The Myopia Boom

The myopia boom

Short-sightedness is reaching epidemic proportions. Some scientists think they have found a reason why.
Elie Dolgin
18 March 2015
Nature - International Weekly Journal of Science

This article discusses recent research on myopia.  It also brings up the possible benefit of the use of 10 000 lux lamps indoors, given the potential role of some aspect of natural sunlight in controlling myopia.  The role of bright light is unclear, but it seems to be related to myopia in animal studies.

From the article:

"Based on epidemiological studies, Ian Morgan, a myopia researcher at the Australian National University in Canberra, estimates that children need to spend around three hours per day under light levels of at least 10,000 lux to be protected against myopia. This is about the level experienced by someone under a shady tree, wearing sunglasses, on a bright summer day. (An overcast day can provide less than 10,000 lux and a well-lit office or classroom is usually no more than 500 lux.) Three or more hours of daily outdoor time is already the norm for children in Morgan's native Australia, where only around 30% of 17-year-olds are myopic. But in many parts of the world — including the United States, Europe and East Asia — children are often outside for only one or two hours."

Link:

http://www.nature.com/news/the-myopia-boom-1.17120

The complex interactions of retinal, optical and environmental factors in myopia aetiology

D.I. Flitcroft
Progress in Retinal and Eye Research
Volume 31, Issue 6, November 2014, pages 622-660

Visual experience and the physical environment seem to have an impact in the development of myopia. Experiments and observations in animals have shown that the eye can become myopic in response to visual stimuli from the environment. It is less clear in humans, though people who work in submarines tend to have higher levels of myopia than other military personnel, while rural populations are less likely to be nyopic than urban populations, and higher levels of education (more time spent doing near work and indoors) appears to also be related to myopia development.


Also, this article points out the need to study myopia carefully considering the three-dimensionality of the environment and the eye, and the interaction of these two.


Because near and distance visual experiences indoors and outdoors may affect the eye differently, different corrective powers might be needed for different tasks.

From the abstract:

"Animal studies, observational clinical studies and more recently randomized clinical trials have demonstrated that the retinal image can influence the eye's growth. To date human intervention trials in myopia progression using optical means have had limited success but have been designed on the basis of simple hypotheses regarding the amount of defocus at the fovea. Recent animal studies, backed by observational clinical studies, have revealed that the mechanisms of optically guided eye growth are influenced by the retinal image across a wide area of the retina and not solely the fovea. Such results necessitate a fundamental shift in how refractive errors are defined. In the context of understanding eye growth a single sphero-cylindrical definition of foveal refraction is insufficient. Instead refractive error must be considered across the curved surface of the retina. This carries the consequence that local retinal image defocus can only be determined once the 3D structure of the viewed scene, off axis performance of the eye and eye shape has been accurately defined. This, in turn, introduces an under-appreciated level of complexity and interaction between the environment, ocular optics and eye shape that needs to be considered when planning and interpreting the results of clinical trials on myopia prevention."

From the text:
“Optical structure of the environment
Several early studies that predate the current interest in off axis refraction have pointed to a possible influence of the structure of the environment on eye growth in the form of lower field myopia, a phenomenon first described in pigeons by Catania (1964). In a more detailed analysis it has been shown that the refraction of pigeon eyes is essentially uniform off-axis in the superior visual field but shows progressive myopia up to 5 Dioptres which closely followed the geometric distance from the pigeon’s eye to the ground suggesting it is an adaptive phenomenon (Fitzke et al., 1985). Lower field myopia is a phenomenon that has now been described in a range of ground feeding bird species (Hodos and Erichsen, 1990) and amphibians (Schaeffel et al., 1994b) but not in raptor bird species that spend little time on the ground (Murphy et al., 1995). Young, 1961 and Young, 1963 demonstrated that rearing monkeys in highly restrictive visual environments led to myopia, a finding that was an extension of a much earlier study in German by Levinsohn published in 1919. Studies in chicks have also demonstrated that rearing in a low ceiling environment creates the inverse of lower field myopia with development of myopia in the superior field associated with local expansion of the inferior sclera (Miles and Wallman, 1990).”

“In humans, there is some limited evidence that the local environment influences refractive development. Time spent in restrictive environments such as submarines or underground ballistic missile installations has been found to be associated with increased rates of myopia as compared to military personnel in more usual working environments (Greene, 1970 and Kinney et al., 1980). Rural populations have been observed in epidemiological studies to have very low levels of myopia as compared to urban populations. For example school children in rural Melanesia have a reported myopia prevalence of only 2.9% (Garner et al., 1988) as compared to a myopia rate in Taiwanese cities of 12% at the age of 6 increasing to 84% by age 16–18 (Lin et al., 1999). Myopic prevalence in children has been correlated with increasing urbanization in both the far east (Yang et al., 2007 and Zhan et al., 2000), Greece (Paritsis et al., 1983) and Australia (Ip et al., 2008).
Intriguing recent results have demonstrated that time spent outdoors (Rose et al., 2008) is associated with refractive status. Children who spent little time outdoors and large amount of time on near-work activities were more likely to be myopic than the control group (odds ratio = 2.6; 95% CI, 1.2–6.0). Yet the group who were in the highest third for near work and highest third for outdoor activity had no significant increased myopia risk suggestive of a protective effect of time outdoors. The authors proposed light exposure as the most likely factor in preventing myopia progression. An alternative possibility that merits consideration… is that the three dimensional structure of the environment is an important factor due to the impact this has on the patterns of defocus across the retina.”

