peripheral refraction in myopia
TRANSCRIPT
Asieh Ehsaei, PhD
Peripheral Refraction in Myopia
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)
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)
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.
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
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.
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
Peripheral refraction studies
fovea
The emmetropic eye grows axially to eliminate peripheral hyperopic defocus and produce central myopia.
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)
Peripheral refraction technique
fovea
Shin-Nippon NVision-K 5001 autorefractometer
Valid technique compared to wall fixation (Bland and Altman, 1986)
Instrumentation:
Instrument alignment
fovea
Results: MSE
fovea
y = 0.03x2 - 0.06x - 0.75r² = 0.70
y = 0.21x2 - 1.56x - 2.94r² = 0.97
-6.5
-5.5
-4.5
-3.5
-2.5
-1.5
-0.5
0.5
-30 -20 -10 0 10 20 30
SR Eccentricity (degree) IR
(b)
M (D
)
y = 0.01x2 - 0.04x - 0.43r² = 0.84
y = 0.21x2 - 1.67x - 2.11r² = 0.99
-6.5-5.5-4.5-3.5-2.5-1.5-0.50.5
-30 -20 -10 0 10 20 30
M (D
)
TR Eccentricity (degree) NR
Emmetropia Myopia(a)
b)
SR Eccentricity (degree) IR
y = 0.01x2 + 0.03x - 0.75r² = 0.88
y = 0.18x2 - 1.41x - 3.13r² = 0.96
-6.5
-5.5
-4.5
-3.5
-2.5
-1.5
-0.5
0.5
-30 -20 -10 0 10 20 30
STR Eccentricity (degree) INR
c)
M (D
)
y = 0.01x2 - 0.04x - 0.43r² = 0.84
y = 0.21x2 - 1.67x - 2.11r² = 0.99
-6.5-5.5-4.5-3.5-2.5-1.5-0.50.5
-30 -20 -10 0 10 20 30
M (D
)
TR Eccentricity (degree) NR
Emmetropia Myopia(a)
c)
STR Eccentricity (degree) INR
y = 0.03x2 - 0.30x + 0.22r² = 0.66
y = 0.20x2 - 1.67x - 2.41r² = 0.98
-6.5
-5.5
-4.5
-3.5
-2.5
-1.5
-0.5
0.5
-30 -20 -10 0 10 20 30
SNR Eccentricity (degree) ITR
d)
M (D
)
y = 0.01x2 - 0.04x - 0.43r² = 0.84
y = 0.21x2 - 1.67x - 2.11r² = 0.99
-6.5-5.5-4.5-3.5-2.5-1.5-0.50.5
-30 -20 -10 0 10 20 30
M (D
)
TR Eccentricity (degree) NR
Emmetropia Myopia(a)
d)
SNR Eccentricity (degree) ITR
M (D
)
y = 0.05x2 - 0.33x + 0.14r² = 0.94
y = 0.23x2 - 1.86x - 2.13r² = 0.99
-6.5
-5.5
-4.5
-3.5
-2.5
-1.5
-0.5
0.5
-30 -20 -10 0 10 20 30
TR Eccentricity (degree) NR
(a)
y = 0.01x2 - 0.04x - 0.43r² = 0.84
y = 0.21x2 - 1.67x - 2.11r² = 0.99
-6.5-5.5-4.5-3.5-2.5-1.5-0.50.5
-30 -20 -10 0 10 20 30
M (D
)
TR Eccentricity (degree) NR
Emmetropia Myopia(a)
a)
TR Eccentricity (degree) NR
fovea
y = -0.15x2 + 1.30x - 3.16r² = 0.95
y = -0.16x2 + 1.30x - 3.14r² = 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 - 3.51r² = 0.95
y = -0.19x2 + 1.51x - 3.50r² = 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 - 3.23r² = 0.92
y = -0.16x2 + 1.31x - 3.29r² = 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 - 2.13r² = 0.98
y = -0.17x2 + 1.30x - 3.03r² = 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
Overall power of refraction (P)
0
1
2
3
4
5
6
S
SN
N
IN
I
IT
T
ST
Overall refractive error (P)
10 �
20 �
30 �
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.
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.
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
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?
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.
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 lensesTraditional lenses
Impact on visual performance
Peripheral refraction should be considered when assessing visual performance?
Thanks
Collaboration with Dr Catharine Chisholm Dr Ian Pacey Dr Edward Mallen