Myopia: what is it?

La myopia is not a disease but a blurred vision which is characterized by a close vision but clear vision blurry from afar. Affecting about a third of adults in Europe and North America, myopia is the most common visual defect, and its prevalence is steadily increasing.

It usually appears at theschool age (in childhood or adolescence) and progresses to early adulthood, where it tends to stabilize. Certain strong myopias, called myopia “diseases”, unfortunately evolve throughout life.

It exists different levels of myopia varying from one subject to another which result in a visual penalty more or less important. “Light” myopic people are not obliged to correct their myopia permanently but only in risky or necessary situations such as driving, going to the cinema, etc … Others will have very deteriorated vision, even near.

In ophthalmology, the severity of refractive errors (including myopia) 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 diopters for mild myopia, – 2,75 to -6 diopters for medium myopia, -6 diopters and above for strong myopia.

Who is affected by myopia?

The prevalence of myopia in different populations varies with age,geographic origin, and theenvironment. In France, according to the Haute Autorité de Santé (HAS), 29% of the population is nearsighted. This is also the figure found in North America.

On the other hand, Asian countries are more affected: 80 to 90% of school-age children are short-sighted in certain urban areas of China, Taiwan, Hong Kong, Japan, or even South Korea. Among them, 10 to 20% have high myopia, which can lead to complications graves.

According to several estimates, 2,5 billion people (a third of the world population) will be nearsighted in 2020, compared to 1,6 billion today².

Causes of myopia

In a normal eye, the image of objects is projected onto the retina (a kind of “photographic film” located at the back of the eye). The cornea and lens, the lenses at the front of the eye, work to produce a sharp image on the retina.

In the case of myopia, the point of sharpness is not on the retina, but in front of it. Most often, this phenomenon is related to an eyeball that is too long. We then speak of axile myopia.

More rarely, an excessive curvature of the cornea can also be involved. In all cases, the image of distant objects appears blurry, because the lens cannot compensate.

The causes of myopia are both genetic et concerns, but they are not very well known. So far, more than 20 genetic regions have been identified and may harbor genes involved in myopia³. According to some studies, more than 70 genes play a role in anomalies de la refraction¹. Some of these genes code for growth factors, or even for elements of the ocular matrix².

However, as the prevalence of myopia continues to increase worldwide, researchers are finding that environmental factors also play an important role in the development of this visual disorder. According to a recent study⁴, lack of exposure to natural sunlight disrupts the growth of the eye and may promote myopia. Current lifestyles (video games, reading, screens, few outdoor activities, etc.) should therefore be avoided as much as possible.

Course and possible complications

In most cases, axile myopia corrects itself well and corrected, does not pose a problem in everyday life. It generally stabilizes around the age of 25 and often does not exceed -6 diopters.

However, some myopia are progressive (also called myopia diseases) and do not stabilize. They require a regular visual check by an ophthalmic doctor, and an adaptation of the frequent optical correction.

In addition, myopia (especially when strong) is associated with an increased risk of developing serious eye diseases.¹Including:

• un retinal detachment which can cause blindness;
• glaucoma (deterioration of the optic nerve);
• cataracts (clouding of the lens);
• bleeding from the macula (central area of ​​the retina).

Finally, it is important to note that not all people in the world benefit from adequate visual correction. It is estimated that 150 million people on the planet suffer from uncorrected refractive errors, 8 million of whom are considered blind².

The symptoms of myopia are:

• a loss of visual acuity from afar (The term “far” is relative. Sight may begin to blur from a few tens of centimeters away in cases of high myopia);
• a need to get closer to see more clearly (this is one of the very recognizable signs of early myopia);
• difficulty seeing when driving a car, which is particularly dangerous for oneself and for others;
• sometimes headaches.

Low myopia appears gradually. Distant objects appear blurry, while near objects remain crisp.

Usually, myopic children or adolescents have difficulty reading what is written on the blackboard when they are seated at the back of the classroom. Reading distant signs or street names becomes difficult.

Myopia disease, or strong myopia, begins earlier in childhood. It evolves rapidly, throughout life, and does not stabilize in adulthood. It can reach – 30 diopters. It is especially this type of myopia that risks causing complications (retinal detachment, glaucoma, early cataracts, 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.
• in people of Caucasian and Asian descent, and less common in those of African descent1.

Risk factors

Several environmental factors seem to increase the risk of myopia:

• le little time spent outdoors during childhood5, and therefore the lack of exposure to sunlight;
• excessive practice of certain activities forcing the eyes to work closely, such as reading, embroidery, some video games, etc… 2;
• The strong demand for close work during childhood and adolescence: we speak of school myopia.

Our doctor’s opinion

As part of its quality approach, Passeportsanté.net invites you to discover the opinion of a health professional. Dr Jacques Allard, general practitioner, gives you his opinion on the myopia :