“An alternative or additional possibility for the impact of being outdoors on myopic progression may be the profound differences in the pattern of retinal defocus generated indoors and outdoors. On the basis of animal studies, sustained hyperopic defocus should promote local eye growth and myopia. Contrasting indoor scenes with outdoors reveals a marked increase in the level of hyperopic defocus for both near and distant fixation while indoors. Being outdoors may therefore be protective on the basis that it provides minimal amounts of peripheral defocus and hence may provide a so-called STOP signal for eye growth. Even if the human eye were responding only to the amount of blur and not its sign, the amount of blur across the retina and indeed its variation with eye movements is far less outdoors than indoors. This optical effect may indeed be further enhanced by the impact of light levels on pupil size which would be expected to be much smaller outdoors so light might interact with peripheral defocus via the depth of focus changes induced by pupil constriction.”

“The impact of the environment and its three dimensional structure have still to be taken into account in such designs. A specific lens design will have different impact on off-axis retinal blur when used for reading than for outdoors for example. This suggests that lenses designed for specific tasks may be more appropriate than a general-purpose lens. This may be a practical option for glasses but is less practical for contact lenses. A combination of contact lenses for general use with additional glasses that correct detrimental patterns of retinal defocus for specific tasks may prove to be a workable solution. “

“Incorporation of the full range of interactions detailed in this paper into optical strategies should provide a method of designing appropriate corrections for different tasks, viewing conditions and eye shapes.”

Link:
http://www.ncbi.nlm.nih.gov/pubmed/22772022

Relationship between changes in crystalline lens shape and axial elongation in young children.

Relationship between changes in crystalline lens shape and axial elongation in young chilren.

Ishii K, Yamanari M, Iwata H, Yasuno Y, Oshika T.

Department of Ophthalmology, Faculty of Medicine, University of Tsukuba, Ibaraki, Japan.

Invest Ophthalmol Vis Sci. 2013 Jan 28;54(1):771-7.

This study of 25 children highlights the interaction between the lens and the length of the eyeball in the development of myopia.  It's not just that the eyeball is longer; the lens also works differently in myopic children, affecting the length of the eyeball, and playing a role in the development and progression of myopia.

From the text:
"CONCLUSIONS:
Axial elongation is related to the entire contour of the crystalline lens. This result shows that axial elongation progresses in parallel to change in the crystalline lens shape."

Link to abstrract:
http://www.ncbi.nlm.nih.gov/pubmed/23307966

Other articles that highlight the role of the lens in the development of myopia:

How does nearsightedness develop in children?." ScienceDaily. ScienceDaily, 1 March 2012. http://www.sciencedaily.com/releases/2012/03/120301113258.htm

Myopia: It's Not Just the Length, but the Lens
Myopia is commonly described as having an eyeball that is “too long.” Not exactly.

By Colleen Mullarkey, Senior Editorhttp://www.revoptom.com/content/c/33495/x

Crystalline Lens Power in Myopia
GARNER, L F O.D., Ph.D.; YAP, M O.D., Ph.D.; SCOTT, R O.D., M.Sc.http://journals.lww.com/optvissci/Abstract/1992/11000/Crystalline_Lens_Power_in_Myopia.5.aspx

Current and Future Developments in Myopia Control Researchers continue to seek effective methods to slow the progression of myopia.

Current and Future Developments in Myopia Control
Researchers continue to seek effective methods to slow the progression of myopia.
By Jeffrey J. Walline, OD, PhD, FAAO
Contact Lens Spectrum, Volume: 27 , Issue: October 2012, page(s): 34 - 38

This article summarizes the current approaches to myopia control, and lists various studies. Atropine has a high success rate, but the effect may be short-lived and its side effects long term are not known.

Orthokeratology and dual focus contact lenses appear to have some impact in controlling myopia in children.  

http://www.clspectrum.com/printarticle.aspx?articleID=107513

Light Exposure and Physical Activity in Myopic and Emmetropic Children.

Light Exposure and Physical Activity in Myopic and Emmetropic Children.

Read SA, Collins MJ, Vincent SJ.
Optom Vis Sci. 2014 Jan 9. 

This study measured ambient light exposure and physical activity of 102 children, 10 to 15 years old over a 2-week period, using a measuring device worn on the wrist.  The device registered much less light exposure and time spent in bright light conditions among myopic children, and no significant difference in daily physical activity between myopic and emmetropic (not myopic) children.  Other studies have also found that myopic children seem to spend less time in natural sunlight and bright light conditions.

Link to abstract:
http://www.ncbi.nlm.nih.gov/pubmed/24413273

Integration of Defocus by Dual Power Fresnel Lenses Inhibits Myopia in the Mammalian Eye

Integration of Defocus by Dual Power Fresnel Lenses Inhibits Myopia in the Mammalian Eye.Invest Ophthalmol Vis Sci. 2014 Jan 7McFadden SA, Tse DY, Bowrey HE, Leotta AJ, Lam CS, Wildsoet CF, To CH.

