Can eyesight be improved?

Today I went to the optometrist and he told me that eyesight cannot be improved; it will continue to worsen. I have horrible eyesight (-6.00) and this was clearly disappointing. Even if I had better eyesight, is it possible for it to get better? I'm only 16, and my eyesight has been declining rapidly; I'm not sure if it's genetics or if I'm doing something to hasten bad eyesight. Also, he told me that computers and reading in the dark does not have any effect on getting bad eyesight. True or false?