Seeing “objects” floating or flashing in your vision can be a sign that there is damage to your retina. An article in the NY Times explains why seeing these things suddenly (rather than gradually) is cause for immediate concern:
The retina is a layer of tissue at the back of the eye that collects light relayed through the lens. Special photoreceptor cells in the retina convert light into nerve impulses, which are transmitted to the brain. At the retina’s center is an especially critical area called the macula, which enables you to see anything directly in front of you, like words on a page, a person’s face, the road ahead or the image on a screen.
When blood flow through the retina is blocked or when the retina pulls away from the wall of the eye, getting the problem properly diagnosed can be an emergency. Modern treatments can do wonders if they are begun before the damage is irreversible. But a delay in getting to a retinal specialist can diminish the ability of even the best therapy to preserve or restore normal vision.
It truly is an eye emergency, it there is a SUDDEN change in floaters or flashes. The inside of the eye is made of mostly water, with a little jelly, called the vitreous. Over time, it is normal for the vitreous to move, and there to be a sudden increase in floaters. Just about everyone gets that. What is of concern is if the vitreous is pulling on the retina as it moves and can cause a retinal bleed or tear which causes blindness.
Unfortunately, there are no pain receivers in the eye, so beyond the sudden increase of floaters and flashes, there is nothing except for the doctor to look in the eye to know if it is just the vitreous moving, or a retinal tear.
When I see a patient that reports a sudden increase of floaters and flashes, I assume it is a tear until I prove, by looking in, that it is just the vitreous just moving.
The bottom line is if you ever, and most likely you will, see a sudden increase of floaters and/or flashes, go see your eye doctor pretty quickly. Most likely it is not a tear, but, as I tell my patients, “it is not rare if its in my chair!”