Because you have two eyes, if you are talking about bi focal lenses then it is so that you can use a single glass both for reading and for outdoor use (looking at objects that are for.
If a person is wearing spectacles it means he is wearing a pair of glasses. The word spectacles is rarely used in this day and age.
I assume glasses refers to spectacles? If so, then the hinges allow the two arms of the spectacles to lay flat when not being worn.
You just wear them over your glasses. The 3d glasses are a bit bigger than normal glasses so they will easily fit over your spectacles.
Spectacles and glasses are exactly the same in meaning but different in usage. The word spectacles is considered to be an old-fashioned and formal term for Americans but it is still used in British.
Glasses (ie. spectacles)
glasses, spectacles
Spectacles is a plural. As a noun, plural terms which are equivalent to their singular term (consider glasses) are usually used without change. I.e.) He wears glasses (singular) They all liked their glasses (plural). The spectacles were quite useful (singular). No matter how many spectacles (plural) you own, one is often enough.
no...
glasses
Glasses for lasses.
Spectacles is another name for glasses and you wear them on your face/head
glasses are 'des verres' in French. If you think of spectacles, they are called 'lunettes'.