Eyeworld Supplements

EW MAY 2017 – Sunday – Supported by Alcon A Novartis Division

This is a supplement to EyeWorld Magazine.

Issue link: https://supplements.eyeworld.org/i/824595

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After entering the subjective refraction and other re- quired information, the ablation profile is displayed. Treatment Planning Pearls: The parameters for treat- ment planning include the following: • The line "Clinical Refraction" displays the entered subjec- tive refraction Vertex Distance (VD). • The line "Measured Refraction" is the refraction calcu- lated by the Contoura Vision algorithm for the chosen optical zone and entered VD. • The line "Modified Refraction" is the correction for sphere and cylinder (selectable in 0.01-D steps) to be applied to higher-order aberrations (HoAs). • The optical zone is adjustable in 0.50-mm steps. • The transition zone is adjustable in 0.25-mm steps. The ablation profile display assists the surgeon in pre- dicting the residual stroma after ablation by selecting the flap thickness. Setting the sphere and cylinder (at the modified col- umn) to Plano refraction will expose the ablation profile addressing all corneal irregularities. Please see Important Product Information about the products in this supplement on pages 7–8. by Sissimos Lemonis Getting the most out of the Vario algorithm 3 The ablation algorithm is based on Zernike polynomi- als and uses the WaveLight proprietary correction algo- rithm to compensate for loss of the ablation efficiency towards the periphery. This ablation efficiency correction algorithm is applied for all Zernike polynomials and is based on the preoperative corneal curvature and to the corneal asphericity. This customized addition/reduction of laser energy to compensate for efficiency losses related to the angle of incidence (for every position of the cor- nea based on the individual preoperative curvature and asphericity) would qualify the topography-guided ablation as a custom treatment, more so than wavefront-guided ablations that don't consider the true preoperative corne- al curvature and asphericity. The necessary ablation to balance irregularities is calculated automatically and consists of flattening (visi- ble as ablation within the optical zone) and/or steepen- ing (shown as ablation out of the optical zone, similar to hyperopic ablation profiles) elements. All known customized ablation profiles efficiently correcting HoA will affect sphere and cylinder. The effect to sphere and cylinder will depend on the shape of the related aberration. The following figure demonstrates the effect of spherical aberration on the corrected sphere. In this example, we are demonstrating the C12 value ampli- tude and compensate the additional flattening/steepening caused by C12 with spherical correction (c4) (while sphere and cylinder both have been set to Plano refraction pre- viously). In doing so, the resulting ablation profile is as- sumed to be sphere correction neutral. To estimate the amount of spherical compensation needed to neutralize the applied ablation profile, the C4 value is brought close to the C12 value (Zernike button).

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