Question: Why do I see stars?
Every now and then I see stars. What is it I am actually seeing? Is this bad for my eyes?
Answer: "Seeing stars" is a common visual complaint, but it is usually a normal and harmless occurrence. If you close your eyes and rub them, you will probably see spots and flashes of light. These images you see are called "phosphenes," an entoptic phenomenon characterized by the experience of seeing light without having light actually enter the eye. Phosphenes are produced by pressure on the eye. This pressure is translated into various patterns by the optic nerve.
These stars, or spots of light, that you see can occur after a sneeze, a deep cough, a blow to the head or low blood pressure (such as standing up too quickly.)
Some people see flashes or lines of light that last up to 10 to 20 minutes. These flashes of light are generally caused by a spasm of blood vessels in the brain, or migraine. If a headache follows the flashes, it is called a "migraine headache." If these flashes or lines of light occur without a headache, it is called an "ophthalmic migraine," or migraine without a headache.
While usually harmless, frequent flashes of light can be a warning sign of something more serious. A comprehensive eye examination will be needed to determine the cause.
Patient Education Institute. Flashes and Floaters. National Institutes of Health, 2004.