The limit is 90ml in the US and 100ml in Europe, plenty of lens fluid suppliers offer travel sized bottles that spare you the discussion of medical or not with security. The TSA allows over the counter medication (which BTW includes lens cleaner fluid) to be of a larger size than 90 ml, but it needs to be highlighted to the screeners before you put your bag on the xray machine belt. FRA says it should be below 100ml, Swiss says its OK, etc etc. Very very grey area, just get a travel sized bottle and avoid discussions...