The back cavity of the inner eye is filled with clear jelly called vitreous. When the vitreous
jelly undergoes the natural aging process it deteriorates and becomes liquid. As the
eyeball moves, small pockets of liquid vitreous can move around
as well inside the vitreous cavity. This movement causes the
vitreous to pull on the retina, causing flashing (photopsia).
Normally the jelly is only loosely adherent to the retina and
easily peels away from the retina during vitreous degeneration
(syneresis). This event is called a posterior vitreous detachment
(PVD) and again is a normal event occurring in most people
sometime between 50 and 70 years of age.

When a PVD occurs, the detached vitreous can tug on the retina
as it attempts to break free. The brain interprets these tugs as
flashes or large spots in the vision, and flashes of light may
appear periodically for several weeks. Flashes of light are usually
a result of the aging process and do not indicate a serious vision problem.
However,flashes which appear with a large number of new floaters
(see below) or with a loss of part of the field of vision may indicate retinal
detachment, requiring an immediate eye exam.

The usual causes of light flashes are:

• Retinal tear or detachment
• Posterior Vitreous Detachment (common)
• Migraine Headache (common)
• Rapid Eye Movements (very common)
• Retinal Infections or Inflammations (rare)
• Central Nervous System Disorders (rare)

Any flashing light or visual disturbance that lasts more than twenty to forty minutes is
considered an ocular emergency and requires immediate medical attention.

Floaters

The vitreous in addition to or instead of tugging on the retina, can also become stringy,
and form visible strands which appear in the field of vision as floating threads or small
spots and circles. Floaters become visible when they fall within
the line of sight and these small specks in the vitreous cast a
shadow on the retina, particularly when viewed against a light
background. A patient with these floaters should be examined, to
check for other retinal damage. If there are no problems, the
patient can fairly easily learn to ignore the floaters.

There are a number of possible causes for floaters. They may be
small flecks of protein or other matter that were trapped during
the formation of your eyes before birth and remain suspended in
the clear fluid of the vitreous. Sometimes the deterioration or
even detachment of the vitreous fluid may also cause floaters to
develop and though very annoying, it is often not serious. In fact,
the floaters will eventually fade from the vision as the brain adapts to the
floaters and "tunes out" your awareness of them. However, the floaters do
not actually disappear and no treatment is available to eliminate them.

Occasionally though floaters are warning signs of imminent danger or damage occurring
somewhere in the eye. An internal hemorrhage of blood from a leaking vessel may cause
floaters. They can also be caused by a Posterior Vitreous Detachment (PVD), a
degenerative change in the vitreous allowing it to fall away from its normal position
against the retina. This usually causes an acute increase in the number of floaters and is
associated with increased risk of retinal complications. This is rare in the under 50 crowd,
with the incidence becoming more common by age 70 or so. The rapid onset of large and
numerous floaters may signal an impending retinal detachment.

The floaters which indicate a serious condition usually can be differentiated by some
important factors:

• They occur suddenly
• They are accompanied by visual field defects including flashes of light and areas of vision loss (as if a dark curtain is placed in front of the eyes)
• They appear numerous or large
• They are associated with a trauma or a blow to the eyes or head
• They are increasing in number over a short period of time, often minutes or hours

These signs and symptoms are considered ocular emergencies and require immediate
medical attention.

Treatment

The phenomena of flashes and floaters are most often harmless but also may be a sign of
important health problems. The sudden onset of flashes or floaters should be checked by
an eye doctor. Though the possibility of something serious occurring is low, the
advantages of an exam outweigh the inconveniences involved.

On rare occasions when the vitreous pulls on the retina, the resulting vitreous detachment
can cause small tears or holes in the retina which could lead to a retinal detachment. The
damaged part of the retina subsequently does not work properly and a blind or blurred
spot in vision results. This a serious problem which needs prompt medical treatment by an
ophthalmologist. If untreated, retinal tears or holes can continue to worsen and severe
vision loss can result should the retina becomes detached.

An eye examination with dilation of the pupil is the only way to determine if you have
developed a tear in the retina. You should have a prompt comprehensive examination
anytime you experience the onset of flashes, floaters, decreased vision, or if you become
aware of an increase in the number or intensity of flashes or floaters. In a such an eye
exam your ophthalmologist can use a variety of special instruments to look at the vitreous,
the retina and the other interior parts of your eyes to determine the causes of the flashes
and floaters that you see.