When the eye doctor said that my vision was measured at 20/400, what did he mean?

Question

More specifically, what do the numbers mean and what causes me to be so nearsighted?

Answer 1

That simply means you have to be at 20 feet to see an object that a normal eye can see at 400 feet.

Your eyes have just developed that way , genetics mostly.

That would be your UNcorrected vision. You are most likely 20/20 with your glasses or contacts on.