This is what The Ophthalmoscope by Alfred Schett has to say about the Amsler ophthalmoscope:
“Amsler modified the ophthalmoscope of Eperon which was used at the Lausanne clinic. The clip with the convex lens of 2.5 diopters in the Eperon model was mounted on the side of the mirror with two swivel joints. This arrangement did not allow a rapid swinging to the side, in front, or behind the mirror. With a cylinder at the upper end of the handle this disadvantage was remedied. Now the convex lens could be easily shifted with the thumb and index finger. The improved instrument found further use in the examination of the fundus of the eye with the inverted image, as well as the media of the eye and illumination of the pupil with the entering light. There is a mounted indirect lens of 13 diopters in the case.
Manufacturer: Haag-Streit AG work place for precision machinists, Liebefeld near Bern. “