Answer:

Vitreous is the name of the clear material that fills the eyeball. 80% of the eye's volume is vitreous -- just like a small spherical fish tank! You may recognize the word "vitreous" as molten glass. Human vitreous has a similar appearance and physical properties.

The vitreous in children is very firm and gelatinous. In older folks, the vitreous is like water. That means there's a transition period during which the gel "melts." The medical term for this process is "syneresis." (Hey, you knew we had a term for this!)

When the vitreous separates from the retina along the wall of our "fish tank" eye, it can stimulate light flashes in the retina.

Your coughing fits have provided us all with a textbook description of "entoptic phenomena" -- the visualization of images and colored flashes that are not really there, but you perceive them anyway.

All of us experience entoptic phenomena -- it's just that some of us are not as alert an observer as you.

In order to communicate with the brain, the retina transmits a nerve signal that describes light. That is to say, the retina's language is light. Any stimulation of the retina (inflammation, pressure, traction, etc.) will activate the retina, and so the stimulated retina transmits a visual signal to the brain -- even if your eyes are closed and even if the room is totally black!

Many WebMD visitors recall playing in bed at night as a child and gently pressing on their eyeball. C'mon, 'fess up, you all did it at one time or another! You may have noticed a yellow or greenish crescent or halo in that eye. That was your introduction to entoptic phenomena.

In your eyes, the entoptic stimulation may have been caused by your wobbling vitreous. In the absence of all other stimuli (darkened, quiet bedroom) your eye finally had a chance to appreciate what was going on INSIDE your eye.

It's possible to have flashes only without any vitreous floaters.

Since coughing can certainly wobble the fish tank, it is not surprising you associated the flashes with your cough.

Persistent or progressive flashes should alert you to get a comprehensive eye exam.