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Causes of Flashes in the Outer Corner of the Eye

author image Dr. Tina M. St. John
Dr. Tina M. St. John owns and operates a health communications and consulting firm. She is also an accomplished medical writer and editor, and was formerly a senior medical officer with the U.S. Centers for Disease Control and Prevention. St. John holds an M.D. from Emory University School of Medicine.
Causes of Flashes in the Outer Corner of the Eye
Causes of Flashes in the Outer Corner of the Eye Photo Credit: mishooo/iStock/GettyImages

The appearance of flashes of light in your eye understandly incites concern if not alarm. This symptom, known medically as photopsia, occurs with conditions that affect the eye itself as well as a number that do not. Although photopsia can signal a potentially vision-threatening condition, several causes do not pose this risk. However, experiencing phantom flashes of light requires prompt medical evaluation to distinguish between serious versus less serious causes.

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Posterior Vitreous Detachment

The transparent vitreous gel fills most of the eyeball, helping maintain its round shape. Minute fibers and sticky molecules adhere the vitreous to the retina, the vison perceiving structure at the back of the eyeball. With advancing age, the vitreous becomes increasingly watery and shrinks. With posterior vitreous detachment, or PVD, the vitreous separates from the retina. People who experience PVD symptoms commonly report seeing floaters and/or flashes of light, usually at the outer edges of their vision. Temporary blurred vision might also occur. PVD most frequently occurs in people older than 45. PVD itself poses no long-term threat to vision and symptoms usually decrease without treatment over several weeks to months.

Retinal Detachment

As the vitreous pulls away from the retina with PVD, it sometimes causes a retinal tear. These tears occur in approximately 14 percent of people with PVD and 33 to 46 percent of people with such a tear experience a retinal detachment, as reported in an April 2014 Australian Family Physician article. The detachment occurs due to accumulation of vitreous liquid behind the tear. Symptoms of a PVD-related retinal detachment largely mimic those of PVD without this complication, namely light flashes and/or floaters. Painless loss of side vision, often described as a dark curtain or shadow, might also occur and substantially increases the likelihood of a retinal detachment. It's important to contact an eye specialist immediately if you experience any of the symptoms discussed as only an eye professional can distinguish between PVD with or without retinal detachment. Early treatment prevents or limits permanent vision loss with a retinal detachment.

Other Eye-Related Causes

Although PVD and related retinal detachments account for the majority of eye-related causes of seeing light flashes, a lengthy list of other eye conditions can also trigger this symptom. A few representative examples are discussed.

Diabetic Retinopathy

Long-term exposure to high blood sugar levels damages the retinal blood vessels. With advanced disease, fragile new blood vessels grow on the retinal surface and into the vitreous. Retinal detachment is a possible complication with phantom light flashes in the affected eye.

White Dot Syndromes

White dot syndromes share the common sign of white dots seen upon examination of the back of the eye. These conditions inflame the retina, triggering flashes of light and often other visual symptoms, including possible vision loss.

Eye Tumors

Eye tumors are an uncommon cause of seeing phantom light flashes. Melanoma of the eye is the leading cancerous tumor originating within the eye, although it is rare. Noncancerous tumors can also develop in the eye. Eye tumors can trigger light flashes by inflaming or exerting pressure on the retina.

Non-Eye-Related Causes

Migraine aura is the leading non-eye-related cause of perceiving phantom light flashes. According to the American Migraine Foundation, approximately 25 to 30 percent of people with migraines experience an aura -- sensory abnormalities that might include seeing flashes, spots, stars, zigzags or glitter-like shimmers in one or both eyes. Numbness, tingling or speech problems might also occur. The aura precedes a headache in most cases, although a visual aura without a headache occurs in some people. Light flashes and other visual disturbances associated with a migraine aura usually disappear within 10 to 30 minutes.

A wide variety of other non-eye-related conditions can potentially cause phantom light flashes in one or both eyes, including:

  • Multiple sclerosis
  • Stroke or transient ischemic attack, also known as a mini stroke
  • Cancerous or noncancerous brain tumor
  • Infectious or autoimmune inflammation of the eye nerve
  • Blood vessel malformation in the brain
  • Head injury
  • Medication side effect
  • Overactive thyroid gland
  • Preeclampsia or eclampsia, pregnancy-related conditions

Warnings and Precautions

Call your doctor right away if you experience unexplained phantom light flashes in one or both eyes. Seek immediate medical care if this symptom began after a blow to the head, or is accompanied by loss of vision, sudden severe headache or other nervous system symptoms.

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