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Myopia and outdoor activities: new study

Photo JPL-blogueFor about 5 years, a new theory was launched: kids who do not play outdoors regularly are on average more myopic (or less farsighted) than those who practice outdoor activity on a regular and prolonged basis. Children with few outdoor activities and who practice activities requiring near vision (reading, video games on portable console, etc.) were three times more likely to be myopic as those who practice many outdoor activities and some reading activity.

Professor Ian Morgan (from the Australian National University), highlights another risk factor: for him the crucial factor is simply the lack of natural light. A neurotransmitter produced in the retina under the influence of light, dopamine, could avoid excessive growth of the eye in childhood. If spending hours reading, playing or working on a screen promotes myopia, according to Morgan, this is indirectly because children spend much less time outside {1}.

These data were corroborated with those of a study of adolescents in Singapore, which were much less myopic (or farsightedness) when they practiced much more outdoor activities. {2}

It seems that this is the time that is spent outside that protects against myopia, rather than the sport itself (no influence of indoor sports on the prevalence of myopia). This was corroborated by a more recent study by Guggenheim et al. {3}

  1. Rose et al. Outdoor activity reduces the prevalence of myopia in children. Ophhalmology 2008 115: 1279–1285.
  2. Dirani et al. Outdoor activity andmyopia in Singapore teenage children. Br J Ophthalmol. 2009; 93: 997–1000.
  3. Guggenheim JA, Northstone K, McMahon G, Ness AR, Deere K, Mattocks C, St Pourcain B, Williams C. Time outdoors and physical activity as predictors of incident myopia in childhood: A prospective cohort study Invest Ophthalmol Vis Sci. 2012 Apr 6.

myope-enfant

Source: http://www.alancarlsonmd.com/wp-content/uploads/2011/06/im084057.jpg

New study

Another recent study (February 2013) conducted in Denmark shows that for children with myopia, vision deteriorated rapidly when the days were shorter (winter period) and more slowly during the summer months. This study aimed to determine whether daylight could slow the progression of myopia in children.

“Most likely it is the light exposure that causes the reduced myopia progression during periods with longer days,” said lead author Dr. Dongmei Cui, an ophthalmologist at SunYat-senUniversity in Guangzhou, China.

Cui and his colleagues analyzed data from a clinical trial that included more than 200 children aged 8 to 14 years old with myopia, or nearsightedness, in Denmark – where day length ranges from seven hours in winter to almost 18 hours in summer.

Over the six months with the least daylight, nearsightedness progressed by 0.32 diopter. In comparison, children’s vision deteriorated by 0.28 diopter over the sunniest months.

Accumulated hours of daylight ranged from 1660 to 2804 hours. Significant correlations were found between hours of daylight and myopia progression (P = 0.01). In children with an average of 2782 ±19 myopic progression was greater.

With the increase in the length of the eyeball (axial length) from the front to the back, myopia tends to worsen. During the winter period, the axial length among study participants increased by an average of 0.18 mm compared to 0.14 mm in the summer, according to results published in the journal Ophthalmology.

Note: if statistically there is a difference in the progression of myopia between the two groups, can we say that these results are clinically significant? No! Over a period of one year, we can estimate an increase of 0.60 diopter if the children of both groups react in the same way. The only difference is the seasonal variation during the year.

myope-enfant2

Source: http://www.cataract.com.sg/neuro.htm

The researchers did not analyze how much time the children spent outside, just how much they probably did based on the season. Danish children spend much more time outdoors in summer, and very little in winter, when temperatures hover around freezing for four months, according to Cui.

Past research on nearsightedness in children in the U.S. found the condition deteriorated more during the six months of the school year and less during the six months that include summer. But another study in Singapore, where days are about the same length all year, found no seasonal difference in the progression of nearsightedness.

The idea that daylight might protect children from worsening nearsightedness is a relatively new theory, said professor Jeffrey Cooper of the College of Optometry at the State University of New York in Manhattan.

