Correlation Of Corneal Contour With Higher Order Ocular Aberrations (HOA) In Indian

Eyes

Manish Chaudhary MSAmit Gupta MS

Advanced Eye Centre, Postgraduate Institute of Medical Education &

Research, Chandigarh

India(Email : amitguptaeye@gmail.com)

The authors have no financial interest in the subject matter of this posterThe authors have no financial interest in the subject matter of this poster

ID 737882

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;23:505-514.

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

0+0.25 D) Group II : 500 myopic eyes (refractive error > -

0.25 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:Patient Workup:

• Best Corrected Visual Best Corrected Visual

Acuity, Acuity,

• Slit Lamp Biomicroscopy, Slit Lamp Biomicroscopy,

• Refraction, Refraction,

• Schirmer’s test, Schirmer’s test,

• Aberrometry:Aberrometry: Optical Path Optical Path

Difference (OPD) Scanning Difference (OPD) Scanning

done after dilating with done after dilating with

0.8% tropicamide and 5% 0.8% tropicamide and 5%

phenylephrine using ARK-phenylephrine using ARK-

10000 OPD scan (NIDEK 10000 OPD scan (NIDEK

Technologies, Japan)Technologies, Japan)

Inclusion criteria

• Age 18-40 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 Z4 0 and Z6

0),

•RMS of coma (square root of the sum of the squared coefficients of Z3

-1, Z31, Z5

-1,and Z51),

• RMS of trefoil (square root of the sum of the squared coefficients of Z3

-3, Z33, Z5

-3,and Z53

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)

Male 147147 9090

Female 103103 160160

Mean age

(Years)

28.40 28.40 ++ 7.4 7.4 27.82 27.82 + + 5.49 5.49

Group I (Emmetropic

group)

Group II

(Myopic groups)

K1 (diopter) 43.93 + 1.73 44.33 + 2.84

K2 (diopter) 43.25 + 1.61 43.65 + 1.53

Average

(diopter)

43.6 + 1.66 44.06 + 1.57

Prolate (Q < 0)

Oblate (Q > 0)

Emmetropia (no of eyes)

420 80

Myopia

(no of eyes)442 58

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

Group Keratometry value Number of eyes

A < 44 diopter 317

B 44-46 diopter 141

C > 46 diopter 42

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

Group Keratometry value Number of eyes

A < 44 diopter 230

B 44-46 diopter 221

C > 46 diopter 49

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)420 80

Myopia

(number of eyes)442 58

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

0.95 + 0.56 1.48 + 1.81 0.137

Total HOA 0.321 + 0.16 0.37 + 0.14 0.001

2nd order 0.52 + 0.57 0.65 + 0.94 0.686

3rd order 0.14 + 0.09 0.15 + 0.08 0.242

4th order 0.054 + 0.04 0.066+ 0.054 0.078

5th order 0.026 + 0.017 0.027 + 0.025 0.233

6th order 0.0113 + 0.0116 0.012 + 0.016 0.831

Coma 0.082 + 0.053 0.093 + 0.057 0.034

Spherical aberration 0.096 + 0.080 0.125 + 0.107 0.042

Trefoil 0.118 + 0.084 0.116 + 0.078 0.96

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

4.60 + 2.76 4.59 + 2.37 0.91

Total HOA 0.49 + 0.46 0.49 + 0.33 0.017

2nd order 2.45 + 1.58 2.03 + 1.38 0.08

3rd order 0.21 + 0.20 0.19 + 0.11 0.163

4th order 0.08 + 0.10 0.09 + 0.08 0.058

5th order 0.038 + 0.046 0.032 + 0.023 0.74

6th order 0.023 + 0.033 0.023 + 0.033 0.1

Coma 0.12 + 0.153 0.11+ 0.07 0.227

Spherical aberration 0.15 + 0.20 0.17 + 0.18 0.005

Trefoil 0.16 + 0.16 0.15 + 0.10 0.58

Emmetropic eyes • Higher keratometric value > 46 diopter was associated with

significantly higher value total wavefront aberration, total HOAs, 3rd order, 5th 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