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Carlos G. Arce, MD

Qualitative and Quantitative Analysis of Aspheric Symmetry and Asymmetry on Corneal Surfaces . Associate Researcher and Ophthalmologist Ocular Bioengineering & Refractive Surgery Sectors, Institute of Vision, Department of Ophthalmology,

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Carlos G. Arce, MD

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  1. Qualitative and Quantitative Analysis of Aspheric Symmetry and Asymmetry on Corneal Surfaces Associate Researcher and Ophthalmologist Ocular Bioengineering & Refractive Surgery Sectors, Institute of Vision, Department of Ophthalmology, Paulista School of Medicine, Federal University of São Paulo, Brazil Carlos G. Arce, MD Medical Director - R & D Consultant, Ziemer Group AG, Port, Switzerland carlos.arce@ziemergroup.com Speaker, Bausch & Lomb do Brasil Territory Manager for Latin America, Vista Optics Limited, Widnes, UK Author does not have financial interest in the commercialization of equipments mentioned

  2. Purpose: • To describe a method how aspheric symmetry or asymmetry of corneal surfaces may be assessed and the patterns found in normal corneas and with keratoconus • Qualitative:Galilei best fit toric aspheric (BFTA) elevation maps with a custom ANSI style 5 μm color scale were used to evaluate the aspheric symmetry or asymmetry of both corneal surfaces • Quantitatively 1:Kraneman-Arce index was defined • Quantitatively 2:The coma found with the Galilei corneal wave front report was correlated with the patterns found using the BFTA elevation maps Methods:

  3. Concept of Asphericity: • All corneas have symmetric or asymmetric toric aspheric surfaces. • Symmetric aspheric meridians have uniform change of curvature from the center to the periphery in both hemimeridians • Symmetric aspheric meridians fits well the BFTA referential surface and therefore will have elevation values close to zero with points within the green range (± 5 µm) • Asymmetric aspheric meridians have different change of curvature from the center to the periphery in each hemimeridian • When curvature has a slower progression rate the elevation values are negative and therefore points are within the blue range (≤ -10 µm) • When curvature has a faster progression rate the elevation values are positive and therefore points are within the yellow range (≥ +10 µm)

  4. Concept of Asphericity: • Kranemann-Arce index: Designed to quantify the asymmetry of asphericity of a corneal surface • K-A Index is the total difference between the maximum negative BFTA elevation and maximum positive BFTA elevation (without considering mathematic sign) within central 6-mm-diameter data zone • Example (Anterior Surface): • Max negative elevation (in the blue range) = -10 µm • Max positive elevation (in the yellow range) = + 15 µm • Kranemann-Arce index = 10 + 15 = 25 µm • Example (PosteriorSurface): • Max negative elevation = -28 µm • Max positive elevation = + 30 µm • Kranemann-Arce index = 28 + 30 = 58 µm • Symmetric aspheric meridian: Both hemimeridians within the green range in the 120° to 300° meridian (blue line) • Asymmetric asphericity: Hemimeridians with blue or yellow in the 20° to 200° meridian (red line) • In this case both surfaces had congruent symmetry and asymmetry of asphericity

  5. Case A: Congruent symmetric asphericity of both surfaces in normal astigmatic cornea Case B: Incongruent symmetric asphericity of anterior surface and asymmetric asphericity of posterior surface in a cornea with crossed astigmatic Case C: Congruent asymmetric asphericity of both surfaces in normal astigmatic cornea with asymmetry more related with the flatter axis of astigmatism Case D: Congruent asymmetric asphericity of both surfaces in a cornea with keratoconus with asymmetry more related with the steeper axis of astigmatism BFS (at left) and BFTA (at right) elevation maps of anterior (top) and posterior (bottom) corneal surfaces • Red line: • - Steeper axis of astigmatism • Asymmetric aspheric meridian • Blue line: • - Flatter axs of astigmatism • - Symmetric aspheric meridian C

  6. Custom Selection of IOL Coma = 0.91 D @ 62.7° • Standard (SA = +0.18 μm) • AcrySof IQ (SA = -0.20 μm) • Tecnis (SA = -0.27 μm) • SofPort (SA = 0 μm) • Rayner (SA = 0 μm) Spherical Aberration = 0.29 μm = -0.22 D central rays focus beyond outer rays central rays focus in front of outer rays • Galilei measures the total corneal wave front from • both surfaces • Spherical aberration is linked to contrast sensitivity • Coma is linked to aspheric asymmetry and • keratoconus progression • Hypothesis: Symmetry or asymmetry of aspheric corneal • surfaces may be related with satisfaction or visual symptoms • and complains after implantation of IOLs with symmetric • aspheric surfaces All rays are focused at same point

  7. Conclusions: • Normal corneas and with keratoconus have a variety of patterns of BFTA elevation maps. • Aspheric asymmetry of corneal surfaces is easy recognized by using the BFTA elevation maps. • Aspheric symmetry was represented by a more green map and asymmetry was recognized by blue and yellow zones usually in the same meridian but opposite side. • Aspheric asymmetry of anterior surface seems to correlate with the amount of corneal coma especially when asymmetric (irregular) astigmatism was present. • Normal corneas had aspheric symmetry of both corneal surfaces, asymmetry of only one of them, or asymmetry on both. • The axis of the aspheric asymmetry may fit the flatter axis of astigmatism, the steeper axis of astigmatism or none of them. • The aspheric asymmetry of both surfaces may be oriented in the same or in different axis. • Corneas with keratoconus use to have congruent asymmetry of both surfaces at the same axis. • The relation of these corneal surface shapes and visual symptoms after multiphocal IOL implantatio is under study

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