This study found that in guinea pigs, myopia can be induced and then reduced by using plus lenses and dual focus fresnel lenses.  In this study, like in many other animal studies, this reduction of myopia through the use of plus lenses seems to be fairly effective, but it's on induced myopia, so it might not be as effective in human myopia, which is not induced.  The question that remains for me is, what are the triggers that begin the process of developing myopia?  Since there appears to be a very strong genetic component to human myopia, and many have proposed that genetic predispositions are triggered by environmental factors, what are the triggers?  And in the cases where these genetic predispositions exist, can environmental changes (like more sunlight as is suggested in many studies, or plus lenses, for example) be as effective as in the cases of induced myopia?

Link: http://www.ncbi.nlm.nih.gov/pubmed/24398103

Peripheral defocus link

Below is a link to a website (myopiaprevention.org) that offers information on myopia.  The link opens a page on the site that lists articles on peripheral defocus.  Peripheral defocus in myopia is interesting, because it has been shown to impact the development and progression of myopia in some animal studies.  Myopic defocus at the periphery appears to slow the progression of myopia, and single vision glasses and lenses work in the opposite way: they make the peripheral vision more hyperopic, and may therefore encourage myopia progression.  This argument has been made for a long time (that minus glasses might worsen myopia)  but the exact mechanism by which single vision glasses or contact lens wear might affect the development of myopia is unknown; peripheral refraction possible plays a role.  Radial refractive glasses like Myovision (Zeiss) and dual focus contact lenses are designed to address this issue.

http://www.myopiaprevention.org/references_peripheral_defocus.html

The effect of simultaneous negative and positive defocus on eye growth and development of refractive state in marmosets.

The effect of simultaneous negative and positive defocus on eye growth and development of refractive state in marmosets.
Benavente-Perez A, Nour A, Troilo D.
SUNY College of Optometry, New York, New York.
Invest Ophthalmol Vis Sci. 2012 Sep 21;53(10):6479-87.

In this study dual focus contact lenses used on ten marmosets were shown to alter refraction and eye length in a period of 10-12 weeks.  The length of their eyes was compared to those of marmosets who wore contact lenses without prescription and others who wore contact lenses with +5 or -5.  The marmosets with the dual focus lenses had smaller eyes than the ones who wore -5 lenses, slowing down their myopia progression.

From the abstract:
"Conclusions. Imposing hyperopic and myopic defocus simultaneously using concentric contact lenses resulted in relatively smaller and less myopic eyes, despite treated eyes being exposed to a greater percentage of negative defocus. Exposing the retina to combined dioptric powers with multifocal lenses that include positive defocus might be an effective treatment to control myopia development or progression."

Link to the abstract:

http://www.ncbi.nlm.nih.gov/pubmed/22918633

Effect of Dual-Focus Soft Contact Lens Wear on Axial Myopia Progression in Children

Effect of Dual-Focus Soft Contact Lens Wear on Axial Myopia Progression in Children
Nicola S. Anstice, BOptom, PhD; John R. Phillips, MCOptom, PhD
Department of Optometry and Vision Science, New Zealand National Eye Centre, The University of Auckland, New Zealand
Ophthalmology
Volume 118, Issue 6 , Pages 1152-1161, June 2011

In this study, dual focus lenses (center of the lens has the minus prescription surrounded by a concentric zone with a lowered prescription, in this case a reduction of 2 diopters),  slowed the progression of myopia in comparison to the use of single vision lenses (lenses with only the full minus prescription).

From the abstract:

"Participants

Forty children, 11–14 years old, with mean spherical equivalent refraction (SER) of −2.71±1.10 diopters (D).
Methods
Dual-Focus lenses had a central zone that corrected refractive error and concentric treatment zones that created 2.00 D of simultaneous myopic retinal defocus during distance and near viewing. Control was a single vision distance (SVD) lens with the same parameters but without treatment zones. Children wore a DF lens in 1 randomly assigned eye and an SVD lens in the fellow eye for 10 months (period 1). Lens assignment was then swapped between eyes, and lenses were worn for a further 10 months (period 2).
Main Outcome Measures

Primary outcome was change in SER measured by cycloplegic autorefraction over 10 months. Secondary outcome was a change in axial eye length (AXL) measured by partial coherence interferometry over 10 months. Accommodation wearing DF lenses was assessed using an open-field autorefractor.
Results

In period 1, the mean change in SER with DF lenses (−0.44±0.33 D) was less than with SVD lenses (−0.69±0.38 D; P < 0.001); mean increase in AXL was also less with DF lenses (0.11±0.09 mm) than with SVD lenses (0.22±0.10 mm; P < 0.001). In 70% of the children, myopia progression was reduced by 30% or more in the eye wearing the DF lens relative to that wearing the SVD lens. Similar reductions in myopia progression and axial eye elongation were also observed with DF lens wear during period 2. Visual acuity and contrast sensitivity with DF lenses were not significantly different than with SVD lenses. Accommodation to a target at 40 cm was driven through the central distance-correction zone of the DF lens.