Studies in mammals and birds have found that light exposure plays a role in the development of the eye, and that animals reared from a young age with frequent exposure to high intensity light may be somewhat protected from myopia. No similar effect has been seen with light exposure in adulthood.

The new study’s results can’t prove that daylight causes vision loss to slow down, Cooper said. “There is no evidence that increasing outside exposure will actually reduce the progression of myopia,” Cooper, who was not involved in the work.

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Headaches, again…

In the previous text, we shared a study on headaches in children and the lack of relevance to either having to wear glasses or changing the lens power of the glasses. One of the issues discussed was the biased scientific methodology and the art of making such statements without seeing further than one’s nose…

Contrary to the statement of the authors and of the American Association of Ophthalmology, there is a source more relevant and of more scientific relevance about headaches and vision of children that is free of any bias examiner. In 2009, a major study both from optometrists and ophthalmologists concerning convergence insufficiency and its symptoms, the CITT study (Convergence Insufficiency Treatment Trial) began. They created a questionnaire called CISS (Convergence Insufficiency Symptom Survey) to link the symptoms to convergence insufficiency. All one has to do to determine if the visual requirements are linked to headaches is to ask! The CISS questionnaire showed that it could be done reliably. You will find the questionnaire at the end of the text. Note the number of items that relate to visual discomfort. You can also download it from: http://www.aoa.org/x13917.xml

Q1: Do your yes feel tired when reading or doing close work?

Q2: Do your eyes feel uncomfortable when reading or doing close work?

Q3: Do you have headaches when reading or doing close work?

Wait a second! Why is it that the best standardized questionnaire in the history of joint studies of optometry and ophthalmology, studies funded by the U.S. government, directly ask a question about headaches associated with visual tasks, while the recent study talked about “proofs beyond doubt” that it is not relevant?

Let’s dispense with the simplistic notions of the latest press release, and set the record straight:

  1. Headaches can be associated with vision problems.  Unless you ask the question, you can’t get an answer.
  2. Pediatrician screening is not a substitute for a complete eye exam performed by an optometrist. A child who complains of headache associated with visual tasks near (reading, writing, drawing, etc.) might show a functional problem (alignment problem like convergence and/or focusing), while having no problem with distance visual acuity (vision of 20/20 or 100%).
  3. A change in glasses may sometimes not completely solve the headache. But often wearing new glasses for an individual who was not wearing any will solve the problem.
  4. If the underlying cause of headaches is a functional problem, the treatment of choice according to proved scientific studies is proven optometric vision therapy.

Adapted from VisionHelp Blog (a super blog!): http://visionhelp.wordpress.com/

The abstract of the study on the CISS questionnaire can be found here: http://www.ncbi.nlm.nih.gov/pubmed/19289977

Even in ophthalmology, here is what is said about eyestrain and headaches:

“The visual symptoms are caused by because focusing of the eyes becomes increasingly difficult due to fatigue especially at the end of the day after prolonged reading. Vision becomes blurred and sometimes even double. Vision at near can be uncomfortable.

Eyestrain occurs mainly in the late afternoon as near vision is constantly at work by efforts of focusing in work and in leisure with particularly computer screens, mobile phones, television, console games…

Eye symptoms reflecting visual fatigue include a feeling of discomfort, tension, and heaviness in the region of the eye, orbit or eyelids. There may be feeling of irritation, burning, stinging, and itching, sometimes with red eyes, some tearing or irritation due to dry eye. The subject may feel dull pain but not very intense that may become acute generally behind the eyes.

Headaches can be felt around the eyes, on the forehead above the eyebrow line, temples or behind the head. These headaches are related to eye strain, occur after a certain period of work at the end of the day, fade and disappear after cessation of work.” (Source: http://www.ophtalmologie.fr/fatigue-visuelle-yeux.html)

Young myopes: go play outside?

Introduction

An early study in Australia reported that playing outdoors more could have a link with a lower prevalence of myopia in children was published in 2008 by Kathlyn Rose and colleagues (1) ; this study was impressive with the number of children involved: over 4000 children were included in the “Sydney Myopia study”, which took place between 2003 and 2005.

