What is the medical explanation for why some peoples vision is better than others. am i just born with bad eyes? or a dysfunction while developing?

It is in our genes: Bad eyes, usually means just strong glasses. I believe it has been shown that kids who do a lot of near work, may make themselves more near sighted. Most of where we end up with our glasses, in my opinion, is determined by the genes we inherited. But, it may skip generations and can be different from your parents.

Few are perfect. : Vision is determined by the shape and clarity of the lens and cornea and the length of the eye. In addition there ha to be normal retina and optic nerve. I see hundreds of patients where these are not normal. Most commonly people are myopic-the eye is long and people need glasses. Very few are perfect. They just put up with less than perfect vision and don't wear glasses.

I agree: There are 'bad eyes' that are correctable (near sighted, astigmatism, etc) and then there are really bad eyes that cannot be corrected by glasses, a much more serious problem. Both heredity and environment play a role in how your vision develops.