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Flashes, Floaters and Posterior Vitreous
Detachment
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The eye is a hollow spherical structure.
Internally, a delicate sheet of nerve tissue called the retina lines the
wall of the eye like wallpaper. The central cavity of the eye is filled
with a sticky gel called the vitreous. The vitreous gel is
99% water and 1% solid elements. Of the solid portion, there are filaments
that help to support the shape and tenacity of the gel, similar to steel
bars reinforcing concrete. At the back of the eye, the filaments attach the
vitreous to the optic nerve and blood vessels. Over time, the vitreous gel
tends to liquefy in its center, creating liquid pockets surrounded by the
more formed gel. This process is known as vitreous degeneration or
"syneresis." |
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Now, the filaments in these pockets are free to clump together. The clumps
may 'float' within the liquid vitreous pockets, giving the patient a
sensation of floaters. Floaters
appear as dots, spots, or curly lines that appear suspended in front of you
and move as your eye moves. The floaters are most noticeable when viewed in
bright illumination because they cast a shadow on the retina. |
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Eventually, with enough
degeneration within the vitreous gel, the filamentous scaffold collapses and
the vitreous separates from the retina.
This event is called a posterior vitreous detachment (PVD) and is a
normal event occurring in most people sometime between 40-70 years of age. A
PVD will often occur at an earlier age in people who are nearsighted or have
undergone cataract surgery.
Flashes of light are also a common symptom
of a PVD. When the vitreous pulls on the retina - to which
it is attached - the photoreceptors are mechanically stimulated. The retinal
cells are incapable of perceiving pain, pressure, or temperature. The only
stimulus that the retina responds to is 'light'. So when the retinal
photoreceptors experience mechanical stimulation because of this vitreous
pull, they send a signal to the brain in the form of disorganized light,
which is perceived by the brain as a flash.
If a retinal blood vessel is broken from
the pulling a vitreous hemorrhage can occur. A small amount of blood may be
seen as a shower of spots. Larger hemorrhages can cause large dark blobs in
the visual field or a overall decrease in vision. When hemorrhage occurs,
retinal tears and or retinal detachment are very frequent (90%).
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If the vitreous gel is abnormally adherent
to the retina or the retina is weak in a certain area a retinal tear can
occur as the gel separates and pulls away from the retina. Once a retinal
tear develops there is a significant risk of the liquid vitreous going
through the break and detaching the retina from the back wall of the eye. If a
retinal tear can be discovered before a retinal detachment develops it can
be treated with the laser to seal the break and prevent a retinal
detachment. Finding a retinal break can be difficult and requires a very
complete examination of the edge of the retina (the retinal periphery).
Fortunately the great majority of PVDs do not cause a retinal tear and not
all retinal breaks will lead to a detachment. In general, though, if a tear
is associated with a symptomatic PVD, the tear is at high risk for leading
to a retinal detachment and should be treated.
If
you have new symptoms of a PVD (new floaters, flashes of light, shower of
spots or a curtain or shade in your vision) it is important to have a prompt
and thorough examination of the retina.
Retinal detachment
should it occur, requires surgical correction. There are a variety of
procedures that might be used, depending upon the nature of the specific
patient's problem. These surgeries are highly successful at reattaching the
retina, and usually succeed at preserving useful vision. |
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