[HN Gopher] Short-sightedness was rare. In Asia, it is becoming ...
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Short-sightedness was rare. In Asia, it is becoming ubiquitous
Author : kasperni
Score : 30 points
Date : 2022-06-13 18:13 UTC (4 hours ago)
(HTM) web link (www.economist.com)
(TXT) w3m dump (www.economist.com)
| jsnell wrote:
| Related discussion from yesterday:
| https://news.ycombinator.com/item?id=31711990
|
| (I guess Economist must have a theme week on this...)
| blakesterz wrote:
| Pretty interesting. The dominant hypothesis now is that exposure
| to daylight is the main variable. It explains why myopia seems,
| like diabetes and heart disease, to be what doctors call a
| "disease of affluence"--more common in rich countries than poor
| ones--since economic growth brings with it more education, and
| therefore, for children, more time inside.
| User23 wrote:
| > The dominant hypothesis now is that exposure to daylight is
| the main variable.
|
| Which is obviously wrong. The main variable is the time the eye
| spends at a short focal length. Like every other part of the
| body, the eye adapts to the stresses it experiences. Focusing
| on nearby objects for extended periods is stressful for a
| normal eye and as is the case for so many stressors, the body
| adapts[1]. This is easily seen in that ceteris paribus a person
| with myopia can comfortably focus on much closer objects than
| someone with normal vision.
|
| Incidentally this means that corrective lenses can actually
| cause myopia to progress. Contrariwise a prescription can be
| written such that there is an effective training stimulus to
| reverse myopia[2]. However, that won't fix the decreased focal
| range due to age related hardening of the lens of the eye.
|
| [1] See Selye for details.
|
| [2] Inexplicably, most optometrists refuse to do so.
| helloworld wrote:
| https://newsroom.uw.edu/news/glasses-stop-myopia-are-success...
|
| Their big breakthrough in understanding myopia occurred in 2008
| when they studied a particular group of people who had a
| genetic form of myopia that's very severe. They discovered a
| gene mutation that was causing the myopia.
|
| "It turns out it was a mutation in the cone photoreceptors,"
| said Jay Neitz. "We then realized that it's really just the way
| that the images are being encoded on the retina."
|
| What's supposed to happen as your eye grows, is that things
| should begin to go out of focus in the periphery of your
| vision. That's a signal for the eyes to stop growing.
|
| But as long as things are still clear in the periphery, the
| eyes think this person must still be farsighted, because in the
| natural world things in the periphery are far away.
|
| Neitz said his team was able to design a lens to make central
| vision clear and in focus, and give the peripheal vision much
| lower contrast.
|
| "It recreates what is supposed to be going on with our eyes
| before we started putting all of these things in front of our
| face like computer screens and tablets," he said.
| corrral wrote:
| Exposure to very bright light (even standing under a shade tree
| on a cloudy day is far brighter than normal indoor lighting)
| specifically during key years had been nailed down with high
| confidence as the primary cause of _most_ near-sightedness,
| last time I looked into this.
|
| Not sure if they'd figured out the mechanism, but speculation
| was that bright light is involved in signaling the eye to stop
| lengthening at the right time.
|
| IOW the cause is, basically, school. In Winter months, kids may
| hardly see the Sun at all, with very short days and recess
| often indoors (too cold, too snowy, too wet) especially as
| schools have seemed to grow more wary of taking kids out in
| poor weather, over the last few decades. Plus anything else
| that keeps kids indoors, sure (video games, social media[0])
| but school seems to be _a lot_ of it.
|
| [0] And actually, the social media factor likely kicks in well
| after it matters. Ditto video games unless your kid becomes a
| gaming addict in the 3-7 age range and you just _let that
| happen_.
| exceptione wrote:
| If exposure to bright light is the primary cause of most
| near-sightedness, than not seeing the sun would be
| beneficial. I don't get it, typo?
| dan-robertson wrote:
| Yeah typo. The theory is that eyes change shape over time
| (I think starting out longsighted) and at some point a
| hormone is released to stop this changing. It is released
| when (a) the eyes are typically around the middle of their
| focal range (ie looking at middle-distance things is done
| with relaxed eyes) and (b) there is a lot of light. Without
| the second condition the shape of the eyes will continue to
| change and then you get myopia.
| wenc wrote:
| I grew up near the equator where there is a very high rate of
| myopia despite exposure to sunlight. (Sure we spent a lot of
| time indoors, but we were exposed to sunlight all year round
| since there's only one season: summer).
|
| I think genetics has a larger predictive effect than
| sunlight.
| doliveira wrote:
| There's a reason why they're not just saying "it's
| genetics"...
| v8xi wrote:
| https://archive.ph/FrRiG
| pixelkritzel wrote:
| Thank you! For the article and the trick.
| baal80spam wrote:
| It's strange but I don't get paywalls on The Economist, I
| wonder why. I'm using Brave.
| libx wrote:
| simmerup wrote:
| There's a similar story with balding rates increasing in Asian
| countries
| mc32 wrote:
| Huh? Would be interesting if you have a reference for that as
| it's not something I had heard of.
| kgc wrote:
| Also never heard of this. Source?
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