What
is myopia control?
Myopia, or short-sightedness, is becoming increasingly common with each generation. Typically, myopia starts between the ages of 7 years to 14 years and then progresses for a few years. As a general rule, the later that myopia starts the less it is likely to progress. If it starts as young as at 5 or 6 years then it is likely to progress to be a high degree of myopia. Myopia is often classified as follows:
·
Low
(physiological): up to -3.00D
· Intermediate: -3.00D to -5.00D
· High (pathological): more than -5.00D
One of the most common activities of eyecare practitioners
is to correct myopia with glasses, contact lenses, or laser surgery. A few
optometrists, like those at Cole Martin Tregaskis Optometrists, have an
interest in myopia control. This involves controlling (reducing) the rate of progression
of myopia. At the moment, this means adopting strategies to slow down myopia
progression. In the future it is hoped optometrists may be able to reverse
myopia and maybe even cure myopia.
Our principal optometrist, Professor Bruce Evans, has a special interest in myopia control and this is shared by the other optometrists at Cole Martin Tregaskis Optometrists. Professor Evans wrote this summary of recent thinking on myopia control as a guide for patients and as an outline of the methods of myopia control which are available at Cole Martin Tregaskis Optometrists.
Why
worry about myopia?
Myopia is
easy to correct with spectacles or contact lenses, so why is anyone bothered with
trying to control myopia progression? Low degrees of myopia are not a major
problem, and indeed when people reach their 40s and the eyes lose their ability
to focus close to then there are advantages to having a low degree of myopia. But
intermediate and high degrees of myopia cause people to be visually impaired without
their glasses. For example, a high myope may not be able to see the alarm clock
when they wake in the night. For high myopia, glasses will be thicker and less
attractive, although modern high index spectacle
lenses can make glasses thinner than used to be case and contact lenses are another solution. More
importantly, high myopia is associated with an increased risk of significant
eye diseases, such as retinal detachment and glaucoma. If myopia progression
could be controlled in a child then this might mean that they only ended up
with an intermediate degree of myopia, say -4.00D, instead of a higher degree,
say -6.00D. This would reduce the risk of eye disease and improve the quality
of life.
What
are the risk factors for myopia?
There is a genetic component to myopia, and this partly explains
why in some Asian countries (e.g., Singapore) up to 80% of young people have
myopia. If one or both parents are myopic then this increases the risk of a
child being myopic. For example, in one study children with two myopic parents
were 
over
six times more likely to become myopic than children when neither parent is
myopic.
Environmental factors have also been linked with myopia, and
many people have wondered whether part of the
reason for the high prevalence of myopia in countries like Taiwan may be linked
to intensive studying from a very young age. In particular, experts have
wondered whether the eyes constantly focussing close to on books may be a
trigger for myopia. In fact, the evidence suggests that this is not a very
strong risk factor for myopia, but may be a contributory factor in some cases.
This has led many eyecare practitioners to wonder whether bifocals, which
reduce the amount by which the eyes have to focus during near vision, might slow
down the progression of myopia. There is some evidence that bifocals may help
in certain cases and this is discussed below.
Interest in this topic has
been increased with the publication of two recent research studies indicating
that children who spend a few hours a day outdoors are less likely to become
myopic. Interestingly, this may be more related to light levels than to
focussing in the distance.
Bifocal
spectacles for reducing myopia progression in children
As noted above
,
many experts have suggested that if children are fitted with bifocal spectacles
when the child first becomes myopic then this might slow the progression of
myopia. There have been some quite large studies of the use of bifocals for
myopia control and the results have been mixed. It seems that bifocal
spectacles are only helpful at reducing myopia progression for children whose
myopia is associated with a particular condition called near esophoria. Near
esophoria describes a latent tendency for the eyes to turn inwards. The
tendency is latent and so parents would not be likely to notice an eye turning.
Near esophoria is something that we test for at Cole Martin Tregaskis Optometrists
and your optometrist will be able to explain whether your child has a near
esophoria.
When bifocals are fitted to children with near esophoria then research suggests that, on average, myopia progression will be reduced by between 20% and 46%. Some children with near esophoria experience eyestrain and headaches associated with the condition and these children would benefit from bifocals to reduce these symptoms, as well as to reduce the risk of myopia progression.
When children are fitted with bifocal spectacles they tend to adapt to them very well, finding them much easier to adjust to than adults. The top line of the bifocal is usually fitted a little higher than in adults and the child will need regular adjustments of the spectacles to check that the bifocal is at the correct height.
Peripheral defocus and new developments in myopia control
Recent research has uncovered a new major factor associated
with myopia development. The central area of the retina (fovea or macular)
gives us our sharpest vision and traditionally the emphasis has been on how
sharply spectacles and contact lenses focus an image on the retina. But recent
research indicates that the way in which light is focussed in the peripheral
retina may be very important for myopia control. 
For children who are becoming myopic, it seems that the peripheral image focus is behind the retina, and this might trigger the eye to grow which is what happens in myopia. This is explained in more detail on two very good websites: www.myopiaprevention.org and www.myopiaprevention.com. Special contact lenses have been developed by two contact lens manufacturers which are designed to correct this peripheral defocus, but these are not yet available in the UK. Professor Evans has provided advice as a key opinion leader consultant to both companies and when their products are available in the UK then Cole Martin Tregaskis will be amongst the first practices to fit them. In the meantime, there are two other approaches that also correct this peripheral defocus and which are available in the UK: Orthokeratology and multifocal contact lenses.
Orthokeratology
Orthokeratology, also known as corneal reshaping treatment,
involves fitting the eyes with rigid gas permeable contact lenses to be worn
overnight. The contact lenses are fitted with great accuracy using a 
corneal
topographer and the lenses are precisely manufactured so as to reshape the
cornea overnight. The reshaping of the cornea is temporary, but usually lasts
for a day or two. The idea is that the cornea is reshaped in a way that
corrects myopia, so as long as the contact lens is worn overnight then no glasses
or contact lenses need to be worn during the day. Another area of this website is
dedicated to Orthokeratology.
For many years, Orthokeratology practitioners noticed that when myopic children were fitted with Orthokeratology the myopia seemed to progress much less than usual. This is now believed to be because the reshaping of the cornea corrects the peripheral defocus. Studies indicate that Orthokeratology reduce myopia progression on average by about 50%.
Multifocal contact lenses
Multifocal contact lenses were originally designed to work rather like varifocal glasses to give adults over the age of 45 years clear vision at distance and near. Several scientists observed that the optics of some types of multifocal contact lenses are such that they correct the peripheral defocus in myopic children. Research studies have therefore been carried out in which myopic children were fitted with multifocal contact lenses in an attempt to slow myopia progression. The early results are very encouraging, indicating that myopia progression can be slowed by about 50%. These soft multifocal contact lenses are worn during the day. They are comfortable and give good vision, so are popular with children. More information can be found in the page on this website about contact lenses.
A word of caution
Two points need to be stressed. First, none of the interventions described here are likely to stop myopia progression, just to slow it down. Second, although both Orthokeratology and multifocal contact lenses on average slow myopia progression by about 50%, these are average results and cannot be guaranteed in an individual case. For some children, the myopia progression may be slowed more than this but for others it may be slowed less, or not at all.