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Supplementary Material
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APPENDIX
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Example 1. In this 44 year old patient with WTR astigmatism the following
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astigmatisms and toric IOL orientations were recorded:
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Preoperative Keratron Keratometric astigmatism = 1.91 D @ 80⁰, preoperative
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Pentacam Total corneal astigmatism = 1.70 D @ 72⁰, intended SICA = 0.2 D @
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90⁰, observed SICA = 0.0 D @ 90⁰, IOL astigmatism from the Alcon web
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calculator = 2.06 D @ 171⁰, intended IOL minus meridian (markings) = 81⁰,
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observed IOL minus meridian (markings) = 77⁰, ACD-adjusted toric power = 2.01
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D, and postoperative Refractive Astigmatism = 1.0 @ 180⁰, For the sake of
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simplicity, the two polar values characterizing the net cylinder are separated by a
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slash in the general format KP(Φ)/ KP(Φ+45)
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Model 1.
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Keratometric astigmatism and SICA were transformed to polar values with the
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fixed reference meridian at zero degrees (equations 3-4), and converted back to net
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astigmatisms with equations ( 5-6).
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Keratometric astigmatism = 1.91*cos(2*(80))/ 1.91*sin(2*(80)) = -1.79/0.65
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SICA = -0.2 D/0
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Target corneal astigmatism = -1.79/0.65 + -0.2/0 = -1.99/0.65. These polar
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values were back calculated to the net cylinder = 2.1 D @ 81⁰. This reference
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meridian Φ = 81⁰ was used with equations 1-2 in the following calculations,
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yielding the polar values = 2.1/0 for the. Target corneal astigmatism
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The toric implant was inserted with its minus power meridian along 81⁰ and the
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plus power meridian along 171⁰; IOL Astigmatism = -2.06/0.
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Target refractive astigmatism = (2.1/0) + (-2.06/0) = 0.04/0.
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Refractive astigmatism = 1.0*cos(2*(180-81))/ 1.0*sin(2*(180-81)) = - 0.95/-
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0,31
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ERA = (-0,95/-0.31) – (0.04/0) = (-0.99/-031). In this case there was an
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overcorrection of 0.99 D and an unintended clockwise rotation of 0.31 D.
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Model 2
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Total corneal astigmatism = 1.7*cos(2*(72)/ 1.7*sin(2*(72)) = -1.39/0.98
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Target corneal astigmatism = (-1.39/0.98) + (-0.2/0) = -1.59/0.98. These polar
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values were back calculated to the net cylinder = 1.87 D @ 74⁰. The reference
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meridian Φ = 74⁰ was used with equations 1-2 to characterize the Target corneal
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astigmatism as 1.87/0.
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IOL Astigmatism = 2.06*cos(2*(171-74))/ 2.06*sin(2*(171-74)) = -2.0/-0.49
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Target refractive astigmatism = (1.87/0) + (-2.0/-0.49) = -0.13/-0.49.
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Refractive astigmatism = 1.0*cos(2*(180-74))/ 1.0*sin(2*(180-74)) = - 0.85/-
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0,52
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ERA = (-0,85/-0.52 – (-0.13/-0.49) = (-0.72/-0.04). With the Pentacam
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measurements there was an overcorrection of 0.72 D and small 0.04 D clockwise
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torsion.
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Model 3
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As the observed SICA = zero, the Target corneal astigmatism = Total corneal
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astigmatism =1.70 D @ 72⁰. The reference meridian Φ = 72⁰ was used with
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equations 1-2 to characterize the Target corneal astigmatism as 1.70/0.
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IOL Astigmatism = 2.06*cos(2*(171-72))/ 2.06*sin(2*(171-72)) = -1.97/-0.61
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Target refractive astigmatism = (1.70./0) + (-1.97/-0.61) = -0.27/-0.61.
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Refractive astigmatism = 1.0*cos(2*(180-72))/ 1.0*sin(2*(180-72)) = - 0.82/-
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0,58
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ERA = (-0,82/-0.58) – (-0.27/-0.61) = (-0.55/0.03). This model disclosed an
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overcorrection of 0.55 D and 0.03 D counter- clockwise rotation.
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Model 4
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Target corneal astigmatism and Refractive astigmatism as in model 3.
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IOL Astigmatism = 2.06*cos(2*(167-72))/ 2.06*sin(2*(167-72)) = -2.03/-0.33
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Target refractive astigmatism = (1.70./0) + (-2.03/-0.33) = -0.33/-0.33
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ERA = (-0,82/-0.58) – (-0.33/-0.33) = (-0.48/0.25).
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Model 5
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Target corneal astigmatism and Refractive astigmatism as in model 3 and 4.
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IOL Astigmatism = 2.01*cos(2*(167-72))/ 2.01*sin(2*(167-72)) = -1.99/-0.32
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Target refractive astigmatism = (1.70./0) + (-1.99/-0.32) = -0.29/-0.32
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ERA = (-0,82/-0.58) – (-0.29/-0.32) = (-0.53/0.25).
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