"I see these black dots and squiggly lines on a bright day or when I look at a white background. They're really annoying!" As an optometrist, I hear that statement a lot and many of my patients ask "What are floaters? What causes them?"
Without going into great detail about the anatomy of the eye, the answer is as follows:
The gel that fills the center of our eyes is called the vitreous and within the vitreous are protein particles or fibers. These protein particles or fibers cast a shadow on the retina and therefore causes us to see the "floaters". The brighter the day or the brighter the background we are looking at, the more noticeable the floaters are.
As annoying as they are, floaters are generally benign and should simply be ignored. However, if one notices a sudden shower of black/grey dots or a large floater that looks like a curtain/veil covering your vision, then those are not normal and may be an indicator of a retinal detachment.
A retinal detachment is when the tissue at the back of the eye (the retina) has torn and has begun to peel away from the eye. Flashes of light that are consistent throughout the day is a result of the rods/cones in the retina being pulled away. A sudden showering of black/grey dots are the shadows of red blood cells floating in the vitreous from a torn blood vessel. The sensation of a veil/curtain over your vision is the detached retina coming over your line of sight.
I always tell my patients after they've been diagnosed with floaters that if there are any changes in size, shape, or amount of floaters from this point forward, then return to the clinic or go to the ER to have it checked. By advising my patients to be more observant of any subtle changes in their vision and warning them of the symptoms of a retinal detachment, it allows them to be more proactive in their eye health. Education, is without a doubt, the key!