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Unexpected causes: Why people become short-sighted through reading


Simple strategy against myopia: read white on black

Health experts say over 40 percent of Germans are short-sighted and need visual aids. It is anticipated that the number of people with myopia will increase massively in the coming years. But something can be done about it: Researchers have now found that a very simple strategy could help against the development of myopia.

Increase in myopia

Two years ago, scientists from Singapore and Australia reported a study that concluded that half the world's population will be nearsighted by about 2050. The number of nearsighted people is also very high in Germany: According to a study by the University of Mainz, more than half of high school graduates and university graduates suffer from nearsightedness (myopia). But something could be done about it: Scientists from Tübingen have now found that a very simple strategy can help to prevent myopia.

The level of education is crucial

Ophthalmologists expect a significant increase in myopia due to smartphones. Because permanent close work is partly responsible for myopia.

It is also known from previous studies that "a high level of education often goes hand in hand with the development of myopia," as Professor Dr. Norbert Pfeiffer, director of the eye clinic and polyclinic of the University Medical Center Mainz explained in an older message.

Together with colleagues, the expert had also examined whether myopia can be a result of intelligence.

At that time, the researchers came to the conclusion that in this context the level of education of a person and not his intelligence is primarily decisive for the development of myopia.

Many smart people have a visual aid

Why many smart people wear glasses is also due to the fact that they usually read a lot. But why does reading actually make myopia short-sighted?

Scientists Andrea C. Aleman, Min Wang and Frank Schaeffel from the Research Institute for Ophthalmology at the University Hospital in Tübingen have now gained new knowledge.

They derive a surprisingly simple strategy against developing myopia. They report on their research results in the scientific reports Nature.

Myopia is the price of good training

As explained in a communication from the University Hospital Tübingen, the eye grows too long in myopia, the image is sharply imaged in front of the retina and one can see blurred in the distance.

Accordingly, myopia is the price for good training: an average of around a quarter of a diopter gets shortsighted each year. The myopia is increasing worldwide, because good education is more and more important, write the experts.

According to the information, myopia begins at a later point in life in children who spent a lot of time outdoors in daylight before starting school.

However, if children read a lot during their education, the risk of developing myopia increases.

Visual information is massively reduced

According to the experts, it is still not clearly researched what exactly makes myopic when reading at school.

It has long been assumed that too little accommodation during reading places the sharp image somewhat behind the retina, which causes the retina to make the eye grow faster. However, this data was never completely convincing.

Andrea C. Aleman, Min Wang and Frank Schaeffel from the research institute for ophthalmology at the University Hospital Tübingen have now found an unexpected reason why reading could make myopic.

Unlike a digital camera that reads every pixel, the retina mainly measures differences between neighboring “pixels”, the photoreceptors, the statement says.

This is achieved by cells comparing the brightness in the middle and the periphery of their light-sensitive area and only relaying the difference to the brain.

The visual information is therefore massively reduced, which is necessary because the retina has around 125 million “pixels”, but the optic nerve only has about one million “cables”. The optic nerve is the bottleneck of the transmission of information.

ON and OFF cells

There are cells in the retina that assess whether the center of the light-sensitive area (receptive field) is lighter and the surroundings darker (ON cells). Others assess whether the middle is darker and the surroundings are lighter (OFF cells).

During our normal visual experience, both types are stimulated to a similar extent. But what about reading text?

Schaeffel has developed software that quantifies the stimulus strength for ON and OFF cells in our visual world.

It has been shown that dark text on a light background mainly irritates the OFF cells, while light text on a dark background mainly irritates the ON cells.

It was already known from previous experiments with chickens and mice that stimulation of the ON cells was more likely to inhibit eye growth, but stimulation of the OFF cells could increase it.

Light text on a dark background inhibits myopia

Using optical coherence tomography (OCT), the thickness of the tissue layers in the living eye can be measured precisely (micrometer range).

In chickens, various types of monkeys and children, research has already been carried out to the effect that the change in the thickness of the choroid, that is the layer behind the retina, predicts how the eye will grow in the near future.

If the choroid becomes thinner, this indicates the development of a myopia, if it becomes thicker, eye growth remains inhibited and no myopia develops.

The three researchers had subjects read dark text on a light background and light text on a dark background.

After only 30 minutes, they were able to measure that the choroid became thinner when reading black text and thicker when reading text with reverse contrast.

This suggests that black text on a light background promotes myopia development, and light text on a dark background inhibits myopia.

Easy to implement measure

Reversing the text contrast would therefore be an easy to implement measure to stop the development of myopia, because more and more time is being spent working and reading on computer screens and tablets.

This strategy against the development of myopia has yet to be verified. The Tübingen scientists have already planned a study with schoolchildren.

However, your current investigation already shows in the experiment that the choroid thickness can change in both directions, only by reading with different text contrasts. (ad)

Author and source information

Video: Ophthalmology Made Ridiculously Easy. 1st Edition. Digital Book (August 2020).