Phosphenes or Seeing Stars

Boy getting an eye exam
Boy getting an eye exam. NEI/NIH

Definition: A visual occurrence characterized by seeing light without having light actually enter into the eye. The word phosphene comes from the Greek words phos (light) and phainein (to show).

Flashes of Light

If you've ever noticed flashes of colorful light when your eyes are closed, you've probably seen phosphenes. These light flashes happen inside your eyes because atoms in the eye emit and absorb tiny particles of light.

The optic nerve sends the light signals to the brain, the result being visible phosphenes. 

Pressure Phosphenes

The most common phosphenes are pressure phosphenes. Rubbing the eyes while they are closed stimulates the cells of the retina. The optic nerve translates this pressure into various images. Pressure phosphenes can remain for a few seconds after the rubbing stops and the eyes are opened, allowing the phosphenes to be seen. Isaac Newton demonstrated an example of a pressure phosphene by gently pressing the side of the eye to reveal a colored ring of light on the opposite side. Another common phosphene is "seeing stars." Sometimes a person can see flashes or spots of light from a sneeze, a heavy cough, a strong blow to the head or low blood pressure (such as after standing up too quickly.) While seeing stars usually results from mechanical stimulation, it may also result from mechanical and metabolic stimulation of neurons of the visual cortex or of other parts of the eye.

Have you ever had anything happen to your vision a day or so before getting a headache? Some people see flashes or lines of light prior to having a migraine headache. These types of flashes are usually caused by a spasm of blood vessels in the brain. These light flashes or lines can also occur without a headache.

In this case, the light flashes are called an ophthalmic migraine, or a migraine without a headache.

Phosphenes can also be caused by some diseases, such as multiple sclerosis. In addition, phosphenes can also result as a side effect of certain medications. Sometimes phosphenes are caused by movement of the retina inside the eye, as a consequence of retinal detachment.

Electrical Stimulation

Researchers have developed programs that stimulate phosphenes to help restore vision to people who have lost their vision blinded in accidents. Electrodes are also being used on the scalp to produce phosphenes. Research has shown that when the visual cortex is stimulated enough, phosphenes are produced in the lower part of the visual field.

Did You Know?

People who are born blind never see phosphenes. However, if you lose your vision as a result of an  illness or injury, you usually won’t end up losing all visual function. Phosphenes can originate in different parts of the visual system, so people who could once see could remain with the ability to see phosphenes. 

Also Known As: Seeing stars

Alternate Spellings: Phosphine

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