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Michael: Believe it or not, the Victorian era wasn’t all about corsets and funny-looking bikes, there was a lot of science happening in the 1800s, too. You might have heard of Charles Darwin and his theory of evolution. Or the physicist Lord Kelvin, who worked on thermodynamics problems. But for all the groundbreaking theories and technological advancements, there were also a handful of pseudosciences that were spreading misinformation.

Take forensic optography. It’s the idea that you can use an image imprinted on the light-sensitive tissue in the back of someone’s eye – their retina – to figure out who murdered them. There wasn’t much interest in the idea of optography until the 1840s, when photography became practical with the invention of the daguerreotype.

If a camera can filter light through a lens onto a light-sensitive surface, and create a permanent image if you expose the surface to the right chemicals... maybe our eyes could work the same way? In 1876, the German physiologist Franz Christian Boll learned more about how the retina detects images. Specifically, he discovered this pigment called rhodopsin, which helps detect light and send a signal from your eyes to your brain.

When light hits rhodopsin, part of it changes shape and dissociates, so the pigment is temporarily bleached. Then, your cells regenerate the rhodopsin, so it can be stimulated by light again. It’s similar to how light causes a chemical change on those photographic plates, except light makes photographic emulsion darker instead of lighter. And this is where the idea of optography came in.

Another German physiologist named Wilhelm Kühne thought he could fix the rhodopsin in the retina with the right chemicals. That way, the pattern of bleached rhodopsin would show where light was hitting an animal’s eye, and reveal the general shape of big objects. Theoretically, he could develop what he called an optogram, an image of the last thing an animal saw. He did this by experimenting on animals like rabbits and frogs – and it wasn’t pretty.

Kühne’s most successful optogram was created by sticking a rabbit in the dark, and then forcing it to stare at a bright, sunny window for several minutes. He immediately killed it, dissected its eyes, and stuck the retina in a solution of alums — a group of chemical compounds that are used in lots of manufacturing processes and photography. The alums probably hardened the retina by shrinking and constricting the tissue, and fixed all the cells in place.

After that, he produced an optogram that showed the bright light coming through the bars of that window. Excited by Kühne’s research, many people living in Western countries basically believed that optography could be used to solve murders, CSI-style. The idea spread like wildfire, in fiction and real life.

In a Jules Verne novel, for example, the protagonists were absolved of a ship captain’s murder because of forensic optography. Newspapers featured headlines like "Photos Show Killer's Face in Retina," and "Slain Man's Eye Shows Picture of Murderer." Thanks to all the hype, sometimes police would take photos of murder victim’s eyeballs, in case they’d be useful as evidence in court cases.

There wasn’t really anything there except kinda gross eyeballs. They definitely weren’t “optograms” that showed the victims’ last moments. But all that sensationalism was enough that some murderers destroyed their victim’s eyeballs – just in case.

So, even though optography has some scientific backing, it was never a forensic science. It just got blown way out of proportion. Let’s go back to Kühne’s animal experiments for a second.

Even in perfect conditions – dark rooms, with high-contrast surroundings – the animal optograms faded quickly and were very murky most of the time. Plus, eyes start to decompose pretty quickly once the owner dies, so you have to act fast to retrieve an image. Hypothetically, to produce an optogram from a human eye, the victim would have to stare at their well-lit murderer’s face for at least a few solid minutes in a dark room.

Then, a scientist would have to take out the victim’s eyeballs right after they died to preserve the retina and develop the image. Wilhelm Kühne supposedly claimed that he created a optogram using the eyes of a decapitated prisoner, but only a sketch of it exists — which he drew. Some people claim the sketch looks like a guillotine blade, but the prisoner was blindfolded when his head was chopped off, so... it’s probably fake.

The last serious attempt to replicate Kühne’s methods was by physiologist Evangelos Alexandridis in 1975, who was approached by police in Heidelberg, Germany to see if forensic optography had any merits. It was pretty controversial because Kühne’s experiments involved harming and killing animals, but he did produce a few somewhat-readable rabbit optograms.

Optography might technically work under precise conditions, but it was conclusively deemed impractical for forensic use in humans. So even though the idea of solving a murder by using human eyes as cameras makes for a pretty good mystery novel... it’s stuck in fiction, not fact.

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