Huh, I didn't know this was something special. I used to swim underwater with my eyes open all the time when I was little and I could see underwater just fine like the article describes. I just assumed everyone could :).
Although I couldn't do it in salt water, it stung my eyes too much but that might also be due to me learning to swim in pools instead of the sea.
You can see underwater, but you don't see as well as they do:
> The kids had to dive underwater and place their heads onto a panel. From there they could see a card displaying either vertical or horizontal lines. Once they had stared at the card, they came back to the surface to report which direction the lines travelled. Each time they dived down, the lines would get thinner, making the task harder. It turned out that the Moken children were able to see twice as well as European children who performed the same experiment at a later date.
I suspect this is mostly just a question of how much time people spend under water. When I used to swim a lot I did not notice my vision being worse underwater. I could easily read an underwater wrist watch for example.
PS: I still have better than 20/20 vision. But, I think your eyes age faster than most people suggest as I can't see as well even at just 35 vs 15.
Hm. Salt water is (according to my google-fu) denser than fresh water. The article says, "When the eye is immersed in water, which has about the same density as the cornea, we lose the refractive power of the cornea..."
I wonder if this refers to salt or fresh water. Maybe both, if the density delta between the two is trivial.
I know, but the crux of the article seems to be that you shouldn't be able to see underwater even if you can keep your eyes open. I could/can see underwater just fine but only if I can keep my eyes open of course. I cannot keep my eyes open in salt water, but that might be a lack of acclimatization is what I'm saying.
Gislen was able to test a few Moken adults in the same way. They showed no unusual underwater vision or accommodation – perhaps explaining why the adults in the tribe caught most of their food by spear fishing above the surface. “When we age, our lenses become less flexible, so it makes sense that the adults lose the ability to accommodate underwater,” says Gislen.
Although I couldn't do it in salt water, it stung my eyes too much but that might also be due to me learning to swim in pools instead of the sea.