Optics and lenscraft didn't really hit its heyday until well into the Renaissance, and even then the equations necessary to create extremely reliable lenses weren't developed until centuries later. However, the classical world did have its share of optical science (and the Arab philosophers after the Muslim Conquest had many interesting things to add to the science).
The first thing we'll look at is the so-called "burning glass." The most famous of these is, without a doubt, the lens of Archimedes of Syracuse which was said to set the ships of Rome on fire during the Punic Wars. Whether or not that's true, the burning glass did in fact exist in the classical world and was sometimes in the guise of a transparent urn full of water or of a series of joined mirrors. The sacred fires of classical Greek temples were not to be lit with profane sources, but rather directly with the sunlight—this was how that was accomplished.
Another important development that we can see represented by the Visby Lenses is that it was possible through practice to achieve a magnification technique not equalled by theory and equation until the late 1950s; the Visby Lenses might have been what were known as "reading stones." These are essentially glasses that don't go on your face but rather rest on the document you are attempting to read.
Just some things to think about the next time you want to dole out some treasure... or if you feel like creating some new and interesting magical items.