Correlation Of Corneal Contour With Higher Order Ocular Aberrations (HOA) In Indian Eyes Manish Chaudhary MS Amit Gupta MS Advanced Eye Centre, Postgraduate Institute of Medical Education & Research, Chandigarh India ( The authors have no financial interest in the subject matter of this poster ID

Role of Corneal Contour The anterior corneal surface is the major refractive component of the human eye and major determinant in quality of optical image Ideally, cornea must have an optical zone consisting of an elliptical surface with an adequate shape factor (Q factor or asphericity) to minimize curvature induced ocular aberrations and optimal image formation. Calossi A. Corneal Asphericity and Spherical Aberration. J Refract Surg 2007;23: Limited literature exists correlating corneal asphericity with ocular aberrations. To the best of our knowledge, this is the first study correlating Higher order ocular aberrations with asphericity of corneal contour.

Study Design: An observational cross sectional prospective study Study Population  Group I : 500 emmetropic eyes (refractive error D)  Group II : 500 myopic eyes (refractive error > to < -6.0 diopters) Purpose Patients and Methods Correlation Of Corneal Contour With Higher Order Ocular Aberrations (HOA) In Indian Eyes

Methods Exclusion criteria Corneal degenerations and dystrophies Corneal scarring after infective diseases Dry eye patients Any Other ocular pathology Patient Workup: Best Corrected Visual Acuity, Best Corrected Visual Acuity, Slit Lamp Biomicroscopy, Slit Lamp Biomicroscopy, Refraction, Refraction, Schirmer’s test, Schirmer’s test, Aberrometry: Optical Path Difference (OPD) Scanning done after dilating with 0.8% tropicamide and 5% phenylephrine using ARK OPD scan (NIDEK Technologies, Japan) Aberrometry: Optical Path Difference (OPD) Scanning done after dilating with 0.8% tropicamide and 5% phenylephrine using ARK OPD scan (NIDEK Technologies, Japan) Inclusion criteria Age years. Best corrected visual acuity (BCVA)of 6/9 or better. Normal ocular examination, emmetropia or Myopia < 6 D.

Aberrometric Analysis by OPD Scan Thibos et al. Standards for reporting the optical aberrations of eyes. J Refract Surg 2002; 18:S652–S660 Aberrometric Data Interpretation and Analysis Step 1: OPD Scan Analysis Step 2: Zernike polynomials at 6mm transformed into Step 3: Statistical Analysis  ‘t-test’ (for normal Distribution) & for skewed data Mann- Whitney test.  Relationship between different variables using Spearman and Pearson correlation coefficient Root mean square (RMS) of higher order aberration (HOA) from the 3rd to 6th orders RMS of the spherical aberration (SA) (square root of the sum of the squared coefficients of Z 4 0 and Z 6 0 ), RMS of coma (square root of the sum of the squared coefficients of Z 3 -1, Z 3 1, Z 5 -1,and Z 5 1 ), RMS of trefoil (square root of the sum of the squared coefficients of Z 3 -3, Z 3 3, Z 5 -3,and Z 5 3

Results Patients characteristics in emmetropic and myopic group Keratometric values in emmetropic and myopic group Number of eyes in different subgroups Group I (Emmetropic group) Group II (Myopic groups) Male14790 Female Mean age (Years) Group I (Emmetropic group) Group II (Myopic groups) K1 (diopter) K2 (diopter) Average (diopter) Prolate (Q < 0)Oblate (Q > 0) Emmetropia (no of eyes) Myopia (no of eyes) 44258

Emmetropic group : Emmetropic group : Higher keratometry values (>46 D) were associated with significantly higher amount of total wavefront aberration, total higher order aberrations, 3rd, 5th order as well as trefoil Comparison of wavefront error and keratometry value in emmetropic eyes GroupKeratometry valueNumber of eyes A< 44 diopter317 B44-46 diopter141 C> 46 diopter42 keratometry value in Emmetropic eyes

Myopic group : Higher keratometry values (>46 D) were associated with significantly higher amount of trefoil Comparison of wavefront error and keratometry value in myopic eyes GroupKeratometry valueNumber of eyes A< 44 diopter230 B44-46 diopter221 C> 46 diopter49 keratometry value in Myopic eyes

Figure : Distribution of asphericity coefficient (Q) in emmetropic and myopic eyes Figure : Comparison of asphericity coefficient (Q) value along steep, flat axis and average in emmetropic versus myopic eyes Distribution of Q value in emmetropic and myopic eyes (prolate versus oblate cornea) We found most common Asphericity coefficient (Q) value is between 0 to -1 (prolate ellipse) in both the groups Prolate (Q < 0)Oblate (Q > 0) Emmetropia (number of eyes) Myopia (number of eyes) 44258

Significance of wavefront aberrations with Corneal Asphericity in emmetropic eyes Significant association of total HOA, coma, spherical aberration with Oblate cornea in emmetropic eyes The mean RMS value of total HOAs, coma, and spherical aberration were significantly higher in oblate then prolate corneas Prolate (mean +SD mm) Oblate (mean + SD mm) Significance ( p-value ) Total wavefront aberration Total HOA nd order rd order th order th order th order Coma Spherical aberration Trefoil

Significance of wavefront aberrations with Corneal Asphericity in myopic eyes Significant association of total HOA, spherical aberration with Oblate cornea in myopic eyes The mean RMS value of total HOAs and spherical aberration were significantly higher in oblate then prolate corneas Prolate cornea (mean +SD mm) Oblate cornea (mean + SD mm) Significance ( p -value ) Total wavefront aberration Total HOA nd order rd order th order th order th order Coma Spherical aberration Trefoil

Emmetropic eyes Higher keratometric value > 46 diopter was associated with significantly higher value total wavefront aberration, total HOAs, 3 rd order, 5 th order as well as trefoil We found Oblate corneas (Q > 0) were associated with higher total HOAs, coma and spherical aberration Myopic eyes Higher keratometric value > 46 diopter was associated with significantly higher value of trefoil Oblate corneas (Q > 0) were associated with higher total HOAs and spherical aberration Our study highlights the association of corneal asphericity with HOA Higher keratometric (>46 D) and oblate cornea were associated with significantly higher amount of HOAs