What happens is that we are witnessing the so-called phosphenes, from the Greek "phos" (light) and "phainein" (show). They are flashes that are perceived, although there is no light on the outside, because of the stimulation of the retina and the visual cortex. Researchers can induce them through magnetic or electrical stimuli, but usually appear simply by the basal excitation of the visual system. We can also provoke them by putting pressure on the eyes. For many researchers, they are interesting because they provide information on how the nervous system works, and others believe that inducing them in people who are blind from birth is a way to cure blindness. However, the truth is that the phenomenon is now anecdotal and is not actively investigated.
"Once the eye has adapted to the darkness, and particularly if one relaxes, the visual field lights up: ethereal clouds and light particles appear, usually with pastels of blue, green, orange and yellow. If you squeeze your eyes, figures appear, "he wrote in 1970 and in Scientific American Gerald Oster.
Luminous and moving patterns
When we press the eyeball there is a phenomenon that has many variants. Sometimes the visual field is obscured or simply a strip of color appears at the opposite end of where we press, as described by Isaac Newton himself. At other times we see a luminous pattern, of geometric shapes, that moves and twinkles, as if it were a kaleidoscope.
In addition, many drugs, such as alcohol or hallucinogenic substances, can cause phosphenes because of their effects on the visual cortex.
What if there is light inside the eye?
Most researchers believe that phosphenes are created by the normal activity of the visual system, or when this system is stimulated by factors other than light. However, some researchers have proposed an alternative explanation for many years, according to which a small number of photons are produced inside the eye.
This is the case, for example, of the researcher István Bókkon, a Hungarian neuroscientist, who remembers that the atoms that make up the molecules of the cells emit and absorb photons. It considers that, depending on where the phosphenes originate in the retina, certain shapes, patterns and colors are perceived.
Be that as it may, what is clear is that the only people who do not see phosphenes are those who are blind from birth. Therefore, studying this curious phenomenon and trying to provoke it to blind people may perhaps help to work on recovering the vision.