What causes myopia?

People with myopia have an eyeball that is too long, so the focused light terminates in the middle of the eye rather than on the retina. The length of your eyeball is determined by your genes.

You're referring to age-related myopia, or pseudo myopia. This one is caused by overused eye muscles (aging). People who read, sew, repair clocks, or perform another form of close work for long periods of time may simply wear out the muscles in the eye. These muscles don't repair themselves, so once they're tired out, you get this affect.

Eye muscles don't repair themselves? New muscles can't take their place? NAD+ is directly tied to muscle health. In mice anyway increasing NAD+ caused a regrowth of muscles and blood vessels returning a more youthful state. I sincerely hope eyes can focus correctly again without firing lasers in there medically.

Not sure why your response comes across as smug to me, but I find it rude. You asked a question, and I used my knowledge to help you understand it better. The least you can do is start by saying "thank you" , then add criticism. What in the world are you talking about NAD+ for, do you even know what that is? What's all this talk about mice, I thought we were discussing human eyesight. Lord almighty