I would appreciate any info on the mystery object a friend of mine has had in the family for many years. It is a flat box that measures 8x4.5x0.7 cm and opens to reveal a sliding sheet with two holes. Can anyone shed a light on the usage of this object please? I thought it might be a sort of optical equipment but it's rather inconvenient for the eyes and it doesn't have a handle etc. Could it be for miniature portraits? Or perhaps for pills or medicine?
It's made of silver and has a turquoise cabochon on the clasp.
Any help is much appreciated.