Conclusions
Dual-Focus lenses provided normal acuity and contrast sensitivity and allowed accommodation to near targets. Myopia progression and eye elongation were reduced significantly in eyes wearing DF lenses. The data suggest that sustained myopic defocus, even when presented to the retina simultaneously with a clear image, can act to slow myopia progression without compromising visual function."

Link to the abstract:http://www.ophsource.org/periodicals/ophtha/article/S0161-6420(10)01154-1/abstract

Annual Changes in Refractive Errors and Ocular Components before and after the Onset of Myopia in Chinese Children.

Annual Changes in Refractive Errors and Ocular Components before and after the Onset of Myopia in Chinese Children. (2012)
Xiang F, He M, Morgan IG.State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat-sen University, Guangzhou, China; ARC Centre of Excellence in Vision Science and Visual Sciences Group, Research School of Biology, College of Medicine, Biology and Environment, Australian National University, Canberra, Australia.Ophthalmology. 2012 May 9

In this study, participants had their eyes examined every year from 2006 to 2010 -- kids who developed myopia were followed.  The question is, why do children develop myopia, especially if there is a low or no genetic predisposition?  Animals generally seem to not develop myopia in their natural environments (but in the lab, they can become myopic under certain conditions); I read an article that   said that dogs can become myopic naturally...  In this study, it is suggested that myopic defocus possibly slows myopic development, though it does not stop it.  According to this theory, becoming myopic and experiencing defocus sends a signal to the eye to slow down axial growth.  In most  infants these visual input is enough to direct the eye towards emmetropic refraction: unaided good vision at near and far.  Why does this process fail in myopic children?
From the text:"Children who were not myopic at the first examination and myopic in at least 1 subsequent examination from 2006 to 2010 were included in the analysis. Annual change in SER increased slowly from 4 years before the first detection of myopia to 2 years before myopia onset (-0.25 to -0.4 diopter [D]). The rate of progression was the highest during the year of onset (-0.92 D). After the first detection of myopia, the rate of progression decreased to -0.71 D in the following year and kept decreasing. Annual change in axial length showed a similar, but inverse, shape to that of SER. Annual change in lens power did not change significantly around the onset of myopia.Before the onset of myopia, axial elongation and progression accelerate. After a myopic refraction is established, axial elongation and progression decrease. We suggest that the increases before myopia may be due to increased intensity of study and decreased time outdoors. In contrast, the rapid slowing after the onset of myopia may represent an inhibitory effect of myopic defocus on eye growth."
Link to abstract:
http://www.ncbi.nlm.nih.gov/pubmed/22578257

The effect of bright light on lens compensation in chicks.

The effect of bright light on lens compensation in chicks.
Ashby RS, Schaeffel F.
Institute for Ophthalmic Research, Section of Neurobiology of the Eye, University of Tübingen, Tübingen, Germany. regan.ashby@anu.edu.au
Invest Ophthalmol Vis Sci. 2010 Oct;51(10):5247-53.

This study looked at how bright light affected the development of refractive error (myopia or hyperopia) induced by optical defocus (caused by plus or minus lenses, +7 or -7).   The chicks with minus lenses that were exposed to 15, 000 lux (brighter than a SAD lamp, much brighter than typical indoor lux levels) for 5 hours per day developed myopia at a slower rate than those exposed to 500 lux (what one might be exposed to typically indoors).    The role of dopamine was found to be important: when the chicks were injected with a dopamine antagonist,  the protective effect of the light against myopia was negated.

From the abstract:
"It has been shown that sunlight or bright indoor light can inhibit the development of deprivation myopia in chicks. It remains unclear whether light merely acts on deprivation myopia or, more generally, modulates the rate of emmetropization and its set point. This study was conducted to test how bright light interacts with compensation for imposed optical defocus. Furthermore, a dopamine antagonist was applied to test whether the protective effect of light is mediated by dopamine.

Exposure to high illuminances (15,000 lux) for 5 hours per day significantly slowed compensation for negative lenses, compared with that seen under 500 lux, although full compensation was still achieved. 


High illuminance also reduced deprivation myopia by roughly 60%, compared with that seen under 500 lux. This protective effect was abolished, however, by the daily injection of spiperone, but was unaffected by the injection of a vehicle solution.

High illuminance levels reduce the rate of compensation for negative lenses and enhance the rate for positive lenses, but do not change the set point of emmetropization (target refraction). The retardation of myopia development by light is partially mediated by dopamine, as the injection of a dopamine antagonist abolishes the protective effect of light, at least in the case of deprivation myopia."


From the full text:
"A possible interaction that should be considered is the change of pupil size in bright light. Schaeffel et al.²⁷ found that the pupil size in chicks is reduced by roughly 50% of its maximum diameter under an illuminance of only 1000 lux. It is clear that a smaller pupil size increases the depth of focus and may therefore diminish the error signal driving emmetropization. However, changes in depth of focus cannot explain why bright light accelerated compensation for positive lenses. Furthermore, the development of deprivation myopia was also significantly suppressed under bright light, even though depth of focus does not play a role under the diffusers. In summary, changes in depth of focus cannot explain the effects of high illuminance on compensation for imposed defocus. Pupil constriction apparently also has no effect on refractive development in the uncovered fellow eyes.

