Medical Director - R & D Consultant, Ziemer Group AG, Port, SwitzerlandMedical Director - R & D Consultant, Ziemer Group AG, Port, Switzerlandcarlos.arce@ziemergroup.comcarlos.arce@ziemergroup.com

Speaker, Bausch & Lomb do Brasil Speaker, Bausch & Lomb do Brasil Territory Manager for Latin America, Vista Optics Limited, Widnes, UKTerritory Manager for Latin America, Vista Optics Limited, Widnes, UK

Author does not have financial interest in the commercialization of equipments mentionedAuthor does not have financial interest in the commercialization of equipments mentioned

Carlos G. Arce, MDCarlos 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, Paulista School of Medicine, Federal University of São Paulo, Brazil

Purpose: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:Methods:

Concept of Asphericity: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: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 µmMax positive elevation (in the yellow range) = + 15 µmKranemann-Arce index = 10 + 15 = 25 µm

Example (PosteriorSurface): Max negative elevation = -28 µmMax positive elevation = + 30 µmKranemann-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

BFS (at left) and BFTA BFS (at left) and BFTA

(at right) elevation(at right) elevation

maps of anterior (top) maps of anterior (top)

and posterior (bottom) and posterior (bottom)

corneal surfacescorneal surfaces

Case A:Case A: Congruent symmetric asphericity of both surfaces in normal astigmatic cornea Congruent symmetric asphericity of both surfaces in normal astigmatic cornea

Case B:Case B: Incongruent symmetric asphericity of anterior surface and asymmetric asphericity of Incongruent symmetric asphericity of anterior surface and asymmetric asphericity of posterior surface in a cornea with crossed astigmaticposterior surface in a cornea with crossed astigmatic

Case C:Case C: Congruent asymmetric asphericity of both surfaces in normal astigmatic cornea with Congruent asymmetric asphericity of both surfaces in normal astigmatic cornea with asymmetry more related with the flatter axis of astigmatismasymmetry more related with the flatter axis of astigmatism

Case D:Case D: Congruent asymmetric asphericity of both surfaces in a cornea with keratoconus with Congruent asymmetric asphericity of both surfaces in a cornea with keratoconus with asymmetry more related with the steeper axis of astigmatismasymmetry more related with the steeper axis of astigmatism

C

Red line: - Steeper axis of astigmatism-Asymmetric aspheric meridian

Blue line: - Flatter axs of astigmatism- Symmetric aspheric meridian

• Standard (SA = +0.18 μm)

• AcrySof IQ (SA = -0.20 μm)

• Tecnis (SA = -0.27 μm)

• SofPort (SA = 0 μm)

• Rayner (SA = 0 μm)

Custom Selection of IOLCustom Selection of IOL

• 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

central rays

focus beyond

outer rays

central rays

focus in front of

outer rays

All rays are

focused at

same point

Coma = 0.91 D @ 62.7°

Spherical Aberration = 0.29 μm = -0.22 D

Conclusions: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