I'm guess, I'm really hoping here...
IF they absolutely must do this, they should take a sample (a drop) into a separate, clean container and then put whatever test chemicals in that.
Now, from the threads on here, I would assume they test it in the same way that they "test" drinks purchased on the secure side - by holding a strip above the container and allowing the vapor to interact with the strip (and by chasing down everyone in a game of tag rather than periodically testing soft drink dispensers and randomly selected bottled or canned beverages, of course).
I personally would escalate. In the first case, if every screener in every airport "only took one or two drops" you'd be out of medication that you can't just by over the counter and might be very expensive (how DO you explain to your health insurance provider that you lost your medicine from transiting airport security too often?)
Even more important, such medication - especially eye drops - must remain sterile. With all the jostling and apathy of the screeners, it's too high a risk for a gloved/ungloved hand that didn't get washed in the bathroom and touched a hundred other passengers, coming into contact with the tip of the eye drops. That could spell serious infection.
I would escalate, escalate, escalate. The label on the bottle is proof enough, and certainly if you have a full copy of the prescription/doctor's note.
Glaucoma is a serious disease - blindness isn't worth the risk. This is just another example of how TSA actively makes our lives more dangerous.