Stenopeic lorgnette 1900
Stenopeic lorgnette was used for determining the axis of astigmatism in the course of a refraction.There is no consensus on who developed the stenopeic slit lorgnette.
It has an appearance somewhat like an old ophthalmoscope. However, there is no mirror and it is not meant for viewing the fundus of the eye.
There is a slot for a corrective lens. This specimen has a biconvex, glass lens of +16 diopters of power (etched onto lens edge)
There are three different slits of various widths. In between these are five small holes of different diameters, to narrow the central bundle of rays. The instrument was described by Landoldt in 1920 but probably dates back to around 1900.
There is no apparent maker’s mark on this unit.