The authors showed that higher levels of outdoor activity (sports and leisure) were associated with more hyperopic refractions and lower myopia prevalence among students 12 years of age. Students who performed a lot of near work indoor and spent the least time playing outside showed less hyperopia and more myopia. The opposite is also true.

The same research team (2) measured the presence of myopia in two of age- and ethnicity-matched primary school children participated: 124 from the Sydney Myopia Study and 628 from the Singapore Cohort Study on the Risk Factors for Myopia.

The prevalence of myopia in 6- and 7-year-old children of Chinese ethnicity was significantly lower in Sydney (3.3%) than in Singapore (29.1%) (P< .001). The prevalence of myopia in 1 or more parents was 68% in Sydney and 71% in Singapore. Children in Sydney read more books per week (P < .001) and did more total near-work activity (P = .002). Children in Sydney spent more time.

On outdoor activities (13.75 vs 3.05 hours per week; P < .001), which was the most significant factor associated with the differences in the prevalence of myopia between the 2 sites.

They then examined teenage children (3) (1249 participants) in the Singapore Cohort study Of Risk factors for Myopia (SCORM), during 2006.

The mean total time spent on outdoor activity was 3.24 h/day. The total outdoor activity (h/day) was significantly associated with less myopia. In addition, the total time spent outdoors was associated with significantly less myopia. Total sports time was also significantly associated with less myopia, but not indoor sports.

Participants who spent more time outdoors were less likely to be myopic. Thus, outdoor activity may protect against development of myopia in children, supporting recent Australian data (see above).

Other studies have followed thereafter and future research will surely come.

Other studies

In 2010, Deng (4) investigated the association of children’s refractive errors with their visual activities assessed by questionnaire in the school year and summer break (June, July, and August).

During the school year, myopes spent significantly fewer hours (8.25 ± 6.24 h/week) than non-myopes (10.95 ± 5.95 h/week) in sports/outdoor activity (p < 0.05). In addition, myopes (12.78 ± 9.28 h/week) watched more television than non-myopes (8.91 ± 5.95 h/week) (p = 0.02). No significant refractive group differences were found for other activities.

A new finding is the high number of sports/outdoor activity hours for both myopes and non-myopes during the summer break, which may contribute to slowed eye growth in all children during these 3 months.

Guggenheim (5)  followed participants in the Avon Longitudinal Study of Parents and Children (ALSPAC) who were assessed at ages 7, 10, 11, 12, and 15 years, and classified as myopic (≤-1 diopters) or non myopic.  Physical activity at age 11 years was measured objectively using an accelerometer, worn for 1 week. Time spent outdoors was assessed via a parental questionnaire administered when children were aged 8-9 years.

Time spent outdoors was predictive of incident myopia independently of physical activity level. The greater association observed for time outdoors suggests that the previously reported link between “sports/outdoor activity” and incident myopia is due mainly to time outdoors rather than physical activity.

Dharani et al. (6) analyzed the time spent outside in, using a log notes and a light meter over a period of 1 week in Singapore for 117 children aged 6-12 with and without myopia. All children wore the light meter for 1 week and parents completed the log outdoor activities for children for 7 days.

The agreement between the light meter measures and the activity logbook was poor to fair. Both instruments measure different parameters, without doubt, time spent outside and the light intensity that results, and it does not seem a useful approach to understand the different aspects of risk in future studies for myopia.

Donovan (7) has analysed seasonal variations in the myopic progression of Chinese children.

They examined a total of 85 Chinese children with myopia between -0.75 D and -3.50 D and astigmatism ≤ -1.50 D, who wore glasses to see far away. They measured refraction and the axial length of the eye at 6 month intervals. The growth rate of the right eye was defined for the first and second 6 months of the study and classified according to “summer”, “autumn”, “winter” or “spring.”

