make Sure Your Lab Knows What They Are Doing!
                                                          One Can Use a Back Toric Trial Set, But It Is a Nightmare




                                                                                                                                 37
                                                                                                                 4/11/2010




                                                            The Parameters to Order
                                                             Overall Diameter (O.A.D.)
                                                             The Posterior Optic Zone Diameter (P.O.Z.)
O      g
Ordering Lenses                                                                              (B.C.R.)
                                                             The Base Curve Radius or Radii (B C R )
                                                             The Lens Powers
                                                                Order These Powers Meridian-By-Meridian, and
                                                                Specify to the Lab That They Are, “Back Vertex
                                                                Drum Readings”)




An Example of How You Can Get
Into Trouble With Power                                     The Parameters to Order
   In Our Example, the Back Vertex Power Readings           Overall Diameter (O.A.D.)
    Were:
       - 2.25 D @ 161 & - 5.50 D @ 071                       The Posterior Optic Zone Diameter (P.O.Z.)
   These Powers Could Be Expressed As:                                                      (B.C.R.)
                                                             The Base Curve Radius or Radii (B C R )
       - 2.25 / - 2.25 X 161
                                                             The Lens Powers
   HOWEVER, If One Gives the Lab These Two Powers,
    and Does Not Tell the Lab That They Are Drum
    Readings, the Lab Might Think That the Lens Power Is:
       - 2.25 / - 5.50 x 161
   Which Is Equivalent to:
       - 2.25 D @ 161 & - 7.75 D @ 071




                                                                                                                       38
                                                                                                                            4/11/2010




The Parameters to Order                             The Parameters to Order
 Overall Diameter (O.A.D.)                          Overall Diameter (O.A.D.)
 The Posterior Optic Zone Diameter (P.O.Z.)         The Posterior Optic Zone Diameter (P.O.Z.)
                                 (B.C.R.)
 The Base Curve Radius or Radii (B C R )                                            (B.C.R.)
                                                     The Base Curve Radius or Radii (B C R )
 The Lens Powers                                    The Lens Powers
 The Center Thickness (C.T.)                        The Center Thickness (C.T.)
    As Thin As Possible (T.A.P.) Per The Material    The Edge Thickness (E.T.)
    Manufacturer                                            Somewhere in the 0.13 mm Range




The Parameters to Order                             Materials Selection
                                                       Use a Mid-Range Dk Material!?!
 Overall Diameter (O.A.D.)                                Boston XOTM Has a DK of 100
 The Posterior Optic Zone Diameter (P.O.Z.)           Use a Stiff Material
                                                           Boston ES™ and Boston XOTM Are the Stiffest
                                 (B.C.R.)
 The Base Curve Radius or Radii (B C R )
                                                       Use a Low Index Material
 The Lens Powers                                          Boston XO™ Is the Lowest
 The Center Thickness (C.T.)                          Use A Low Specific Gravity Material
                                                           Well…Boston ESTM XOTM Are Fairly Dense at Roughly 1.27
 The Edge Thickness (E.T.)
                                                       I Like Boston XO™ & XO2™ & Menicon ZTM
 The Peripheral Curve Sets                                Not the Lowest Specific Gravity In the World, But a Great All-
                                                           Around Material For Toric Lenses




                                                                                                                                  39
                                                                                    4/11/2010




Ordering Lenses: Other
Considerations
 Have the Lab Place a Dot In the Meridian of the
  Flattest Base Curve Radius (You Can Verify This Dot
  With the Your Keratometer)                                   p     g
                                                        The Dispensing Visit
 Verify These Lens Parameters




                                                        Use a Barrier Filter With
The Dispensing Visit                                    Fluorescein!
 Follow the Steps In the Handout
 Use the Burton Lamp to Evaluate Lens
  Positioning Lens Movement, and Fluorescein
  Positioning,     Movement
  Patterns




                                                                                          40
                                                                                   4/11/2010




The Newman-Scarbrough
Fluorescein Delivery System




                               Patient Follow Up Evaluation
                                Follow the Steps In the Handout
                                See the Patient Frequently Until the Lenses Are
Patient Follow Up Evaluation     Deemed Appropriate
                                Take Post-Keratometry Readings Or Do Corneal
                                 Topography and Evaluate the “Difference Image”




                                                                                         41
                                                                                   4/11/2010




                   Trouble Shooting
                    Get The Back Surface Geometry Correct Before
                     Trying to Tackle Power Problems
        S      g
Trouble Shooting    Check and Control Lens Rotation
                    Compensate For Residual Astigmatism




