I get sample sizes of contact solution from my eye doctor for flying. The solution my DD uses comes in a 2 oz sample, but the kind I use (Clear Care) comes in a 4 oz sample. However, Clear Care has now started SELLING 2 oz bottles- at ridiculous prices, with the airplane on them. The free samples are still 4oz.

Recently they had a promotion where you could buy two 12 oz bottles and get a 2 oz free, so we stocked up.
We flew to Disney in 2007, before they made 2oz bottles (I even called the company and they said they didn't MAKE them at that time!) and were given a very hard time about it. We had separated our contact solution and declared it as the TSA guidelines said to do, we even had a print out of the page, but wow, it was horrible. The agent said we should have bought a smaller size.

Considering I had been to my eye doctor AND called the company trying to get a smaller size, that was really annoying. He was VERY condescending and told us he had "seen it at
WalMart" when we tried to explain that they didn't MAKE a smaller bottle.
We didn't want to check our contact solution as we have experienced "misdirected bags" on at least 4 occasions, and if we didn't have our contacts, we wouldn't be able to see normally! Fortunately, on our way back, we got a VERY nice agent in Orlando and had no problems at all.
This year, since we do have the 2 oz bottles, I hope it won't be an issue. We are separating it from our 3-1-1 bag and declaring it, as it won't fit in there this time. (if it fits, and it's under 100mL you don't have to declare it).
Although size isn't supposed to matter on medical liquids, so long as you declare them, it seems that individual agents have a lot of discretion on what they will and won't allow.