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 often last up to 10 to 20 minutes. These flashes of light are generally caused by a spasm of blood vessels in the brain, called a 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.
Source: Patient Education Institute. Flashes and Floaters. National Institutes of Health, 2004.
Patient Education Institute. Flashes and Floaters. National Institutes of Health, 2004.