                   Conclusion
                      Be Aggressive About Aligning the Back Surface
                          The New Lens Fabrication Technologies Facilitate These
Conclusion
C                  
                          Lens Designs
                       Be Confident About Correcting Residual Astigmatism
                          Use Spherical Power Effect Lenses Whenever Possible
                      Profit From Your Expertise
                          These Are Specialty Lenses—Charge Accordingly




                                                                                         42
                                     4/11/2010




`Thank You!!
       Enjoy the Rest of OptoWest!
        cdnewman@earthlink.net




                                           43
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   The Scarbrough-Newman Delivery
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• 5 ml Solution
• 0.50% Lissamine Green And
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  technique
• 0.22 µm Millex®-GV Leur-
  Lock micropore filter         Abrams Royal Pharmacy
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Instilling Fluorescein
   RADIUS CONVERSION TABLE      12 MM VERTEX CONVERSION TABLE                                   MANIFEST REFRACTION
  D        r      D        r     MINUS       POWER         PLUS                           SPHERE             CYLINDER                             AXIS
                                                                                                                                                                       SCRATCH
36.00    9.37   48.00    7.03     -3.87        4.00        +4.25
36.12    9.33   48.12    7.01     -4.00        4.25        +4.50        OD                      .              -         .                                              PAPER
36.25    9.30   48.25    7.00     -4.25        4.50        +4.75
36.37    9.27   48.37    6.98     -4.50        4.75        +5.00        OS                      .              -         .
36.50    9.24   48.50    6.96     -4.75        5.00        +5.37                              VERTEX CORRECTED POWERS
36.62    9.21   48.62    6.95     -5.00        5.25        +5.62                          SPHERE             CYLINDER                             AXIS
36.75           48.75                          5.50
36.87
         9.18
         9.15   48.87
                         6.92
                         6.91
                                  -5.12
                                  -5.37        5.75
                                                           +5.87
                                                           +6.12        OD                      .              -         .
37.00
37.12
         9.12
         9.09
                49.00
                49.12
                         6.89
                         6.87
                                  -5.62
                                  -5.87
                                               6.00
                                               6.25
                                                           +6.50
                                                           +6.75        OS                      .              -         .
37.25    9.06   49.25    6.85     -6.00        6.50        +7.00                                     MEASURED KERATOMETRY
37.37    9.03   49.37    6.84     -6.25        6.75        +7.37                        FLAT            MERIDIAN       STEEP                MERIDIAN
37.50
37.62
         9.00
         8.97
                49.50
                49.62
                         6.82
                         6.80
                                  -6.50
                                  -6.62
                                               7.00
                                               7.25
                                                           +7.62
                                                           +8.00        OD               .                                    .
37.75
37.87
         8.94
         8.91
                49.75
                49.87
                         6.78
                         6.77
                                  -6.87
                                  -7.12
                                               7.50
                                               7.75
                                                           +8.25
                                                           +8.50
                                                                        OS               .                                    .
38.00    8.88   50.00    6.75     -7.25        8.00        +8.87                                    IMPORTANT MEASUREMENTS
38.12    8.85   50.12    6.73     -7.50        8.25        +9.12                                      O.D.                             O.S.
38.25
38.37
         8.82
         8.79
                50.25
                50.37
                         6.72
                         6.70
                                  -7.75
                                  -7.87
                                               8.50
                                               8.75
                                                           +9.50
                                                           +9.75
                                                                        H.V.I.D.                       .       MM                       .          MM
38.50
38.62
         8.76
         8.73
                50.50
                50.62
                         6.68
                         6.67
                                  -8.12
                                  -8.37
                                               9.00
                                               9.25
                                                          +10.12
                                                          +10.37
                                                                         V.V.A.                        .       MM                       .          MM
                                                                    SUP. LID
38.75
38.87
         8.70
         8.68
                50.75
                50.87
                         6.65
                         6.63
                                  -8.50
                                  -8.75
                                               9.50
                                               9.75
                                                          +10.75
