Myopia: what is it?
The myopia is not a disease but a vision disorder that is characterized by a sharp near vision but a vision blurred from afar . Affecting about one-third of adults in Europe and North America, myopia is the most common visual defect, and its prevalence is increasing.
It usually appears at school age (in childhood or adolescence) and evolves to early adulthood, where it tends to stabilize. Some strong myopia, called myopia “diseases”, evolve unfortunately all the life.
There are different levels of myopia varying from one subject to another which result in a more or less significant visual penalty . Myopic “light” are not obliged to correct their myopia permanently but only in situations of risk or necessary like driving, going to the cinema, etc … Others will have a vision much deteriorated, even close.
In ophthalmology, the severity of refraction anomalies (of which myopia is one) is measured in diopters. By convention, the degree of myopia is described with a minus sign, ranging for example from -0.25 to -2.50 dioptres for mild myopia , – 2.75 to -6 diopters for medium myopia , -6 diopters and beyond for strong myopia .
Who is affected by myopia?
The prevalence of myopia in different populations varies by age, geographical origin , and environment . In France, according to the Haute Autorité de Santé (HAS), 29% of the population is short-sighted. This is also the figure found in North America.
In contrast, Asian countries are more affected: 80 to 90% of school-age children are nearsighted in some urban areas of China, Taiwan, Hong Kong, Japan, or South Korea. Of these, 10 to 20% have severe myopia, which can lead to serious complications .
According to several estimates, 2.5 billion people (one third of the world population) will be myopic in 2020, compared to 1.6 billion today.
Causes of myopia
In a normal eye, the image of the objects is projected onto the retina (a kind of “photographic film” at the back of the eye). The cornea and lens, the lenses present at the front of the eye, have the role of producing a sharp image on the retina.
In case of myopia, the point of sharpness is not on the retina, but in front of it. Most often, this phenomenon is linked to an eyeball that is too long. This is called axillary myopia .
More rarely, excessive curvature of the cornea may also be involved. In any case, the image of distant objects appears blurred because the lens cannot compensate.
The causes of myopia are both genetic and environmental , but they are not very well known. So far, more than 20 genetic regions have been identified and could harbor genes involved in myopia. According to some studies, more than 70 genes play a role in refraction anomalies. Some of these genes code for growth factors, or for elements of the ocular matrix.
However, as the prevalence of myopia around the world continues to increase, researchers are finding that environmental factors also play an important role in the development of this visual disorder. According to a recent study, lack of exposure to natural sunlight would disrupt the growth of the eye and could promote myopia. Current lifestyles (video games, reading, screens, few outdoor activities, etc …) should therefore be avoided as much as possible.
Evolution and possible complications
In most cases, axillary myopia corrects well and corrected, does not pose a problem in everyday life. It usually stabilizes around the age of 25 and often does not exceed -6 diopters.
However, some myopia is progressive (also called myopia diseases) do not stabilize, and require regular visual control in an ophthalmic doctor, and an adaptation of the frequent optical correction.
In addition, myopia (especially when it is high) is associated with an increased risk of developing serious eye diseases, including:
- a detachment of the retina that can cause blindness;
- a glaucoma (optic nerve damage);
- a cataract (clouding of the lens);
- haemorrhage of the macula (central area of the retina).
Finally, it is important to note that not all individuals in the world receive adequate visual correction. An estimated 150 million people worldwide suffer from uncorrected refractive disorders, 8 million of them are considered blind.
The symptoms of myopia are:
- a decrease in visual acuity from a distance (the term “far” is relative: the view can begin to blur from a few tens of centimeters away in cases of high myopia);
- a need to come closer to see more clearly (this is one of the most recognizable signs of early myopia);
- a difficulty to see when driving, which is particularly dangerous for oneself and for others;
- sometimes headaches.
Low myopia appears gradually. Remote objects appear blurry, while nearby objects remain perfectly clear.
Generally, myopic children or adolescents have difficulty reading what is written on the board when they are sitting in the back of the classroom. Reading distant signs or street names becomes difficult.
