It is important to understand that the eye is not in focus across its entire retinal (back) surface at any one time. The idea that the peripheral retina can be out of focus, either under or over focused, while the central straight ahead vision is in sharp focus is an important concept to understand. It turns out that such differences are important in understanding the methods by which an eye develops normally and how it might develop myopia instead.GO TO TOP Kang, Pauline; Fan, Yvonne; Oh, Kelly; Trac, Kevin; Zhang, Frank; Swarbrick, Helen. (2012) Effect of Single Vision Soft Contact Lenses on Peripheral Refraction. (ABSTRACT) Optometry & Vision Science Volume 89 - Issue 7 - p 1014–1021 doi 10.1097/OPX.0b013e31825da339
MyopiaPrevention.org comment: From the conclusions: "Under-, full, and over-correction of central refractive error with single vision (soft contact lenses) caused a hyperopic shift in both central and peripheral refraction at all positions in the horizontal meridian." In other words, fitting an eye with single vision soft lenses creates greater peripheral hyperopia, a possible risk factor for greater myopic progression.Liu Y, Wildsoet C. (2012) The effective add inherent in 2-zone negative lenses inhibits eye growth in myopic young chicks. (ABSTRACT) Invest Ophthalmol Vis Sci. Epub ahead of print 2012 July 3
MyopiaPrevention.org comment: Growing chicks fittted with contact lenses that created a perhipheral zone of relative positive power were shown to slow myopic progression, another piece of evidence "for a role of the peripheral retina in ocular growth regulation."Queirós, António; Villa-Collar, César; Jorge, Jorge; Gutiérrez, Ángel Ramón†; González-Méijome, José Manuel. (2012) Peripheral Refraction in Myopic Eyes After LASIK Surgery. (ABSTRACT) Optometry and Vision Science Volume 89 - Issue 7 - p 977–983 doi 10.1097/OPX.0b013e31825ddf54
MyopiaPrevention.org comment: From the conslusions: "Unlike orthokeratology, which increases the peripheral myopia, LASIK reduces myopia across the horizontal visual field out to at least 35° from fixation."
Although both Ortho-K and LASIK create a topographical ring of increased plus power on the cornea, this study says that LASIK results in more peripheral hyperopia (less myopia). If correct, it would indicate that LASIK is potentially creating a stimulus for myopic progression.Backhouse, S; Fox, S; Ibrahim, B; Phillips JR. (2012) Peripheral refraction in myopia corrected with spectacles versus contact lenses. (ABSTRACT) Ophthalmic & Physiologic Optics May 12, 2012 E Pub ahead of print. doi 10.1111/j.1475-1313.2012.00912.x
MyopiaPrevention.org comment: The assumption that creation of a myopic peripheral focus slows myopia is the basis for most optical interventions such as orthok and bifocal-type soft contact lenses. Since rigid gas permeable (RGP) and soft spherical contact lenses have been shown to not slow myopia significantly, one common assumption was that these modalities were not creating a peripheral myopia. This study, however, shows that soft spherical contact lenses create a peripheral myopic focus, unlike spectacle lenses which created a peripheral hyperopia as expected.
"...these results suggest that myopia progression should be slower with conventional contact lens wear than with conventional spectacle wear. However, previous studies comparing myopia progression with conventional spectacles and conventional contact lenses have reported no such difference."Smith, Earl L. (2011) Prentice Award Lecture 2010: A Case for Peripheral Optical Treatment Strategies for Myopia. (FULL TEXT) Optometry & Vision Science September 2011 - Volume 88 - Issue 9 - pp 1029-1044 doi: 10.1097/OPX.0b013e3182279cfa
MyopiaPrevention.org comment: The author lays out the arguments for peripheral defocus controlling myopic development. Be sure to at least read the abstract. The following topic headings summarize the discussion:
Ocular Growth and Refractive Development Are Regulated by Visual Feedback. The Vision-Dependent Mechanisms That Regulate Refractive Development Operate in a Regionally Selective Manner. Visual Signals From the Fovea Are Not Essential for Many Aspects of Vision-Dependent Growth. When Conflicting Signals Exist between the Central and Peripheral Retina, Peripheral Visual Signals Can Dominate Central Refractive Development. Refractive Errors Can Vary with Eccentricity and Peripheral Optical Errors Can Alter Central Refractive Development. Results From Clinical Studies Indicate That Peripheral Treatment Strategies Are Effective in Slowing Myopia ProgressionSchmid, Gregor F. (2011) Association between Retinal Steepness and Central Myopic Shift in Children (ABSTRACT) Optometry & Vision Science June 2011 - Volume 88 - Issue 6 - pp 684-690 doi: 10.1097/OPX.0b013e3182152646
MyopiaPrevention.org comment: Does a person's individual steepness of the retina cause myopic shift? Retinal steeepness was calculated at four peripheral points, measured as eye length axial compared to eye length peripheral. The group of 140 7-11 year old children were chosen for not having any myopia, so the small amounts of myopic shift found are perhaps not surprising. Over half of the subjects were African-American, no Asians and 34% were lost to followup. A weak correlation was found between temporal retinal steepness and myopic shifts, another study to indicate that the retina is not uniform in its control of myopia.Kang, Pauline; Swarbrick, Helen.(2011) Peripheral Refraction in Myopic Children Wearing Orthokeratology and Gas-Permeable Lenses. (ABSTRACT) Optometry & Vision ScienceApril 2011 - Volume 88 - Issue 4 - pp 476-482 doi: 10.1097/OPX.0b013e31820f16fb
MyopiaPrevention.org comment: This study basically shows that the creation of a peripheral myopia in an orthokeratology child is the same as an adult and does not occur in a GP lens wearer. Peripheral refraction after ortho-k wear was more myopic in the nasal field.Tabernero, Juan; Ohlendorf, Arne; Fischer, M. Dominik; Bruckmann, Anna R; Schiefer, Ulrich; Schaeffel, Frank.(2011) Peripheral Refraction Profiles in Subjects with Low Foveal Refractive Errors. (FULL TEXT) (Optometry & Vision Science March 2011 - Volume 88 - Issue 3 - pp E388-E394 doi: 10.1097/OPX.0b013e31820bb0f5
MyopiaPrevention.org comment: Right eyes of 43 adults aged 18 - 80 were scanned for retinal shape. Most were box-like, meaning the shape was flat centrally with a linear change after a certain peripheral angle was reached. However, the shapes were very variable even within each of the four models chosen (box-like being one of the models.)
