The Pince-Nez style was popular from the 1880s until the 1940s. There are two types of Pince-Nez frames and many variations within each type. One style has a hard unmovable bridge. The tension is provided by two small coil springs attached to the nose pads. This type of frame was used to make the sunglasses used in the movie Matrix.
The hard bridge type is preset at the factory. Generally, such frames have very little adjustment. When ordering, you must know your bridge width to get a proper fit. Your optician can provide this information.
Learn more about Pince-Nez styles and fit here.