Floaters, Flashes & Posterior Vitreous Detachment
Floaters and flashes can be warning signs signaling a more severe problem in your eye, including retinal tears and detachments. This section covers the symptoms related to vitreous separation. (See also: section on Retinal Tears and Detachment)
What Are Floaters?
The central cavity of the eye is filled with a gel-like substance called the vitreous gel. Floaters are small clumps of cells, pigment, and or gel matrix, which “float” inside the vitreous gel. Floaters may appear as small specks or clouds moving in front of your vision. They are especially apparent when looking at a plain white background, or looking at a brightly illuminated sky. Floaters often appear as if they are floating in front of the eye, and sometimes imitate a swarm of small insects. In actuality they “float” entirely inside the eye, and typically move when you attempt to look at them or look in different directions. Floaters are usually quite small and what you see are the shadows cast upon the retina and nerve fiber layer.
Floaters that you have noticed or been aware of for some time are typically benign; however, a “shower” of new floaters may indicate that you have experienced a new retinal tear, a new vitreous hemorrhage, or a posterior vitreous detachment, or that there is inflammation in the eye (see section on uveitis). A shower of new floaters signifies a problem that requires prompt attention and you should see your eye doctor immediately.
How are floaters treated?
Typical floaters are not usually treated. If the floaters have been caused by a posterior vitreous detachment without a retinal tear, the floaters will typically “settle” out of the line of vision over several weeks to months. Severe floaters caused by a vitreous hemorrhage (blood) that does not clear after several months and prevents useful vision can be removed surgically by a procedure called pars plana vitrectomy. Laser treatment to reduce the symptoms of floaters is not a recommended treatment at this time.
What Are Flashes?
Flashes are the experience of brief sensations appearing to be bright lights at the edge of vision. Flashes are usually noticed all the way to one side and are more prominent in the dark or when going from a well-lighted area to a darker area. Usually the flashes have no specific shape, but can sometimes have the appearance of lightning bolts. The experience of flashing lights, especially in conjunction with new floaters, can be an indication of a posterior vitreous detachment, retinal tear, or a retinal detachment. Flashing lights represent stimulation of the retina from pulling by the vitreous gel inside the eye. There is a release of an electrical signal from the nerve tissue of the retina from the pulling caused by the vitreous gel separating from the retina. If the pulling is especially strong, or at the site of a weakness in the retinal tissue, a retinal tear may occur. Any experience of new flashes should be reported to your ophthalmologist and he or she will usually perform a prompt dilated exam of the retina.
Some flashing light phenomena involve the experience of a very distinct, often multicolored or fiery jagged line of light with or without an adjacent black spot in the vision. Such “fortification scotomas” may start in the center of vision and then spread to the side, or start at the side in the first place. Often, if you carefully close one eye and then the other, you will notice that the flashes are actually going on in both eyes, but are just more prominent in one or the other. This type of flashing light typically lasts from 5 to 30 minutes, and may or may not be followed by a bad headache. These flashing lights are different from the flashing lights caused by tugging on the retina described above, and represent the eye portion of a migraine (with or without a migraine headache). This type of flashing lights is usually not serious, but if it is the first time you are experiencing them, or you have any doubts, you should contact your ophthalmologist.
For further information on migraine, see: AAO: What Is Migraine?
How are flashes treated?
If you are experiencing new flashes, it is important to undergo a dilated exam of the eye with a careful exam of the far peripheral edge of the retina. It is at this very edge of the retina, which is thinner than the more central part of the retina, where most retinal tears occur. The ophthalmologist will often use a device called a scleral depressor to gently indent the side of the eyeball in order to bring the peripheral edge of the retina into better view. If no retinal tear or retinal detachment is found, then no treatment is usually indicated. However, after the initial exam, it is helpful for you to screen yourself periodically by carefully observing the world around you with one eye at a time. Look for new symptoms such as increased floaters, new or increased flashes or flash intensity, or a shadow. If any of these additional symptoms occur, you need to return to your ophthalmologist for a repeat dilated exam, immediately.
What is a Posterior Vitreous Detachment?
The vitreous is the gel-like substance that fills the back of the eye. When you are young, this gel is quite firm and has a uniform consistency; however, as you get older, the gel develops liquid pockets. Within these pockets, the condensations develop which lead to the experience of floaters. In most people, at some point in life (usually between the ages of 40 and 60, but earlier for moderately to severely near-sighted persons or people who experience a severe trauma to the eye), the pockets of liquefaction become so numerous that they combine to form larger pockets, and then break through the boundary membrane at the back of the eye. When this occurs the “membrane” of the posterior vitreous separates from the retina at the back of the eye. This is called a posterior vitreous detachment.
The connection between the posterior vitreous gel and the retina is not usually firm, but is more like the attachment of a suction cup to a glass window, or the attachment together of the two sides of a new plastic trash bag. The seal is firm, but once a separation begins, all the strength is lost and the separation proceeds quickly in a peeling process. The place where the posterior vitreous is attached to the optic nerve at the back of the eye is usually a point of more firm attachment than to the retina. When this firm attachment separates, a ring of condensed vitreous gel, which previously had been the site of attachment to the optic nerve, “floats” in the middle cavity of the eye. Often this ring appears as a gray, white or black donut if seen dead on, or as a squiggly line if seen from the side. It is this separation of the vitreous gel from the optic nerve with the creation of this ring floater, which is the hallmark of a completed posterior vitreous detachment. Usually this peeling of the posterior vitreous from the retina goes smoothly, and does not present a problem or danger to vision.
How is a posterior vitreous detachment treated?
An old posterior vitreous detachment or a new posterior vitreous detachment that is not associated with any retinal tear or retinal detachment requires no treatment. New floaters associated with a new posterior vitreous detachment typically resolve over several weeks to months and are not harmful even if they don’t go away completely. If, however, a patient with a recent posterior vitreous detachment also has a retinal tear or retinal detachment, then these require urgent treatment.
For Further Information
- AAO: What Are Floaters and Flashes?
- American Society of Retina Specialists: Posterior Vitreous Detachment Fact Sheet