The sparkles or colored spots you see during a hard cough are usually phosphenes, light your eye reports even though no light reached it.1EyeRounds. Photopsias They belong to the same family as the lights you see when you rub closed eyes or sneeze hard, and they are part of normal vision.2Disabled World. Phosphenes: Why You See Light That Is Not Really There In most people they are a harmless side effect of a forceful cough rather than a sign of eye damage. The kind of flash matters, though, because a few patterns of flashing point to problems worth checking quickly.
How Your Eye Makes Light Without Light
The back of your eye is lined by the retina, a thin layer of cells that turns light into signals for the brain. These cells can also be set off by pressure or tension on the eye, even with your eyes closed.3Ohio State Health & Discovery. What happens when you rub your eyes and see colors? The brain gets a normal-looking signal and has no way to tell it came from pressure rather than light.4Wikipedia. Phosphene So you see flashes, bars, spots or colored blotches with no actual light source.5EyeRounds. Photopsias Pressure fires many cells at once, without the orderly pattern a real image would make, so the brain fills the gap with random dots, swirls or colored patches that fade within a second or two as the pressure drops. Rubbing your eyes, coughing and a knock to the head can all produce these lights.6EyeRounds. Photopsias
Why a Cough Puts Pressure on Your Eyes
A hard cough sharply raises pressure inside your chest and abdomen. That pressure is passed through the large veins up into the skull, briefly raising pressure around the brain.7PubMed. Transient cerebral circulatory arrest coincides with fainting in cough syncope Pressure in the veins on the surface of the eye rises during a cough too.8Healio. Normal-tension glaucoma and chronic cough: an association?
When pressure in those eye veins jumps, pressure inside the eye rises by the same amount.9Healio. Normal-tension glaucoma and chronic cough: an association? Fluid that normally drains out of the eye is held back until pressure inside climbs high enough to push it out again.10Healio. Normal-tension glaucoma and chronic cough: an association? On top of that, the white outer wall of the eye can barely stretch, so a little extra fluid volume makes pressure inside rise a lot.11Healio. Normal-tension glaucoma and chronic cough: an association? For a moment during a cough, the retina is pressed harder than usual, which can make its cells fire.
That is why a long coughing fit causes more lights than one small cough. Each cough adds a brief spike, and repeated hacking keeps pressure high for longer stretches. Bearing down and holding your breath, as in a deep chesty cough, pushes it higher still.
It also explains why the lights often show up at the end of a bad fit rather than the start. A fit chains many coughs together with little time to recover between them, so pressure stacks up across the run and the strongest effect arrives near the end. Lights can appear in the moment after the last cough too, when you gasp or hold your breath before breathing normally again. Sneezing, straining on the toilet and heavy lifting do the same thing, sending the same surge up the veins to the head and eyes.
The spike does not harm a healthy eye. It is brief, and the eye’s drainage returns pressure to normal once the cough stops. If you are already treated for an eye pressure problem, mention a chronic cough to your eye doctor.
Lights From Standing Up or Blood Flow Changes
The brain’s vision area can make lights too. The brief flashes many people see when they stand up quickly are also phosphenes, linked to a short drop in blood flow to the part of the brain that handles vision.12Disabled World. Phosphenes: Why You See Light That Is Not Really There Long coughing fits can raise pressure in the head enough to briefly squeeze blood flow to the brain.13PubMed. Transient cerebral circulatory arrest coincides with fainting in cough syncope So after a hard bout of coughing, some sparkles may come from the brain side rather than the eye.
When you stand, gravity pulls blood toward your legs, and for a moment less blood returns to the heart and then to the brain. Your body normally corrects this within seconds by tightening blood vessels and speeding the heart slightly. In that short gap the vision area can misfire and produce sparkles or a dimming of the view. This is common in healthy people, and more likely if you are dehydrated.
Being sick makes it more likely. A cold or flu often means eating and drinking less, sweating from fever and losing fluid, all of which lower the volume of blood in circulation. With less blood volume, the dip when you stand up or cough hard is larger. Drinking fluids can make these episodes less frequent, though it will not stop lights caused by eye pressure.