Exposure to high illuminance levels reduces the rate of ocular growth normally seen in response to the fitting of negative lenses or translucent diffusers, and enhances the growth suppression of plus lenses, but does not alter normal ocular development. Further, the protective effect of light against the development of myopia appears to be mediated by dopamine, as the injection of a dopamine D2-specific antagonist abolishes the protective effect of light, at least in the case of deprivation myopia."
Link to the text

http://www.iovs.org/content/51/10/5247.full

Review of existing literature on myopia (2012)

Myopia
Prof Ian G Morgan PhD , Prof Kyoko Ohno-Matsui MD , Prof Seang-Mei Saw PhD 

The Lancet, Volume 379, Issue 9827, Pages 1739 - 1748, 5 May 2012

The authors of this article searched the Medline and Online Mendelian Inheritance in Man (OMIM) databases for research on myopia.  They note that there's is not enough epidemiological support for the idea that intense near work is related to myopia development; that environmental conditions (such as increased study indoors) might play a stronger role than genetics in many cases of school myopia ;  that peripheral defocus might be be a consequence rather than a cause of myopia,  and that orthokeratology might not work long term.   Here are some passages that seemed particularly interesting or informative to me:

From the text:
On myopia development:
"Most children are born hyperopic, with a normal
distribution of refractive errors.7 During the fi rst year or
two after birth, the distribution narrows,8 with a mean in
the hyperopic range of +1–2 dioptres (D). This change
indicates that there is an active process shaping the
distribution of refraction, known as emmetropisation.
After that period, the cornea stabilises,9 but refraction
can become more myopic as axial length can continue to
increase for another two decades. By contrast, lens power
decreases substantially up to the age of about 12 years,10
with slower decreases for most of adult life.9 Myopia
generally develops during the early to middle childhood
years, but significant myopia can also develop in the late
teenage years or early adulthood.11 Axial length is the
most variable factor during development, with the
strongest correlation with refractive status, with longer
eyes more likely to be myopic than shorter eyes.12 Control
of the axial elongation of the eye during development is
thus crucial for achieving normal vision, and therefore is
a primary site for prevention."


"Increased accommodation due to intensive near
work, such as reading and writing, could mediate the
association of myopia with schooling, but epidemiological
support for this idea is not strong. Although Saw and
colleagues31 showed that Singaporean children who read
more than two books per week were more likely to have
higher myopia than those who read less, the Sydney
Myopia Study showed that near work per se was a weak
factor, but that children who read continuously or at a close
distance were more likely to be myopic.32 Results from the
US Orinda Longitudinal Study of Myopia33 showed weak
albeit signifi cant eff ects of increased hours of near work,
and the authors of this study argued that the evidence did
not support a signifi cant effect of near work.27"



"A consistent finding is that children with myopic
parents have a higher prevalence of myopia,33,52,53 but the
relative risk varies substantially, and is lower in locations in which the prevalence of myopia is high, such as in east
Asia. No consistent relation with number of myopic
parents exists. At this stage, the impact of parental
myopia might be evidence of genetic effects. Differences
in family behaviour associated with myopic parents seem
less likely, but cannot be excluded at this time."



"The development of peripheral hyperopia now seems
to be a consequence, rather than a cause of myopia,
because it seems to appear in parallel with the
development of myopia, rather than before.90 Peripheral
hyperopia nevertheless could contribute to myopic
progression, and this perspective does not preclude the
use of localised manipulation of defocus to control
myopia, whatever the developmental mechanisms."



"Preliminary reports have also suggested overnight
orthokeratology contact lenses, which correct refractive
errors by physically flattening the cornea, might also
protect against myopic progression,96 and it has been
proposed that this might due to peripheral myopic
defocus imposed by the distorted cornea. However, the
eff ects might not be permanent and there might be
a rebound of progression rates of the cessation of
orthokeratology treatment."

Link to abstract:
http://www.thelancet.com/journals/lancet/article/PIIS0140-6736(12)60272-4/abstract

Moderately Elevated Fluorescent Light Levels Slow Form Deprivation and Minus Lens-Induced Myopia Development in Tree Shrews

Moderately Elevated Fluorescent Light Levels Slow Form Deprivation and Minus Lens-Induced Myopia Development in Tree Shrews

             

John T. Siegwart, Jr., Alexander H. Ward1, Thomas T. Norton. Vision Sciences, Genetics and Genomic Sciences,Univ of Alabama at Birmingham, Birmingham, AL.

              

This abstract is from the ARVO (The Association for Research in Vision and Ophtalmology) website.  This study was presented at the May 2012 meeting.  Many articles on myopia were presented at that meeting.  This study looked at the effect of elevated artificial light levels on young tree shrews with induced myopia and deprivation myopia, and found that the tree shrews exposed to elevated light levels (around 16,000 lux, brighter than a SAD lamp for almost 8 hours) developed induced and deprivation myopia more slowly.  Myopia in humans is different, since it generally is not caused by deprivation or induced in a lab, but the studies on time spent outdoors and ocular sun exposure also show that exposure to sunlight is related to lower levels of myopia. This study is interesting because artificial fluorescent light was shown to have an effect too, in animals with induced and deprivation myopia.  

