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
Friday, November 9, 2012
Wednesday, October 3, 2012
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
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
Tuesday, September 11, 2012
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
"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.
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
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
Friday, July 27, 2012
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
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
Wednesday, June 13, 2012
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.
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.
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.
"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 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
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
Sunday, May 13, 2012
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
Wednesday, May 9, 2012
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:
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
"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:
Wednesday, May 2, 2012
The Impact of Severity of Parental Myopia on Myopia in Chinese Children.
The Impact of Severity of Parental Myopia on Myopia in Chinese Children.
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:
Monday, April 23, 2012
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
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
Saturday, April 14, 2012
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:
Saturday, April 7, 2012
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
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
Monday, March 19, 2012
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:
Wednesday, March 7, 2012
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:
Saturday, March 3, 2012
Hereditary and environmental contributions to emmetropization and myopia
Hereditary and environmental contributions to emmetropization and myopia.
Mutti DO.
Source
The Ohio State University College of Optometry, Optom Vis Sci., Apr;87(4):255-9.
2010
This abstract also discusses the role of the lens in myopic eyes. The lens of myopic eyes does not vary its thickness in relationship to focal distance, as it's supposed to. Time outdoors is also highlighted. I haven't read the whole article, but time outdoors has recently been found to be a deterrent to myopia development and progression, that is, the more time outdoors children spend, the less likely they are to be myopic.
From the text:
"The ciliary muscle may play a greater role in emmetropization and myopia than previously thought. Time spent outdoors, not near work, may be the more important environmental variable in myopia. The effect of time outdoors shows an important interaction with a substantial genetic contribution to the risk of myopia."
Link to the abstract:
Corneal and Crystalline Lens Dimensions Before and After Myopia Onset
Corneal and Crystalline Lens Dimensions Before and After Myopia Onset
Mutti, Donald O.*; Mitchell, G. Lynn†; Sinnott, Loraine T.‡; Jones-Jordan, Lisa A.§; Moeschberger, Melvin L.‡; Cotter, Susan A.‖; Kleinstein, Robert N.*; Manny, Ruth E.*; Twelker, J. Daniel*; Zadnik, Karla*; The CLEERE Study Group
Optometry & Vision Science:
March 2012 - Volume 89 - Issue 3 - p 251–262
This article found that the lens of children who become myopic stops functioning properly about a year before the onset of myopia; the lens doesn't thin and thicken in response to visual input at different focal lengths. The lens impacts the axial length of the eye, so if it doesn't thin and thicken as it's supposed to, that has an impact on the elongation of the eye. The ciliary muscle might have something to do with this.
I've read before that the lens will adopt the optimal thickness for near work and stay like that if, for example, a person spends most of her time doing near work (like reading or using a computer). So the observations in this article were interesting in this respect to me because they add to the ongoing debate about whether the eye elongates primarily because it is genetically predisposed to, or if it elongates primarily because of visual experience (near work, minus lenses, diminished exposure to sunlight, etc.) There are a lot of pieces in understanding how myopia develops, and I'm very interested in this dynamic view of the body and of the development of the eye and vision that finds that the eye changes as it responds to visual experience. It seems that the mechanism that allows the lens to adjust to different focal lengths breaks down in myopes, and I've also read that the ciliary muscle, that pushes and pulls the lens into a thicker or thinner shape, is thicker (contracted?) in the myopic eye. If the lens doesn't adjust, the image doesn't fall on the retina at far, for myopes, and the eye elongates. The question for me is here, what could be done to get the ciliary lens and the lens to gain back the ability to contract and relax? I think this is what the Accommotrac biofeedback therapy was trying to do. But it didn't work, apparently...
From the text:
"The behavior of the crystalline lens before and after myopia onset indicates that the previously correlated, compensating response of the crystalline lens is interrupted at myopia onset. Optically this result is axiomatic; myopia would be impossible if the crystalline lens and axial length always changed in tandem. Yet myopia is almost always thought of first as excessive length. These results suggest that while excessive growth is important, growth only becomes myopic when an independence develops between the anterior segment (crystalline lens) and posterior segment (axial growth). For the sample as a whole, for each ethnic group (with the possible exception of African Americans), and for each gender (with girls showing a greater effect for lens thickness), this independence appeared at onset or within a year of onset. The crystalline lens ceased to thin, flatten, and lose power even as the eye continued to grow. It is noteworthy that despite differences in myopia prevalence between ethnicities, there seems to be some consistency in this process for most ethnic groups."
"In summary, the process of becoming myopic appears to be more than just one of excess axial elongation. The myopic eye is certainly elongated relative to the emmetropic eye, but the elongation is accompanied at myopia onset by an abrupt independence between axial growth and longstanding, compensatory optical changes in the crystalline lens likely in place from infancy up to the time of myopia onset. At onset and for at least the following 5 years, VCD-adjusted lens parameters stopped thinning, flattening, and losing power in children who became myopic compared with children who remained emmetropic. The stability of corneal power suggests that it is unrelated to this process. Future studies should seek to determine the source of this departure from correlated growth that characterizes myopia onset."
http://www.ncbi.nlm.nih.gov/pubmed/22227914
http://www.ncbi.nlm.nih.gov/pubmed/22227914
Wednesday, February 29, 2012
The effect of daily transient +4 D positive lens wear on the inhibition of myopia in the tree shrew.
McBrien NA, Arumugam B, Metlapally S.
Department of Optometry and Vision Sciences, The University of Melbourne, Victoria
Invest Ophthalmol Vis Sci. 2012
Wearing a strong (-9.5) lens induced -10.8 myopia. When the tree shrews were given a break from the minus lenses for an hour a day, a lower amount of myopia was induced. When they wore a +4.00 lens for an hour a day (even if the time was divided in 30 minute shifts), they had a much smaller amount of induced myopia. If the human eye works the same way, plus lens wear, even for an hour a day, might slow progression of myopia in children.
From the text:
"Daily intermittent +4 D positive lens wear effectively inhibits experimentally-induced myopia and may prove a viable approach for preventing myopia progression in children."
Abstract:
http://www.ncbi.nlm.nih.gov/pubmed/22323488
And this is what a tree shrew looks like:
http://ntopt.opt.uab.edu/comet/vision.htm
Monday, February 27, 2012
Human optical axial length changes in response to defocus
Human optical axial length changes in response to defocus
Scott A Read (PhD)
Michael J Collins (PhD)
Beata Sander (MD)
Contact Lens and Visual Optics Laboratory
School of Optometry
Queensland University of Technology
Brisbane, Queensland, Australia
2010
There have been numerous studies showing that myopia can be induced in chicks and monkeys, and that plus lenses (myopic defocus) can diminish induced myopia in animals. (studies by Schaeffel, Wallman and Wildsoet). This study shows that in the human eye is also affected by minus (hyperopic defocus) and plus (myopic defocus) lenses, at least in the short term. The strength of the lenses used was -3 or +3, for a period of 60 minutes.
From the text:
"In conclusion, we have demonstrated for the first time that imposing a short period of defocus on the human visual system leads to significant changes in axial length. These changes are bi-directional in nature, consistent with previous findings in experimental animals, and suggest that the human visual system is capable of detecting the sign of defocus and altering axial length accordingly in order to move the position of the retina
towards the image plane. Whilst further research is required to more comprehensively describe the characteristic features of the response of the human visual system to defocus, these findings of short term ocular change associated with defocus may have significant implications for human refractive error development."
http://www.iovs.org/content/early/2010/06/30/iovs.10-5457.full.pdf
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