Soon after the discovery of “visual purple” or rhodopsin by physiologist Franz Boll of the University of Rome in 1876, Wilhelm “Willy” Friedrick Kühne (1837-1900), a physiologist and Helmhotz’s successor in Heidelberg, intensely studied its properties. Comparing the retina to a camera, he convinced himself by experiment on a rabbit and a guillotined human criminal that the visual purple retained a photographic image or “optogram” of whatever object was seen just before death. Kühne’s observation seized the popular imagination. Photographs were taken of the eyes of murder victims in hopes that they would reveal images of the perpetrators. Jules Verne in 1902 wrote a novel whose plot centered on the idea. Unfortunately, a modern understanding of retinal physiology makes a human optogram obtained under these circumstances an impossibility.

Submitted by John W. Gittinger, Jr, from the Cogan Ophthalmic History Society.