Great question. And the answer generally is no. You will not be able to get a seal on your mask if you are wearing your glasses.
But people have been creative, and taken apart a pair of glasses and put them in their mask. Read these two posts here and here to learn what they have done.
But there are lots of problems with trying to stick your glasses inside your mask, particularly when they fog up and get water on them.
We actual snorkeled once with a family member who tried to just hold their glasses up outside of their snorkeling mask, but it did not really work, and she ended up putting in some contacts (and was shocked by the amount of beauty she had been missing). Glasses are designed to work an exact distance from your face. Change that and it messes up the prescription.
The Solution?
You have two good options. The first is to get contacts. I (Galen) have always worn contacts snorkeling. I find it the best because then I can see when I pull off my mask above water (I am pretty blind without them). You just don't want to pull your mask off underwater and risk having your contacts washed away (it has never happened to me in hundreds of times in the water).
The second good option is to get a snorkel mask that has lenses installed that are made to your glasses prescription. Then you can see perfectly through your mask. Look for a mask that is "Corrective Lens Compatible". Depending on your prescription you can buy standard correction lenses, or have your exact prescription made.
I will be writing a detailed page about Prescription Snorkel Masks in the future - sign up for our newsletter to keep in touch about updates.