The average increase of 6 months was -0.31 ± 0.25 D for the summer, -0.40 ± 0.27 D for the fall, -0.53 ± 0.29 D for the winter, and -0.42 ± 0.20 D in the spring (p <0.001). The increase in axial length was 0.17 ± 0.10 mm for the summer, 0.24 ± 0.09 mm for autumn, 0.24 ± 0.09 mm for the winter, and 0.15 ± 0.08 mm for the spring (p <0.001). In addition, data for summer and winter were different from each other for the progression of myopia and axial elongation.

Myopia progression in summer months was approximately 60% of that seen in winter, and axial elongation was likewise significantly less in summer. It is unclear whether more time spent outdoors in summer vs. winter is a contributing factor, or the difference in progression rates is a result of “seasonal” variations in the intensity or amount of close work performed.

Jones-Jordan (8) has also investigated the association between myopia progression and time spent outdoors and in various visual activities.

Their results indicate that the number of hours of reading for pleasure per week was not significantly associated with annual myopia progression, nor were the other near activities. The magnitude of effects was clinically small.

Despite previous associations between time spent outdoors and the risk of developing myopia, these authors were unable to obtain the same results …

Conclusion:

One of the surprises of recent research is the importance of how the increased time spent outdoors helps prevent myopia. At present, it seems that 14 hours per week or more outside are significantly effective in reducing the progression of myopia.

Why this surprising relationship? Here are some suggestions:

• Exposure to sunlight increases the production of vitamin D (vitamin D is produced by the skin, using sunlight)? But a study showed that blood concentrations of this vitamin is not significantly different in children who spend more time outdoors than others…

• Exposure to sunlight increases the production of chemicals in the retina such as dopamine which controls the growth of the eye?

• Children often look away when they play outside?

• Exposure to beneficial microorganisms (production of serotonin, which is part of the signaling system in the retina of the eye to counter the growth of the eye)?

We know it is not sports and physical activities are involved. The benefits are possible for the children to play outside without organized sport activity.

References:

(1) Rose KA, Morgan IG, Ip J, Kifley A, Huynh S, Smith W, Mitchell P.Outdoor activity reduces the prevalence of myopia in children. Ophthalmology. 2008 Aug;115(8):1279-85.

(2) Rose KA, Morgan IG, Smith W, Burlutsky G, Mitchell P, Saw SM. Myopia, lifestyle, and schooling in students of Chinese ethnicity in Singapore and Sydney. Arch Ophthalmol. 2008 Apr;126(4):527-30.

(3) Br J Ophthalmol. 2009 Aug;93(8):997-1000. Epub 2009 Feb 11. Outdoor activity and myopia in Singapore teenage children. Dirani M, Tong L, Gazzard G, Zhang X, Chia A, Young TL, Rose KA, Mitchell P, Saw SM.

(4) Deng L, Gwiazda J, Thorn F. Children’s refractions and visual activities in the school year and summer. Optom Vis Sci. 2010 Jun;87(6):406-13.

(5) Mutti DO, Marks AR. Blood levels of vitamin D in teens and young adults with myopia. Optom Vis Sci. 2011 Mar;88(3):377-82.

(6) Dharani R, Lee CF, Theng ZX, Drury VB, Ngo C, Sandar M, Wong TY, Finkelstein EA, Saw SM. Comparison of measurements of time outdoors and light levels as risk factors for myopia in young Singapore children. Eye (Lond). 2012 Jul;26(7):911-8. doi

(7) Donovan, L, Sankaridurg, P, Ho, A. Chen, X. Lin, Z. Thomas, V. Smith, E L. III, Ge, J. Holden, B. Myopia Progression in Chinese Children is Slower in Summer Than in Winter.  Optometry & Vision Science. 89(8):1196-1202, August 2012.

(8) Jones-Jordan LA, Sinnott LT, Cotter SA, Kleinstein RN, Manny RE, Mutti DO, Twelker JD, Zadnik K; for the CLEERE Study Group.Time Outdoors, Visual Activity, and Myopia Progression in Juvenile-Onset Myopes. Invest Ophthalmol Vis Sci. 2012 Oct 15;53(11):7169-7175.

