What are Phosphenes?
Phosphenes are perceived flashes of light that occur without an actual light source. They cause a visual phenomenon called photopsia (seeing stars).
Here’s how the visual pathway works:
- Light is received through the cornea (the clear surface that covers the front of the eye)
- Then it’s transferred to the retina (light-sensitive nerve layer at the back of the eye)
- Lastly, it passes to the optic nerve, which relays vision signals to the brain
Phosphenes stimulate the retina like a light source but come from inside the eye (entoptic phenomena). Phosphenes are commonly caused by increased pressure on the eye (rubbing, sneezing, bearing down), eye trauma, and optic nerve inflammation.
While phosphenes usually go away after a couple of seconds and are nothing to worry about, persistent photopsia can result from an underlying medical condition.
What Do Phosphenes Look Like?
Phosphenes are described as illusionary flashes of light that chaotically move across the visual field, including:
- Darting flashes of color
- Temporary dots
- Swirls of light
- Geometric patterns
Phosphenes are also linked to visual hallucinations, which include more complex, picturesque images. These are typically caused by drugs, alcohol, stress, fever, or psychotic conditions.2
Why Do Phosphenes Occur?
Phosphenes occur when the retina is activated by stimuli other than light, falsely sending signals of light flashes to the brain. These internal and external stimuli to the primary visual cortex can include:
Putting pressure on the eye, orthostatic hypotension (low blood pressure caused by sitting or standing too quickly), and retina or optic nerve inflammation can cause photopsia.
Transcranial magnetic stimulation (TMS)
This non-invasive procedure uses magnetic fields to stimulate phosphenes in the brain. TMS on the visual cortex helps produce phosphenes that can help test neural activation and cortical excitability.
Electrical stimulation (ES)
ES refers to electrical stimulation of the retina using an occipital electrode attached to the skin around the eye. This creates phosphenes and helps test retinal function and the visual system.
Various medical and eye conditions can induce phosphenes and continuous photopsia, altering visual processing and negatively affecting a person’s quality of life.
Posterior Vitreous Detachment
A posterior vitreous detachment (PVD) is when the vitreous (gel-like fluid that fills the eye) is separated from the retina. It causes retinal cells to fire, resulting in the perception of flashing light, similar to lightning streaks or a camera flash in the peripheral vision (side vision).
People experiencing an ocular migraine with aura have visual disturbances that may or may not be accompanied by a headache. Visual symptoms include:
- Visual loss
- Blind spots
- Zig zag lines
- Seeing stars
- Flashes of light
Ocular migraines are caused by abnormal electrical activity in the brain or reduced blood flow to the retina.
Vertebrobasilar insufficiency is reduced blood flow to the back of the brain, typically caused by aging. Decreased blood flow can lead to temporary photopsia in both eyes with symptoms including:
- Broken flashes of light lasting seconds to minutes
- Fogging of vision
Age-Related Macular Degeneration (AMD)
Exudative (also called neurovascular or wet) age-related macular degeneration causes a gradual decline in central vision. It’s a frequent cause of photopsia, lasting seconds to a few minutes. Exudative AMD phosphenes are linked to an accumulation of fluid stimulating the outer retina.
Visual symptoms are reported to include multiple colors of light, including:
- Centrally located flashes of light
- Spinning lights
A retinal detachment is a medical emergency that occurs when the retina is separated from the rest of the eye, resulting in vision loss and even blindness if left untreated.
Visual disturbances can include:
- Flashes of light
- Bands of light
- Dark shadows or a curtain covering part of your vision
Optic neuritis is the inflammation of the optic nerve often associated with multiple sclerosis (MS).
Optic neuritis can also cause phosphenes in the form of bright colored flashing lights upon entering a dark room, usually triggered by horizontal eye movements.
Diabetic retinopathy is damage to the blood vessels in the eye caused by uncontrolled blood sugar in people with diabetes.
As the blood vessels heal, scar tissue is formed. When the scar tissue contracts, it can cause photopsia and floaters.
Charles Bonnet Syndrome (CBS)
Charles Bonnet syndrome (CBS) is characterized by release hallucinations in people with partial or complete blindness caused by damage to the visual pathway. Release hallucinations are described as flashes of white or colored lights originating from the retina.
People with CBS report seeing things that aren’t there, such as:
- Multi-colored shapes
Clinical pharmacological medications can also trigger the phosphene phenomenon.
Ivabradine, an antianginal used to reduce the heart rate of people with heart disease, induces phosphenes in some people.2
Studies suggest that over 300 clinical and abused drugs, including phosphenes, are known to cause visual hallucinations. Some of these drugs include:9
Other Common Symptoms of Photopsia
Classic symptoms of phosphenes include flashes of light, stars, and squiggly lines that move across your field of vision. While these stimulation sources seem external, they are actually coming from inside the eye.
Other common symptoms of photopsia include:
- Visual snow, the perception of static or fuzz in the visual field
- Bright colors
- A light that shimmers and twinkles
- Flickering zig-zag lines
- Shapes or dots that appear to be floating
How to Get Rid of Phosphenes
Since phosphenes are a side effect of visual stimulation (pressure, magnetic, or electrical) or various health conditions, removing phosphenes includes eliminating the stimuli and treating the underlying medical condition.
While many cases of phosphenes go away on their own (migraine, optic neuritis), phosphenes could become permanent if there is structural damage to the eye or brain. This suggests the underlying condition is worsening.
When to See a Doctor
Occasional phosphene perception is common and typically goes away after a few seconds.
However, if phosphenes are persistent and don’t go away on their own, you should see a doctor, especially when they are accompanied by:
- Double vision
- Nausea or vomiting
- Low blood pressure
- Loss of consciousness
Getting routine comprehensive eye exams with an ophthalmologist is the best way to catch vision problems early before they affect your quality of life.
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