When the vitreous gel pulls on the retina, you may see what look like flashing lights or lightning streaks. These are called flashes. You may have experienced this same sensation if you have ever been hit in the eye and seen "stars." The flashes of light can appear off and on for several weeks or months.
As we grow older, it is more common to experience floaters and flashes as the vitreous gel changes with age, gradually pulling away from the inside surface of the eye.