From the text:

"Children who spend more time outdoors have a lower prevalence of myopia (Rose et al., Ophthalmol. 2008) and slower myopic progression (Parssinen and Lyyra, IOVS, 1993). We examined whether elevated light levels (ELL), produced with fluorescent bulbs, slow the development of form deprivation myopia (FDM) and minus lens-induced myopia (LIM) in tree shrews (small diurnal mammals closely related to primates).

Juvenile tree shrews wore a monocular diffuser to produce FDM (n=4) or a −5D lens to produce LIM (n=5) starting at 24 days of visual experience. During treatment, the animals were exposed to ~16,000 lux for ~7.75 hours per day (~9:15 AM - 5 PM) produced with an array of compact fluorescent bulbs. The refractive changes in the FDM and LIM animals were compared to animals from previous studies (FDM, n=6; LIM, n=6) that were treated in standard light levels of 500 - 1000 lux.

After 11 days of treatment, ELL reduced FDM (treated-control eye) by 44% (−3.6 ± 0.1 D vs. −6.4 ± 0.7 D) and LIM by 39% (−2.9 ± 0.4 D vs. −4.8 ± 0.3 D) (figure). Control-eye refractions remained hyperopic compared with standard lighting control eyes. When ELL stopped and form deprivation continued, the myopia progression rate increased to parallel that of standard light-treated animals but did not “rebound”, suggesting a permanent saving from the reduced rate during ELL. Two LIM animals continued lens wear and ELL and fully compensated for the −5 D lens after 16 and 23 days.

Moderately elevated light levels, comparable to those in the shade on a sunny day, slow the development of FDM and LIM in tree shrews. These findings are consistent with reports that ELL reduces FDM in chicks and macaque monkeys (Ashby et al., IOVS 2009; Smith et al., ARVO E-Abstract 3922, 2011) and LIM in chicks (Ashby & Schaeffel, IOVS 2010). ELL, from fluorescent bulbs that emit minimal UV radiation, may become a useful tool to slow the progression of environmentally-induced myopia in children. The minimal UV in the ELL is consistent with a previous finding that vitamin D supplementation did not reduce FDM or LIM in tree shrews (Siegwart et al., ARVO E-Abstract 6298, 2011), and suggests that the effect is not due to a light-induced increase in vitamin D levels."

Link:

http://www.abstractsonline.com/Plan/ViewAbstract.aspx?sKey=c3a18ab8-817a-45ba-b076-1f73afdb5eca&cKey=85e862ad-d81d-4397-aeef-2a80da11aefb&mKey=%7bF0FCE029-9BF8-4E7C-B48E-9FF7711D4A0E%7d

An Objective Biomarker Of Ocular Sun Exposure Is Inversely Correlated With Myopia In Young Adults: The Raine Eye Health Study

An Objective Biomarker Of Ocular Sun Exposure Is Inversely Correlated With Myopia In Young Adults: The Raine Eye Health Study

Charlotte M. McKnight, Seyhan Yazar, Justin Sherwin, Hannah Forward, Alex Tan, Terri L. Young, Christopher J. Hammond, Craig Pennell, Minas T. Coroneo, David A. Mackey. 

Centre for Ophthalmology & Visual Science, University of Western Australia, Lions Eye Institute, Crawley, Australia; Department of Public Health and Primary Care, University of Cambridge, Cambridge, United Kingdom; Ophthalmology, Duke University Eye Center, Durham, NC; Ophthalmology, King's College London, London, United Kingdom; School of Women's and Infants' Health, University of Western Australia, Subiaco, Australia; Ophthal-Prince of Wales Hosp, Univ of New South Wales, Randwick, Australia; Lions Eye Institute, Perth, Australia.

This abstract is from the ARVO (The Association for Research in Vision and Ophtalmology) website.  This cross-sectional study was presented at the May 2012 meeting.  Many articles on myopia were presented at that meeting.  This one measured ocular sun exposure objectively using conjunctival ultraviolet autofluorescence photography which the authors describe as "an objective, quantitative and reliable method of assessing ocular sun exposure".  The study found that there was a relationship between myopia and ocular sun exposure measured this way: the higher the degree of myopia, the lower the amount of ocular sun exposure measured.  So this supports other studies that found that the more time children are outdoors, exposed to sunlight, the lower their risk of myopia.

From the text:

"Several studies have demonstrated an inverse association between outdoor activity and myopia. Many of these studies have been limited by subjective measurement of outdoor activity, such as parental or participant recall via questionnaire. We used conjunctival ultraviolet autofluorescence photography, an objective, quantitative and reliable method of assessing ocular sun exposure, to investigate the relationship between outdoor activity, ultraviolet light exposure and myopia.

This was a cross-sectional study of 1231 young adults aged 19 to 22 years in the Raine cohort, Western Australia. Ultraviolet fluorescence images of the interpalpebral conjunctiva (right and left eye, nasal and temporal regions) were taken using a specially designed camera system.

