Optogram

Optography is the process of viewing or retrieving an optogram, an image on the retina of the eye. A belief that the eye "recorded" the last image seen before death was widespread in the late 19th and early 20th centuries, and was a frequent plot device in fiction of the time, to the extent that police photographed the victims' eyes in several real-life murder investigations, in case the theory was true. The concept has been repeatedly debunked as a forensic method.

Much of the scientific work on optography was performed by the German physiologist Wilhelm Kühne. Inspired by Franz Christian Boll's discovery of rhodopsin (or "visual purple")—a photosensitive pigment present in the rods of the retina—Kühne discovered that, under ideal circumstances, the rhodopsin could be "fixed" like a photographic negative.

Kühne experimented on numerous animals to refine the process and determine the chemicals used to fix the image on the retina. His most successful optogram was obtained from an albino rabbit, with its head fastened to face a barred window. The rabbit's head was covered for several minutes to allow rhodopsin to accumulate on the retina. It was then uncovered for three minutes to expose it to the light, then decapitated and its eyeball sliced from top to bottom. The rear half of the eye was placed in an alum solution to enable fixation of the bleached rhodopsin, which resulted in a distinct image of the barred windows.

Kühne was eager to demonstrate the technique in a human subject, and in 1880, got the opportunity. On 16 November, Erhard Gustav Reif was executed by guillotine for the murder of his children in the nearby town of Bruchsal. Reif's eyes were extracted and delivered to Kühne's laboratory at the University of Heidelberg, where he set about dissecting them in a darkened room with filtered windows. After ten minutes, Kühne showed his colleagues an image on the left retina, however his sketch of the image did not appear to match any object visible to the subject at the time of his death—although the outline of the image resembled a guillotine blade, Reif was blindfolded at the time of his beheading.

An issue that Kühne encountered when attempting to produce an image from a human eye is that the size of the fovea centralis, the actual focal point of the image on the retina, is very small (about 1.5 millimetres). Kühne had considerably more success producing optograms from animals such as rabbits and frogs, and the Reif image ended up being the only known "human optogram". The original image from Reif's eye no longer exists, apart from a simple line drawing of the shape in Kühne's 1881 paper "Observations for Anatomy and Physiology of the Retina".

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