How is it possible to have bad eyesight at 21 for example, if the body is at one of its most effective years, health wise? How can the lens become out of focus so fast?
Edit: Hoooooly moly that’s a lot of stuff after I went to sleep. Much thanks y’all for the great answers.
In: 4262
Healing is basically the body making more of the damaged thing. When you get a paper cut, your body makes extra skin and sticks it in there. Same thing when you break a bone. There are some things the body can’t make more of, or it’s so precise that just lumping extra material in doesn’t work. And it’s possible to have permanent damage if enough is gone or it’s killed in a special way.
Eyesight has to do with the flexibility of the lens, a plastic-y thing about the size and shape of an m&m. Muscles are attached to the edges to pull it into the right shape. Over time, the lens gets less flexible. Pulling harder would risk breaking it. The body can’t “repair” it because it’s not broken. And putting more lens material on it only make vision worse, because then it’s thicker. Imagine the difference when looking through a cup made of thin glass, versus a cup made of thick glass.
Bad eyesight becoming so common is because of evolution. In the 1700s, it was rare for someone to have less than perfect vision, even as they got older. But because we’re no longer looking out for bears or hunting for rabbits, we don’t automatically die if we get near-sighted. As a result, people with bad eyes live long enough to have kids.
Things that can’t heal themselves: teeth, bone coating (like inside the knee), cut tendons, cut nerves. That’s why fake teeth, knee replacements, tendon transplants, and paralysis are so common.
Things that can heal, but are bad at healing: nerves, kidneys. Which is partially why so many people need kidney transplants.
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