Peripheral refraction in myopia
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Peripheral refraction in myopia

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  • I would like to thank the BCLA for the opportunity to present some of our research to you today. What I am going to discuss in next few minutes is to look at what happens to the myopic eye in terms of visual function.
  • Myopia has become an important topic for many reasons. It’s a major cause of visual impairment throughout the world and a high proportion of our CL patients in clinical practice are myopic. There has been a rapid increase in myopia prevalence in different populations reaching 80 percent in some East Asian communities and it is a risk factor for a range of ocular problems such as myopic degeneration.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.
  • In terms of shape, myopic eyes tend to be greater in all dimensions than emmetropic eyes specially elongation of the vitreous chamber is known as the main indication of the myopic eye. Of relevance to us as eye care practitioners and researchers, is a potential loss of visual function in myopic eyes. Retinal stretching due to axial elongation of the myopic eye reduces the sampling density of retinal neurons which has implications for resolution acuity in the periphery.

Peripheral refraction in myopia Peripheral refraction in myopia Presentation 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 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
  • 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
  • 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.
  • 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 lenses Traditional 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