Floaters

What are floaters?  And why do eye doctors always ask you if you've seen flashes or floaters recently?

Floaters in and of themselves are harmless, albeit annoying.  They are the result of the gradual breakdown of the vitreous (the gel-like substance that makes up most of the inner eye) and are essentially particles of collagen floating in your eye.  What you see as moving gray lines or dots are actually shadows cast on the retina (the light-sensitive tissue that lines the back of the eye) due to collagen's interference with light entering the pupil.  That is why floaters are more noticeable when looking at a bright sky, white wall, or computer screen: more light enters the eye, thus there is a greater potential for shadows to be cast on the retina by the floating collagen particles.

When are floaters more of a concern?

If you notice an increase in the number or frequency of floaters, flashes of light in your vision, or an apparent "curtain" coming down over your vision, this could be a sign of a serious problem with the retina and should be investigated immediately.  Increasing floaters, flashes of light, and a curtain over the vision are all signs of a retinal tear or detachment and could potentially lead to loss of vision.

As proof that you're not imagining your eye floaters, check out this video which shows what the eye doctor sees when he or she looks into the eye of a patient with significant floaters:

http://www.youtube.com/watch?v=sxroMCVgpPk