What do the numbers mean on an eye prescription?

My friend says that her eye perscription is -75 in both eyes. Does that mean she has a small amount of nearsightedness? Does she really nead glasses for that small amount of nearsightedness or was her doctor just trying to sell her a pair of glasses?

The person that said she probably sees about 20/75 is right. That of course is just a ruff estimate but gives you an idea of how much closer she has to be to see things than others. 20/20 is not normal - it is subnormal. Most people are easily corrected to 20/15 vision.
Most doctors would prescribe glasses for someone with -0.75DS, especially if they are in school and need to see the board.

20/20 is normal.

My vision was -250 before I had laser surgery in my right eye, now it is 20/25! I think -75 is a very very low level degree of nearsightedness. I don't know enough about it to determine her Dr's motives!http://www.ebookgiveaways.com/forms/visi...

Nearsightedness means that images that are far away are out of focus. Your friend's perscription is probably 20/75 which means that what most people can clearly see at 20 feet away actually looks to be 75 feet away to your friend.

Your friend will probably only need glasses in school or while driving. I had 20/150 in one eye and 20/200 in the other. I had Lasik about 5 years back and I'm now at 20/20. It was the best money I ever spent.

Hope that helps!
Scotrates