Extreme Nearsightedness?

The strength on my contact lenses (I am not sure what it is called) is a -12.5. I've been told this is very near sighted. I cannot function without contacts in. I've had to miss school/work a few times because I was out of lenses and my gles are coke bottles. I was just wondering how this compares to other people's strengths. How nearsighted is a -12.5? Will this just keep getting worse? I had to start wearing gles in kindergarden and had to start wearing hard contact lenses when I was 10 in hopes that it would slow down my vision changes.