There are some loose clues to which kind you’re having, though they overlap. Lights from blood flow tend to come with lightheadedness or a dimming of the whole view. Lights from eye pressure are usually sparkles or spots right during the cough. Both fade within seconds once you breathe normally.
Nearly fainting or blacking out after coughing should be reported to a doctor. Sitting down at the start of a fit lowers the chance of falling.
Flashes That Mean Something Else
The eye is filled with a clear gel that is attached to the retina. When this gel pulls on the retina, the tension makes retinal cells fire and you see flashes.14EyeRounds. Photopsias These usually last under a second and look like a lightning streak or camera flash off to the side.15EyeRounds. Photopsias Because the gel shrinks and pulls away with age, these flashes become more common after middle age.
Most of the time the gel separates cleanly and the flashes settle over weeks, but a doctor must check that no tear has formed. Being very nearsighted or having had eye surgery raises the chance of this happening earlier.
If the pull tears the retina, it can lead to a detached retina, which can cost sight if not treated quickly. A tear lets fluid seep behind the retina and lift it off the wall of the eye. The retina cannot work once lifted away, so vision in that area dims, often as a shadow moving in from the side or top. Caught at the tear stage, a doctor can often seal it with a quick laser or freezing treatment in the office.
These signs need an eye doctor or emergency department the same day:
- A sudden shower of new floaters, like specks or cobwebs, along with flashes
- A dark curtain or shadow spreading across part of your vision
- Flashes that keep coming without coughing, rubbing or another trigger
Ordinary cough lights look different. They appear only with the cough and stop when it stops. They are sparkles or colored spots across both eyes rather than a streak in one eye, and your vision is completely normal between coughs. Covering one eye at a time during flashes can help tell whether only one eye is involved, which is more typical of a retinal problem.
A different problem is raised pressure around the brain. In that condition, vision can go dark or greyed out for a few seconds at a time.16nhs.uk. Intracranial hypertension These episodes can be set off by coughing, sneezing or bending down.17nhs.uk. Intracranial hypertension It usually comes with a constant throbbing headache that may be worse in the morning or when coughing or straining.18nhs.uk. Intracranial hypertension
See a doctor promptly for a headache that started with your cough or worsens each time you cough, for repeated episodes of vision going dark, or for flashes after a recent blow to the head. Lights with numbness, weakness or trouble speaking need emergency help.
What to Expect at an Eye Exam
The visit usually starts with reading an eye chart, one eye at a time, to confirm your sharpness of sight is normal. The doctor may then check how your pupils respond to light and test your side vision by asking you to notice objects at the edges.
Next come drops to widen the pupil so the doctor can see the whole retina. They sting briefly, and within about twenty to thirty minutes the pupils open wide enough. A small pupil shows only the central part of the back of the eye, but flashes often come from the edges, so a wide pupil matters. With it, the doctor can look for a tear or pulling from the gel inside the eye. A swollen optic nerve at the back of the eye can also be a sign of raised pressure around the brain.
Tell the doctor when the lights happen and whether only with coughs, what they look like and in which eye, and about any floaters, shadows or headaches. Say how long you have been coughing.
The drops blur vision for a few hours, so arrange a ride, and bring sunglasses because your eyes will be sensitive to light.
How to See Fewer Lights While You’re Coughing
Treating the cause of a lingering cough often makes the lights stop on their own. A cough lasting more than about three weeks is worth a doctor’s visit in its own right.
Most coughs after a cold fade as the airways heal. Meanwhile, sip warm drinks or honey to calm an irritated throat. A humidifier or steamy shower loosens mucus, and avoiding smoke keeps it from feeding the cough. If the cough comes with wheezing, shortness of breath, fever that returns or coughing up blood, get seen sooner than the three-week mark.
How you cough matters too. When you feel one building, a slow breath in through the nose can calm the urge and prevent a sudden deep gasp that sets off a big strained burst. A few small, controlled coughs, or a gentle huff out as if fogging a mirror, move mucus with less pressure than one violent cough. Swallowing or sipping water when the tickle starts can interrupt a fit before it gathers force. These methods soften each cough without stopping you from clearing your airways.
During a long fit, sit or lean on something in case you feel faint. Don’t rub your eyes afterward, since that adds more pressure lights. If the sparkles are distracting, keep your eyes open and look at a fixed point.