When you experience a sudden, forceful cough, you may briefly see flashes or streaks of light in your vision. This phenomenon is medically known as photopsia, and the specific flashes are called phosphenes. Phosphenes are the visual sensation of light that occurs without any actual light entering the eye. While seeing these flashes can be alarming, they are typically a temporary and harmless side effect of the physical pressure generated during a strong cough.
Understanding Phosphenes and Intraocular Pressure
The flashes of light you see are a direct result of mechanical stimulation within the eye, not a problem with your vision itself. A forceful cough requires contracting muscles in the chest and abdomen, dramatically increasing intra-thoracic and intra-abdominal pressure. This pressure wave quickly transmits through the body, including the head and eyes.
The sudden spike in pressure compresses the delicate structures of the eyeball, leading to a transient increase in intraocular pressure (IOP). This pressure exerts a physical force on the retina, the light-sensitive tissue lining the back of the eye. When the retina’s photoreceptor cells are stimulated by mechanical pressure instead of light, they misfire, sending a false signal to the brain. The brain interprets this electrical impulse as a brief flash, spark, or streak. These phosphenes typically last only as long as the pressure spike occurs, which is why they disappear immediately after the cough subsides.
Common Triggers Beyond Coughing
This pressure-induced visual effect is not unique to coughing and can be triggered by any activity that involves a sharp increase in internal body pressure. The mechanism is similar to the physiological Valsalva maneuver. Other common actions that produce phosphenes include a hard sneeze or straining heavily during a bowel movement. Performing intense, strenuous exercise, like heavy weightlifting, can also momentarily elevate pressure enough to cause a fleeting flash. The classic experience of “seeing stars” after being hit in the head is another example of this mechanical stimulation of the retina. All these activities temporarily pressurize the visual system, resulting in the benign sensation of light without an external source.
When Flashes Indicate a Serious Eye Condition
While phosphenes from coughing are typically harmless, flashes of light can also be a symptom of more serious underlying eye problems. Pathological photopsia differs from pressure-induced phosphenes because it is caused by the vitreous humor pulling on the retina. The vitreous is a clear, gel-like substance that fills the center of the eye.
As people age, the vitreous naturally shrinks and liquefies, a process that can cause it to pull away from the retina. This separation is known as a Posterior Vitreous Detachment (PVD) and is a common cause of flashes and floaters. The danger arises if the pulling is too strong, leading to a retinal tear or a Retinal Detachment.
Unlike the quick, transient flashes from coughing, flashes caused by vitreous traction are often described as lightning streaks in the peripheral vision and may persist or recur spontaneously. Seek immediate medical attention if the flashes are accompanied by a sudden, significant increase in floaters, or if you notice a curtain or shadow descending over part of your vision. If flashes persist for more than a few moments after a cough or start occurring spontaneously, an eye examination is necessary to rule out a serious condition.
Reducing the Frequency of Vision Flashes
Since the flashes are a direct result of the force of the cough, the most effective way to reduce their frequency is by addressing the root cause of the coughing itself. Chronic or frequent forceful coughing is often a symptom of conditions such as respiratory infections, allergies, asthma, or gastroesophageal reflux disease (GERD). Treating the underlying issue will reduce the intensity of the pressure spikes.
If you are experiencing a temporary cough, you can try to reduce the severity of the expulsive force. Staying well-hydrated helps thin mucus, making coughs less forceful. Sucking on lozenges or hard candy can soothe an irritated throat, reducing the urge to cough violently. When a cough is unavoidable, turning your head and slightly bending your torso can help dissipate some of the pressure, minimizing the mechanical impact on your visual system.