Nearsightedness (myopia)

Myopia is a condition in which people can see objects up close well but have difficulty seeing objects in the distance. The more severe the myopia, the less clear objects in the distance appear.
Compared to before, myopia in children is increasing worldwide and has become an issue.

You may have such questions as follows,

What causes myopia?
What habits can I use to prevent myopia?
How do I use my glasses and contact lenses properly?

This article describes following topics.

・Why myopia occurs
・Symptoms and causes
・How to correct myopia and cautions

Humans are informed by the use of their senses to look, listen, smell, taste and touch. Of these, around 80% are based on sight, and it is very important that we see things correctly in order for us to live their daily lives.
The structure of the eye is often compared to the structure of a camera. Let’s review the names and roles of the main parts.

・Cornea, Lens…Lens are similar to a camera lens. Refract light on the surface
・Pupil…The role of aperture. The opening at the center of the iris that allows light to enter the eye. Adjust the amount of light according to ambient brightness
・Iris…It controls the size of your pupil to let light into your eye
・Ciliary body…The role of focusing with regulating the thickness of the lens
・Retina…The role of the film. Image of what you want to see is reflected focused

Information about the image on the retina is sent to the brain, which recognizes that a person has seen an object. By changing the thickness of the lens, you can see clearly whether it’s far or near.
As myopia progresses, the image is blurred out of focus on the retina in far-seeing even when the lens thickness is adjusted.

Myopia vs. emmetropia

When looking into the distance with no change in the thickness of the lens, the retina is correctly in focus, which is called emmetropia. On the other hand, with myopia, when looking at distant objects, they come into focus in front of the retina. On the retina, it is out of focus and therefore not clearly visible.
The more advanced the degree of myopia, the more difficult it is to see objects at greater distances.

Let’s look at how changes occur in the human eye from birth to growth.

Newborns have small eyes, and the depth of the eyeball, called the (ocular) axial length, is about 17mm. Mild farsightedness happens when the focus is behind the retina.
As your body grows, so do your eyes, cornea and lens. As the eyeball grows larger, the axial length also becomes longer, and visual acuity grows to about 1.0 by around the age of 5. The axial length elongates to about 24 mm by the age of 16 and generally does not lengthen thereafter.
However, if only the axial length is elongated due to some effect, it becomes difficult to focus on the retina, resulting in myopia.

An increase of children with Myopia

According to school health statistics surveyed by the Ministry of Education, Culture, Sports, Science and Technology (MEXT) in Japan, the number of elementary school students with naked eye visual acuity of less than 0.3 has increased approximately 4 times over the past 40 years. Many are presumed to have myopia.

References: School Health Statistic Survey/2021 | MEXT in Japan

Perhaps due to the rapid penetration of smartphones over the past ten years or so, the percentage of children with myopia has increased in the last decades.
Myopia is a growing problem in many countries around the world, but it is especially noticeable in East Asian countries. In Singapore, it is said that 60% of schoolchildren aged 12 years are myopic, and there are also concerns about the negative effects of myopia by increasing the risk of various eye diseases in the future.

<Degree of myopia and susceptibility to eye disease>

Reference: The Complications of Myopia: A Review and Meta-Analysis” (Annechien E. G. Haarman)

D (diopter) is the refractive power and is a unit of measurement for the strength of myopia. The shorter the distance visible to the naked eye (focal length), the higher the value: -1D at a focal length of 1 m, -2D at a focal length of 50 cm, and so on. -6D or higher is referred to as a high degree of myopia.
Even with mild myopia, the risk of developing myopic maculopathy is approximately 14 times greater than with the absence of myopia. In order to maintain good vision throughout life, it is important to prevent the onset and progression of myopia in childhood.

There are two main types of myopia:

・Simple myopia
・Pathologic myopia

Simple Myopia

Simple myopia is likely to be caused by genetic and environmental influences and is often referred to as school myopia or childhood myopia since it often begins between elementary and junior high school
It can be corrected by the use of lenses without visual dysfunction, and the majority of people fall into this category of simple myopia.

Pathologic Myopia

Pathologic myopia is generally seen earlier than simple myopia, with abnormalities in visual acuity beginning in early childhood. The axial eye length becomes extremely long, resulting in a high degree of myopia, which is difficult to correct with glasses or other means.
Because the eye is larger and the stretched retina is thinner, even the slightest impact to the eye can lead to retinal hemorrhage or retinal detachment.
The cause of its occurrence is not known in detail and is thought to be a genetic effect. If your infant appears to have difficulty seeing, please see an ophthalmologist as soon as possible, as this can lead to blindness.

Myopia is believed to be primarily caused by two factors: genetics and the environment.

Genetic and environmental factors

If a parent has myopia, there is a relatively high probability that the child will also have myopia; moreover, it is believed that myopia is caused by genetic factors.
On the other hand, the external environment is also thought to influence simple myopia. Studying, reading, computers, and other display-viewing tasks for long periods of time can stress the eyes. The same is true for looking at a smart phone screen up close for long periods of time. These stresses may be related to the progression of myopia.

