Alcohol will affect acrylic/plexiglass, but its not necessarily a fast reaction. I don't know what specific plastic glasses lenses are made of. Also, the UV coating might protect them from the alcohol.
I worked in optical it's polycarbonate. Can be a plastic called cr39 or it could be a high index lens if they have a very high prescription generally alcohol won't hurt it. If the frame is plastic the alcohol could potentially fog the plastic.