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!