Why You Might Be Seeing Stars

5 Top Causes of Photopsia—Flashes of Light in Your Vision

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Seeing stars can be unsettling but it's rarely anything to worry about. Often such flashes of light, known as photopsia, are the result of temporary physical pressure on the eyes—from rubbing them, for example, or sneezing really hard.

Photopsia also can be a symptom of migraine headache or a problem with the health or structure of the eye. For that reason, if you see stars—or, similarly, flashing lights, bands of light, sparks, or colorful rings—frequently or for extended periods of time, make an appointment with your opthalmologist. It may take a comprehensive eye examination and certain diagnostic tests to find out why.

Seeing Stars and Flashes of Light Common Causes
Illustration by Joshua Seong. © Verywell, 2018. 

How Photopsia Happens

When the eye perceives "real" light, the optic nerve stimulates the retina, which sends the message to the brain for processing and identification. In most instances of photopsia, however, something other than visible light stimulates the retina—rubbing the eyes, sneezing, a blow to the head.

Besides pressure or another source of stimulation of the retina, photopsia also is associated with certain medical conditions such as low blood pressure, disease of the eye or brain, or migraine. Mechanical pressure and metabolic stimulation of neurons of the eye or the visual areas of the brain can trigger phosphenes.

Doctors and scientists sometimes stimulate photopsia using a special type of ultrasound as part of treatment for certain vision problems or in research.Artificially induced photopsia are called phosphenes.

Eye Pressure

Phosphenes caused by mechanical pressure can last for a few seconds—for example, if the result of rubbing the eyes, sneezing, coughing, or straining—or they may last longer, as with a retinal vitreous detachment.

Pressure phosphenes can also occur due to issues within the eye, such as infection, tumor, inflammation, a blood vessel abnormality, or thyroid disease. A disease like multiple sclerosis (MS) can affect the pressure in the eye and also cause phosphenes due to inadequate function of the optic nerve.

Posterior Vitreous Detachment

Posterior vitreous detachment (PVD) is a common condition associated with normal aging. The vitreous, which lies against the retina, is a water-based substance with a jelly-like texture that fills in the center of the eye and gives it shape. It also attaches to the retina.

With normal aging, the vitreous becomes less firm and in the process can pull on the retina. If the force of the pulling becomes strong enough, the vitreous may separate from the retina. When this occurs, it can cause a person to see flashes of light or stars.

Retinal Disease

Conditions that affect the function of the eye, including retinitis pigmentosa, diabetic retinopathy, macular degeneration, and optic neuritis (often due to MS), can cause gradual vision loss.

As the eye loses the ability to perceive the visual input that will eventually be sent to the brain for processing, subtle symptoms such occasional phosphenes lasting for seconds at a time can occur. These eye conditions sometimes cause pressure in the eye in addition to the loss of retinal function.

Certain medications also can alter the function of the retina in ways that produce phosphenes. One such drug is Corlanor (ivabradine), which is used to treat tachycardia (rapid heart rate).

Migraines

Visual changes, known as auras, are a common symptom of migraine headaches. An aura typically lasts about 20 to 30 minutes and then goes away on its own—without any treatment.

With some ocular migraines or retinal migraines, a visual aura may occur without head pain. The aura can be in the form of prismatic colors, flashes of light, and sometimes stars, and it often affects one eye, although it can affect both.

If a headache follows the flashes, the episode is diagnosed as a migraine headache. If these flashes or lines of light occur without a headache, it is often described as a migraine without a headache.

Impaired Visual Function in the Brain

While less common, phosphenes can occur due to dysfunction of the visual areas of the brain. This may occur as a result of a lack of blood flow or damage to the brain.

Medical issues such as MS, brain tumors, and strokes may impair the visual regions of the brain and cause stimulation that produces a sense of seeing fleeting images of light that aren't there.

Cerebrovascular disease (blood vessel disease in the brain) or systemic low blood pressure can result in diminished blood supply to the brain, and consequently, diminished brain function.

Orthostatic hypotension, also called postural hypotension, is a sudden drop in blood pressure that typically occurs when someone who already has high or low blood pressure rapidly moves from lying down or sitting to standing up. This drop in blood supply can briefly impair brain function, causing flashing lights or similar phenomena for a few seconds.

While usually harmless, seeing frequent flashes of light can be a warning sign of something more serious. If you experience this symptom, talk to your doctor about it.

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