These opera glasses are from 1920 and are made with mother of pearl, otherwise known as nacre.  Nacre can be found in some molluscs and is iridescent. The eye piece of these opera glasses read Lemaire ft. Paris D.R. Dingwall, Winnipeg.

Opera glasses are also known as Galilean or theater binoculars.  Galilean is named after Galileo who developed a telescope with the magnification capability of x30.  Early opera glasses were telescopes, and it wasn’t until around 1823 that the first binocular pair appeared.  Pierre Lemiere improved the design of the glasses by adding in a center focus wheel to help focus both telescopes at the same time.  You can still find modern opera glasses today, some more intricate than the rest.