Seeing flashes of light can be caused by a variety of factors. Some common reasons include:

1. Detachment or Tears in the Retina: If the retina pulls away from the back of your eye, it can cause flashes, often accompanied by other symptoms like floaters.
2. Vitreous Humor Changes: The gel-like substance inside the eye can shrink with age, leading to shadows or flashes of light as the vitreous pulls on the retina.
3. Migraine Aura: Migraines can sometimes cause visual disturbances, including flashes of light or zigzag patterns.
4. Eye Trauma or Injury: An impact or injury to the eye can result in flashes.
5. High Myopia: Severe nearsightedness increases the risk of retinal issues, including flashes.

If you experience sudden or persistent flashes, especially if accompanied by floaters, a shadow or curtain over part of your vision, or a sudden increase in floaters, it’s important to seek prompt medical attention from an eye care professional, as these might indicate serious conditions requiring urgent treatment.