This really depends on the design of the full face snorkel mask and the size of your glasses. Some full face snorkel masks have enough room to accommodate glasses underneath, but others may not.
If you wear glasses, it’s important to check the specifications of the particular full face snorkel mask you’re considering and consult the manufacturer’s instructions before attempting to wear glasses with it.
In the case of the Cressi Duke full Face Snorkel Mask, which we mainly stock here at Oceansports, we do not recommend to wear glasses underneath as it may cause discomfort, a poor seal, or water leakage.
If you need corrective lenses, you may want to consider using a more traditional style prescription snorkel mask instead. These goggles have built-in corrective lenses and can provide clear vision while snorkeling without the need for glasses.