What causes dry eyes?

What causes the colorful patterns when you squeeze your eyes shut tightly? And what is its biological purpose?

• It's more prevalent in younger people. It's like a colorful kaleidoscope pattern. It happens when you either squeeze your eyes shut tight, or close your eyes and press on your eyelids. What causes this? What is the purpose of this internal light show?

• Answer:

  It's your brain's misconception of sensory information. The typical input for visual sensory information is light energy. This excites molecules on photoreceptor cells, and sends a signal down the optic nerve to various processing centers in your brain to let you know that you saw something. But, if there is a strong enough mechanical stimulus to the eye, it can cause nerve firing down the optic nerves that causes you to perceive light. It's kind of similar to hitting your funny bone (which is actually a nerve!). Hitting this part of your body causes you to perceive a sort of tingling pain down your arm and fingertips, even though it was not your arm and fingertips that you hit. There are some other examples of this that I'm sure you can look up. It's funny to think that even something as intricate as our central nervous system can still have glitches.