WHAT CAUSES MYOPIA?
The causes of myopia are complex, multifactorial and vary between individuals. Both genetics and environmental influences in at play.
It is well known that myopia runs in the family. A child with one parent with myopia is 3 times more likely to develop myopia, and 6 times more at risk if both parents are myopic. However many children whose parents have perfectly good eyesight can still develop myopia, hence genetics cannot be the only reason.
Ethnicity also plays a role in the genesis of myopia. Children of East Asian and South Asian descent are most at risk, followed by Middle Eastern, Hispanic, African/Caribbean children, with Caucasian children being at relatively lower risk. This is evident in the large proportions of Asian children with myopia in Asia as well as in Australia, although the number of Caucasian children developing myopia is certainly on the rise.
It's very common for parents to think too many time on the iPad, smartphone, computer games and watching TV are making their kids' eyes worse. While these activities may certainly be contributing factors, it may not necessarily be these devices per se but the amount of time spent on near activities in total and the relative lack of time spent outdoors. Let's examine the environment factors in more detail.
All activities that require the eyes to focus at a close distance (within 1 metre) can contribute to myopia development. This includes school work, homework, reading, computer use, drawing, crafts, tutoring sessions, playing and learning music, as well as iPad and smartphone time. When a child is focusing up-close, the focusing state of the eye and the workings of the eye muscles are linked to signals that stimulate eye growth. These are also mostly indoor rather than outdoor activities, another major contributing factor.
Myopia is very much an eye condition attributed to our modern society and lifestyle. The human eye has not evolved to keep up with the demands of our visual needs. Children are using their eyes for many more near-viewing tasks than before, there is a greater emphasis on formal education from an earlier age in our highly competitive society, and kids are spending less time playing outdoors than a generation ago. As our homes become smaller, backyards shrinking and more families living in apartments and units, children's viewing distances are becoming shorter. All these are contributing to myopia development in our society. In many ways, the rise of myopia in western societies is mirroring what occurred earlier in Asia with their educational cultures for younger children and more compact living spaces.
Eyestrain and focusing issues at near
Some children have additional individual factors involved with their close-up focusing that can increase myopia development. Two of these factors are 'near esophoria' and 'accommodative lag'. Essentially, these relate to how well the two eyes are working as a team when aiming focus at an object at close range, such a book when reading.
Significant additional demands on the focusing system and muscles due to an inefficiency in eye-teaming and inaccuracy in focus aiming can lead to eyestrain, which in turn is linked to myopia progression. A detailed assessment of a child's close-up focusing is part of our comprehensive children's eye examination, to detect these potential issues. Caucasian children and teenagers have a greater tendency for these near focusing issues than Asian children.
Not enough outdoor time
There is strong research to suggest that kids who spend too little time outdoors are more likely to develop myopia. And spending more time outdoors can help prevent or delay myopia onset. While the exact mechanism of how this works is still unclear, it is believe to be related to the amount of ambient light received by the eye outdoors versus indoors and that large amounts of sunlight helps modulate proper and correct eye growth. It is not so much the type of outdoor activities involved but the total amount of outdoor time that matters. We recommend all children to spend an average of 1.5 hours per day participating in any outdoor activity — this may include walking to and from school, in the playground, playing sport or walking the family dog.
WHAT CAUSES MYOPIA TO PROGRESS?
Delayed vision correction
Younger children often develop early stages of myopia without being aware that their vision is blurred and hence may not complain to their parents about not seeing clearly. We often see children attend for their first eye test with already -1.50 or even -2.00 of myopia. This delay in diagnosing and correcting myopia contributes to progression due to the prolonged defocus and blur in the retina, stimulating the eye to grow longer.
For this reason, we highly recommend that all children — and even more importantly children with a family history of myopia — are routinely tested from age 3 onwards, so that myopia can be detected as early as possible. We can often even predict when a child may become myopic by monitoring their eyes' natural change in focusing state over time as they grow.
Some older children who already wear glasses for myopia can also be in denial about their vision deterioration, and some out of fear of being told off for their worsening eyesight and losing access to their computer games or iPad. By not telling their parents about their blurred vision and not wearing the best correction possible they are potentially making their eyes even worse. Children with myopia should be tested every 6-12 months regardless of whether or not they complain of blur.
Under-correction of myopia
Some people believe that deliberately making glasses weaker than the actual prescription needed to see clearly can help prevent eyes from getting worse. This is called 'under-correction'. In some parts of the world, particularly in Asian countries, this was and still is common practice. Clinical research has found that under-correction does not reduce myopia progression but may actually increase progression, because of the increase in retinal image blur. Prescribing the full myopia prescription needed for best distance vision is the current evidence-based approach to help minimise progression.
Wearing incorrect prescription or lens type
Patients and children wearing an incorrect prescription — one that may be too weak or too strong — can lead to accelerated progression. A pair of glasses that is too strong can cause eyestrain and focusing fatigue, particular when focusing up-close. For this reason it is important for parents to seek an experienced and trusted optometrist for their children. Children's eye test results can be more variable and focus-numbing eye drops are sometimes needed for a more accurate assessment of their eyes' focusing status.
For children who have an eye-teaming and near focusing issues in addition to their myopia, . Not all optometrists carry out detailed binocular eye-teaming tests as part of a children's eye examination, and as a result sometimes these issues can be missed. A children who is wearing single-vision distance glasses for full-time use but has close-up focusing issues with these glasses during reading may have increased myopia progression as a result of not being prescribed the optimum lens type for his or her focusing needs.
Wearing regular glasses and/or contact lenses
The traditional method of vision correction for myopia in children has largely been with glasses, and occasionally with contact lenses. That is what optometrists have long been taught to do for the past hundreds of years, to prescribe corrective glasses and lenses to refocus light into the eye, providing clear vision to the wearer.
New eye research within the past 5 years have found that while regular glasses correct sight they do not help prevent myopia progression but may even contribute to progression. This is due to the way central and peripheral light is focused in the eye with traditional glasses or single-vision contact lenses (click on the following image for a more detailed explanation). For children with progressive myopia and rapid increases in their prescription, glasses and regular contact lenses are no longer the best method of correcting their sight.
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