Qualitative and Quantitative Analysis of Aspheric Symmetry and Asymmetry on Corneal Surfaces Carlos G. Arce, MD 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 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

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:

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)

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

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

Custom Selection of IOL Spherical Aberration = 0.29 μm = -0.22 D 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

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