
Episode #20
Copenhagen: The Country That Built What It Needed
Something most people don't know about the human eye: the retina is installed backwards. The photoreceptors — the cells that actually detect light — face the back of the eye rather than the front. Light entering the eye has to pass through several layers of neurons and capillaries before reaching them, traveling in the wrong direction through the mechanism it's meant to activate. Scientific American has described the arrangement as equivalent to putting a microphone in backwards and using the wired end to capture sound. The octopus and the squid solved this 400 million years ago; their photoreceptors face the light directly. Vertebrate eyes — ours — did not solve it. An engineer who submitted this design would be sent back to revise it.






