ID 737882
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
(Email : amitguptaeye@gmail.com)
The authors have no financial interest in the subject matter of this poster
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.
Purpose
Correlation Of Corneal Contour With Higher Order Ocular
Aberrations (HOA) In Indian Eyes
Patients and Methods
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)
Methods
Inclusion criteria
•
•
•
Age 18-40 years.
Best corrected visual acuity
(BCVA)of 6/9 or better.
Normal ocular examination,
emmetropia or Myopia < 6 D.
Exclusion criteria
• Corneal degenerations and
dystrophies
• Corneal scarring after
infective diseases
• Dry eye patients
• Any Other ocular pathology
Patient Workup:
•
Best Corrected Visual Acuity,
•
Slit Lamp Biomicroscopy,
•
Refraction,
•
Schirmer’s test,
•
Aberrometry: Optical Path
Difference (OPD) Scanning
done after dilating with 0.8%
tropicamide and 5%
phenylephrine using ARK10000 OPD scan (NIDEK
Technologies, Japan)
Aberrometric Data Interpretation and Analysis
Step 1: OPD Scan Analysis
Step 2: Zernike polynomials at 6mm transformed into
•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 Z60),
•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
Thibos et al. Standards for reporting the optical aberrations of eyes. J Refract Surg
2002; 18:S652–S660
Aberrometric Analysis by
OPD Scan
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
Results
Keratometric values in emmetropic
and myopic group
Patients characteristics in
emmetropic and myopic group
Group I
Group II
Group I (Emmetropic
Group II (Myopic
(Emmetropic
(Myopic groups)
group)
groups)
K1 (diopter)
43.93 + 1.73
44.33 + 2.84
K2 (diopter)
43.25 + 1.61
43.65 + 1.53
Average
43.6 + 1.66
44.06 + 1.57
group)
Male
147
90
Female
103
160
Mean age (Years)
28.40 + 7.4
27.82 + 5.49
(diopter)
Number of eyes in different subgroups
Prolate (Q < 0) Oblate (Q > 0)
Emmetropia
(no of eyes)
Myopia
(no of eyes)
420
80
442
58
Comparison of wavefront error and keratometry value in emmetropic eyes
keratometry value in Emmetropic eyes
Group
Keratometry value
Number of eyes
A
< 44 diopter
317
B
44-46 diopter
141
C
> 46 diopter
42
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 myopic eyes
keratometry value in Myopic eyes
Group
Keratometry value
Number of eyes
A
< 44 diopter
230
B
44-46 diopter
221
C
> 46 diopter
49
Myopic group : Higher keratometry values (>46 D) were associated with significantly higher
amount of trefoil
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
We found most common Asphericity coefficient (Q) value is between 0 to -1 (prolate ellipse) in
both the groups
Distribution of Q value in emmetropic and myopic eyes
(prolate versus oblate cornea)
Emmetropia
Prolate (Q < 0)
Oblate (Q > 0)
420
80
442
58
(number of eyes)
Myopia
(number of eyes)
Significance of wavefront aberrations with
Corneal Asphericity in emmetropic eyes
Prolate
mm)
Total
aberration
Total HOA
(mean
wavefront 0.95 + 0.56
+SD Oblate
mm)
(mean + SD Significance
( p-value )
1.48 + 1.81
0.137
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
The mean RMS value of total HOAs, coma, and spherical aberration were
significantly higher in oblate then prolate corneas
Significant association of total HOA, coma, spherical aberration with Oblate
cornea in emmetropic eyes
Significance of wavefront aberrations with
Corneal Asphericity in myopic eyes
Prolate cornea (mean Oblate cornea (mean Significance
+SD mm)
+ SD mm)
( p -value )
Total
aberration
Total HOA
wavefront 4.60 + 2.76
4.59 + 2.37
0.91
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
The mean RMS value of total HOAs and spherical aberration were significantly
higher in oblate then prolate corneas
Significant association of total HOA, spherical aberration with Oblate cornea in
myopic eyes
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
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