Phosphenes
Also called: Pressure phosphenes · "Seeing stars"
The flashes, rings, and patterns of light you see when you rub or press your closed eyes, or after a knock on the head. Pressure on the eye makes the retina fire without any light.
How common
Does this happen to you?
How it works
The retina turns light into nerve signals2. It also responds to other things: mechanical pressure, electric current, magnetic fields, and radiation1. The brain does not know the difference. Any signal from the retina is seen as light.
Pressure phosphenes are the everyday kind. Press gently on a closed eye and the pressure bends the retina. Its cells fire. You see a ring, a spot, or a spreading patch of colour, usually on the side of the visual field opposite the pressure1. The faint drifting patterns you see with eyes closed and no pressure are a related effect3. A blow to the head can make you “see stars”. The knock may stimulate the retina, or it may stimulate the visual part of the brain directly1. Astronauts on the Apollo missions reported flashes of light once their eyes adapted to the dark4. Cosmic rays cause them, but the exact mechanism is unknown4.
Electric stimulation of the visual cortex, the back of the brain, also produces phosphenes. Researchers use this to design artificial vision for blind people1.
How common it is
Pressure phosphenes come from the retina’s own cells1. So anyone with a working retina should be able to produce them. No survey counts this. There is no formal count of how often people notice them in daily life, since most only appear after rubbing the eyes, a knock to the head, or deliberate pressure.
Try it
- Close your eyes.
- Press very gently on the outer corner of one eye, through the eyelid, with a fingertip.
- Watch for a spot or ring of light on the side away from your finger.
- Release. The spot fades in a few seconds.
Gentle pressure is safe. Hard pressure is not. Skip this if you have any eye condition or recent eye surgery.
Is it a problem?
No. A brief flash from gentle pressure or rubbing is normal. The retina is responding to pressure, not light1. It is not the same as seeing stars from a hard blow, which deserves more caution.
See a doctor promptly if you see flashes that are:
- new,
- frequent,
- unrelated to any pressure or knock.
Go sooner if they come with floaters or a shadow at the edge of your vision. That pattern can point to a retina problem6.
History and culture
Isaac Newton recorded coloured circles after pressing on his own eye with a blunt needle, an experiment nobody should repeat5. The word phosphene comes from the Greek for “light” and “to show”.
Sources and further material
- Wikipedia Phosphene
- Wikipedia Retina
- Wikipedia Cosmic ray visual phenomena
- newtonproject.ox.ac.uk Of Colours Newton's notebook, MS Add. 3975, Cambridge University Library. He pressed a bodkin against the back of his eye and saw coloured circles.
- Wikipedia Retinal detachment
Missing something your body does? Tell me about it.
Related oddities
Closed-eye hallucinations
Close your eyes and you do not see nothing. You see speckle, drifting colour, and, as you fall asleep, moving patterns and even scenes. Almost everyone sees the speckle, and many people see more. Almost nobody talks about them.
Seeing stars when standing up
You stand up fast, your vision goes grey or sparkly, and your head feels light for a few seconds. Blood has briefly pooled in your legs. It passes on its own.
Floaters
Small grey threads, dots, or cobwebs that drift across your vision and dart away when you look at them. They are shadows of tiny clumps inside the eye. They are common and usually harmless.
Blue field entoptic phenomenon
Tiny bright dots that dart along wiggly paths when you look at a clear blue sky. They are your own white blood cells moving through the capillaries of the retina.
Oculocardiac reflex
Pressure on the eyeball, or a pull on an eye muscle, makes the heart slow down. It matters most during eye surgery, especially in children. It is not a safe way to slow your own heart.