Because it is difficult to place any one patient into a pre-set model, the authors argue for the need for customized lens designs if myopic control lenses are to be designed. This would require knowledge of a patient's peripheral refraction, how that affects their risk and how to best compensate for that specific risk/shape with custom lenses.
MyopiaPrevention.org comment: Peripheral hyperopia is cited by others as being present in myopic eyes and not so in emmetropic and hyperopic eyes. Thus it may have predictive value for who will develop myopia. This is another report of the CLEERE study, a multi university, 12 year 2.043 student endeavor. The conclusion of this paper is: "Relative peripheral hyperopia appears to exert little consistent influence on the risk of the onset of myopic refractive error, on the rate of myopia progression, or on axial elongation." In other words, all the hype over peripheral hyperopia is overblown.Pauline Kang, Paul Gifford, Philomena McNamara, Jenny Wu, Stephanie Yeo, Bonney Vong, Helen Swarbrick.(2010) Peripheral Refraction in Different Ethnicities. Investigative Ophthalmology & Visual Science (FULL TEXT) November 2010 vol. 51 no. 11 6059-6065 doi: 10.1167/iovs.09-4747
MyopiaPrevention.org comment: 35 White and 37 East Asian adults with self reported stable vision were measured with an auto-refractor out to 35 degrees nasally and temporally. East Asians with myopia 2.50 and 5.50 diopters were shown to have a greater peripheral hyperopia by about .62 diopters. Lower amounts of myopia did not show the effect. The conclusion is that East Asians with greater myopia have greater peripheral hyperopia compared to whites of the same myopic levels and this may account for why they appear to progress faster than whites.
If peripheral hyperopia drives myopia, it would have been useful to see what the peripheral refractions were when performed through the corrective spectacles instead of the naked eye. Normal spectacles have been shown to increase peripheral hyperopia in higher powers.
MyopiaPrevention.org comment: "Significant changes in optical axial length occur in human subjects following 60 minutes of monocular defocus. The bi-directional optical axial length changes observed in response to defocus implies the human visual system is capable of detecting the presence and sign of defocus and altering optical axial length to move the retina towards the image plane." In other words, the human eye responds rapidly, within minutes, to compensate for blurred vision by changing the axial length, either increasing or decreasing length as required for better focus.Lin Z, Martinez A, Chen X, Li L, Sankaridurg P, Holden BA, Ge J. (2010) Peripheral defocus with single-vision spectacle lenses in myopic children. (FULL TEXT) Optom Vis Sci. 2010 Jan;87(1):4-9.
MyopiaPrevention.org comment: Peripheral refractive hyperopia was increased for moderate myopes (-3.00 to -6.00) when glasses were worn, compared to uncorrected refraction. This did not happen for lower myopes. In other words, if peripheral hyperopia drives myopic progression, wearing regular glasses for moderate myopes drives myopic progression.Earl L. Smith, III, Juan Huang, Li-Fang Hung, Terry L. Blasdel, Tammy L. Humbird, and Kurt H. Bockhorst.(2009) Hemiretinal Form Deprivation: Evidence for Local Control of Eye Growth and Refractive Development in Infant Monkeys. (ABSTRACT) Invest Ophthalmol Vis Sci. 2009 Nov;50(11):5057-69
MyopiaPrevention.org comment: A study with rhesus infant monkeys shows that the eye responds in a localized manner to image quality, so that, for example, the left and right halves of the eye can be made to become myopic or not depending on the visual image that half of the eye receives.Fedtke C, Ehrmann K, Holden BA.(2009) A review of peripheral refraction techniques. (FULL TEXT) Optom Vis Sci. 2009 May;86(5):429-46.
