Comment by tominous | Hacker News Reader

Comment by tominous | Hacker News Reader

Almost all children are born hypermetropic (far-sighted). The growth of the eyeball is calibrated by the amount of defocus (blur) experienced. More defocus, more growth, which reduces hypermetropia.

My hypothesis is that less sunlight means wider pupils and more defocus (contrast to a pinhole camera), so more eye growth.

Even with perfect eyesight, there's a 2-diopter difference between focussing blue light and red light due to chromatic aberration. Only narrow pupils can reduce this blur in white light.

I'm also curious whether older TVs with big blurry pixels (or low res images upscaled and smeared onto newer screens) trigger the same mechanism. These days I certainly feel physically uncomfortable looking at media like that, like my eyes aren't focussing quite right.

The other problem is that once eyes have grown too long and are myopic (near-sighted) they experience even more defocus and grow more. See for example [1] which discusses how under-correction of myopia accelerates progression.

[1] https://reviewofmm.com/does-the-undercorrection-of-myopia-in...

Mine is genetic.

I have very similiar values than my mother.

So i'mnot sure if / how your theory is correct or not.

Also there are a lot of normal people in the world who live outside and also don't have perfect eye sight at all. This goes back a long time.

Can you also elaborate on your 2 diopter difference between red and blue light? For one i find that number very very big but i'm very good in seeing full color without any chromatic aberration.

The effect of your theory would need to be less relevant than other factors.

Not denying that there are many ways in which development can go wrong, whether that's genetic or the environment. What I'm responding to is the sudden change seen in many populations as per the article.

Re: the chromatic aberration spread, see e.g. https://pubmed.ncbi.nlm.nih.gov/3716229/

They measured 1.82 diopters between 420nm and 660nm. Visible light is a bit wider, 380nm to 720nm, so 2 diopters is about right.

You easily can see this in a dark data centre. If your vision is perfectly corrected (which normally means perfect for red-green light) you won't be able to focus on a blue LED unless you are about 50cm away.

Huh, I always wondered why blue LEDs that were further away would be hard to look at & make me dizzy, that’s crazy!

Pure blue light does the least to stimulate the rods that help you see shapes clearly, only activating blue cones. This is why compression algorithms and some screens use 2 or 4 times as many bytes or phosphors for green as they do for blue https://biodifferences.com/difference-between-rods-and-cones...

This is also why writing a word in pure blue neon lights is really dumb. Adding just a little bit of green to it helps readability immensely.

I'm really interested in this topic since I've always noticed this, but not sure about this explanation as to why. I mean, yes, Bayes filter is like 2x1x1 for green, *red* and blue, and the most popular explanation has always been that our eyes perceive green better than both red and blue. Yet I don't have issues with red LED lights.

> Mine is genetic.

> I have very simil[a]r values than my mother.

Well, everything is genetic. The amount of sunlight you're exposed to is no less a genetic effect than how tall you grow to be. Without genes, you wouldn't have any behaviors or phenotypes at all.

So the interesting question is not "is this phenomenon genetic?", because the answer to that is always "yes". The interesting question is "what can influence this phenomenon?". In this case, we already know that (1) within a given culture, genetics are a strong predictor for myopia; and (2) once you do a cross-cultural comparison, the effect of culture absolutely overwhelms genetic measurements. Most people who become nearsighted in modern cultures would never become nearsighted in premodern cultures.

This is 100% true. Genetic predisposition to something != inevitability.

All of my immediate family members need glasses but me, which is pretty interesting.

My wife is -3 myopic, I'm -6 from childhood. And our 3 kids of 19, 17 and 10, have all a perfect sight.

They went outside often but nothing extreme. We have big luminous windows. And they spend a fair amount of time on screens too.

It can be so multifactorial, I have no idea why this luck. As I was convinced they would all wear glasses.

> Genetic predisposition to something != inevitability.

That depends on the thing. Whether you grow five or six fingers on your hands is determined by your genes without much reference to anything else. Whether you reach a "natural" height or develop stunted by malnutrition is also determined by your genes. It is more responsive to environmental conditions than the number of fingers on your hand is - but that responsiveness is determined by your genes.

Genes can cause or prevent myopia. However, genes do not spread rapidly and therefore cannot cause an epidemic. Obviously environmental factors are the major cause.

I think there's genetic predisposition but unless you have a separate disease, myopia is unlikely to just emerge out of thin air. There's probably something that we do that harms our ways and the studies point to the time outside as the key factor (screen time was just a correlation).

Something like this is beginning to be accepted. At least that's the impression I got from the eye doctor when I had PRK surgery. FWIW I had 20/15 vision until starting college and consequently being indoors in the dark much more often (staying up late to program).

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