Myopia disease, or strong myopia, starts earlier in childhood. It evolves rapidly, all life, and does not stabilize in adulthood. It can reach – 30 diopters. It is especially this type of myopia that may lead to complications (retinal detachment, glaucoma, early cataracts, and blindness).
People at risk of myopia
Myopia is more common:
- in some families, for genetic reasons . Children with one or both parents who are nearsighted are more likely than others to be nearsighted.
- among people of Caucasian and Asian origin, and less frequent among those of African origin.
Several environmental factors seem to increase the risk of myopia:
- the short time spent outdoors during childhood5, and therefore the lack of exposure to sunlight;
- the excessive practice of certain activities forcing the eyes to work closely , such as reading, embroidery, certain video games, etc;
- The strong solicitation of work closely during childhood and adolescence: we talk about school myopia.
The opinion experts
|Myopia is the most common visual disorder and its prevalence is increasing. It usually appears at school age and it is important to detect it as early as possible. If your difficulty in seeing from afar is marked enough to interfere with the performance of a task or prevent you from taking full advantage of certain activities, consult a vision specialist (optometrist in Quebec or ophthalmologist in France).
In addition, if you do not suffer from any visual disturbances, it is recommended to have an initial examination of your eyes at age 40 and at regular intervals thereafter, every 2 to 4 years between 40 and 54 years, all 1 to 3 years between 55 and 64 years, and every 1 to 2 years after 65 years.
Can we prevent myopia?
|No scientifically validated method can prevent or slow the progression of myopia and noconclusive clinical trial has been published, although several drugs have been tested, including so-called “anti-muscarinic” drugs.
Although no studies have shown that it is possible to prevent myopia, it seems that children who play a lot outdoors are less likely to become myopic.
It is therefore recommended to find a balance between outdoor activities and reading or video games, if only for the general well-being and physical health of the child.
Myopic people must have regular ophthalmic (or optometrist) monitoring in Quebec to adjust vision correction if vision changes, but also to prevent serious complications of myopia. The ophthalmologist will perform an examination of the fundus to ensure in particular that there is no detachment of the retina.
The treatment of myopia is based on:
- a correction of the sight by glasses (divergent concave lenses);
- correction by contact lenses (there are many types: soft or rigid, monthly, daily, or of longer duration);
- a surgical treatment (refractive surgery radial keratotomy or laser), provided that myopia is stabilized.
It is the ophthalmologist who will prescribe lenses or lenses adapted to correct your vision. Note that in Quebec, the optometrist is also authorized, and in France, the optician can renew the optical equipment after a visual examination with an order valid for 3 years, under certain conditions. The visual examination will make it possible to control the quality of the vision, the medical control carried out by the ophthalmologist doctor will prevent possible ocular diseases.
The glasses or lenses will be worn permanently or not, depending on the degree of myopia. In case of low myopia, it may be necessary to wear them when driving or going to the cinema.
The refractive surgery corrects myopia by reshaping or “planing” the cornea, usually laser to force the image to form on the retina and not in front of it.
The operation is painless (embarrassing at most) and is performed very quickly, in an hour or less. The sight is immediately improved, but an eye discomfort can persist a few days.
The different operating modes are as follows :
- The LASIK ( laser-assisted in-situ keratomileusis ). This is by far the most used technique. The surgeon cuts a small “bonnet” on the cornea, using a laser or an ophthalmic instrument. He lifts it and then removes it from the corneal thickness to correct its curvature, using a laser beam. The hood, or shutter, is put back in place and heals quickly.
- The PRK , or photorefractive keratectomy also called excimer laser surface. This technique makes it possible to modify the curvature of the cornea by removing tiny fragments using a laser, after having “brushed” the outermost layer of the cornea, which is very thin (the epithelium). The epithelium is naturally reconstituted after the operation.
- The LASEK ( Laser-assisted subepithelial keratomileusis ). Rather than cutting a flap in the cornea, the surgeon takes off the epithelium on the surface of the cornea. Unlike PRK, the epithelium is then repositioned. An ocular dressing should be worn for a few days to promote healing.
- The intraocular lenses are implanted lens directly into the eye, as the cornea, in front or behind the iris. The implant is effective for correcting high myopia that cannot be operated by refractive surgery (often because the cornea is too thin to be “planed”).