Yes of course you can wear glasses with a motorcycle helmet. Some helmets are designed for those who need to wear prescription eyeglasses.
If you wear open helmets, it is OK for you to wear any glasses and you won't feel uncomfortable.
If you want to wear a full face one, then you need to make sure that there are spaces enough for your glasses so that you will not feel tight.
You should not wear glasses with a motorcycle helmet especially the framed eyeglasses, because it is not safe for you to do that. When you wear glasses with a motorcycle helmet, your motorcycle helmet may be full of frog while you are breathing and speaking. Imagine that your eyeglasses will also be full of frog and you could not see the things in front of you, including the roads. Therefore it is very dangerous to wear glasses with a motorcycle helmet while you are riding.
However, If you are heavy prescription problems and you have to wear glasses while riding, I suppose you can have a kind of half helmet which means your face are not covered with the half motorcycle helmet, so that your glasses may not be full of frog while you are breathing or speaking. And we know it is not good to wear glasses with a motorcycle helmet, you should avoid wearing glasses with helmet in case there will be some dangerous situation.
Yes, you can. But the problem is that whether the inner space allows you to wear the glasses when the shield of the motorcycle helmet is closed. If you just not use the shield for you to protect from the wind or sand during the riding, it is OK for you to wear the glasses to see clearly. However, you can wear the contact lenses. Thus, the shield can be used to resist the wind and sand.
It's fine to do that. Nowadays, there are some helmets models have a groove in the foam on each side of the head for the frame to slide past the ears. Whatever kind of helmet you would purchase, you have to make sure whether your glasses would be comfortable with the helmet on. Because of the padding of the helmet would put excessive pressure on the eyeglasses temples.
Yes, you can wear glasses under a motorcycle helmet. Some helmet models even have a groove in the foam on each side of the head for the frame to slide past the ears. Whether the helmet you buy has this or not, you need to make sure that your glasses will be comfortable with the helmet on