Written by Karyn Zhao, Optometrist
What is myopia
Myopia - also known as short-sightedness - is where vision is blurry in the distance but may be clear up close. Myopia has become increasingly more prevalent around the world, with around 30% of New Zealanders falling into the short-sighted category. It is thought that by 2050, half the world’s population will be myopic.
Myopia occurs when the eye grows longer, resulting in light rays focusing in front of the retina (light-sensitive layer of the eye) rather than onto it. As a result, myopic people need glasses or contact lenses to focus the light onto the retina. As their myopia progresses, they will need to replace their glasses or contacts with updated prescriptions.
Milburn & Neill Optometrists now have an Lenstar 900 Biometer to more accurately measure the axial length or growth of the eye. This will soon becoming the standard of care in myopia control management will help to assist in measuring the success of the different methods of myopia control in your child.
Genetics, visual environment, and ethnicity can all play a role in the risk of your child and whether or not they are likely to develop myopia.
Spending more time doing close work like reading/using smart phones and tablets, and playing computer games have been linked to the development of myopia.
Myopia can be hereditary - a child with one myopic parent has 3x the risk of developing myopia, and a child with two myopic parents has 6x the risk.
What are the risks of myopia
Myopia tends to progress/worsen as children age, with younger myopic kids being associated with higher levels of myopia in adulthood. Increasing levels of myopia are associated with higher risks of eye disease during the child’s lifetime, including but not limited to retinal detachment, myopic macular degeneration, glaucoma and cataracts.
Of the most concern is that any level of myopia increases the chance of blinding eye-conditions, such as retinal detachment, cataracts, glaucoma and myopic retinal degeneration later in life. The higher the level of myopia, the higher the risk.
What is myopia control
Myopia control involves the use of various methods with the aim to slow down or stop the progression of myopia. These methods can include prescribing specialty myopia-control glasses, soft or hard contact lenses, or eyedrops. Additionally, modifications to one’s visual environment such as limiting screen time and increasing outdoor play can also be beneficial in slowing down myopic progression.
Prescribing standard glasses or contacts does nothing for slowing down myopic progression and will lead to frequent changes in spectacle/contact lens powers, as well as increase the risk of sight-threatening problems in the future. When conventional spectacles or contact lenses are used to correct myopia, light entering the eye centrally is accurately focused onto the retina. On the other hand, light entering off-centre will focus behind the retina, which stimulates the eye to lengthen and hence leading to increased myopia.
Unfortunately, the lengthening of the eye which results in myopia is irreversible, and hence early intervention is critical in myopia control - thus bringing us to myopia control.
Miyosmart & Stellest Lenses
Miyosmart lenses work through multiple little honeycomb-shaped segments which form a ring-shaped “treatment zone”. This treatment zone creates defocus which slows down the eye’s elongation and hence myopic progression, whilst retaining sharp focus for the central vision so that activities are not affected.
Essilor’s newest lens - the Stellest lens - acts in a similar way with 1021 highly aspheric lenslets arranged in concentric circles providing the peripheral defocus which acts to slow down the progression of myopia in its wearers. Similarly, a clear zone is left in the centre to allow for clear central vision so that everyday vision and activities aren’t impacted.
Miyosmart and Stellest lenses have both been shown to be able to slow myopic progression by up to approximately 60%.
Misight/NaturalVue daily disposable soft contact lenses
Misight contact lenses were designed by a research team at the University of Auckland and aims to slow down myopia progression. Misight contacts have been shown to slow the progression of myopia by over 59% compared to a standard contact lens over a 3-year period.
Both Misight and NaturalVue contact lenses work to slow myopia by altering how off-axis light is focused on the retina. Both contacts are made with the peripheral defocus theory in mind - where peripheral light is focused in front of the retina, leading to myopic defocus and acting as a signal to slow or stop further eye elongation. These contacts do not compromise on the clarity of central vision, and are worn during the day and disposed of at night after each wear without any cleaning or storage required.
Orthokeratology lenses are hard contact lenses that are designed specifically for each patient’s eyes, and worn overnight to correct vision during the day. They work by gently reshaping the surface of the front of the eye overnight, which counteracts myopia. This means that no glasses or contacts need to be worn throughout the day.
Recent research has shown an average reduction in myopia progression of approximately 50% with orthoK lens wear. OrthoK lenses act to slow myopic progression by altering the shape of the eye’s surface, which in turn leads to central light focusing accurately on the retina and peripheral light in front of the retina which - similarly to misight/naturalvue contact lenses above - act to slow down or stop further eye elongation.
Atropine Eye drops
Atropine eye drops have been used for a number of years in the control of myopia progression. Low dose atropine has been found to be effective in the control of myopia without any major effect on pupil size or near-focusing ability.
While there have been recent studies into the effectiveness of lower dose atropine, current studies suggest 0.05% as the most effective concentration that balances risk of side-effects whilst also providing control of eye length elongation.
Atropine drops are instilled once nightly in each eye and can be used on their own or combined with other therapies such as OrthoK in order to maximise myopia control effect.
As atropine is not readily available at concentrations below 0.5%, these drops will need to be specially made by a compounding pharmacy.
The current theory for how atropine works is that the atropine molecule acts on a receptor in the back of the eye, which sends a signal for the eye to stop growing excessively. This is still an ongoing area of research, and the mechanism is being studied closely as to exactly how atropine acts to slow myopia progression.
Why is myopia control important
Besides a lower final prescription meaning thinner lenses, myopia control can also mean less frequent changes needed to be made to glasses or contacts as the prescription stays stable for longer. Quality of life is also improved, as low myopes are typically still functional without glasses but higher myopes will not be able to function much without visual correction.
Once a child is myopic, it tends to progress and worsen every few months and the younger a child is when they become myopic, the faster that this progression typically is which leads to higher levels of myopia as an adult.
A childhood myopia worsens, the eye is growing at an accelerated rate. This excessive growth stretches the light sensitive layer in the back of the eye, which in turn increases the risk of eye diseases and vision impairment occurring across your child’s lifetime.
As for laser surgery later on in life, a lower prescription is often associated with better visual outcomes post-surgery, and higher prescriptions can complicate these procedures. Additionally, laser surgery does not change the inside/back of the eye and hence the increased risk of blinding conditions remains unchanged even if vision is now good without correction.
Myopia control is all about slowing down this excessive eye growth to be as close to the normal rate expected in childhood as possible, which limits both the final prescription of your child’s glasses, as well as reducing the risk of future eye diseases which can be increased even with low levels of myopia
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