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