                                                          +11.00
                                                                    STATION                            .       MM                       .          MM
                                                                    INF. LID
39.00
39.12
         8.65
         8.62
                51.00
                51.12
                         6.62
                         6.60
                                  -8.87
                                  -9.12
                                              10.00
                                              10.25
                                                          +11.37
                                                          +11.75
                                                                    STATION                            .       MM                       .          MM
39.25    8.59   51.25    6.59     -9.37       10.50       +12.00
                                                                                                            LENS PARAMETER SELECTION CHART
39.37    8.57   51.37    6.57     -9.50       10.75       +12.37
                                                                      H.V.I.D.                10.00 mm          10.50 mm      11.00 mm               11.50 mm           12.00 mm
39.50    8.54   51.50    6.55     -9.75       11.00       +12.62
                                                                       O.A.D.                  8.50 mm           8.80 mm       9.20 mm                9.60 mm           10.00 mm
39.62    8.51   51.62    6.54     -9.87       11.25       +13.00
                                                                       P.O.Z.                  7.10 mm           7.40 mm       7.70 mm                8.00 mm            8.40 mm
39.75    8.49   51.75    6.52    -10.12       11.50       +13.37
                                                                       A.O.Z.                  7.50 mm           7.80 mm       8.10 mm                8.40 mm            8.80 mm
39.87    8.45   51.87    6.51    -10.25       11.75       +13.62
                                                                    HORIZONTAL
40.00    8.43   52.00    6.49    -10.50       12.00       +14.00                                    On K        0.25 D Flat        0.25 D Flat           0.25 D Flat    0.75 D Flat
                                                                    FIT FACTOR
40.12    8.41   52.12    6.48    -10.62       12.25       +14.37
                                                                     VERTICAL
40.25    8.38   52.25    6.46    -10.87       12.50       +14.75                              1.00 D Flat       1.25 D Flat        1.25 D Flat           1.25 D Flat    1.75 D Flat
                                                                    FIT FACTOR
40.37    8.36   52.37    6.44    -11.00       12.75       +15.00                                B.C.R. +        B.C.R. +         B.C.R. +        B.C.R. +       B.C.R. +
40.50    8.33   52.50    6.43    -11.25       13.00       +15.37         2˚ R / W              1.00 mm /       1.00 mm /        1.00 mm /       0.80 mm /      0.80 mm /
40.62    8.30   52.62    6.41    -11.67       13.50       +16.12                                0.30 mm         0.30 mm          0.30 mm         0.30 mm        0.30 mm
40.75    8.28   52.75    6.40    -12.00       14.00       +16.87                                B.C.R. +        B.C.R. +         B.C.R. +        B.C.R. +       B.C.R. +
40.87    8.25   52.87    6.38    -12.37       14.50       +17.50         3˚ R / W              1.50 mm /       1.50 mm /        1.50 mm /       1.00 mm /      1.00 mm /
41.00    8.23   53.00    6.37    -12.75       15.00       +18.25                                0.20 mm         0.20 mm          0.20 mm         0.30 mm        0.30 mm
41.12    8.20   53.12    6.35    -13.12       15.50       +19.00                                B.C.R. +        B.C.R. +         B.C.R. +        B.C.R. +       B.C.R. +
41.25    8.18   53.25    6.34    -13.37       16.00       +19.75         4˚ R / W              2.00 mm /       2.00 mm /        2.00 mm /       1.50 mm /      1.50 mm /
41.37    8.15   53.37    6.32    -13.75       16.50       +20.62                                0.20 mm         0.20 mm          0.30 mm         0.20 mm        0.20 mm
41.50    8.13   53.50    6.31    -14.12       17.00       +21.37            C.T.                       As Thin As Possible (T.A.P.) Per the Material Manufacturer
41.62    8.10   53.62    6.29    -14.50       17.50       +22.12            E.T.               ≈0.13 mm        ≈0.13 mm         ≈0.13 mm        ≈0.13 mm       ≈0.13 mm
41.75    8.08   53.75    6.28    -14.75       18.00       +23.00
41.87    8.06   53.87    6.26    -15.12       18.50       +23.75
42.00    8.03   54.00    6.25    -15.62       19.00       +24.62                       NEWMAN’S VERSION OF THE MANDELL-MOORE BITORIC LENS GUIDE
42.12    8.01   54.12    6.24    -15.75       19.50       +25.50                          O.D.                                         O.S.
42.25    7.98   54.25    6.22    -16.25       20.00       +26.37                   HORIZONTAL MERIDIAN                       HORIZONTAL MERIDIAN
42.37    7.96   54.37    6.21    -16.75       21.00       +28.00                        CURVATURE       POWER                      CURVATURE     POWER
42.50    7.94   54.50    6.19    -17.37       22.00       +29.87        ENTER                                                         ENTER
                                                                     HORIZONTAL                                                    HORIZONTAL
42.62    7.91   54.62    6.18    -18.00       23.00       +31.75
                                                                      (K) VALUE                                                     (K) VALUE
42.75    7.89   54.75    6.16    -18.62       24.00       +33.75       VERTEX                                                        VERTEX
42.87    7.87   54.87    6.15    -19.25       25.00       +35.75     CORRECTED                                                     CORRECTED
43.00    7.84   55.00    6.14    -19.87       26.00       +37.75      SPECTACLE                                                     SPECTACLE
                                                                        ENTER                                                         ENTER
43.12    7.82   55.12    6.12    -20.37       27.00       +40.00
