I bought this old Placido Disk, or Keratoscope, not knowing exactly what it was, because it reminded me of Duchamp's "Rotoreliefs," and also because I thought it could serve as a great prop for all sorts of things, including perhaps a low budget Sci-Fi film!  I've since learned that this device, invented in the late 19th century, is an ophthalmic instrument used to assess the shape of the anterior surface of the cornea: a series of concentric rings is projected onto the cornea and their reflection viewed by the examiner through a small hole in the centre of the disk.

This one, which I believe dates to the1960's or so (I found one exact match online, which had sold for $200, though with the face in better condition) was German made by the company Oculus. Made of powder coated steel, I believe, with a gripped handle, it feels substantial, with a nice weight. The face of the disk shows brown where it was once white, and a few small tears--I believe the pattern was printed on a sort of film and adhered. On the back is a bit of rust around the edges and a little scratching the surface of the metal. Structurally in great shape, and a really a cool object!

10 5/8" tall x 6 1/4" wide x 3/4" thick.