Myopia – Written by Arief Tjitra Salim, BEng (Hons), Bioengineering.
Myopia, also known as short-sightedness or near-sightedness, is a refractive error in the eye that affects a person’s ability to focus on distant objects. Distance vision and visual acuity can be tested by assessing one’s ability to see near and distant objects and the letters on a vision chart held at 3 metres (or 10 feet) away. Those with myopia typically see objects less than 50 centimetres away, such as books and device screens clearly.
This type of refractive error occurs when the axial length of the eye (distance from the front to the back of eye) grows too long or the optical power of the cornea or lens is too high. This mismatch of the eye and its optical components causes incoming light rays to focus in front of the retina, resulting in blurry distance vision (figure 1).
Figure 1. Comparison between an eye with and without myopia.
(Source: Plano, 2021)
The following sections will briefly outline the public health implications of myopia, what causes myopia, its signs and symptoms, and some insights into its management and treatment.
Myopia currently affects approximately 1 in 3 people in the world and by the year 2050, almost 5 billion people (that’s half of the world’s population) are expected to have myopia .
Myopia affects people of every race and gender in every country. In countries such as Singapore, Hong Kong, Taiwan, and South Korea, the proportion of young adults (19 – 25 years of age) who have myopia has quadrupled in the past 60 years to approximately 80 to 90%. Similarly, other regions such as the United States, Europe and Australia have also reported a rise in myopia, with up to 40% of people now affected .
From an economic perspective, myopia also poses major problems to the economy, with recent estimates suggesting that the loss of productivity associated with myopia costs the global economy up to US$244 billion per year . These costs are almost 30 times higher than dengue, which has been estimated to cost US$8.9 billion in lost productivity globally each year.
Myopia is a serious eye condition that can develop at any age, although it typically develops during primary school years, with most cases of myopia reported between 8 to 14 years of age. In the last decade, studies have shown that the average age of children who develop myopia is decreasing. A study conducted in Singapore showed that 11% of children aged 6 to 72 months already had myopia . This is of concern because, the younger a child develops myopia, the more likely their myopia may worsen over the years before it stabilises at around 15 to 21 years of age. The younger you develop myopia, there is a greater risk of developing its severe form called high myopia (or severe myopia).
The degree of myopia is measured in dioptres (D), which is the power of the concave (inward curving) lens required to correct the myopia, and is generally classified into 3 categories:
High myopia is associated with an increased risk of developing sight-threatening eye conditions such as myopic macular degeneration, retinal detachment, and glaucoma. This is because people with high myopia have an even longer eyeball shape as compared to those with low and moderate myopia. The longer the eyeball, the more susceptible it is to get damaged due to the excessive thinning of the outer walls of the eye (also called the sclera).
Recent estimates predict that high myopia is expected to affect 1 billion people by the year 2050, putting a great number of people in the world at risk of developing significant vision loss and in some cases irreversible blindness .
Myopia is an eye condition that is influenced by both our genes (family history) and the environment, such as increased near work activities (for example digital device use), lack of outdoor time and physical activity, urbanisation, educational attainment, and even sleep.
To date, more than 20 genes have been associated with myopia, and a further 10 in high myopia . However, there is no single gene that explains the development of myopia. Studies have found that children whose parents (both parents) have myopia were reported to have a 3 times higher risk of developing myopia themselves compared to those whose parents have no myopia .
To an even greater extent, the environment and lifestyle choices that people make have been linked to the development and progression of myopia in both children and adults.
Too much time spent engaged in near work activities such as reading, writing, and using digital devices, as well as a lack of outdoor time during childhood years are seen to be the leading environmental factors that increase the risk of myopia.
Typically, near work is defined as books read per week or time spent on reading per week. With the rapid emergence of technology, device screen time is now considered as a new form of near work, bringing rise to a new and emerging phenomenon known as ‘digital myopia’ .
More than 20 studies in Europe and Asia have shown a link between device screen time and myopia. Myopia was often reported to be more commonly found and more severe in 2 groups of people;
1) those who engaged in higher device screen time, commonly measured in hours per day; and
2) those who start using digital devices at a younger age (from as young as 4 months old) .
There is emerging evidence that sleeping late at night and not getting enough sleep, as well as a lack of physical exercise during childhood are important factors that may increase the risk of myopia by up to 50% .
These are just some of the selected risk factors for myopia, with people living in urbanized regions and having higher levels of educational attainment have also been commonly associated with a greater risk of myopia .
If you experience any of these signs and symptoms, schedule an appointment with an eye health professional to get your eyes checked. It is also important to note that the development of eye conditions may even start before symptoms appear, which makes going for regular and timely eye checks that much more essential.
Myopia is usually diagnosed by an eye health professional based on the results of a comprehensive eye exam. This includes a vision test, a subjective and/or objective refraction (a process of determining the degree of optical defocus typically experienced at an optometry clinic), and an assessment of the health of the eyes (front and the back of the eye). Recommendations for when eye exams should occur differ between countries and age groups.
