Flashes and Floaters
Floaters are usually seen as spots, cobwebs or strands moving across the vision. They are usually due to particles floating in the vitreous (jelly-like substance that fills the eye).
Sudden occurrence or increase of floaters especially when accompanied by flashes of light may be a symptom of a retinal tear or retinal detachment. These are usually caused by the vitreous separating from the retina (the lining in the back of the eye functioning as the film of the eye). The separating vitreous can pull a hole in the retina. The hole needs to be treated with laser promptly before the retina itself detaches off the wall of the eye. This is called a retinal detachment which appears as a dark shadow initially in your side vision. The dark shadow can expand to affect your whole vision.
This is more common with age and in short-sighted people or those who have had an eye injury or eye surgery. Inflammation of the eye or bleeding into the vitreous from the retina may also cause floaters. Flashes caused by separation of the vitreous most often decrease over a few weeks but can persist for many months. Floaters can become less noticeable with time but many of them persist indefinitely. Surgery to remove the floaters is rarely performed due to the potential risks of surgery and only considered in extreme circumstances.