Individuals with a high risk of Myopia

The following is a summary of the tendencies of people at high risk of developing or progressing myopia.

< Characteristics of people at high risk of myopia >

・Parent(s) have myopia
・Less outside playing (less time spent outdoors)
・Looking at your phone within 20cm from your eyes
・Playing a smartphone or video game continuously for more than 1 hour

The increase in myopia in children compared to a few decades ago is thought to be largely relevant to the fact that they spend less time outdoors.

Vision is essential for humans to obtain more information in their daily lives. Therefore, your eyes are subject to heavy use and damage.
Making time to look into the distance, improving posture and room brightness, and taking time to rest the eyes will help reduce and even prevent myopia.
This section describes lifestyle habits that should be taken into consideration to prevent myopia.

Spend more time outside

Children with less outside play in sunlight are more likely to have myopia. Having time to play outside in moderate sunlight is considered the easiest and most reliable way for children to prevent myopia.
Children who already have myopia symptoms can also spend about two hours a day outdoors for effective prevention. Even in the shade of buildings or trees, you’ll still get plenty of light. Even when it is cloudy or before sunset, there is about 1,000~3,000 lux outdoors, which is brighter than a typical indoor room.
If you’re spending time in the tree shade, it’s a good idea to move around instead of staring at your phone screen.

Brighten up your room

When reading a book in a dark room or on a bus or train, it is said that the lack of brightness tends to put unnecessary strain on the eyes. Ensure that there is adequate illumination.

Correct posture

In addition to good lighting, good posture is also important. Keep your spine straight and your eyes at least 30 cm away from the book or screen.
Poor posture, lying down and watching television or reading books is often the cause of myopia progression or disparity in vision. This is because the distance between the eyes and the screen or book tends to be closer, and in addition, there is a difference between the left and right eye with respect to the distance between the object and the eye.
After an hour of studying, reading or holding your phone, you should give your eyes a break for several minutes.

Glasses and contact lenses are commonly used to correct myopia. This section explains how to adjust eyeglasses and what to look for when children use eyeglasses.

Glasses and contact lenses

When a myopic person wears concave lenses of appropriate power, the retina comes into focus and the distance is seen clearly. A person with simple myopia can be corrected to normal vision by wearing glasses.
However, just because you’ve got myopia doesn’t mean that you immediately need glasses or contact lenses. If you experience any inconvenience, such as difficulty seeing letters on a blackboard, you may want to wear glasses.
Contact lenses are in contact with the surface of the cornea and are useful for sports activities. It can also be used to correct only one eye when there is a difference in vision between the left and right eye and it is difficult to use glasses.
They also have the advantage that they do not fog up like spectacle lenses and provide a wider field of vision.

On the other hand,

・It takes time to get used to the handling of the lenses
・There is a sensation of having a foreign object
・May damage the cornea

And other reasons, contact lenses are also not universal.

Eyeglass fitting

Fitting refers to an adjustment technique that pursues both comfort in wearing and seeing, and makes them conform to the shape of the user’s face.
Glasses may slip off or become painful due to pressure when used. Fitting is performed to ensure that the glasses conform to the shape of the ear and to adjust the height, angle, and position of the temples, nose pads, etc.
It is also important for glasses to be comfortable, so that the wearer can see clearly and not tire his or her eyes. Keeping right angle between the line of sight and the lens surface and the appropriate distance from the eyeball to the lens have a significant impact on whether the eye can see clearly. To ensure that the distance and position between the face and glasses are always appropriate, it is advisable to request an annual inspection at the eyeglass store where the glasses were purchased.

Cautions for children’s glasses

Although there is no age limit on contact lenses, they are laborious to handle and manage. If contact lenses are used in elementary school, it is generally recommended that glasses are mainly used.
Children have many opportunities to move their bodies through play and exercise, and their skeletal structure is in the process of growing, so it is easy for glasses to lose best fitting. Parents or guardians should regularly check the glasses from the front or side to see if they are unnaturally distorted or if there are any areas of pressure. Just like adults, children should have their glasses checked at your retailer once a year.

Q: What does myopia mean in simple terms?

With myopia, the shape of the eyeball is elongated in the front-back direction, and a condition in which the light rays entering the eye are focused in front of the retina.
A concave lens is then used to focus on the retina to give a clearer view.

Q: Are there any effects of smartphones and TV on myopia?

Prolonged screen viewing at a distance of 20 cm or less, such as operating a smartphone or playing a game, is hard on the eyes. Since TV screens are usually about 2 meters away, your eyes will be less stressed comparison with smartphones.
Children are unlikely to notice eye fatigue on their own. Parents and other guardians should observe the child carefully when children do work to look close-up and encourage the child to take breaks for a few minutes every hour to look at something further away.

Q: Is there a cure for myopia?

Unfortunately, once deformed, your eyes will not return to their original shape.
Working at a close distance of 20 cm or less (called “near work”) or continuing to work at a close distance for more than one hour can cause myopia to progress. It’s a good idea to avoid these causes and spend more time outside.