What is myopia?
Also known as short-sightedness/ near-sightedness, it is a condition where the eye is unable to see objects in the distance clearly.
A myopic eye sees better when:
– Squinting (partially closing the eyes)
– Wearing corrective spectacles or contact lenses
– Objects are closer
Why does myopia occur?
Imagine the eyeball as a camera. When the camera is not in focus, the photos appear blurry.
When the eye’s optical system cannot focus the light rays properly on the back of the eye (retina), our image of the world is blurry.
This is because the eyeball is too long, so the eye’s image is focused in front of the retina, not on it.
What other problems can myopia cause?
There are short and long-term problems.
Short-term: poor vision for far objects, affecting daily activities such as learning at school, driving, watching TV/ movies/ theatre, sports, eyestrain, headaches.
Long-term: accelerated aging of the eye. Degenerative conditions such as cataracts, retina aging/ detachment, floaters, reduced vision can occur earlier.
Some of the degenerative conditions of the eye cannot be reversed or cured, even with surgery.
When does myopia start and can it be cured?
Myopia can start at any age. When myopia occurs, it is usually progressive.
In Singapore, our myopia rates are one of the highest in the world: About 20% of our 6 year olds, 65% of our 12 year olds and 83% of our 18 year olds are myopic.
Myopia usually stabilize at adulthood (i.e. 20 years old)
Myopia is usually irreversible. Some low degrees of myopia can be diminished, but seldom happens.
Recent research has shown that eyeball growth is accelerated just before myopia starts. This eyeball growth is known as axial elongation.
Why is axial elongation a concern?
When the eyeball grows too long, the retina at the back of eye becomes more susceptible to degeneration, tears, detachments, macula degeneration, glaucoma and ultimately loss of vision. The optic nerve, is also at higher risk of degeneration.
These risk factors remain even with refractive or laser surgery to correct myopia.
Since the retina and the optic nerve are irreplaceable, any damage is permanent.
During childhood, the rate of axial elongation is the fastest.
That is why myopia control during childhood is the most important consideration in slowing myopia progression.
Images of damaged retina: from Verkicharla, Pavan & Ohno-Matsui, Kyoko & Saw, Seang-Mei. (2015). Current and predicted demographics of high myopia and an update of its associated pathological changes.
Normal eyeball growth vs excessive axial elongation
Normal eyeball length for a “perfect sighted eye” depends on age, gender and ethnicity.
In general, a normal/ average eye ball length for
6 years old 22.7mm (annual growth 0.24mm)
9 years old 23.24mm (0.09mm)
12 years old 23.45mm (0.04mm)
14 years old 23.51mm (0.02mm)
16 years old 23.55mm (0.01mm)
18 years old 23.57mm (0.01mm)
20 years old 23.58mm (0.00mm)
As it can be seen, the growth rate reduces as the child gets older.
Even before myopia sets in, if the eyeball length exceeds the average for age, it means that the risk of myopia or even getting high myopia, is greater.
Therefore, the younger the child, the more important it is to follow-up on the child’s myopia progression.
What can we do about myopia?
There are short and long-term management.
Short-term: corrective glasses and contact lenses to see clearer.
Long-term: reducing the progression of myopia to prevent high myopia, which can significantly reduce the risks of degenerative conditions of the eye. (Pathological myopia)
Myopia control intervention
Pharmaceutical or optical
Pharmaceutical refers to Atropine eye drops. This is a medicated eyedrop that has been shown to reduce the rate of myopia progression in children. It is available in a range of dosages starting from 0.01% up to 1%.
The higher the dosage, the more effective the myopia control, but side effects are more apparent.
Up to 0.05% is commonly well-tolerated with little side effects.
Side effects include glare sensitivity, blur vision at near, itchy and/or red eyes, eye dryness etc.
Atropine drops do not correct myopia, so optical aids are required.
Optical options include myopia control spectacle lenses, contact lenses, orthokeratology and red light therapy.
The myopia control lenses inhibit eyeball length growth (axial elongation) by focusing light inside the eye in a unique way, to allow clear vision and control eyeball growth.
This is different to standard spectacle lenses or contact lenses.
In summary, myopia is not just a vision impairment, it is also a disease of the eye which can result in permanent visual loss.
There is no “safe” level of myopia. The lower the myopia or axial elongation, the lower the risk of future vision loss. Intervention is most effective during childhood or when myopia progression is imminent.
The measurement of myopia is not only the power of the eye, but also the eyeball/axial length.
It is important to monitor both during the routine eye exam of a child/ teenager.