Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Why might reading make myopic?

18.07.2018

About half of the students finishing high school in Germany are myopic. In myopia, the eye grows too long, and the focus of the image is in front of the retina. The visual scene is out of focus when people are looking at a distance. Myopia is the prize to pay for good education - statistically, one year of education makes about a quarter diopter more myopic. Myopia is increasing worldwide, since a solid education becomes more and more important.

It is known that myopia develops later when children are more outside before school and are exposed to bright illumination. What exactly makes them myopic when they start reading at school is still not fully understood. For a long time, it was assumed that too little accommodation during reading moves the sharp image behind the retina, which would stimulate further eye growth.


Figure 1. Qantification of the relative input strength to ON or OFF cells when dark text on bright background is read (A) or vica versa (B), using custom-developed software. Below: results of the automated analysis. Dark blue: preferential OFF stimulation, pink: preferential ON stimulation. Curves below show the quantitative data on realtive ON and OFF input strength. Note that input strength flips over when text contrast is inverted.

Frank Schaeffel / Institute for Ophthalmic Research Tuebingen


Figure 2. Left: OCT scan of the retina and the choroid in the living eye. The pit in the center is the fovea, ther area of sharpest vision. The thickness of the choroid is measured under the fovea (yellow line). Severeal hundred meausrements have shown that the thickness of the choroid increases when subjects read bright text on dark, and decreases when they read dark text on bright background - standard text. Right: change in choroidal thickness over time, averages from 7 subjects.

Frank Schaeffel / Institute for Ophthalmic Research Tuebingen

However, data were never fully convincing. Andrea C. Aleman, Min Wang and Frank Schaeffel (Institute for Ophthalmic Research) have now found a new unexpected reason why reading may make myopic.

Different from a digital camera which reads out each single pixel, the retina mainly evaluates differences between neighbouring pixels (photoreceptors). This is achieved by cells which compare the brightness in the center and the periphery of their light sensitive area („receptive fields“). These cells send mainly data on the differences to the brain. Doing this, the amount of information is massively reduced.

However this is also necessary since we have about 125 Million pixel in the retina but only about 1 Million “cables” in the optic nerve. The optic nerve is therefore a „bottleneck“ for transmission of visual information.

There are cells that respond mostly to brightness in the center of the receptive fields and darkness in the periphery (ON center cells), and cells that respond preferentially when the center is dark and the periphery is bright (OFF center cells). During our normal daily visual experience, both types are similarly stimulated. But what happens during reading of text?

Software was developed to quantify the relative stimulus strength for ON and OFF cells for various visual environments. The software showed that dark text on bright background stimulates mainly OFF cells (Figure 1 A), while bright text on dark background stimulates mainly the ON cells (Figure 1B).

It was known from earlier experiments in chickens and mice that stimulation of ON cells tended to inhibit eye growth while stimulation of OFF cells tended to increase eye growth.

How can one show that such a mechanism may also operate in humans? Using optical coherence tomography (OCT) it is possible to measure the thickness of tissue layers in the living eye with very high resolution (micrometer range).

The layer behind the retina, the choroid, is of particular interest since it has earlier been shown in chickens, various species of monkeys and children that changes in choroidal thickness can predict future changes in eye growth. When the choroid thins, the eye typically starts growing, when it thickens, eye growth is inhibited and no myopia will develop.

Alleman, Wang and Schaeffel asked their subject to read dark text on white background or bright text on dark background. Already after 30 minutes it was found that the thickness of the choroid either decreased (when reading standard text) or increased when reading text with inverted contrast (Figure 2).

One would therefore expect that dark text on bright background would stimulate myopia development and bright text on dark background would inhibit myopia. Simply inverting text contrast is therefore strategy to inhibit its development. This is easily achieved on computer screens and tablets but certainly more demanding when it comes to printed books.

The potency of the potential new strategy to inhibit myopia has still to be verified in a (planned) study in school children - but at least there is experimental confirmation that the choroid can change its thickness in either direction, depending on the contrast polarity of the text that is read (Figure 2).

Figures
Figure 1. Qantification of the relative input strength to ON or OFF cells when dark text on bright background is read (A) or vica versa (B), using custom-developed software. Below: results of the automated analysis. Dark blue: preferential OFF stimulation, pink: preferential ON stimulation. Curves below show the quantitative data on realtive ON and OFF input strength. Note that input strength flips over when text contrast is inverted.

