The retina, which lines the inside, back portion of the eye, responds to light entering the eye, and thus plays a vital role in vision. Changes in the retina may cause flashes of light in any area of vision, though commonly in the side vision. Some causes stem from vision-threatening conditions while others do not have lasting effects on the eyes. As such, a person should seek medical attention for persistent flashes in the outer corner of the eye.
Vitreous Detachment
The back chamber of the eye contains a jelly-like substance called vitreous fluid that helps maintain the eye's shape. Small fibers tether the vitreous to the retina, and, with age, the vitreous may shrink and pull away from the retina, says the National Eye Institute. 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.
A person with a vitreous detachment may also experience floaters in the vision. For many people, the flashes will ease, and they will not have any further problems from the vitreous pulling. In some cases, however, the vitreous pulling away may tear a hole in the retina, often resulting in vision changes and many new floaters. Anyone experiencing these symptoms should contact an eye doctor since a tear may require a surgical repair to prevent damage to vision.
Detached Retina
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. Eye surgeons repair a detachment surgically, using different methods depending on the extent of the retinal detachment, says the Digital Journal of Ophthalmology. Many people who seek immediate treatment after a detachment will not have permanent vision damage.
Ocular Migraine
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 or appearance of a headache, explains MayoClinic.com.
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. If loss of vision occurs even briefly with the flashes, however, the person should discuss the changes with an eye doctor.
