pre- & post-operative evaluation: correcting the right...
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Astigmatism CorrectionPre- & Post-operative Evaluation: Correcting the Right Amount and
AxisJack T. Holladay, MD, MSEE, FACS
Clinical Professor of OphthalmologyBaylor College of Medicine
• I have the following financial interests or relationships to disclose:
• Consulting Fee: • Abbott Medical Optics• AcuFocus• Alcon Laboratories, Inc.• Carl Zeiss Meditec• Oculus• Visionmetrics• WaveTec Vision Systems, Inc.
Financial Disclosure
60% > 0.50 D of Astig
34% > 1.00 D of Astig
Myths• Never flip axis of Residual
astig only true if glasses –MINIMIZE!
• A little WTR or ATR is good for improving depth of field … NO!
• Toricity of IOL is always 1.46 X the Corneal Astig … No!
Truths• Amount of Toricity in IOL w
Lower Power & Deeper ELP• ATR is usually undercorrected
even w EXACT CALCULATOR• MINIMUM RESIDUAL ASTIG is
ALWAYS the BEST OUTCOME
Always Topography/Tomography if
Correcting Astig• To determine if REGULAR and
does not change radially• Tomography can confirm if
posterior astig is WTR (~ 0.22D)
Never Perfect Bow Tie43.5 @ 105 & 41.2 @ 15
ASIG = +2.3 @ 10544.8 @ 96 & 40.6 @ 6
ASIG = +4.2 @ 96
Astigmatism Measurementfor a 44 D Cornea
• Manual Keratometer• 3.2 mm Diameter
• IOL Master Keratometer• 2.5 mm Diameter
• LenStar Keratometer• 2.35 & 1.65 mm Diameters (Average 2.0 mm Diameter)
Astigmatism Measurementfor a 44 D Cornea
• Manual Keratometer• 44.00 D
• IOL Master Keratometer• 44.30 D
• LenStar Keratometer• 44.30 D
Human Cornea is ProlateAverage Q-value = -0.26Diff Diameters = Diff K’s
3.2 mm44.0 D2.5 mm44.3 D2.0 mm44.5 D44.6 D
Manual Keratometer Measures 44.0 DCauses Optical A-Constant to be
~ 0.3 D Higher than Manual Keratometry
Pre Op Astig Measurements
J Cataract Refract Surg 2012; 38:2080–2087
Pre Op Astig Measurements• If Topography, Keratometry or
Sagittal Front Surf Tomography• WTR – SUBTRACT 0.37 D• ATR -- ADD 0.37 D
• If Tomography w Net or EKR• No adjustment for Post Cornea
(but) … IOL dec, tilt or drift.
Holladay Report Equivalent K-Reading
EKR or Net Astig – No Adj
Holladay JT, Hill WE, Steinmueller A: Corneal Power Measurements Using Scheimpflug Imaging in Eyes With Prior Corneal Refractive Surgery. J Refrac Surg. 2009;25:862-868.
Toric IOL’sSteep K calc yields 24.1 DFlat K calc yields 27.3 DIdeal Toricity is 3.2 D (27.3 – 24.1)SEQ = 25.7 D [(27.3 +24.1)/2]Ratio of IOL to Corneal Toricity is
NOT A CONSTANT (1.46)Always choose toricity to undercorrectcorneal astigmatism – WRONG!LEAVE MIN RESIDUAL CYL!
A-constant—> 116.346 117.203 118.059 118.916 119.773 120.630Surgeon Factor—> 0.287 0.772 1.257 1.742 2.227 2.713
ELP—> 4.000 4.500 5.000 5.500 6.000 6.500IOL POWER
10 1.359 1.424 1.494 1.571 1.654 1.74522 1.277 1.330 1.387 1.450 1.519 1.59534 1.198 1.239 1.284 1.334 1.390 1.45246 1.121 1.151 1.185 1.223 1.267 1.316
Effective Lens Position (ELP)
Resulting Ratio of IOL Toricity to 2 D of Corneal Astigmatism
TABLE 1
A-constant(D) —> 116.346 117.203 118.059 118.916 119.773 120.630Surgeon Factor(mm) —> 0.287 0.772 1.257 1.742 2.227 2.713
ELP(mm) —> 4.000 4.500 5.000 5.500 6.000 6.500IOL POWER
10 2.718 2.848 2.988 3.141 3.308 3.49022 2.554 2.659 2.774 2.900 3.038 3.19034 2.396 2.477 2.568 2.668 2.780 2.90446 2.242 2.302 2.369 2.446 2.533 2.631
Effective Lens Position (ELP)
Required IOL Toricity for 2 D of Corneal Astigmatism
TABLE 2
Ratio and Power of IOL Cylinder to 2 D Corneal Cylinder
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Design & Optimize
Toric Optimization
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Dioptric Error vs. Angular Errorfor a 1.00 D of astigmatismAngle Error ( ) Dioptric Error (D)
Dioptric Error = 2 * Cyl * sin (angular error)
% Error0° 0.00 0%
15° 0.52 52%30° 1.00 100%45° 1.41 141%60° 1.73 173%75° 1.93 193%90° 2.00 200%
Post Op Toric SurpriseTwo methods for Back Calculation – should always do both!
Method 1: 1) Post Op Refraction2) Post Op Ks
Method 2:1) Post Op Refraction2) Observed IOL Meridian (0° - 180°)
PREOP 6 D Toric IOLLEFT
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PREOP 6 D Toric IOL -- ODLEFT
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PREOP 6 D Toric IOL -- OSLEFT
Conclusions – Toric IOL• Always review at Topography/Tomography• Use EXACT Forward TORIC CALC to avoid
unnecessary errors for low & high power IOLs
• Keratometry: + 0.37 D to ATR, -0.37 D WTR• DO NOT adjust Ks with EKR or Net Astig• Use EXACT Post Op Back Toric Calc with
Post Op Refraction and both methods 1)Post Op Ks & 2) IOL Axis to determine Ideal Rotation for MIN Residual Astig
12/23/2013 JTH 27
And that’s the point! !Thank You!