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July 20, 2018
Why does reading make us short-sighted? Researchers in Tübingen have now found a possible cause. The results suggest that the development of myopia could be stopped. The measurement is surprisingly simple.
Experts estimate that by 2050, half of the population will suffer from myopia. In Germany, the number of people affected is currently about a quarter. With them, the eyeball has grown too long, so that the focus is in front of the retina. Remote objects appear blurry. In addition to genetic causes, lack of time on the outside as well as reading seem to increase the risk of myopia. How the reading makes you short-sighted is not yet fully studied. Andrea C. Aleman, Wang Min and Frank Schaeffel of the Ophthalmology Research Institute of Tübingen University Hospital found a possible reason:
ON and OFF Cells
Unlike a Camera Digital that reads each pixel, retina measures (Retina) differences between "pixels" neighboring our environment. Bipolar cells in the retina compare the brightness in the middle and at the periphery of their photosensitive area. They only transmit the difference, that is, the contrast with the brain. The so-called ON cells react when the center is brighter in the photosensitive zone (the receptive field) and the periphery is darker. In contrast, OFF cells send signals to the brain when the center is darker and the environment brighter. During our normal visual experience, both types are also irritated. But what about reading text?
Schaeffel developed software that quantifies the intensity of the stimulus for ON and OFF cells in our visual world. It has been shown that the dark text on a light background mainly irritates the OFF cells, while the light text on a dark background mainly irritates the ON cells. Previous experiments with chickens and mice have already shown that stimulation of ON cells tends to inhibit eye growth, but stimulation of OFF cells can improve it. Does this mechanism also play a role in humans?
Using optical coherence tomography (OCT), the thickness of the tissue layers in the micrometer range can be measured in the living eye. The change in thickness of the choroid, the layer behind the retina, predicts whether the eye will develop in the near future. This has already been explored in chickens and various species of monkeys as well as in children. As the choroid thins, it indicates the development of myopia, it becomes thicker, eye growth retarded, myopia does not develop.
Inverse Contrast
Researchers also have subjects who read dark text on a light background. bright text on a dark background. After only 30 minutes, they were able to measure that the choroid thinned by reading the text in black, and thicker by reading the text with the opposite contrast. This suggests that black text on a light background promotes the development of myopia, and that the light text on a dark background inhibits myopia. Reverse text contrast would therefore be an easy way to stop the development of myopia, as more and more time is spent working and reading computer screens and tablets.
This strategy against the development of myopia has yet to be verified. Scientists in Tübingen have already planned a study with schoolchildren. However, their current research already shows in the experience that the choroidal thickness can change in both directions, only by reading with a different text contrast.
The text is based on a press release from the Tübingen University Hospital
University Hospital Tübingen
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