New study supports orthokeratology for myopia control and for astigmatism correction

The Faculty of Health and Social Sciences at Hong Kong’s Polytechnic University issued a press release today on the results from two studies on orthokeratology. One, called the “ROMIO” study (Retardation of Myopia in Orthokeratology), was a single blind, randomized, controlled clinical trial on the effectiveness of orthokeratology for myopia control.  The other, called the “TO SEE” study ((Toric Orthokeratology-Slowing Eyeball Elongation), looked at the effectiveness of orthokeratology for astigmatism correction.

Brief description of orthokeratology

Patients who wish to receive an orthokeratology treatment must undergo a comprehensive oculo-visual exam and specific measures of the shape of their eyes to see if they are good candidates for the treatment. Using computer software, the optometrist is able to design special contact lenses adapted to the shape of the eyes of each candidate. These contact lenses are rigid gas permeable lenses and are made from high oxygen content materials, which can be worn during sleep. The aim is to reshape the cornea in order to obtain perfect vision the next day without having to wear glasses or contact lenses.

Orthokeratology is the only non-surgical treatment that allows you to be free of corrective lenses like eye-glasses and contact lenses. For cons, the treatment must be continuous.

Progression of myopia 

Myopia and its progression is a serious problem. Not only does it cause a gradual decrease in the uncorrected vision, but it ensures that the individual needs thicker and thicker and more expensive glasses. In addition, severe myopia increases the risk of retinal tear.

After 24 months of research, the ROMIO study found that the increase in eyeball length (also called “axial length” — the progression of myopia is measured by observing the elongation of the eyeball) in a group of subjects that were treated with orthokeratology was 0.36mm.  In the group that was not treated with orthokeratology and only wore spectacles, the eyeball length was 0.63mm longer. The results indicate that orthokeratology slowed down the progression of myopia by 43%.

Astigmatism

Researchers at the same university also concluded the “TO-SEE” (Toric Orthokeratology-Slowing Eyeball Elongation) study which looked at 37 children aged 6 to 12 years to study the potential of orthokeratology for the reduction of astigmatism. The team found that toric design orthokeratology lens retainers effectively reduced astigmatism by 79% after one month of wear. At the end of 24 months, the eyeball length of the participants was 0.31mm which indicated that myopia was also being controlled.

Orthokeratology is a reversible treatment and can be stopped anytime. The results of these two studies show that orthokeratology is a safe and effective solution for refractive error correction, myopic control and astigmatism reduction.

Myopia (3)

Previously, we said that when we correct myopia regardless of near vision (see image below), one will use an inadequate corrective power (too strong) while reading if the child reads with his glasses. The visual system is highly adaptable, and additional myopia will be created initially at near, and then will appear at far vision. If we increase simply the correcting glasses, a vicious circle sets and myopia progresses over time … This also applies to some adults whose myopia progresses.

But if we respect the balance that exists between distance and near vision, there will be less effort when focusing and there will be less chance of progression. Unfortunately, this option will not always prevent some children to progress.

When bifocals are necessary, they may incorporate either a small round bifocal that does not show much or we can design a special glass with two zones (far vision at the top and reading at the bottom) and the transition between both areas is invisible. Aesthetic is no longer an obstacle to an adequate correction for children.

Child glasses with a small circular bifocal. 

Invisible bifocal suitable for children

I do not really like to use a progressive lens in the case of young myopic children. While glasses with two zones can be adjusted to prevent reading with the upper zone, you never know which area of the progressive lens will be used for reading. If the child leans his head too much, he no longer uses the reading portion essential for the proper control of myopia. The small hallway in the near vision portion of progressives will require the child to move the head and not your eyes. The more we obstruct peripheral vision, to more visual stress we cause.

Progressive lens with narrow reading area

See : http://www.myopiaprevention.org/references_environment.html

Wearing contact lenses

One day or another, many nearsighted young myopic teenagers will want to wear contact lenses for sports or simply to get rid of their glasses…

Regular contact lenses correct only the far vision as glasses that contain only the myopic power, unless they are multifocal. Regular lens wear creates the same situation as to wear glasses for distance vision only: if used for reading, writing and computer for prolonged periods, we may see a more rapid progress of myopia.