                                                                     HORIZONTAL                                                    HORIZONTAL
43.25    7.80   55.25    6.11    -21.00       28.00       +42.25     FIT FACTOR           -                   +                    FIT FACTOR        -                  +
43.37    7.78   55.37    6.10    -21.50       29.00       +44.50        FINAL                                                         FINAL
43.50    7.75   55.50    6.08    -22.00       30.00       +46.87    CONTACT LENS                                                  CONTACT LENS
                                                                    PRESCRIPTION                                                  PRESCRIPTION
43.62    7.73   55.62    6.07    -22.62       31.00       +49.37
43.75    7.71   55.75    6.05    -23.12       32.00       +52.00        B.C.R IN mm.                            POWER             B.C.R. IN mm.                          POWER
43.87    7.69   55.87    6.04    -23.62       33.00       +54.62
44.00    7.67   56.00    6.03    -24.12       34.00       +57.50                        BASE CURVE                                                   BASE CURVE
44.12    7.64   56.12    6.01    -24.62       35.00       +60.37                    VERTICAL MERIDIAN                                            VERTICAL MERIDIAN
44.25    7.62   56.25    6.00    -25.12       36.00       +63.38                        CURVATURE     POWER                                          CURVATURE     POWER
44.37    7.60   56.37    5.99    -25.62       37.00       +66.50         ENTER                                                         ENTER
                                                                       VERTICAL                                                      VERTICAL
44.50    7.58   56.50    5.97    -26.00       38.00       +69.87
                                                                      (K) VALUE                                                      (K) VALUE
44.62    7.56   56.62    5.96    -26.62       39.00       +73.37        VERTEX                                                        VERTEX
44.75    7.54   56.75    5.95    -27.00       40.00       +76.87     CORRECTED                                                      CORRECTED
44.87    7.52   56.87    5.94    CALCULATED RESIDUAL ASTIGMATISM      SPECTACLE                                                     SPECTACLE
45.00    7.50   57.00    5.92                                            ENTER                                                         ENTER
                                    C.R.A = T.R.A. - ∆ K             VERTICALFIT                                                   VERTICAL FIT
45.12    7.48   57.12    5.91                                           FACTOR            -                   +                       FACTOR         -                  +
45.25    7.45   57.25    5.90              RIGHT EYE                     FINAL                                                         FINAL
45.37    7.43   57.37    5.88              CYLINDER       AXIS      CONTACT LENS                                                  CONTACT LENS
                                                                    PRESCRIPTION                                                  PRESCRIPTION
45.50    7.41   57.50    5.87
45.62    7.39   57.62    5.86   T.R.A.         .                        B.C.R. IN mm.                           POWER             B.C.R. IN mm.                          POWER
45.75    7.37   57.75    5.84
45.87    7.35   57.87    5.83                                                             BASE CURVE                                                 BASE CURVE
46.00    7.33   58.00    5.82   (-) ∆ K        .                   1.      Measure the H.V.I.D. and select the proper lens parameters from the Lens
46.12    7.31   58.12    5.81
46.25    7.29   58.25    5.79
                                                                           Parameter Selection Chart.
                                C.R.A.                             2.      Enter the Horizontal Measured Keratometry reading in row one, and the
46.37
46.50
         7.27
         7.25
                58.37
                58.50
                         5.78
                         5.77
                                               .                           corresponding Vertex Corrected Meridian Power in row two.
46.62    7.23   58.62    5.76               LEFT EYE               3.      Enter the Horizontal Fit Factor in row three.
46.75    7.21   58.75    5.75              CYLINDER       AXIS
46.87    7.20   58.87    5.73
                                                                   4.      Subtract the Fit Factor from the Measured Keratometry reading and add the
                                T.R.A.                                     Fit Factor to the Vertex Corrected Meridian Power.
47.00
47.12
         7.18
         7.16
                59.00
                59.12
                         5.72
                         5.71
                                               .                   5.      Convert the Final Contact Lens Prescription Curvature value to millimeters.
47.25    7.14   59.25    5.70                                      6.      Repeat Steps Two through Five, using the Vertical Measured Keratometry
47.37    7.12   59.37    5.68   (-) ∆ K        .                           reading, the corresponding Meridian Power, and the Vertical Fit Factor.
47.50    7.10   59.50    5.67
47.62    7.08   59.62    5.66                                      7.      For obliquely toric corneas use a Fit Factor of 0.75 D throughout.
47.75    7.06   59.75    5.65   C.R.A.         .                   8.      Specify the B.C.R. with the corresponding Power for each meridian.
47.87    7.05   59.87    5.64
 Decision Tree                                  Comecting                             Residual Astignolatismm With R. G.P.
                                        $OF
                                                                                      -
                                                       I             P       h a Mn Reftadion 8 Kernlomeby andlor CwnwlTopography
                                                                                  aW
                                                                                                                                                   I
                                                                                                      I