MyopiaPrevention.org comment: A review of the relatively increased importance of peripheral refraction to aid in myopia prevention. Two methods are identified as the most useful commercially.Li-Fang Hung, Ramkumar Ramamirtham, Juan Huang, Ying Qiao-Grider, and Earl L. Smith, III. (2008) Peripheral refraction in normal infant rhesus monkeys. (FULL TEXT) Invest Ophthalmol Vis Sci. 2008 September; 49(9): 3747–3757.
MyopiaPrevention.org comment: A good introduction of why peripheral refractive error is important in the research of emmetropization is followed by their results showing refractive error varied with eccentricity in the infant monkeys and equaled out over the central 45 degrees of vision with age during emmetropization. They conclude that "it is reasonable to suppose that signals from the peripheral retina normally facilitate emmetropization for the central retina in infant monkeys."Richard Calver, Hema Radhakrishnan, Ebi Osuobeni, Daniel O’Leary.(2007) Peripheral refraction for distance and near vision in emmetropes and myopes. (FULL TEXT) Ophthalmic and Physiological Optics Volume 27, Issue 6, pages 584–593, November 2007 DOI: 10.1111/j.1475-1313.2007.00518.x
MyopiaPrevention.org comment: Ten myopes and ten emmetropes were measured at different eccentricities in the nasal and temporal retina. Various results are discussed but the main result is that near focus (reading) does not generally change the peripheral focus differently for myopes, although myopes had a hyperopic shift in the temporal retina during near focusing tasks.Smith EL III, Kee CS, Ramamirtham R, Qiao-Grider Y, Hung LF. (2005) Peripheral vision can influence eye growth and refractive development in infant monkeys. (FULL TEXT) Invest Ophthalmol Vis Sci 2005:46:3965-72
MyopiaPrevention.org comment: Central vision is not required for normal emmetropization in the studied monkeys. If true for humans, this would indicate that central focus, or what we think of as "clear" vision, is not necessary to for an eye to develop a correct, sharp focus. (Just because an eye is in focus does not mean that it has good vision. All other components of the eye must also be healthy.)Xingwu Zhong, Jian Ge, Haohui Nie, Xiaolian Chen, Juan Huang, and Nian Liu (2004) Effects of Photorefractive Keratectomy-Induced Defocus on Emmetropization of Infant Rhesus Monkeys. (FULL TEXT) Investigative Ophthalmology and Visual Science 2004;45:3806-3811
MyopiaPrevention.org comment: PRK (a refractive surgery related to LASIK) on Rhesus monkeys created peripheral defocus that slowed or sped up myopia progression depending on the direction of defocus, as predicted.Schmid GF. (2003) Variability of retinal steepness at the posterior pole in children 7-15 years of age. (ABSTRACT) Current Eye Research Volume 27, Issue 1 July 2003 , pages 61 - 68
MyopiaPrevention.org comment: This study showed that previously measured variability in peripheral refractions is caused by a matching variability in the shape or steepness of the retina. There is little need to consider cornea/lens/other inputs. Thus the Optical Low Coherence Reflectometer (OLCR) that was developed could be used in addition to peripheral refractions to help determine a person's risk of developing myopia. "If peripheral refraction represents a determining parameter in the control of eye growth, the precise measurement of retinal steepness could be used not only to improve estimates of myopic progression, but also to identify children who are at high risk of developing myopia. It may lead to specialized clinical/optical treatments, e.g. the correction of not only axial but also peripheral refractive errors, which are more effective than current treatments in individuals who are at risk of myopia development or progression."Seidemann A, Schaeffel F, Guirao A, Lopez-Gil N, Artal P. (2002). Peripheral refractive errors in myopic, emmetropic, and hyperopic young subjects. (FULL TEXT) J Opt Soc Am A Opt Image Sci Vis. 2002 Dec;19(12):2363-73.
MyopiaPrevention.org comment: All groups were found to be myopic in the periphery, although the hyperopes were the most myopic, then the emmetropes and least the myopes.Donald O. Mutti, Robert I. Sholtz, Nina E. Friedman and Karla Zadnik.(2000) Peripheral Refraction and Ocular Shape in Children. (FULL TEXT) Investigative Ophthalmology and Visual Science 2000;41:1022-1030
MyopiaPrevention.org comment: Myopic eyes were elongated, were prolate in shape and had relative peripheral hyperopia, compared to hyerpopes and emmetropes who had relative peripheral myopia and an oblate shape. "Thinner crystalline lenses were associated with more hyperopic relative peripheral refractions across refractive error groups, but failure of the lens to thin may account for the association between thicker lenses and more hyperopic relative peripheral refractions within a given refractive group. Increased ciliary–choroidal tension is proposed as a potential cause of ocular distortion in myopic eyes." In other words, as an alternative to peripheral hyperopia causing myopia, perhaps the ciliary body creates tension that results in myopia and peripheral hyperopia.