The phrase that pops into my mind first is "Yes, I've had them before."
All of the phrases you suggest would be understood easily. All would be perfectly polite.
And, yes, "I've tried them before" is just odd enough that it would take a split-second to understand what you meant.
To be very analytical: the reason for choosing "I've had them before" is that, in this situation, I tend to think about _the drops_ rather than _the process._ If I am thinking about the drops, it is natural to say "I've had them before." If I'm thinking about the procedure, it's natural to say "I've had this done before."
Here's an example where "I've tried them before" would be natural. "My eyelids seem to itch a lot, doctor." "Should I write you a prescription for some antihistamine eye drops?" "No, I don't think so--I've tried them before and they didn't work for me."
In the case of a process, I would say "I've had this done before" and not "I've had this done to me before." I'm going to exaggerate and overanalyze in order to try to explain.
"I've had this done to me before" sounds a little odd because, for whatever reason, it seems to emphasize the negative aspects of the process. It suggests something unpleasant. It almost makes "done" into a transitive verb, emphasizes agent and recipient, emphasizes that person A is "doing something to" person B. It's something you'd be more likely to say about a dentist drilling a tooth than an eye doctor putting in drops.