This is called a “Skiascopic Model Eye”. It has been opened up to show the retinal image in the rear. Doctors trained with these to learn how to examine the fundus of the eye and to perform retinoscopy to determine the refractive error of the eye. It is identified to be from the early 1900s. It is made of brass (painted black) and inside the barrel is a detailed print of the inside of an eye. It is made of brass with printed retinal image on focusing slide in a dark chamber, visible through the lens and with a mount and astigmatism scale for use with standard corrective lenses. Size is 3.25″ tall x 3″ deep.