Prevalence of myopia decreased with increasing quartiles of conjunctival autofluorescence, with 32.8% in the lowest quartile, 28.0% in the second quartile, 17.2% in the third quartile and 15.6% in the highest quartile. Participants in the lowest quartile had 2.6 times the odds of myopia than those in the highest quartile (95% confidence interval 1.7 to 3.8, p<0.001). The inverse association between myopia and conjunctival autofluorescence remained significant after adjustment for age, gender, time outdoors, educational activity and parental history of myopia (OR 2.5, 95% confidence interval 1.5 to 4.2, p<0.001).

These findings have implications for our understanding of myopia pathogenesis, of particular importance given the increasing prevalence of myopia worldwide. As causality cannot be inferred given the cross-sectional design of this study, prospective studies looking at conjunctival autofluorescence and development of myopia are required."

LInk:

http://www.abstractsonline.com/Plan/ViewAbstract.aspx?sKey=b5b23b76-e553-4547-aebf-1968a6cf8f47&cKey=6d208530-5bce-4bf8-b88d-055dd03c15a2&mKey=%7bF0FCE029-9BF8-4E7C-B48E-9FF7711D4A0E%7d

The Impact of Severity of Parental Myopia on Myopia in Chinese Children.

The Impact of Severity of Parental Myopia on Myopia in Chinese Children.

Xiang F, He M, Morgan IG.

Source

State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center, Sun Yat Sen University, Guangzhou, Guangdong, PR China (FX, MH), and Research School of Biology, College of Medicine, Biology and the Environment, Australian National University, Canberra, Australian Capital Territory, Australia (FX, IGM).

Optom Vis Sci. 2012  

This study looked at the prevalence of myopia among 12-15 year olds in relationship to the level of myopia in their parents, in China.  The children had one parent who was not myopic and one who either did not have myopia, or had mild, moderate or high myopia. The researchers found that,60-80% of the children who had a parent with mild, moderate of high myopia, also had myopia (the greater percentage was among the children whose parents had high myopia).  Interestingly though, 50% of myopic children had two non-myopic parents, and of  the children with high myopia, 45.3% also had two non-myopic parents.  That seems fairly high for not having a genetic predisposition.

From the abstract:

"CONCLUSIONS.: More severe myopia in one parent results in an increased risk of myopia in the children. However, most highly myopic children did not have a highly myopic parent and also half did not have any reported parental myopia. This suggests that while genetic factors contribute to the development of more severe myopia, environmental factors also contribute to high myopia in children in Guangzhou."

Link:

http://www.ncbi.nlm.nih.gov/pubmed/22544002

Peripheral vision can influence eye growth and refractive development in infant monkeys.

Peripheral vision can influence eye growth and refractive development in infant monkeys.
Smith EL 3rd, Kee CS, Ramamirtham R, Qiao-Grider Y, Hung LF.
Invest Ophthalmol Vis Sci. 2005 Nov;46(11):3965-72.
College of Optometry, University of Houston, TX 


This study investigated the role of peripheral vision in the development of induced myopia in monkeys.  The monkeys in the experiment had their peripheral vision obstructed and were allowed to have clear central vision, and they developed myopia under these conditions.  Once the obstruction was removed (helmets with spectacles) the monkeys recovered from myopia.  


Refractive error at the periphery varies from vision at the center.  People with myopia tend to be hyperopic (blurred vision at near distances) in the periphery and myopic (blurred vision at far distances) in the center.  So an optical correction that is best for the center may be actually detrimental for the periphery.   This is the idea behind the MyoVision by Zeiss lenses that are available currently in Asia.  The center corrects for myopia and the periphery has a lower prescription, like a concentric bifocal.


From the text:
"On the one hand, the peripheral retina can contribute to emmetropizing responses and to ametropias produced by an abnormal visual experience. On the other hand, unrestricted central vision is not sufficient to ensure normal refractive development, and the fovea is not essential for emmetropizing responses."

Link to article:
http://www.iovs.org/content/46/11/3965.full

Monovision slows juvenile myopia progression unilaterally

Monovision slows juvenile myopia progression unilaterally.

Br J Ophthalmol. 2005 Sep;89(9):1196-200.
Monovision slows juvenile myopia progression unilaterally.
Phillips JR.
Department of Optometry and Vision Science, University of Auckland, Private Bag 92019, Auckland, New Zealand.

I've read in various articles and websites that undercorrection (wearing a lower spectacle prescription than the one that gives the sharpest vision at 20 feet) may  improve, may worsen and may not have any impact on myopia progression.  I found every argument and study to be persuasive to some degree.

The purpose of this study was to find if monovision (wearing one lens corrected for distance and another for near vision), would reduce accommodation (the work required to focus) in children with myopia.  It was expected that the children would use  the near corrected eye (undercorrected for distance)  for near activities like reading, and the distance corrected eye for their distance vision, but instead they used the distance corrected eye for both near and far vision.   The result was that myopia progression in the near-corrected eye was slower than in the distance-corrected eye.  So the eye that was corrected for distance vision ended up becoming more myopic under the conditions of this study (monovision).

