Humans would not have evolved as hunters and food gathers if they were myopic (i.e. blurry distance vision would have made catching game or finding food while avoiding getting eaten very difficult). Myopia is one of the most investigated areas within vision science. Yet we still do not fully understand why myopia develops and how to stop it.
There have been many theories as to the possible mechanism that causes myopia. For myopia to occur the eyeball has to grow longer (change in axial length). In the past this axial length change was considered to be either due to genetics, as myopia tends to run in families, or due to prolonged periods of near focus. The rapid increase of myopia over the last 100 years seems to coincide with the increase in literacy and industrialisation in most countries. This could indicate that high near visual demands / visual stress maybe a significant causal factor in developing myopia in some individuals.
Recent research has also found that a blurry image on the peripheral retina can stimulate axial length growth independent of any other factors. This implies that new treatments may need to be designed to compensate for peripheral blur as well as the central blur that normal spectacle or contact lenses already compensate for.
We conclude from all this that: The cause of myopia most likely involves a complex interweaving of genetic and environmental factors. There are different types of Myopia, the possible causes of which may be grouped into the following categories:
There is no one treatment that has been found to be effective in stopping/slowing every type of myopia from progressing. This is understandable if we consider that there is probably more then one causal factor. Based on the present research into treatment options we recommend the following:
You can’t do anything about your myopic genes…yet! Twin and family studies strongly indicate that myopia is highly inheritable. The prevalence of myopia is greater in children of myopic parents than children of non-myopic parents. Parents with a moderate to high degree of myopia should have their children’s vision examined every 12mths while they are at school and every 2 yrs thereafter.
Good visual habits will reduce any near visual stress and may or may not be contributing to the development or progression of myopia. Either way, reducing near visual stress is a good thing for any visual system. Good visual hygiene includes not getting too close to near work (not inside your knuckle to elbow distance) and taking regular breaks by looking away from your near work every 5 mins. If you notice a blur when you first look away it is time to take a longer break. Prolonged close work while tired or sick may also increase near point stress and should be avoided.
A recent Australian study found that students who combined high levels of near work with low levels of outdoor activity were more likely to go myopic, whereas students who combined low levels of near work with high levels of outdoor activity were more likely to stay longsighted. This was confirmed by a Singapore study which also found that lower amounts of sports and outdoor activity increased the odds of becoming myopic in those children with two myopic parents more than in those children with either zero or one myopic parent. The chance of becoming myopic for children with no myopic parents appears lowest in the children with the highest amount of sports and outdoor activity, compared with those with two myopic parents.
Compensating minus lenses (specs or contacts) should be prescribed to clear the distance vision (6/9 VA or worse). Putting up with blurry vision because you don’t want spectacles or wearing a weaker (under – prescribed) lens than required will not stop myopia from increasing. It may in fact cause the myopia to get worse because of peripheral retinal blur.
The Ortho-K technique uses special rigid contact lenses which change the curvature of the cornea to neutralise the myopic prescription. These lenses are worn all night and removed each morning. As the day goes on, the cornea slow returns to its original curvature and the myopic blur returns. How fast this happens varies with individuals. 2010 studies in Australia and Singapore have shown that ortho-K will also slow the rate of progression of myopia. It is thought that the moulded corneal shape induced after lens wear focuses light to both the central and peripheral retina. Unlike glasses or soft contact lenses, which focus light on the central retina but ignore the peripheral retina, ortho-K focuses peripheral blur; one of the recently established causative factors of myopia. This is why ortho-K is now a popular technique for myopia control.
Both rigid and soft contact lenses can be used to compensate for the distance blur. This may be of particular advantage for those involved in sport or who find the appearance of spectacles unacceptable. You will still need a back up distant spectacles for times when you do not wear your contacts. New contact lens designs are presently being prescribed that specifically clear peripheral retinal blur in the hope of stopping / reducing myopic progression. The early studies on this new approach are very promising but the research is still on going.
Wearing plus lenses (or less minus) for close work has the effect of reducing the focusing (accommodative) demand and makes it easier to keep the eyes turned in (converged). This is called reducing near point stress. Some studies have found this to be effective way of slowing / reducing the rate of myopic progression while other studies have found it not to work. A recent study in China found that using progressive addition lenses slowed the myopic progression in children without moderately or highly myopic parents, especially for children whose eyes have a tendency to drift in (esophoria) or were female.
o Over the age of twenty one.
o Have stable myopia for at least twelve months.
o Have corneas of a certain thickness and not have keratoconus.
*** If you require any further information any of these treatment options please do not hesitate to ask your optometrist.