Physics World has been producing a series of short videos in concert with the International Year of Light, which is a big United Nations-sponsored celebration of light technology and light science—they’re pretty good. This is the second entry, produced by London filmmaker Thom Hoffman, and it focuses on research conducted by the Sleep and Circadian Neuroscience Institute at Oxford into what I guess you could call “deep seeing,” or the part of vision that manages to perceive light even in the absence of rods and cones, the eye’s photosensitive microstructures. Turns out that retinal ganglion cells, the neurons that receive visual information from those rods and cones and transmit it back into the brain, are capable of perceiving light all on their own.

The result is that there’s a distinction between blindness and not having eyes, a fact that’s recently called into question procedures that remove blind patient’s eyes, which are sometimes performed for cosmetic reasons. For one thing, the total blindness of eyelessness means dramatic things for sleep cycles, as one patient attests. It’s the difference between blindness and a lightless world.

The first entry in PW’s light series was about the Dark Skies Awareness campaign and the difficult task of spotting stars in an a light-washed major city. Also worth a look.