What is Myopia (short-sightedness)?
Myopia, also known as short-sightedness or near-sightedness, is a common condition where close-up vision is generally clear, but further away objects are blurred. The higher the degree of shortsightedness, the more blurry the distance vision.
Shortsightedness can be easily corrected by wearing glasses and contact lenses, or even eye laser surgery for adults. Myopic patients are accustomed to being told their eyesight has deteriorated at their ongoing eye tests, that their prescription has increased and they need stronger glasses.
What is myopia? Watch this video:
What causes myopia?
Myopia, or shortsightedness, is the result of an eye growing too much. Think of it like a stretched camera system. With stretching, the light rays entering that camera no longer come into sharp focus on the camera film, so our photos are out of focus. In a myopic eye, the light rays entering the eye no longer focus on the retina. This defocus causes distance objects to appear blurry.
All eyeballs stretch with age and normal growth, but when you are shortsighted your eye has grown, or elongated, more than we expect, and certainly more than we would like. The longer the eye is, the more defocus occurs, making the distance vision worse and hence the more shortsighted the prescription.
The causes of myopia are complex and it’s an area of ongoing research, but we know that the visual system is the signal for the eye to elongate. The trigger for this eye growth is inside the eye. It’s not a message from our brain or hormones!
During our growing years, just like our height and weight, the eye adjusts its size based on a combination of both genetic and environmental influences.
Why worry about myopia?
Excessive eye elongation has been linked to higher rates of retinal pathology, giving rise to the new clinical challenge of preserving the retinal function of aging myopes.
The retina is the nerve layer that lines the back of the eye, allowing us to see. An elongated eye has a stretched retina. Besides making the entire retina thinner and more fragile, this stretching stresses the sensitive nerve cells within. This results in an increased risk of developing serious eye conditions such as cataract, glaucoma, choroidal retinal degeneration and retinal detachment later in life2
Slowing progression and myopia control is vitally important as stretching the sensitive nerves in the retina is a risk to the future of your vision.
Explaining the numbers and the risks
A myopic prescription will always start with a minus, this means shortsighted.
Next to the minus, you will see a number which correlates with the degree of myopia. At the end of the number you will see the abbreviation D which means dioptres, the units for measuring eye prescriptions.
- -0.25D is a quarter of a dioptre, and at Custom Eyecare we refer to this as one step shortsighted.
- If your prescription is -1.00D that means 1 dioptre, and at Custom Eyecare we refer to this as 4 steps shortsighted.
- -6.00D is sixteen steps short sighted, and so on.
Currently studies suggest that with every 1 dioptre increase (so four steps change) in myopia the risk of ocular disease increases by 67%, making myopia control extremely important, especially in young eyes3.
3% of the world’s population is already affected by eye disease caused by myopia. Myopic eye disease affects 50-70% of those with high levels of myopia (more than -6.00D).
The risks of developing retinal pathology due to myopia increase with age and the degree of myopia. Left alone, myopia poses a significant risk to ocular health.
The table below details the relative risk of developing eye disease relative to the degree of myopia.
The table explains that a myopic individual who is -6.00D has 22x higher chance of developing a retinal detachment in their lifetime compared to an individual who is not myopic. They are also 41x more likely to develop myopic macular degeneration.
- From the table you can see that a mildly myopic patient (who’s prescription is -1.00D to -3.00D) has a 2x risk of developing cataract, 4x risk of developing glaucoma, a 3x risk of developing retinal detachment, and a 2x risk of developing myopic macular degeneration.
- If we compare the statistics to a patient who is highly shortsighted (over -6.00D) they have a 5x risk of developing cataract, 14x risk of developing glaucoma, a 22x risk of developing retinal detachment, and a 41x risk of developing myopic macular degeneration.
This is where myopia treatment really counts. Historically, the prescription just got stronger as the eyes and the body grew. Nowadays there are treatments available to slow the progression of myopia.
If we look at the numbers there are some clear benefits to actively controlling myopia and implementing some treatment strategies.
- For example, assuming we are able to reduce your child’s prescription during their growing years so instead of reaching -6.00D, we managed to keep them at -3.00D. At -3.00D their risk of retinal detachment is back to 9x (versus 22x) and myopic macular degeneration is back to 10x (versus 41x). And then imagine if treatment was able to reduce the prescription by 75% and they only ended up -1.25D. Then their risk of retinal detachment is back to 3x, and myopic macular degeneration is back to 2x.
What is a safe level of myopia?
The evidence suggests there is no safe level of myopia. Even a -1.25 myope has a 2x lifetime risk of retinal detachment compared to someone who is not myopic.
The Myopia Epidemic
Myopia (short-sightedness) has become increasingly prevalent both in Australia and around the world. The current prediction is that 50% of the world’s population will be myopic by 20504. Now that is almost 5 billion people! Most concerningly, children are becoming shortsighted at a younger age, and this younger age group has the most rapid progression, and worsening of their eyesight.
The latest research shows that currently (published 2020) almost 30% of the world’s population are short sighted. Myopia in the research is defined as -0.50 or worse.
It’s believed that the urbanisation of our lifestyles, and living indoors is a major factor. Our children are spending less time outdoors than a maximum security prisoner! Compared to past generations, children aren’t walking to school anymore. Australia and New Zealand research showed 80% of kids walked to school in the 1970’s and now it’s as little as 10%. Is this because we lead busier lives? Are the streets less safe for our children?
Children these days spend a lot more time indoors and on digital devices than ever before, and this is a growing area of research.
The impact of myopia
Uncorrected myopia is the leading cause of avoidable vision impairment in the world. Complications associated with high levels of myopia can be sight threatening eg) myopic macular degeneration
In children, poor vision or uncorrected vision can impact school and academic performance and result in psychosocial stress.
Reduced quality of life has been demonstrated for myopic as well as myopia-related complications.
The risk factors
- Higher levels of education and hours spent on near work is a risk factor for developing myopia
- Less time spent outdoors is an environmental factor
As much as environmental factors play a part, there are several genetic factors that we know increase the risk of myopia progression2.
- Age is important. The risk of myopia progression increases significantly if a child becomes short-sighted at age 9 or younger
- Our family history is a factor. When one or both parents are myopic, their children are much more likely to become myopic
- Ethnicity is relevant. Children of east Asian descent are more likely to become myopic
- The degree of myopia matters (how high the prescription is). Compared to age matched normals, the more myopic you are for your age, the risk of further progression increases
Research shows that in cities in Hong Kong, Taiwan and Singapore, up to 80% of the citizens are shortsighted, but in rural areas it’s around 6%. Also, only 5% of grandparents in Hong Kong are myopic. It’s not just an issue in Asia as its the same in the US, there has been a 17% increase in myopia over the last decade. So nature and nurture are both factors.
1. Holden BA, Fricke TR, Wilson DA, Jong M, Naidoo KS, Sankaridurg P, Wong TY, Naduvilath TJ, Resnikoff S, Global Prevalence of Myopia and High Myopia and Temporal Trends from 2000 through 2050, Ophthalmology, May 2016 Volume 123, Issue 5, Pages 1036–1042.
2. Huang J, et al. (2016). Efficacy Comparison of 16 Interventions for Myopia Control in Children. Ophthalmology. 123(4): 697-708
3. Bullimore, M. Myopia control: why each dioptre matters. Contact lens and Ant Eye 42 (6)
4. Li SM, Ji YZ, Wu SS, et al. Multifocal versus single vision lenses intervention to slow progression of myopia in school-age children: A meta-analysis. Surv Ophthalmol 2011;56:451–460.