A monocle is a type of corrective lens used to correct or enhance the vision in only one eye. It consists of a circular lens, generally with a wire ring around the circumference that can be attached to a string or wire. The other end of the string is then connected to the wearer's clothing to avoid losing the monocle. The antiquarian Philipp von Stosch wore a monocle in Rome in the 1720s, in order to closely examine engravings and antique engraved gems, but the monocle did not become an article of gentlemen's apparel until the nineteenth century. It was introduced by the dandy's quizzing glass of the 1790s, as a sense of high fashion.
There are three styles of monocle. The first style consists of a simple loop of metal with a lens which was slotted into the eye orbit. These were the first monocles worn in England and could be found from the 1830s onwards. The second style, which was developed in the 1890s, was the most elaborate, consisting of a frame with a raised edge-like extension known as the gallery. The gallery was designed to help secure the monocle in place by raising it out of the eye's orbit slightly, so that the eyelashes would not jar it. Monocles with galleries were often the most expensive. The very wealthy would have the frames custom-made to fit their eye sockets. A sub-category of the galleried monocle was the "sprung gallery", where the gallery was replaced by an incomplete circle of flattened, ridged wire supported by three posts. The ends were pulled together, the monocle was placed in the eye orbit, and the ends released, causing the gallery to spring out and keep the monocle in place. The third style of monocle was frameless. This consisted of a cut piece of glass, with a serrated edge to provide a grip and sometimes a hole drilled into one side for a cord. Often the frameless monocle had no cord and would be worn freely. This style was popular at the beginning of the 20th century as the lens could be cut to fit any shape eye orbit inexpensively, without the cost of a customized frame.
It is a myth that wearing a monocle is uncomfortable. If customised, monocles could be worn securely with little effort. However, periodic adjustment is a fact of life for monocle wearers to keep the monocle from popping, as can be seen in films featuring Erich von Stroheim. Often only the rich could afford to have a monocle custom-fabricated, while the poor had to settle for ill-fitting monocles that were both less comfortable and less secure. The popular perception was (and still is) that a monocle could easily fall off with the wrong facial expression. This is true to an extent, as raising the eyebrow too far will allow the monocle to fall.