Figure 2. Left: OCT scan of the retina and the choroid in the living eye. The pit in the center is the fovea, ther area of sharpest vision. The thickness of the choroid is measured under the fovea (yellow line). Severeal hundred meausrements have shown that the thickness of the choroid increases when subjects read bright text on dark, and decreases when they read dark text on bright background - standard text. Right: change in choroidal thickness over time, averages from 7 subjects.

Wissenschaftliche Ansprechpartner:

Universitiy Hospital Tuebingen
Centre for Ophthalmology, Institute for Ophthalmic Research,
Elfriede-Aulhorn-Strasse 7, 72076 Tübingen, Germany
e-mail: frank.schaeffel@uni-tuebingen.de

Originalpublikation:

http://www.nature.com/articles/s41598-018-28904-x
Reading and Myopia: Contrast Polarity Matters. Andrea C. Aleman, Min Wang & Frank Schaeffel. Scientific Reports volume 8, Article number: 10840 (2018) DOI:10.1038/s41598-018-28904-x


Bianca Hermle | idw - Informationsdienst Wissenschaft
Further information:
http://www.medizin.uni-tuebingen.de/

More articles from Health and Medicine:

nachricht Inselspital: Fewer CT scans needed after cerebral bleeding
20.03.2019 | Universitätsspital Bern

nachricht Building blocks for new medications: the University of Graz is seeking a technology partner
19.03.2019 | Karl-Franzens-Universität Graz

All articles from Health and Medicine >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: The taming of the light screw

DESY and MPSD scientists create high-order harmonics from solids with controlled polarization states, taking advantage of both crystal symmetry and attosecond electronic dynamics. The newly demonstrated technique might find intriguing applications in petahertz electronics and for spectroscopic studies of novel quantum materials.

The nonlinear process of high-order harmonic generation (HHG) in gases is one of the cornerstones of attosecond science (an attosecond is a billionth of a...

Im Focus: Magnetic micro-boats

Nano- and microtechnology are promising candidates not only for medical applications such as drug delivery but also for the creation of little robots or flexible integrated sensors. Scientists from the Max Planck Institute for Polymer Research (MPI-P) have created magnetic microparticles, with a newly developed method, that could pave the way for building micro-motors or guiding drugs in the human body to a target, like a tumor. The preparation of such structures as well as their remote-control can be regulated using magnetic fields and therefore can find application in an array of domains.

The magnetic properties of a material control how this material responds to the presence of a magnetic field. Iron oxide is the main component of rust but also...

Im Focus: Self-healing coating made of corn starch makes small scratches disappear through heat

Due to the special arrangement of its molecules, a new coating made of corn starch is able to repair small scratches by itself through heat: The cross-linking via ring-shaped molecules makes the material mobile, so that it compensates for the scratches and these disappear again.

Superficial micro-scratches on the car body or on other high-gloss surfaces are harmless, but annoying. Especially in the luxury segment such surfaces are...

Im Focus: Stellar cartography

The Potsdam Echelle Polarimetric and Spectroscopic Instrument (PEPSI) at the Large Binocular Telescope (LBT) in Arizona released its first image of the surface magnetic field of another star. In a paper in the European journal Astronomy & Astrophysics, the PEPSI team presents a Zeeman- Doppler-Image of the surface of the magnetically active star II Pegasi.

A special technique allows astronomers to resolve the surfaces of faraway stars. Those are otherwise only seen as point sources, even in the largest telescopes...

Im Focus: Heading towards a tsunami of light

Researchers at Chalmers University of Technology and the University of Gothenburg, Sweden, have proposed a way to create a completely new source of radiation. Ultra-intense light pulses consist of the motion of a single wave and can be described as a tsunami of light. The strong wave can be used to study interactions between matter and light in a unique way. Their research is now published in the scientific journal Physical Review Letters.

"This source of radiation lets us look at reality through a new angle - it is like twisting a mirror and discovering something completely different," says...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

VideoLinks
Industry & Economy
Event News

International Modelica Conference with 330 visitors from 21 countries at OTH Regensburg

11.03.2019 | Event News

Selection Completed: 580 Young Scientists from 88 Countries at the Lindau Nobel Laureate Meeting

01.03.2019 | Event News

LightMAT 2019 – 3rd International Conference on Light Materials – Science and Technology

28.02.2019 | Event News

 
Latest News

Solving the efficiency of Gram-negative bacteria

22.03.2019 | Life Sciences

Bacteria bide their time when antibiotics attack

22.03.2019 | Life Sciences

Open source software helps researchers extract key insights from huge sensor datasets

22.03.2019 | Information Technology

VideoLinks
Science & Research
Overview of more VideoLinks >>>