So, wearing regular contact lenses should be limited to outdoor and sports wear. As there are many reading and writing activities at school, wearing these contact lenses is not recommended.

Some studies have shown that there is a more rapid myopic progression with contact lenses that correct distance vision only than glasses to see far.

The results found in this study show a definite trend towards poorer accommodative (focusing) and vergence (alignment) function with the use of contact lenses in comparison to glasses. This downward trend is possibly creating a lag in accommodation to reduce associated overconvergence. The higher accommodative lags found in this study with single vision contact lenses indicate that prolonged use of these lenses in near tasks may provoke a continuous hyperopic retinal defocus, a risk factor for the onset and progression of myopia, as indicated in numerous studies.

  • Jiménez R, Martínez-Almeida L, Salas C, Ortíz C. Contact lenses vs spectacles in myopes: is there any difference in accommodative and binocular function? Graefes Arch Clin Exp Ophthalmol. 2011 Jun;249(6):925-35.

Alternatives?

Before the availability of multifocal contact lenses (which contain both a correction for distance and near vision), a young myope who wanted to wear contact lenses often had to wear reading glasses (spectacles) for near vision in order to counter the effect of the power of his myopic lenses, or remove the contact lenses.

Today, there are multifocal contact lenses specially adapted for young myopes. Here’s an example:

Contact lenses for young myopes: distance vision is at the center of the lens and reading vision lies in the periphery. Example of a contact lens Proclear EP (from Cooper Vision). There are now several other designs.

Bifocal contact lenses are worn during the day and removed at night. They give clear vision for objects far away and objects nearby. Generally they are worn every day although occasionally a day without the lenses will not adversely affect the treatment. The lenses are worn as long as myopia progression is considered a risk.

Bifocal contact lenses have been shown to slow the progression of myopia. The reason they apparently work is not that they reduce the reading effort, which they do, but rather that they create a ring of increased power surrounding central vision that the eye interprets as a “stop signal” for further growth thus reducing the progression.

New studies about bifocal contact lenses in children

There have not been many published studies of soft bifocal contacts being used for myopia control, but the Aller and Wildsoet study showed an 87% reduction in myopia progression for the first year.

Another example of bifocals with alternating zones for distance vision and near vision.Insight® lens (from Cooper Vision)

Dr John Phillips of the University of Auckland, New Zealand described a dual-focus soft lens with a central correction zone and concentric treatment zones. The lens reduced myopic progression by 37 per cent over 20 months in children aged 11-14 years compared with a standard contact lens. Half of those wearing the lens had their myopia progression slowed by 50 per cent or more, but the effect might be up to 80 per cent in future if combined with medication.

  • Anstice NS, Phillips JR. Effect of dual-focus soft contact lens wear on axial myopia progression in children. Ophthalmology. 2011 Jun;118(6):1152-61.

Professor Earl Smith of the University of Houston said that myopia control lenses needed to be fitted at an early stage and to very young children.

“In the very near future we’ll be using contact lenses to guide eye growth,” he said. “The principle could be applied to all corrections and might also work for hyperopic eyes. “

  • Earl Smith, III OD, PhD (Optometry & Vision Science September 2011 – Volume 88 – Issue 9 – pp 1029-1044

Each of these studies is for one year. Other non-contact lens methods have been found to have less effect after the first year and so it remains to be seen if the contact lens effect is multi-year.

This study has altered our thinking with regard to myopia development and effective treatments to reduce progression. Through extensive research Dr. Smith found that peripheral defocus triggers growth of the eye in a way that leads to an increase of myopia. The signals for this growth are in the peripheral retina. This axial elongation of the eye increases myopia and promotes myopia progression.

For other info or references on bifocal lenses and myopia:

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

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

Orthokeratology

Ortho-K (short for orthokeratology) is a process of gently reshaping the front surface of the eye (in fact, the cornea) to give a clear and comfortable vision. Indeed, the corneal tissue is very malleable and by a slight pressure due to the contact lens, we can change the curvature of the central cornea. This is a non-surgical procedure using specially designed customized contact lenses that are worn only at night and removed when awakening.

