Mario Kaouklis kindly sent me photos and information of this telescopic eyedropper in black hard rubber with a metal overlay. It was described initially as Mabie Todd, probably because it has a Swan nib but it clearly isn’t.
The pen measures 95mm (without ring) closed but extends to a generous 135mm. There’s no indication of a manufacturer but The Sterling Fountain Pen Company, USA may have made a similar pen as well as ordinary BHR eyedropper fillers.
A very handsome and practical curiosity!