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Spherical Aberration and Eccentricity Factor of Normal Corneas and Corneas That Had Underwent Refractive Surgery Carlos G. Arce, MD Ophthalmologist, Private Eye Clinic, Campinas, SP, Brazil Volunteer Ophthalmologist and Researcher, Ocular Bioengineer and Refractive Surgery Sectors, Institute of Vision, Department of Ophthalmology, Paulista School of Medicine, Federal University of São Paulo, SP, Brazil [email protected] Financial Disclosure: Medical Director–Galilei R&D Consultant, Ziemer Group AG, Port, Switzerland Consultant & Territory Manager for Latin America, Vista Optics Limited, Widnes, UK Consultant, Mark’Ennovy Personalized Care, Madrid, Spain Author does not have financial interest in the commercialization of equipments or IOLs mentioned Myopic LASIK Purpose: To study the spherical aberration (SA) and shape profile of normal corneas and that underwent myopic or hyperopic corneal LASIK. Anterior Є2 Setting: Private Eye Clinic, Campinas, SP, Brazil Posterior Є2 Methods: Total corneal SA and eccentricity (Є2) index were assessed with the Galilei (Ziemer Ophthalmic Systems AG, Port, Switzerland) dual ScheimpflugPlacido integrated system were assessed in 39 normal corneas (24 patients) that underwent myopic or hyperopic LASIK. Preoperative spherical equivalent range was -1.75 to -8.25 D in 29 eyes/19 patients, and +2.0 to +5.25 D in 10 eyes/5 patients, respectively. Spherical Aberration Hyperopic LASIK Anterior Є2 Spherical Aberration Posterior Є2 Results: Normal corneas had SA=+0.24 ±0.07 µm (-0.18 ±0.08 D), anterior Є2=+0.20 ±0.16 and posterior Є2=+0.25 ±0.16. Corneas that underwent myopic LASIK had SA =+0.67 ±0.19 µm (-0.50 ±0.14 D) (P<0.005); anterior Є2 = -1.01 ±0.33 (P<0.0005), and posterior Є2 =+0.39 ±0.18 (P<0.05). Corneas with hyperopic LASIK had SA -0.66 ±0.13 µm (0.40 ±0.11 D) (P<0.005); anterior Є2 = +1.54 ±0.22 (P<0.0005) and posterior Є2 =+0.41 ±0.13 (P<0.05), Normal Cornea Without Refractive Surgery • Normal corneal surface is from sphere (Є2=0) to elliptical prolate (0<Є2<1) • Total corneal SA is positive (µm) or negative (D): SA=+0.24 ±0.07 µm (-0.18 ±0.08 D) • Final total eye SA depends on SA of IOL chosen. • Target Rx for IOL calculation may be plano or little negative Example: Є2 = 0.10 SA = 0.28 μm SA = -0.22 D Cornea with Post-Myopic Refractive Surgery • Anterior surface becomes oblate with negative Є2 • Total corneal SA is high positive (µm) or negative (D): SA=+0.67 ±0.19 µm (-0.50 ±0.14 D) • IOL implanted should not be spherical with positive SA (µm) • Target Rx may be plano or negative. Monovision is better accepted Example: Є2 = -1.44 SA = 0.94 μm SA = -0.72 D Cornea with Post-Hyperopic Refractive Surgery • Anterior surface becomes hyper-prolate with high positive Є2 • Total corneal SA becomes more negative (µm) or positive (D): SA= -0.66 ±0.13 µm (0.40 ±0.11 D) • IOL implanted should not be aspheric hyper-prolate with negative SA (µm) • Target Rx may be plano or little positive. Traditional monovision is less tolerated Example: Є2 = 1.83 SA = -0.81 μm SA = 0.62 D Reasoning for Custom Selection of IOL • Galilei measures the total corneal wave front • Spherical aberration (SA) is linked to contrast sensitivity • SA=0 gives sharpness of vision • Larger SA gives depth of focus (multifocal cornea) • When the cornea becomes more prolate • Q factor and Є2 increase • Positive SA reduces • Around Є2 = 0.55 then SA = 0 • Є2 > 0.60 then SA is already negative • When cornea becomes less prolate or oblate • Q factor and Є2 reduce • Positive SA increases • Total SA of the eye increases with age due to lens changes • Total corneal SA maintains a stable value with age in normal corneas that do not change shape • Total corneal SA becomes less positive or negative in typical keratoconus • Total corneal SA becomes some more positive in typical initial pellucid IOL SA + Total Corneal SA = Total eye SA marginal degeneration • Glasser & Campbell. Vision Res, 1998: 38 (2); 209 • Artal et al. J. Opt. Soc. Am. A. Feb 2002 after cataract extraction • Total corneal SA after myopic refractive surgery is more positive • Flatter and more oblate corneas seem to have larger positive SA value V. Trefoil V. Quatrefoil V. & H. Coma H. Trefoil • Total corneal SA after hyperopic refractive surgery is more negative Spherical Aberration • Steeper and more prolate corneas seem to have larger negative SA value H. Quatrefoil Conclusions SA and eccentricity factor Є2 have an inverse correlation Normal corneas and those that underwent refractive surgery have not the same SA Our results suggest that rational IOL selection and the target refraction expected in IOL calculation may be optimized with preoperative data from total corneal wavefront derived by dual Scheimpflug –Placido tomographic system Spherical IOLs with positive SA seem a good option for eyes that underwent hyperopic refractive surgery or with typical keratoconus. Aspheric IOLs with negative SA seem a worst option In these eyes a plano or little positive target would be ideal and classic monovision would not be recommended Aspheric IOLs with negative SA seem a good option for eyes with normal corneas and that underwent myopic surgery Spherical IOLs are also an option in normal corneas when a small negative refractive target is expected Eyes that underwent myopic LASIK seem to be ideal for classic monovision with myopic residual refraction • Standard Sph (SA = +0.18 μm) central rays focus beyond outer rays • • • PhysIOL (SA = -0.11 μm) AcrySof IQ (SA = -0.20 μm) Tecnis (SA = -0.27 μm) central rays focus in front of outer rays • • • • SofPort AO (SA = 0 μm) Crystalens (SA =0 μm) Rayner (SA = 0 μm) Mediphacos (SA= 0) All rays are focused at same point Modified from Koch et al 2009