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Glasses thanks to parents or environment
If as a child you liked to curl up under the covers with a book, your parents have probably told you that this is how you ruin your eyes. Can it really hurt to read by a dim night light?
The idea that reading in the dark makes your eyes worse is probably based on the tiring effect of looking in poor light. You will see less contrast in the twilight, which means that distinguishing letters takes extra effort. Your eye muscles get tired and you can headache to get.
In addition, you blink less when you’re staring at a book. This results in dry, irritated and sometimes watery eyes. These adverse effects are temporary and do not cause permanent damage. A nice read by the light of a flashlight does not seem to do any harm.
Myopic
So why are some children suddenly unable to read the blackboard halfway through school? Mostly because their eyes have grown too long.
Normally, the lens of the eye and the cornea refract the light rays in such a way that they fall exactly on the retina. If the eye is too long or your cornea is too convex, the light rays will not be refracted correctly. As a result, the image of something that is distant falls in front of the retina instead of on it and you see blurry in the distance. That’s called myopia. Myopia usually develops between the ages of 7 and 16 because the eye is still growing and sometimes becomes too long.
Heredity
Whether you are nearsighted is largely due to your parents. Erasmus MC researchers discovered 26 genes that play a role in the transmission of signals in the brain to the eyes, the construction of the connective tissue and the development of the eye. If you have more than one of these genes, you run a much higher risk of myopia.
However, it is not only hereditary factors that determine whether your vision is blurred in the distance. A number of environmental factors probably also play a role. For example, the region where you live: East Asia has far more myopic than in Europe. Highly educated people and people who work a lot close by, such as reading and studying, are also more likely to be short-sighted. A lot of playing outside seems to some to investigate protect the eyes, possibly because one sees more daylight and looks at objects in the distance.
Hard to prove
Or is all that reading really the cause of it impaired vision has never been conclusively proven. It is very difficult to do scientific research into this phenomenon. Researchers would have to follow large groups of children for years and arbitrarily determine which children are allowed to read in the dark and which are not in order to be able to compare them properly. That does not work in practice.
The studies that have been done into the influence of reading in the dark on the eyes usually have all kinds of limitations. For example, adult test subjects were informed whether they used to read a lot in bed, but whether that yields reliable information is open to question.
Your mother probably hoped that you would finally turn off your nightlight and go to sleep. Further investigation will have to show whether there was a grain of truth in her statement. For the time being, optometrists indicate that you can read in low light. Reading at night under a bright lamp can make you no longer sleep comes.
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