                                                       I                               Cakulalethe ResidualAstigmatism
                                                                                                      I
                                                                                                      I
                                                                                                                                                   I
                                                       I                             Trial Fil the BesKa Spherical RGPhs
                                                                                                      I


                                                                                                      I
                                                                             I                                               I
                                                       I            NO L ~ F s ~ r Noted
                                                                             h e                    II              Lens Remrre Noted



                                                                                                            I       No ResidualAstigmalisn Nded
                                                                                                                                                       1
                                    I     Good PhmiralA6Pnment Noted             1
                    Prwcribea Fmnt Totic RGP. Lens                                                                         PreJcnae a Spherical RGP. Lens

                                          Poor PhysiologicalAtignmerd Nded


                                                                         GoodkisRderidianConwioll Nofed

                                           Im a Wr PewerEffectB1wicLens
                                             i e


                                           I ~resaibe CrnsJed
                                                    a                     Bawic Lens
                                                                      ~ffed


                  Designimp                Grassed Cylinder EfEeo&Bitoric R.G.P.                                                                            Lenses

I. Follow the "Dedsion Tree for Correding Residual Asbigmatism With RG.P. Lenses", and compare the flattest corneal meridian with the minus
   cylinder axis of the Spherocylinder Overrefraction. I f there is a poor correlation (fifteen degrees, or more), then a Crossed Cylinder Power Effect
   (C.C.E.) Bitoric Lens is indicated.
2. Using a Spherical Power Effect (S.P.E.) BitoricTrial Set, find the best Base Curve Radlus combination for a low toric, with-therule simulation.
3 Over the S.P.E. Trial Lens, perform a Spherocylinder Overrefraction.
 .
4. Provide the lab with the Base Curve Radius selections, the meridian of the flattest Base Curve Radius (This meridian should be the same as the
   flattest corneal meridian.), and the Spherocylinder Overrefraction data.
5. Tell the lab that this lens is a C.C.E. Bitoric. I f the lab says, "huh?" change labs.
6. Order the C.C.E. Lens with an Identification Dot in the meridian of the flattest Base Curve Radius. Verify that the Dot is in the correct meridian by
   comparing its position with the Radiuxope mire line in focus for the flattest Base Curve Radius.
7. Determine the Lens Power I n Air for verification purposes by:
          a. Place the Badc Vertex Power I n Air of the S.P.E. Trial Lens in a trial frame. Align the cylinder axis with the flattest corneal meridian.
          b. Place the vertex corrected Spherocylinder Overrefraction in the trial frame.
          c. Read the resultant at the Lensometer.
          d. The resultant is the Lens Power In Air of the C.C.E. Bitoric R.G.P. tens.

                                                 Verilfying Toaic                              R..G.P.                   Lenses

    Measure the Overall Lens Diameter (O.A.D.)
    Measure the Posterior Optic Zone Diameter (P.O.Z.)
    Measure the Base Curve Radii.
    Measure the Center Thldvless
                                    n
    Read the Back Vertex Powers I Air (B.V.P.)
          o    For Fmnt Toric R.G.P. Len-          The BVP should be as ordered, in power and meridian, when the prism value is in the desired
                                                         ...
               position.
          o For Back To& R.G.P. Lenses The B.V.P. difference should be 1.5 X A of the Base Curve Radii for high index materials, 1.33 X AK
                                                                                    K
               for mid index materials, and 1.25 X AK for low index materials.
         o     Fortllinder PowerEfiiectLenses:The B.V.P. should be equal to the drum readings ordered from the lab.
         o ForS~heriwl        Power Effect Lenses The B.V.P. difference should be equal to the AK of the Base Curve Radii.
    Verify the amount and position of any prism ordered.

                                                                          .
                                                           O 1999,Clarke D Newman. OD. FAA0

				
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Description: Lecture Correcting Astigmatism With RGP