The retina, which lines the inside, back portion of the eye, responds to light entering the eye. Changes in the retina may cause flashes of light in any area of vision, often in your side vision. Some causes stem from vision-threatening conditions while others do not have lasting effects on the eyes. See your doctor for an accurate diagnosis if you have flashes in the outer corner of your eye.
The back chamber of your eye contains a jelly-like substance called vitreous fluid that helps maintain the eye’s shape. Small fibers secure the vitreous to the retina, and with age, the vitreous may shrink and pull away from the retina. These vitreous detachments do not usually cause a threat to vision or eye health, but may result in flashes of light in the vision -- typically in the outer corner. For many people, these flashes will ease, without any further problems. In some cases, however, the vitreous pulling away may tear a hole in the retina, often resulting in vision changes and many new floaters. Retinal tears may require surgery to prevent damage to vision.
If the retina detaches from the back of the eye, a person may experience flashes of light, either in the corners of the eye or other locations in the side vision. Other symptoms include a number of new black spots in vision, as well as a dark veil-like curtain that will block out an area of the side vision. These symptoms often appear suddenly, but they do not cause pain.
Retinal detachments require immediate evaluation and treatment. If left untreated, the person will have permanent vision loss. Retinal detachments are repaired surgically, using different methods based on the extent of the retinal detachment. Most people who seek immediate treatment after a detachment will not have permanent vision damage.
Ocular migraines, also called visual migraines, may cause flashes of light in the side vision. This will usually happen in both eyes. In some people, this may appear as a precursor to a painful headache migraine while other people may experience the lights without any discomfort.
Ocular migraines do not usually cause changes in overall vision, other than the flashing or shimmering lights in the side vision. The flashes may last only a few minutes, then disappear without further symptoms. Ocular migraines do not indicate medical conditions or cause damage to the eye.