The result is a clear vision all day without lens wear during the day and without glasses. The lenses are inserted in the eyes every night since the procedure is not permanent (such as laser treatment), making this therapy safer for children. When the lenses are removed from the eye for a few weeks, the curvature of the cornea slowly returns to its original shape and myopia also returns after several days or weeks, to its initial pre-fitting parameters.

There are many designs of OK lenses but they are mostly equivalent, and all have the goal of reducing myopia overnight by changing the central curvature of the cornea. Orthokeratology is a great way to slow the progression of myopia (see www.myopiaprevention.org).

Children are excellent candidates for orthokeratology because they are motivated, quick to learn how to care for the lenses and respond quickly to the treatment. Ortho-K lenses are also great for kids who participate in sports activities, because they do not have to worry about losing their contact lenses while they are active.

It is a safe alternative to LASIK or other refractive surgery procedures that are not even available for children.

See: http://en.wikipedia.org/wiki/Orthokeratology

Source : http://www.orthokdoctors.com/what_is_orthokeratology.html

Orthokeratology lens worn on the eye (coloring has been added)

Myopia (2)

What we must understand

Even if myopia cause blurred vision at distance (at far), we know that the origin of the problem comes from using our eyes at near. And often we need to correct the near vision to try to solve the problem.

What can be done? Can we prevent this condition?

 We consider that the refraction state “normal” when a child’s shows a light farsightedness (or hyperopia) which protects against myopia, by acting as a “shock absorber». With time, we can note in the visual examination that some children decrease their farsightedness towards emmetropia (meaning that the child is neither farsighted nor nearsighted). When the child is emmetrope, there is only a slight step to become myopic. And this step sometimes happens very fast.

This is what happens:

Pre-myopia

When we realize that the farsightedness is disappearing, it is necessary to begin to correct the near vision before appears myopia.

We favor bifocal lenses so that the child can see at far and at close without removing his glasses constantly. It is also possible to consider reading glasses only. These lenses are adapted to the near vision: they decrease the tension of how the eyes center and improve the functioning of the focusing system of the eyes.

When the child becomes nearsighted

Even with a little degree of nearsightedness, far vision is significantly reduced.

A complete visual examination will allow us to estimate if we have to correct the near vision and if we have to correct only a portion of the myopia present.

An option, which we unfortunately see too often, is the sole correction of myopia, without taking in consideration the near vision. This last option is the one that can cause most disadvantages. Indeed (see the figure which follows), if we simply correct the myopia, the child will see more clear at far but will be reading through a power of myopia which is not needed for reading.

Thus, the myopia will tend to increase ceaselessly. Sometimes, we see children who double the quantity of their myopia every year!

Peripheral defocus

From 0 to 6 years old, the eyes, like the rest of our body, will grow and all parts of the eye are involved and thus, in the retina, the eye should always receive a clear picture. This growth is called emmetropization and should end around the age of 6 years. This process attempts to eliminate nearsightedness or excessive farsightedness in children.

It seems that in some children, emmetropization does not stop. This creates a defocus (or blurring) called “hyperopic defocus”  in the region of the peripheral retina, thus the periphery of the retina sends a chemical message (via modulators) which will aim to restore the focus by changing the refractive power or size of various parts of the eye… resulting in myopisation. The problem would be that focusing of the central retina and the retina in the periphery is not simultaneous.

This is the same process that is triggered when one corrects myopia regardless of near vision (middle image). Visual acuity is restored but the peripheral defocus persists when the child uses his near vision. Hence the possible increase in myopia over time. A correction that takes into account both distance vision and near vision (right image) is much more appropriate.

Studies show that prescribing single vision glasses (for distance vision only) that are used when reading is the option that causes the greatest increase in myopia. For example:

“Previous investigators have suggested that peripheral hyperopic defocus may play a role in the development and progression of myopia. We have shown that SVLs used to correct myopia can result in increased hyperopic defocus at the peripheral retina in the eyes of Chinese children. The magnitude of this increase tends to escalate with increasing refractive error and eccentricity, especially in cases with moderate levels of myopia.”

