1. Asieh Ehsaei, PhD
Peripheral Refraction in Myopia

2. The worldwide increase in myopia
49% (Rahi et al., 2010)
53.7% (Mallen et al., 2005)
70% (Lin et al., 1988)
84% (Lin et al., 1999)
35% (Blanco et al., 2008)
26.2% (Wang et al., 1994)
41.6% (Vitale et al., 2009)
82.2% (Wu et al., 2001)
85% (Woo et al., 2004)
87% (He et al., 2009)

3. Why do some eyes go myopic?
 Risk factors
 Near work (Rosenfield and Gilmartin, 1998)
 Education (Saw et al., 2002 & 2004)
 Ethnicity (O'Donoghue et al., 2010)
 Genetics (Hammond et al., 2001)
 Other risk factors (prematurity, diet, light
exposure, season of birth, higher IOP,...)
 Principle structural correlate
 Axial elongation of the vitreous
chamber (Atchison et al., 2004)

4. MRI modeling of the myopic eye
Singh KD, Logan NS & Gilmartin B. Three-dimensional modeling of the human eye based on
magnetic resonance imaging. Invest Ophthalmol Vis Sci 2006; 47: 2272-2279.

5. Peripheral optics of the eye
 Peripheral optics is important in understanding:
 Refractive error development
 Process of emmetropisation
 Supported by animal studies (e.g. Smith et al., 2005 & 2007, Hung et al., 2008)
Peripheral deprivation of visual signals produces central myopia.
Clear Vision
Form Deprived
Form Deprived

6. Central versus peripheral vision
 Because resolution acuity is highest at the fovea and decreases
rapidly with eccentricity, it has been assumed that central vision
dominates refractive development.

7. Peripheral refraction studies
fovea
 Back to 1930’s (Ferree et al., 1931, Ferree, 1932, Ferree & Rand, 1933)
 Predict future myopia based on peripheral refraction (Hoogerheide et
al., 1971):
 Emmetropic pilots with
relative peripheral hyperopia
► Central myopia
 Emmetropic pilots with
relative peripheral myopia
► Remained emmetropic

8. Peripheral refraction studies
fovea
 The emmetropic eye grows axially to eliminate peripheral
hyperopic defocus and produce central myopia.

9. Peripheral refraction in 4 meridians
fovea
 Peripheral refraction measurements in horizontal, vertical and
two oblique meridians out to ±30° (±10° steps)
 30 myopes: (MSE: -5.73 ± 1.80 D, J180: 0.13±0.20 D, J45: 0.05±0.13 D)
 20 emmetropes: (MSE: 0.07 ± 0.34 D, J180: 0.06±0.20 D, J45: 0.02±0.15 D)

10. Peripheral refraction technique
fovea
 Shin-Nippon NVision-K 5001
autorefractometer
 Valid technique compared to wall
fixation (Bland and Altman, 1986)
 Instrumentation:

11. Instrument alignment
fovea

12. Results: MSE
fovea M(D)
b)
SR Eccentricity (degree) IR
M(D)
c)
STR Eccentricity (degree) INR
M(D)
d)
SNR Eccentricity (degree) ITR
M(D)
a)
TR Eccentricity (degree) NR

13. fovea
y = -0.15x2 + 1.30x - 3.16
r² = 0.95
y = -0.16x2 + 1.30x - 3.14
r² = 0.95
-3
-2
-1
0
-30 -20 -10 0 10 20 30
Cyl(D)
TR Eccentricity (degree) NR
Emmetropia Myopia
(a)
y = -0.17x2 + 1.46x - 3.51
r² = 0.95
y = -0.19x2 + 1.51x - 3.50
r² = 0.99
-3
-2
-1
0
-30 -20 -10 0 10 20 30
Cyl(D)
SR Eccentricity (degree) IR
Emmetropia Myopia
(b)
y = -0.15x2 + 1.3x - 3.23
r² = 0.92
y = -0.16x2 + 1.31x - 3.29
r² = 0.97
-3
-2
-1
0
-30 -20 -10 0 10 20 30
Cyl(D)
STR Eccentricity (degree) INR
Emmetropia Myopia
(c)
y = -0.11x2 + 0.88x - 2.13
r² = 0.98
y = -0.17x2 + 1.30x - 3.03
r² = 0.98
-3
-2
-1
0
-30 -20 -10 0 10 20 30
Cyl(D)
SNR Eccentricity (degree) ITR
Emmetropia Myopia
(d)
Results: Cyl power

14. Overall power of refraction (P)
SR
STR
TR
ITR
IR
INR
NR
SNR
 Overall power of refraction
was calculated based on
Thibos et al., (1997)
recommendation:
 The overall power of
refraction decreases with
increasing eccentricity.
Thibos LN, Wheeler W & Horner D. Power vectors: An application of Fourier analysis to the
description and statistical analysis of refractive error. Optom Vision Sci 1997; 74: 367-375.

15. Conclusions
 Our findings show a relative hyperopic shift along the
horizontal, vertical and two oblique meridians for the
myopic group, and a relatively constant refractive profile
for emmetropic eye .
 The relatively peripheral hyperopia in myopia suggests
that the myopic retina has a more prolate/less oblate
shape (longer axial length than equatorial diameter) than
emmetropic and hyperopic eyes.

16. Implication of peripheral refraction
 Traditional Correcting
Lenses:
 As a consequence of eye
shape and/or aspheric
optical surfaces,
“corrected” myopic eyes
often experience
significant hyperopic
defocus across the visual
field.
Image ShellCorrected
Myope

17. A better way to correct myopia?
 Myopia Control Lenses:
 By increasing the effective
curvature of field it would
be possible to correct
central errors and either
correct peripheral errors or
induced peripheral myopic
defocus.
Image Shell
(By bringing the peripheral image
forward)
Optimal
correction?

18. Myopia control studies
 Design of the ophthalmic lenses with the aim of reducing the
progression of myopia in human eyes based on multiple axis
analysis of peripheral refraction.

19. Myopia control studies
 BUT
The amount of hyperopic defocus in the periphery applied in these
studies is based on the average amount reported in peripheral
refraction studies....
Sankaridurg P et al. Decrease in rate of myopia progression with a contact lens designed to
reduce relative peripheral hyperopia. Invest Ophthalmol Vis Sci 2011; 52: 9362-9367.
Novel lenses
Traditional
lenses

20. Impact on visual performance
 Peripheral refraction should be considered when assessing visual
performance?

21. Thanks
Collaboration with
 Dr Catharine Chisholm
 Dr Ian Pacey
 Dr Edward Mallen