Why You Sometimes See Stars and Flashes of Light

Do you see stars or flashes of light on occasion? It is not an uncommon complaint, and most of the time you have nothing to worry about. If you close your eyes and rub them, you will probably see spots and flashes of light. However, if it occurs frequently, you should have your eyes examined just in case it is a sign of something serious.

The stars and flashes you sometimes see are called "phosphenes," 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).

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.

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.

A valsalva maneuver is the act of forcibly exhaling while keeping the mouth and nose closed. It creates pressure on the upper body and head. Generally, it is not a very healthy thing to do, although the maneuver is used to help regulate cardiac dysfunctions.

Sometimes this pressure can cause you to see spots of light that also can occur after a sneeze or a hard cough. This can also be caused by straining too hard when lifting something too heavy or trying to have a bowel movement.

Orthostatic hypotension is caused by a sudden drop in blood pressure. The body's reflex mechanisms that attempt to keep blood pressure and blood flow to the brain constantly kick in and the heart is stimulated to increase output.

Blood vessels in our body also change, which affects blood pressure. These changes affect the brain, and we see stars. This happens when we have been laying down for too long and stand up too quickly.

Some migraines have a visual aura that people see, which usually precedes a headache. Some people never get a headache but just see the visual aura. The aura can be in the form of prismatic colors, flashes of light, and sometimes stars.

They usually last about 20 minutes and then go away. If a headache follows the flashes, it is called a "migraine headache." If these flashes or lines of light occur without a headache, it is called an "ophthalmic migraine," or a migraine without a headache.

Posterior vitreous detachment (PVD) is a common condition usually caused by aging. The vitreous, which lies against the retina, is the jelly-like substance that fills the center of the eye. Made mostly of water, the vitreous fluid gives the eye its shape.

As we get older, the composition of the vitreous changes and becomes less firm. This change sometimes causes the vitreous to pull on the retina. If the force of the pulling becomes strong enough, the vitreous may actually separate from the retina. When this occurs, we see flashes of light or stars. Most of the time a PVD is annoying but harmless. However, about 5 percent of the time, a PVD can cause a retinal tear or detachment.

While usually harmless, frequent flashes of light can be a warning sign of something more serious. A comprehensive eye examination will be needed to determine the cause. 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.