You SHOULD be able to take the 4 oz. contact solution with you on the plane as currently specified on the TSA website list of
Permitted and Prohibited Items. Contact solution falls into the medicinal exception category exempting it from the 3 oz limitation, and would need to be "declared" at the screening checkpoint for potential additional screening. So this SHOULD be no problem. That said, there have been
lots of reports on Flyertalk of TSA frankly not following their written rules on this (which IMO don't seem to have much room for additional interpretation) and many have reported being forced to toss their 4 oz. contact solution because it's over the new 3 oz limit, when in fact it should be exempt from that limit. Grrrrr... So right now it's not clear whether you'll be able to get a 4 oz. bottle of contact solution thru security even tho you should be able to. I suspect in a few more weeks there will be enough complaints thru TSA channels that this will be consistently enforced correctly with respect to their written guidelines but if you're traveling soon

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Good luck!