It is quite a grandmother’s and mother’s phrase to hear that spending a long time in front of a screen or being very close to a book can cause us to develop a disease in the eyes like the myopia. However, science has long suspected that “close work” alone does not explain why myopia has become a global pandemic.
The new. Now a revealing study has proposed a physiological mechanism that fits all the pieces of the puzzle together, placing the blame not only on what we look at, but on the amount of light that reaches the back of our eye while we do so.
And the investigation is quite justified, since the data is scary. In Spain, 19% of children between 5 and 7 years old are already myopicand projections estimate that by 2050 half of the world’s population will need glasses. To stop this, we need to understand exactly the mechanism that produces myopia, and a team from New York has found the key.
The famine of light. The work, recently published in the prestigious magazine Cell Reports by researchers, points to a fascinating concept in this case: the light deprivation hypothesis.
Until now we knew that focusing on nearby objects is closely linked to the development of myopia. But what this study has measured with empirical precision is how the myopic eye reacts to the healthy eye during this process.
What they have seen. The main finding is that myopes suffer from excessive accommodative pupillary constrictionthat is, when you look closely, the pupil becomes much smaller than normal. If we add to this that close-up work is usually done indoors where lighting rarely exceeds 500 lux, compared to 10,000 lux outdoors, the result is a lethal cocktail for the eye: the combination of dim light and a maximally contracted pupil causes the retina to “starve” due to lack of light.
The short circuit. Here the question that logically must be asked is: Why does this lack of light cause the eye to grow abnormally, causing myopia? This is where the purest neuroscience comes in, since our retina processes the image through two main channels: the ON path that is activated with increases in light, and the OFF path, which reacts to shadows.
In previous work from 2024, this same team had already shown that in myopic patients the ON pathways have serious deficits, since they are less sensitive and slower. Now the new hypothesis postulates a vicious circle in which, when reading or looking at a cell phone indoors, the pupil closes too much. And this is a problem, since chronic lack of light further weakens the retinal ON pathway, and this imbalance sends erroneous signals that ultimately promote elongation of the eyeball.
The treatments. This proposal not only stands out for explaining the biological mechanism of myopia, but also unifies at once why the treatments that ophthalmologists They have been applying it empirically for years. One of the examples is spending time outdoors, but not because it cures, but because the sunlight is so intense that it more than compensates for having a small pupil, keeping the ON pathway stimulated and slowing the progression of myopia.
Another example is the use of atropine drops in children to stop myopia thanks to the dilation of the pupil so that more light enters the retina. The same goes for multifocal lenses that are used to reduce accommodation effort, since the pupil does not need to constrict as excessively.
It is not definitive. As is almost always the case in science, this work does not demonstrate a direct coincidence yet, but rather offers us an incredibly solid and plausible physiological mechanism supported by very robust data on the behavior of our pupil and neural pathways. But there is still a way to go with new long-term studies to confirm the hypothesis 100%.
While we wait for those results, the practical conclusion seems clearer than ever: the problem is not just the tablet or the book. The problem is doing it in the dark, so if you are going to strain your eyes up close, make sure you turn on a good lamp and, above all, don’t forget to go out into the sun.
Images | Akshit Dhasmana
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