The American Academy of Ophthalmology recommends that routine comprehensive eye exam should be done to screen for myopia at the following time periods:
Infants should get their first eye check between 6 to 12 months of age. To accommodate for infants, techniques called auto-refraction or retinoscopy are used to screen for myopia.
Children in this age group should get a comprehensive eye check at least once, preferably between 3 to 3.5 years of age. Children’s eyes are examined using a vision chart and with autorefraction.
School-age children, between the age of 6 to 19 years should have an eye check every 1 to 2 years, as this is the period in which myopia typically begins to develop.
Adults should have their eyes checked every 2 to 4 years to not only detect myopia, but also other age-related eye conditions such as presbyopia, cataract, age-related macular degeneration, and glaucoma.
The earlier myopia is detected, the earlier its treatment and management strategies can commence. This reduces the likelihood that myopia may progress into its more severe forms and subsequently, lowering the risk of developing significant vision loss later in life.
People with myopia have several available options to correct their myopia to produce clear vision for distance and near viewing. Some of the common strategies to correct myopia include the following:
Spectacles have concave lenses that focus light rays entering the eye onto the retina and are the most common form of correction for myopia. Children whose myopia is still progressing need to undergo regular eye checks and have new lenses made as their prescription changes. Regular spectacles provide clear vision but do not slow the progression of myopia.
Contact lenses are thin corrective lenses that are placed directly onto the front surface of the eye. Like spectacles, contact lenses direct incoming light rays onto the retina. People usually begin to use contact lenses during their teenage years. Like spectacles, contact lenses help provide clear vision but they do not slow the progression of myopia.
In some cases, people may suffer from discomfort, soreness, itching, and redness of the eye from wearing contact lenses. If this happens, it is important to consult and seek help from an eye health professional so they can check if the contact lenses are a suitable treatment for the long term.
Lasers are used to reshape the cornea (the outer clear layer of the front of the eye) so that incoming light rays are focused onto the retina to produce clear vision. Some types of refractive surgeries include laser-assisted in situ keratomileusis (LASIK) and photorefractive keratectomy (PRK).
LASIK is the most common refractive surgery and involves creating a thin flap on the surface of the cornea. A laser then removes the precise amount of tissue from the inner layers of the cornea needed to change its shape for clear vision. The flap is then placed back into its original position to heal. In PRK, lasers remove a thin layer of tissue from the surface of the cornea instead in order to flatten its shape, which helps to refocus incoming light rays onto the retina.
Refractive surgeries are not typically performed until adulthood years and only when one’s myopia has stabilised for at least 1 year.
For people whose myopia is still progressing, there are myopia control strategies that slow or even stop its progression. Some of the common myopia control strategies include the following:
Some studies have shown that the therapeutic, atropine, when given as eye drops, may slow the progression of myopia in children. Atropine dilates the pupil and temporarily suppresses the eye’s ability to change focus from near to distant objects and vice versa (a process called accommodation). This relaxes the eyes’ focusing mechanisms, which may account for atropine’s effectiveness in reducing myopia progression.
Low doses (0.01 – 0.05%) of atropine have been found to be effective in suppressing or slowing myopia progression. A study conducted in Singapore showed that 0.01% atropine eye drops were effective in slowing the progression of myopia in primary school children (aged 6 to 12 years) by 50 to 60% over a 2-year period .
Research investigating the effectiveness of atropine eye drops in controlling myopia is still ongoing. However, the promising results from clinical trials have led researchers in Singapore to produce commercially available atropine eye drops, which are also available in countries such as Malaysia and Japan.
This treatment involves wearing a rigid contact lens overnight during sleep to reshape the cornea. This special contact lens puts pressure on the cornea to temporarily flatten its surface, allowing incoming light to be better focused onto the retina for clear vision without the need for spectacles or contact lenses after the lenses are removed in the morning (figure 2). The effect of ortho-k usually lasts for 1 to 2 days and wearing the lenses every night will give the best results.
Ortho-k has been shown to be effective in slowing the progression of myopia in schoolchildren aged 6 to 10 years by as much as 43% over 2 years compared to those who wore regular spectacles . This effect is achieved by suppressing the axial (front to back) growth of the eye, which is a factor associated with the progression of myopia.
Most people with low to moderate myopia, as well as children and young adults who are not eligible for refractive surgery are generally suitable candidates for ortho-k.
Figure 2. Visualisation of an ortho-k procedure.
(Source: Plano, 2021)
For children with fast progressing myopia, an eye health professional may recommend using special lenses to try to slow the progression of myopia, which include bifocal lenses, multifocal lenses, and progressive lenses. These special lenses have different powers in different zones of the lens and are typically used to correct presbyopia.
Research is beginning to show that these lenses may also help reduce the progression of myopia in children by slowing the axial growth of the eye. Some studies have reported promising results, with a 30 to 50% reduction in the progression of myopia observed after children (aged 7 to 14 years) wore these lenses for 6 to 12 months . However, research is still ongoing to better determine its effectiveness as a myopia control strategy.
A growing body of research is beginning to find that the development of myopia may be delayed (or even prevented) and its progression slowed through lifestyle interventions, which include:
Ensuring that you and your children practice these good behaviour regularly will go a long way in our collective fight against myopia.
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