Eyes, flashing lights in the: There are a number of causes of spontaneous flashing light sensations in the eye. A sensation of flashing lights can be caused when the vitreous (the clear, jelly-like substance that fills the middle of the eye) shrinks and tugs on the retina. These flashes of light can appear off and on for several weeks or months. With age, it is more common to experience flashes. They usually do not reflect a serious problem. However, if you notice the sudden appearance of light flashes or a sudden increase in flashing lights, you should see your ophthalmologist immediately to see if the retina has been torn or if there is another cause. Flashes of light that appear as jagged lines or "heat waves" in both eyes, often lasting 10-20 minutes, are different. They are usually caused by migraine, a spasm of blood vessels in the brain. Jagged lines or "heat waves" can also occur without a headache in which case they are termed ophthalmic migraine, or migraine without headache.