I can barely see the computer screen without my glasses, but I have found that whatever effect the water has on the glass in the mask seems to make it behave like corrective lenses, and I can see quite well underwater. If you are able, you might want to buy a cheap mask and go to a swimming pool to see how your vision is there. If it's acceptable, go ahead and book a snorkle excursion.
You can buy a mask with correective lenses. It makes all the difference in the world.
Go to adive shop and know your prescription. They will insert lenses into mask one prescription less than your normal glasses (that makes up for the "effect"f the water mentioned above. Cost should range , price of mask plus $35 per lens.
I don't vacation without my prescription mask.
I bought masks with corrective lens for myself and my wife. i dive, she snorkles, but swears they made all the diff. They are more expenseive (ours were about $100 each, that included the mask and lens) but if you plan on snorkeling on a regular basis or eventually going deeper and trying scuba diving, a prescription mask is worth the investment.
email me if you have any questions on where to get one.
I too had great luck just using a mask without a lens. I was really surprised because I have really bad eyesight and when I went on my first snorkeling trip I didn't realise lenses were available. If you plan on a few adventures in the future I would get the mask with the lenses-too many interesting things to see blurred.