It's not safe. period. i use to do it but then i stopped because many people said that it didn't allow enough oxygen to reach your eyes therefore it can lead to infections and such. you can do it, but you it will have effects. Once in a while is ok, but on a daily basis it's dangerous and can have long term effects. Your eyes are very valuable don't make a mistake please.
there is potetial damage due to oxygen restriction, but this depends on the typ of contact as well as duration of use (soft lenses will work better) though generally its not a great idea to do this daily, and especially not to sleep in them, as some soft lenses allow when worn without another pair
eye doctor response- (dont do it, it can damage your eyes...oxygen...bad...the end)