Most often, flashes of light happen when the gel inside your eye tugs on the retina, which your brain interprets as a spark. That is common with aging and usually harmless. Flashes can also come from a migraine aura. Sudden flashes, especially with many new floaters or a shadow in your vision, can signal a retinal tear and need an urgent eye exam.
What Is Happening Inside the Eye
The back of your eye is filled with a clear, jellylike substance called the vitreous. It is attached to the retina, the light-sensing layer. According to Virginia Mason, flashes occur when the vitreous gel pulls on the retina, causing a bright streak of light. It notes that most flashes are not serious, but a sudden occurrence should be evaluated to rule out a torn retina, as described on its floaters and flashes page.
As All About Vision explains, seeing flashes occurs when something other than outside light stimulates the retina. Our guide to posterior vitreous detachment explains the usual cause.
Posterior Vitreous Detachment: The Common Culprit
As we age, the vitreous gel changes and can separate from the retina, a process called posterior vitreous detachment, or PVD. The National Eye Institute lists vitreous detachment among the causes of floaters and notes that as you age, tiny strands in the vitreous clump together and cast shadows on the retina, per its floaters overview.
A PVD is typically harmless. Duke Eye Center notes that floaters occur with age and can appear sooner if you are very nearsighted. When the detachment is clean and gradual, an increase in floaters usually subsides in one to six months, according to Duke Health.
When the Tug Becomes a Tear
Sometimes the pulling is strong enough to tear the retina. The National Eye Institute explains that a retinal tear is when vitreous detachment tears a hole in the retina, and retinal detachment is when the retina gets pulled away from the back of the eye.
That is why a new burst of flashes matters. A retina specialty practice notes that retinal tears are usually treated in the office with laser or freezing, while a detachment generally requires surgery in an operating room. Our article on floaters after 50 explains how to judge what is normal.
Warning Signs That Need Prompt Care
The National Eye Institute says a lot of new floaters that appear suddenly, sometimes with flashes of light, is a reason to go to your eye doctor or the emergency room right away. Mayo Clinic lists the warning signs of retinal detachment as the sudden appearance of dark floating shapes, flashes of light in one or both eyes, a curtainlike shadow over your field of vision, reduced vision, and loss of side vision.
Mayo Clinic calls it an emergency that can cause lasting vision loss, and notes that it is painless, so lack of pain is not reassuring. See its retinal detachment overview.
Flashes From a Migraine Aura
Not every flash starts in the eye. The same practice notes that an ocular migraine can cause zigzag shapes like a kaleidoscope, orbs of light, or blind spots. Because they come from the brain, they are not a sign of a tear in themselves.
AARP, citing the American Migraine Foundation, describes retinal migraine as a type of migraine that comes with twinkling lights and can cause temporary vision loss in one eye, with episodes lasting up to an hour. Because migraine can mimic more serious conditions, a first-time episode deserves an exam.
Flashes From Pressure and Rubbing
Pressure can also cause brief sparks. All About Vision lists sneezing, heavy coughing, straining, and eye rubbing as triggers for these pressure-related flashes, called phosphenes. Flashes with no obvious trigger are a different story.
Questions to Ask Yourself
A few details help sort out what is going on. Did the flashes come on suddenly? Are they in one eye or both? Are new floaters appearing? Is there a shadow, curtain, or blank spot in your vision?
Write down the answers. Any yes to sudden onset, new floaters, or a shadow means you should be seen quickly.
What an Exam Involves
The National Eye Institute explains that your eye doctor can check for floaters and flashes as part of a dilated eye exam, using drops to widen the pupil so the retina can be examined. If a tear is found, treatment is often a quick office procedure.
If your flashes were caused by a harmless PVD, the exam gives peace of mind. Your doctor may recommend a follow-up visit. Our guide to eye exams as you age covers routine screening.
