What is the cause of myopia?

myopia glasses

Myopia is the most common vision problem and affects the lives of one in two people

When your vision is blurred this is nearsightedness or myopia. When the optical system of your eye focuses the image on the retina, we have a clear vision, otherwise all around the image form blurred dots.

By a mechanism similar to that of a camera diaphragm, the depth of field varies according to the diameter of the pupil.

The relative size of the blurred dots increases in proportion to the distance of the optical image from the retina.

In myopia the image is focused in front of the retina and therefore appears blurred. The blurred dots are different depending on the shape of the object observed.

A line will appear as a long series of tiny overlapping dots, while in a two-dimensional image, such as a visual acuity chart, the dots follow the shape of the letter observed.

Pinhole glasses (black glasses with perforated lenses) exploit this phenomenon. The tiny holes reduce the blurred dots and the image you see is sharp.

Pinhole glasses allow you to guess how you will see the world once your normal vision is restored.

At first, things in the immediate vicinity still appear quite clear and only distant objects are blurred. Myopia usually begins at school age: at some point the student realizes that he has difficulty reading what his teacher writes on the blackboard.

At first, the child gets by, but then the problem gets worse.

The child goes for an examination and his ophthalmologist orders him to wear glasses. But often wearing glasses only accelerates the loss of vision and then, in order to see well, stronger lenses are needed.

Soon glasses become inseparable companions, even for activities for which they are not really needed.

Myopia is a defect that causes the loss of the ability to see well from a distance and has been known since ancient times.

The ancients believed that the mental vision radiated from the brain was insufficient, making the eyes too weak to distinguish clearly between distant objects.

Up until the 19th century, people did not pay too much attention to vision problems. Indeed it is interesting to note that in the first half of the century the use of glasses was not even recommended, because it was believed that corrective lenses worsened the disorders and were therefore harmful.

German doctor Hermann Cohn and his theory

In the sixties of the nineteenth century, the German doctor Hermann Cohn noticed that as the school progressed, myopia affected more and more pupils.

In 1866 he published the results of a study carried out on 10,000 schoolchildren in Wroclaw. He came to a conclusion that seemed convincing, namely that myopia was caused by the use and abuse of the eyes.

In the years that followed, Cohn’s theory became established. In this way, all German schools began a campaign to improve visual hygiene.

The Dutch ophthalmologist Donders (1864) believed that myopia was caused by the continuous tension of the eyes due to prolonged near vision and an elongation of the eyeball.

As long as there were no instruments to measure the size of the eyeball in a living subject, it was believed that the ciliary muscle weakened and therefore the lens was no longer able to focus images.

Many ophthalmologists still give this explanation today. Ultrasound investigations have clearly shown that in severe myopia the eyeball is elongated.

On the causes of this phenomenon, there are different opinions.

In a study published in 1969, Coleman and colleagues demonstrated the presence of alterations in the axial length of the eye.

According to Dr. Young and Dr. Bell, increased ocular pressure plays an important role in the elongation of the axis and consequently in the onset of myopia.

This seems to be confirmed by the experience of those who use computers and work always looking at objects close by.

Peter Green (1980) examined the pressure exerted on the eyes from a mechanical point of view, studying the way in which accommodation, convergence, fluid pressure and the extrinsic muscles of the eye act on the slit.

Dr. Green came to the conclusion that the mechanical effects of convergence far exceed those caused by accommodation, although the two phenomena occur simultaneously when the eyes are adjusted to a very close object.

According to his calculations, the total pressure exerted on the posterior sclera is the sum of the stresses induced by intraocular pressure and the oblique muscles.

Greene found that the area between the inserts of the two oblique muscles is under greater stress than any other part of the eye.

According to his theory, this could be the cause of the axial elongation of the eyeball found in high-grade myopia.

After four years of research into the processes of accommodation and focusing, Dr. William H. Bates became convinced that the oblique muscles are one of the most important elements in focusing, with the ciliary muscle and the crystalline lens being of secondary importance.

There are people who, after surgical removal of the lens, can see better and do many things without glasses.

Contact lenses

Many people have been using contact lenses daily for years. There is no doubt that manufacturers have made progress, developing new materials.

When a foreign body is inserted, there is always a rubbing between the lens material and the layer of proteins that defends your eye from organisms that could cause corneal ulcers.

Every time you wear your contact lenses, you scrape some of this protective coating off the surface.

It’s unavoidable…

The older model of contact lenses might cause more rubbing and therefore more damage. A damaged or cracked contact lens can have sharp edges and cause corneal abrasions.

In addition, contact lenses prevent your eye from being sufficiently oxygenated. In other words, they choke the cornea.

No matter how carefully you store your lenses, they collect protein all the time and the cleaning fluid damages the protective layer.

Residues of the previous proteins remain on the lenses, and you will begin to react to these foreign proteins like a wasp sting.

The immune reaction leads to the formation of small pustules in the lower part of the eyelid (Papillary Hypertrophy), which increase the sensitivity to contact lenses.

For this reason, use them only as an aid or temporary solution.

Theories about the causes of myopia abound, as do classification models

Functional myopia occurs when we strain our eyes too much for near vision, when we read a lot and have to maintain focus for hours at a distance of less than one meter.

It happens, for example, to people who work too much in front of a computer or spend entire days in front of a smartphone.

The main problem is that the oblique muscles are too tense and it creates a situation that ophthalmologists call hyper-accomodation.

As we have already mentioned, in 1866 Dr. Hemann Cohn observed that overuse of the eyes for near vision was the main cause of myopia.

Which means that we gradually train our eyes to focus only on near objects and neglect distance vision.

In this respect, it is interesting to know that animals kept in close quarters become myopic. There is a lot of scientific evidence that shows the influence of environment on visual acuity.

In short, they all have a good vision

Dr. Bates (1915) was convinced that myopia was caused by mental stress. In fact, it seems he was not wrong, just think of the different distribution of vision problems in different parts of the world.

In regions where reading and book learning are not emphasized, myopia is practically non-existent.

Garner and colleagues visited 977 pupils aged 6-17 years in the Pacific Ocean islands of Vanuatu. During their research in 1985 and 1986 found that only 1.3% (1985) and 2.9% (1986) had myopia greater than 0.25 diopters.

In the cities of Taipei and Kaohsiung in the country of Taiwan, an incredibly high prevalence of myopia was found.

Between 28% of elementary school children, 67% to 71% of middle school children, and 81% to 89% of high school students suffered from the condition. Among medical students at National Taiwan University, the myopia rate was 90.5%.

The Vanuatu way of life is light years away from that of Taiwan, where children are under immense pressure to learn to read and write by age 4 or 5.

It takes a great deal of concentration to draw Chinese ideograms in the perfect shape and absolutely identical size.

Then they must prepare for the difficult examinations on which Taiwan’s school system is based. These children use their eyes primarily to focus on books, and thus over-exert themselves in close-up vision.

The Vanuatu children examined in the research did not use their eyes for near vision. They mainly looked at objects at all distances and therefore had a better chance of maintaining their good natural vision.

We hope you found this explanation of myopia useful. Remember to always ask an opinion to a professional doctor or ophthalmologist and if we have helped you, don’t forget to help someone else by sharing this information.

4 thoughts on “What is the cause of myopia?”

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