Opera glasses were a unique kind of glasses similar to binoculars, used to view an opera from theatre seats which were far away from the stage.
Grace Holloway used a pair of opera glasses during a performance on the night of December 30, 1999, until she was called to perform surgery at Walker General Hospital. (TV: Doctor Who)
The Ninth Doctor had acquired a set of opera lens. He used them as a magnification device to survey a bombing site near Limehouse Green where a Chula ambulance had crashed. (TV: The Empty Child)