From the text:

"A significant finding was that the rate of myopia progression was slower in the near corrected eyes than in the distance corrected eyes. While participant dropout is of some concern, the demonstrated effect in 13 participants suggests that it can be generalised to at least 75% of the equivalent myopic population (p = 0.05).²⁶ Although it is probable that the difference in progression rates can be attributed to a slowing of progression in the near corrected eyes because of sustained myopic defocus, the possibility of some increase in progression rate in the distance corrected eyes cannot be ruled out. Progression is typically most rapid during the initial stages of myopia development and slows to a stable refraction over a number of years.²⁷Accordingly, Grice et al²⁸ reported a mean progression rate in the first year after myopia onset of −0.87 D/year in a group of 19 children, whereas children with longer standing myopia (for example, those wearing single vision lenses as controls in PAL studies) typically have progression rates between 0.5–0.7 D/year.^4–6,29 Therefore, while the progression rate in distance corrected eyes of −0.72 D/year found in the present study is to be expected, that of −0.32 D/year in near corrected eyes is lower than expected for children who had only recently developed myopia and were receiving their first optical correction.

For all eyes myopia progression was closely correlated with changes in VCD. The slopes of the relations were comparable to the theoretical value of −2.70 D/mm³⁰ suggesting that most of the difference in progression rate between the eyes could be accounted for by the difference in their vitreous chamber elongation rates.

In conclusion, monovision is not effective in reducing accommodation in juvenile myopia. However, the results suggest that myopic retinal defocus acts as an anti-myopiagenic stimulus that counters abnormal axial elongation of the human eye. This conclusion is the opposite of that reached after bilateral undercorrection of children with myopia⁹ but it is consistent with the results of animal studies.^1,2,31 "

Link:

http://www.ncbi.nlm.nih.gov/pubmed/16113381

How genetic is school myopia?

How genetic is school myopia?
Morgan I, Rose K.
Visual Sciences Group, Research School of Biological Sciences and Centre for Visual Science, Australian National University
Prog Retin Eye Res. 2005 Jan;24(1):1-38.

Myopia that is detected during childhood is often referred to as school myopia.  Though there is a clear genetic component to myopia and there are several studies that have shown this, the author of this article finds that some of the data is contestable, and that the environment may play an even greater role.  There's a strong link with increased education and urbanization, for example.

Link to abstract:
http://www.ncbi.nlm.nih.gov/pubmed/15555525

Perspective: How Might Emmetropization and Genetic Factors Produce Myopia in Normal Eyes?

Perspective: How Might Emmetropization and Genetic Factors Produce Myopia in Normal Eyes?
Review 
Siegwart, John T. Jr; Norton, Thomas T.
Optometry & Vision Science:
March 2011 - Volume 88 - Issue 3 - pp E365-E372


This article discusses the process the eye goes through to become emmetropic, that is, with good vision at near and far.   This process is very active during the first year of life, and then it slows down.  There's a strong genetic component, and children who have one or two myopic parents, usually have longer eyes.  Animal studies have shown that visual stimuli play an important role in the development of myopia and hyperopia, and that the impact is greater the younger the animal is.  Studies have shown than hyperopic defocus may cause the eye to grow longer and become more myopic.  Minus lenses at near cause hyperopic defocus; but if it they are removed for 2 hours a day, at least in animals, the elongation might be prevented. 

From the text:

"The animal data on which this speculative article is based suggest that there may be a normal decrease in the ability of the emmetropization mechanism to use myopia to slow axial elongation and that this may impart a natural bias toward developing myopia. Throughout evolution, it presumably was rare for juvenile or adult vertebrate eyes to encounter significant periods of hyperopia, so that once eyes had achieved emmetropia it was not an issue whether myopia became less effective in controlling eye growth. However, when humans developed environments with extensive and long-duration nearwork demands, if the accommodative mechanism did not sufficiently remove the hyperopia associated with nearwork, and if myopia, except in infants, is unable to slow the axial elongation rate, it would be natural that at least some eyes develop myopia for distant "

Link to full text:

http://journals.lww.com/optvissci/Fulltext/2011/03000/Perspective__How_Might_Emmetropization_and_Genetic.4.aspx 

Axial length changes during accommodation in myopes and emmetropes.

Axial length changes during accommodation in myopes and emmetropes.
Read SA, Collins MJ, Woodman EC, Cheong SH.
Contact Lens and Visual Optics Laboratory, School of Optometry, Queensland University of Technology, Brisbane, Queensland, Australia. 
Optom Vis Sci.  Sep;87(9):656-62.
2010

and also:


Axial elongation following prolonged near work in myopes and emmetropes.
Woodman EC, Read SA, Collins MJ, Hegarty KJ, Priddle SB, Smith JM, Perro JV.
Br J Ophthalmol. 2011 May;95(5):652-6.

These studies found that the eye elongates during periods of accommodation (when the eye changes to achieve clear focus), and it does so equally in people who are myopic as well as those who are not.  The lens thickness also changes.   In the second study, the myopic eyes elongated more than the non-myopic eyes, during a prolonged period (30 minutes) of near work.

From what I've learned so far, the myopic eye (with axial myopia) is elongated, and its crystalline lens does not function properly.   In induced myopia, these structural changes are induced and can be reversed.  But the studies of induced myopia are on animals.  If lens thickening and axial elongation are part of the process of focusing, I wonder why the myopic eye continues to elongate and loses its capacity to change.

Link to abstracts:

http://www.ncbi.nlm.nih.gov/pubmed/20562668

http://www.ncbi.nlm.nih.gov/pubmed/20829316