What happens when you “see stars”?

Dear Cecil:

How can a person "see stars"? When you exert yourself physically and then stop, you have these hundreds of little BBs zooming in space in front of you. I have actually believed I could touch them.  Try staring at the ground about ten feet in front of you and follow one of the lights out of the corner of your eye until it blinks out. It's kind of a kick. Explain how this physical change of sight and mind can occur as easily as doing a cartwheel.

Cecil replies:

Not being one for cartwheels, Cecil tried to see what kind of business he could drum up doing somersaults. This has moved him to thank God there weren’t any kids around to see what kind of weirdo their father was, particularly after that session last month with the Hula Hoop. Nonetheless I did manage to get a passel of zooming Bbs on one occasion, along with a monster headache.  The little spots of light, which are to be distinguished from the opaque spots or threads we’ve discussed in the past, persist for perhaps five or ten seconds and appear to swim around. But I only got them after a particularly crazed gymnastic exhibition. What do you do, finish your cartwheels by slamming into a wall?

BBs, “stars,” and other “nonphotic” visual stimuli (i.e., those not actually produced by light) are called photopsia or phosphenes. They’re believed to be caused by mechanical stimulation of the nerves of the eye. Another example is the sensation of light produced by pressure on the eye, a phenomenon described by no less an authority than Aristotle.

Young people see stars every once in a while as a result of a blow to the head or some sudden exertion. But the little BBs don’t really become common until retirement age. What happens is that the eyeball fluid, which is contained in a sort of sac, starts to pull away from the back of the eye. This is called “posterior vitreous detachment,” and it usually occurs suddenly, often following a jolt to the head. You see stars and spots and your vision is blurred and distorted. The stars may persist for weeks or even years as fibers from your eyeball sac continue to tug on your retina.

Grim though it sounds, vitreous detachment is normal, occurring in maybe half the population. Apart from stars and spots, your vision usually winds up about the same. But stars and spots can also herald a detached retina, which is bad news indeed. If you’re nearing retirement age, you definitely want to slack off on those cartwheels.

Send questions to Cecil via cecil@straightdope.com.

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