Flashes and Floaters

One of the most common symptoms that we hear about in our clinic are flashes and floaters.

Patients often describe floaters as a sudden onset of tiny dots, a new greyish glob, or a cloudlike film that floats back and forth in their field of vision.  Floaters are most noticeable bright settings and especially against a bright background.

Flashes are usually seen in a dim or dark setting and are described as a brief arc of light in the peripheral vision lasting less than a second.  Flashes tend to occur after a turn of the head or eyes.

What’s going on?  Let’s start by reviewing the pertinent anatomy of the eye.

The vitreous humor (or vitreous for short) is a clear, gel-like sac of material that normally fills 80% of the eye.  It’s made up of 99% clear liquid and 1% of various proteins and hyaluronic acids.

Imagine the vitreous as a water balloon that is lightly attached to all internal parts of the eye that it touches.  However, it is very firmly attached to the retina around the midline of the eye as diagramed below in red.

In a young and healthy eye, the vitreous is usually very clear.  As we get older, the protein and hyaluronic acids in the middle of the vitreous cavity tend to clump together and form strands.  This process is called vitreous syneresis.  The resulting strands are seen as fine semi-translucent strings and globs in your field of vision that builds up slowly over time.

At some point in our lives, this water balloon-like structure that is the vitreous sac collapses.  The wall of the vitreous sac quickly peels away from the back of the eye and the resulting deflated vitreous sac clumps up.  This process is called a posterior vitreous detachment or PVD.

As the vitreous peels away from the back of the eye, it can tug on surface blood vessels of the retina, leading to bleeding into the vitreous cavity (called vitreous hemorrhage).

The clumping of vitreous is seen as new onset of strands, clumps or cloudlike veils that move with eye movement. Vitreous hemorrhage is often seen as hundreds of tiny dots in the field of vision.

What causes the arc of light flash?  Flashes are caused whenever there is tugging on the retina.  The retina is the structure that lines the back of the eye.  It captures the images that you’re looking at and sends this information to the brain.

During the process of a PVD, the vitreous rapidly peels away from the retina.  This bit of tugging can cause the sensation of a light flash.   But why do some people continue to see light flashes?  Remember that the vitreous is very adherent to the retina at the midline of the eye.


In fact, it really cannot let go of the retina beyond this point.  During the process of a  PVD, the vitreous is freed from the back part of the eye, but firmly adherent to the retina in the middle of the eye.  This is why it’s term ‘posterior’ vitreous detachment.

When the eye moves, the free part of the vitreous moves, tugging on the part of the vitreous that is still attached to the retina.  This tugging is what give the symptoms of a light arc.  This process can persist for several weeks or months after the initial onset of a PVD but tends to diminish after about 2 weeks.  Because the vitreous is always adherent to the retina at the midline, it’s not unusual to get an occasional arc of light after rapid eye or head movement even months after the initial onset of a PVD.

In some patients, the vitreous tug can cause the retina to tear where the vitreous is tightly adherent.  If not treated in a timely fashion, a retinal tear can lead to a retinal detachment.


What should you do if you develop new symptoms of flashes and floater?  We recommend that you stop any strenuous physical activities as soon as possible. Then call a retina specialist in your area for an eye exam within 1-3 days to make sure you did not develop a retinal tear or detachment.