Know when to worry about floaters and flashes

When patients present with ophthalmic floaters and flashes of light, asking the right questions can help internists decide when to refer to an ophthalmologist.

Sometimes patients just have to live with ophthalmic conditions such as floaters and flashes, but any sudden progression needs immediate attention, said Stephanie Jones Marioneaux, MD, a cornea and external disease specialist.

During Internal Medicine Meeting 2021: Virtual Experience, she advised internists on evaluation of floaters, flashers, and ophthalmic symptoms of migraines.


Floaters begin in the vitreous cavity of the eye, which is 98% water (the rest being collagen and protein fibrils). By age 50 years, the vitreous tends to contract and break down into its component parts, which are clumps and strands—what patients call floaters.

While a patient reporting ophthalmic flashes of light should immediately trigger suspicions of retinal detachment flashes of light can take on different forms Image by Roman Kulinskiy
While a patient reporting ophthalmic flashes of light should immediately trigger suspicions of retinal detachment, flashes of light can take on different forms. Image by Roman Kulinskiy

Acute events, such as shearing force from head and eye injuries, can also cause floaters to develop, Dr. Marioneaux said. The vitreous is attached to the eye globe loosely at the optic nerve and at two other peripheral locations. Once detached, instead of moving with the head or eye, the vitreous moves independently, lagging behind, she said. “This is why patients view these condensations of protein and collagen as floaters.”

Patients describe floaters in myriad ways. Sometimes they say what they see is like spider webs or an amoeba, Dr. Marioneaux said. Floaters can be large and cast a shadow, which the patient might also report.

Another type of floater is the Weiss ring, resulting when a posterior vitreous detachment occurs around the optic nerve head. “People will see these things in their vision, and sometimes you see [patients appear] as if they're swatting flies,” she said. Other conditions that can cause floaters include vitreous hemorrhage from proliferative diabetic retinopathy.

Other causes of similar symptoms include age-related macular degeneration, diagnosed on ophthalmoscopy when the macula does not have a crisp foveal reflex and the darker areas show subretinal blood. These patients will report shadows. More dramatic causes could include a large malignant melanoma within the eye, which the patient would perceive as an orange lipofuscin pigment.

Some exceptional causes call for action, but not every floater requires treatment, Dr. Marioneaux said. “What do we do about floaters that are benign? We do nothing, generally.”

Exceptions include floaters so large they block the line of vision, which merit immediate referral to ophthalmology. “Even though the eye is quite large, you only have a single line of vision that originates in the fovea,” she said. If floaters don't cross the line of vision, they go unseen. “So that can be quite random,” she said. “That's why patients feel that the floaters have ‘gone away.’ No, you're just very fortunate in that it did not cross the line of vision.”

Dr. Marioneaux said she typically counsels patients that routine vitreous floaters do not go away. She recommends making a very clear mental note of the quantity and size of the floaters so that when patients see them again, even after a long time, they can simply check that they are the same size and number and not hit the panic button.

“If, however, this is a new onset of different floaters—so say they saw three and they were just sort of like clumps, and now they see hundreds of them and they're big blobs—well, that patient needs to absolutely be referred to the ophthalmologist,” she said.


A patient reporting ophthalmic flashes of light should immediately trigger suspicions of retinal detachment and considerations of referral for evaluation, Dr. Marioneaux said. But she cautioned that flashes of light can take on different forms.

“When patients say they have ‘flashes of light,’ there are a few questions that you really need to ask them in order to determine what exactly are the flashes of light,” she said. “You need to ask them, ‘Do you see the flashes of light when the eyes are open, or when the eyes are closed, or both?’”

Ask the patient to cover each eye separately to determine when the flashes are occurring. Also determine the characteristics of the light, Dr, Marioneaux said. “Is it like a bolt of lightning … sort of an on/off flash? Or is there a persistence of colors and patterns? And is it like a kaleidoscope? Are there jagged edges? Is there a possibility of headaches, associated symptoms, blindness, paraesthesia? Those are all very important questions.”

Distortion of light when the patient's eyes are open localizes the pathology to the anterior third of the eye. The cause could be dry eyes. Patients might present with vision that isn't sharp, rather than a loss of visual field. One telltale sign is when blinking restores the clarity of vision, Dr. Marioneaux said.

Patients ages 50 years or older might be experiencing the onset of cataracts, which present as a glare around lights without loss of color vision or distortion, she noted.

Retinal tears and vitreous detachments can both cause flashes. “Sometimes patients will say, ‘When I look in this direction, I can bring the flashes on,’ and our response is, ‘Don't do it,’” Dr. Marioneaux said. She advises patients with that problem to move their head instead of the eye while waiting for an evaluation.

Infections such as cytomegalovirus can also cause flashes. “There's such an extensive infection of various layers of the retina that they disrupt the photoreceptor layer, which in turn results in flashes of light,” she said.

Other flash-like symptoms that patients may describe include rainbows or halos around lights, and that again localizes the pathology to the anterior third of the eye, Dr. Marioneaux said. This can be caused by corneal edema, either by itself or secondary to elevated intraocular pressures due to acute glaucoma. Patients also report such distortions after refractive surgery.


Dr. Marioneaux will ask a patient to cover one eye at a time and report visual disturbances. In retinal migraine, the headache will precede the visual disturbance, whereas in classic migraine, the headache will follow the visual disturbance. Migraines can be associated with a visual disturbance. These are typically the classic migraine followed by a dull headache or an acephalgic migraine without a headache.

Ocular migraines may last between five and 60 minutes. If the patient is older than age 50 years, these symptoms might suggest a transient ischemic attack in the optic nerve.

“As I tell patients when they experience migraines, the first thing they do is come to the ophthalmologist and I tell them that it's very interesting that the migraine does not originate in the eye in a majority of cases,” she said. “The eye simply reports. It originates in the occipital lobe, and so we evaluate them with a visual field, we check the fundus to make sure we don't see anything, and then we refer them back to our internist or neurology colleagues to manage the migraine.”

It is imperative that a full workup for monocular visual loss is completely normal before you conclude that it was a “retinal migraine,” Dr. Marioneaux said. Migraines actually coming from the eye are very rare, she concluded: “The retinal migraine is a diagnosis of exclusion.”