I'm not sure it needs to be an adaptation (in a genetic sense), I think like most things our bodies just get used to it. I used to open my eyes underwater when

I'm not sure it needs to be an adaptation (in a genetic sense), I think like most things our bodies just get used to it. I used to open my eyes underwater when swimming at the beach as a child on holidays, but not an adult. Having a salt water pool at home probably helped, but now that I rarely go to the beach it stings.