Is it safe to buy prescription eyeglasses online?!

Is it safe to buy prescription eyeglasses online?

My frames aren't very common (Revolution Airs) so not many eye stores carry them. My lenses are also really expensive because my eyesight is so poor. I've noticed that you can buy glasses online (ex. www.framesdirect.com) and usually they're cheaper. However, is it reasonable to do this? Is there a catch I'm missing?

2 months ago
By the way, I know what my prescription is.

2 months ago
I would also plan on buying the same exact frames that I have now. About fitting the glasses to your face, a friend said that any optician can do that if you just bring the glasses to them.

If you get your Rx from a doctor, you can get them online without a problem. I wear vintage Rx glasses all the time and have never had a problem:

http://www.eyeglassfactoryoutlet.com...
http://www.globaleyeglasses.com...

My husband has really bad eyes and does it too.