  • Lin Z, Martinez A, Chen X, Li L, Sankaridurg P, Holden BA,  , Ge J. Peripheral defocus with single-vision spectacle lenses in myopic children. Optom Vis Sci. 2010 Jan;87(1):4-9.

Myopia (1)

KNOW EVERYTHING ABOUT MYOPIA (NEARSIGHTEDNESS)

Myopia in children and adults is a complex subject, both by its origin and by its evolution. We will try to clear up all the notions which relate to myopia.

Simplistic explanation:

Uncorrected myopia

In a simplistic way, in a nearsighted eye, rays of light are going to focus in front of the retina, which causes blurred vision at distance (far away). Corrected myopia

When we correct myopia with concave or myopic lenses (also called “minus” lenses), rays of light are going to focus in the plane of the retina and the vision is clear. But this is that a simplistic explanation. In fact, a new study finds that myopia develops in children when the crystalline lens stops adapting to the eye’s continued growth, according researchers at The Ohio State University College of Optometry:

The crystalline lens stopped thinning, flattening, and losing power within ±1 year of onset in children who became myopic compared with those who did not become myopes. Myopia onset is characterized by an abrupt loss of compensatory changes in the crystalline lens that continue in emmetropes (non myopes) throughout childhood axial elongation. The mechanism responsible for this decoupling remains speculative but might include restricted equatorial growth from internal mechanical factors.

  • Mutti DO, Mitchell GL, Sinnott LT, et al. Corneal and crystalline lens dimensions before and after myopia onset. Optom Vis Sci. 2012 March;89(3):251-62

Why Myopia? 

There are two theories: the genetic theory and the environmental theory.

Genetic theory

The genetic theory asserts that people become nearsighted because it is registered in their genes and that there is no relationship between nearsightedness and the use of the eyes… The familial incidence, according to this theory, persuades that children who have nearsighted relatives (father and mother) will have no other choice than to become, them too, nearsighted.

Environmental theory

The environmental theory asserts that besides children that are born nearsighted (often they show a very important nearsightedness), nearsightedness is a possible adaptation to “visual stress”: schooling, long hours to read, write and draw, long hours at a computer, at video games, reading and writing, too short reading, writing and computer distance, body posture while reading, etc.

Several scientific studies show that when we compare two populations presenting homogeneous genetic characteristics (Amerindians, Inuit), the proportion of schooled people who become myopic is significantly more. Optometrists qualify this myopia as “school, stress-related or work-related myopia”. We can even assert that today, children become nearsighted younger and show a progression of their myopia that is more rapid than even twenty years ago! So, it is not surprising that the best readers are often myopic.

Today, adults can also become myopic further to a new and important use of the eyes (working in front of a computer is a good example). We qualify this kind of nearsightedness as “late-onset adult myopia”. At the beginning of the century, it was said that the condition would stop progressing with puberty… but this is true but not «really» true. People at the time would stop going to school at a much younger age than today, stop reading and go work hard with their hands. With all the visual requirements our eyes have to face, it often happens that myopia does not stop progressing. It is then necessary to act upon it.

Morgan & Rose, in 2005, discussed the relative importance of genetics versus environmental induced myopia:

A small proportion of myopia is clearly familial, generally early in onset and of high level, with defined chromosomal localisations and in some cases, causal genetic mutations. However, in economically developed societies, most myopia appears during childhood, particularly during the school years. In addition, high heritability sets no limit to the potential for environmentally induced change. There is in fact strong evidence for rapid, environmentally induced change in the prevalence of myopia, associated with increased education and urbanisation. Environmental change appears to be the major factor increasing the prevalence of myopia around the world.

  •  Morgan I, Rose K. How genetic is school myopia? Prog Retin Eye Res. 2005 Jan;24(1):1-38.

This should not convey the idea that the only correction possible are glasses or contact lenses to see at far and that there is nothing we can try to warn or  control the progression of myopia. This is not really true.