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About half of high school graduates in Germany are short-sighted. In myopia (nearsightedness), the eye develops too long, the image is clearly displayed in front of the retina and you can see off the focus. Myopia is the price of a good training: per year, training is about a quarter of diopter on average. Worldwide, myopia is increasing because a good education is more important.
Children who have spent a lot of time outdoors in the light of day will later become myopic. However, at the latest, if they read a lot during their training, the risk of myopia increases. What exactly is short-sighted reading at school is not yet well understood. For a long time, it was thought that too little accommodation in reading would put the net image behind the retina, causing faster growth of the retina. These data have never been completely convincing. Andrea C. Aleman, Wang Min and Frank Schaeffel of the Ophthalmology Research Institute of Tübingen University Hospital have now found an unexpected reason why reading could be short-sighted.
Unlike a digital camera that reads each pixel, the retina primarily measures the differences between adjacent "pixels", the photoreceptors. This is achieved by comparing the brightness of cells in the center and periphery of their light-sensitive area, and simply transmitting the difference to the brain. Visual information is thus mbadively reduced, which is necessary because the retina has about 125 million "pixels", but the optic nerve only accounts for about one million. The optic nerve is thus the bottleneck of the information transmission.
There are cells in the retina that evaluate whether the center is clearer in the photosensitive area (receptive field) and the surroundings are darker (ON cells). Others judge whether the center is darker and the environment brighter (OFF cells). During our normal visual experience, both types are also irritated. But how is it when you read a text?
Schaeffel developed software that quantifies the stimulus intensity for ON and OFF cells in our visual world. It has been shown that dark text on a light background is mainly irritating to OFF cells (Figure 1A), whereas light text on a dark background is mainly irritating to ON cells (Figure 1B).
Previous experiments with chickens and mice have already shown that stimulating ON cells can inhibit eye growth but stimulate OFF cells
Does this mechanism also play a role in humans?
Using optical coherence tomography (OCT), the thickness of tissue layers in the living eye can be measured accurately (micrometer range). In chickens, various monkeys and children, research has already shown that changing the thickness of the choroid, which is the layer behind the retina, predicts how the eye will develop in the near future . If the choroid becomes thinner, it indicates the development of myopia, it becomes thicker, eye growth delays, myopia does not develop.
Alleman, Wang and Schaeffel have volunteers reading a dark text on a light background and a clear 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 (Figure 2).
This suggests that black text on a light background promotes the development of myopia, and that a clear text on a dark background inhibits myopia. Reverse text contrast would 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 experiment that the choroidal thickness can change in both directions, only by reading with a different text contrast (Figure 2).
Illustrations
All illustrations and portraits of the authors are available in high resolution
http://www.eye-tuebingen.de/files/fia/schaeffel-scientific_reports-bilder.zip
Source: Schaeffel / Ophthalmology Research Institute
Figure 1. ON and OFF relative force badysis Irritation with dark text on a light background (A) or light text on a dark background (B) with software developed by the user. Below: texts evaluated automatically (dark blue areas = OFF stimulation, pink areas = ON stimulation). The curves below quantify the relative strength of ON or OFF pacing. It turns around when the contrast of the text is reversed.
Figure 2. Left: OCT image of the retina and choroid in the living eye. The deepening in the middle is the fovea, the place of the clearest vision. The thickness of the choroid is determined under the fovea (yellow bar). Several hundred measurements have shown that choroidal thickness increases when subjects read a clear text on a dark background, and thinner when they read a standard text. Right: Changes in choroidal thickness, averaged over 7 subjects
Media Contact
University Hospital Tübingen
Ophthalmology Research Institute
Professor Frank Schaeffel
Elfriede-Aulhorn -Str. 7, 72076 Tübingen
Tel. 07071 29-80739
E-Mail [email protected]
Scientific Contact:
University Hospital Tübingen
Institute for Ophthalmology Research
Professor Frank Schaeffel
Elfriede-Aulhorn-Str, 7, 72076 Tübingen
Tel. 07071 29-80739
Email [email protected]
Original Publication:
http://www.nature.com/articles/s41598-018-28904-x
Reading and Myopia: Contrast Polarity Matters. Andrea C. Aleman, Wang Min and Frank Schaeffel. Scientific Reports volume 8, article number: 10840 (2018)
DOI: 10.1038 / s41598-018-28904-x
idw 2018/07
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