Types of Myopia?

I need to know about degenerative myopia. I know there are three types of myopia: normal, hereditary, and degenerative. Normal myopia is if your vision gets worse from watching too much TV and stuff, right? Hereditary is just like normal myopia, except your if runs in the family, so you have a higher chance of myopia. But what about degenerative? I read that even when you're past adulthood, your vision will keep getting worse, and it can't be helped. How can I tell if I have degenerative myopia of not? Both my parents wear gles, and I started wearing them in kindergarten (I wear contacts now). Could someone help me?