Is It a Floateror a Detached Retina?
Nearly everyone experiences small dots, lines,
clouds, or "cobwebs" across the visual field from time
to time. Known as floaters, this phenomenon is caused by shadows
cast on the retina by microscopic structures within vitreous
fluid (the fluid that bathes the inside of the eye). Flashes
of light, which occur when this fluid shifts, are another common
In most cases, flashes and floaters are harmless,
although sometimes annoying, passing experiences. But sometimes,
they indicate that the retina (the light-sensitive structure
at the back of the eye) is tearing or in danger of detaching
from the underlying layers of the eyeball. Retinal detachment
may be a medical emergency that results in blindness.
Under these circumstances, prompt treatment generally
preserves vision. However, the warning signs of detachment and
the retinal tears that precede it are easy to overlook: there
is no pain and early symptoms (if they occur) frequently resemble
benign floaters or flashes.
People over age 50, especially those who have had
cataracts removed, are at increased risk for retinal tears and
detachment owing to normal, age-related changes in the vitreous
fluid. Since saving vision may depend on prompt treatment (sometimes
within 24 hours), it is critical to know when the retina may
be threatened and when to see an ophthalmologist for an evaluation.
A Delicate Membrane
The retina processes visual images focused on it
by the cornea (the outside front portion of the eye) and the
lens (the flexible, transparent structure located behind the
iris and the pupil) in much the same way that film responds to
light focused on it by a camera lens. The retina is held in place
by the vitreous fluid, a nearly transparent gel composed of water,
hyaluronic acid (a lubricant), and collagen fibers (for support).
Vitreous fluid fills most of the space inside the eye. As we
age, the fluid gradually liquifies and its support structures
dissolve. Eventually, it begins to shift within the eye. Sometimes,
this movement prompts the posterior vitreous membrane (a thin
layer of tissue located near the optic nerve) to slide or pull
away from the retina, a condition called posterior vitreous detachment
PVD develops in 10% of adults by age 50 and in
two thirds of those aged 70 and over. In most instances it causes
no problems. But sometimes the movement of vitreous fluid is
abrasive enough to tear the retina. Tears are not necessarily
harmful, but they may permit fluid to collect underneath. If
the fluid spreads, the retina may peel away and detach from the
back of the eye.
Retinal detachment is the most serious complication
associated with cataract surgery. The problem develops in up
to 2% of those who have a cataract removed, about half the time
within a year of surgery. People who are severely nearsighted
(unable to focus on distant objects) are also at increased risk,
possibly because the elongated eyeball characteristic of the
condition stretches and weakens the retina. Additional risk factors
include a personal or family history of retinal detachment, other
eye problems (such as lattice degeneration, which causes retinal
thinning), and eye trauma. People with diabetes are vulnerable
to another, less common mechanism of detachment related to the
formation of scar tissue within the eye. Presbyopia, which affects
the ability to focus on close objects and is universal among
older people, is not related to retinal detachment.
Painless but Serious
Because pain is not associated with retinal tears,
the problem is often discovered during a routine eye examination.
Symptoms that do occur vary, appear in only one eye at a time,
and may develop gradually or suddenly. The most distinctive clue
is a shower of hundreds or thousands of little black dots across
the field of vision, which may signal a hemorrhage caused by
tearing across a blood vessel. Floaters or sudden flashes of
white light also are characteristic. If the retina detaches,
it may seem that a dark curtain or shade is spreading across
the visual field. Detachment near the macula (the part of the
retina responsible for viewing the fine detail necessary for
reading) may cause sudden blurring or loss of vision. Prompt
evaluation by an ophthalmologist is necessary if you experience
a shower of dots or curtain spreading across the visual field,
new unexplained blurred vision, or changes in the number of floaters
or the intensity of light flashes.
Five common procedures are used to treat retinal
tearing and detachment, depending on their extent and location.
In certain cases, small holes in the retina may require no treatment.
In others, combinations of more than one surgical approach may
be required. All are generally performed on an outpatient basis.
The amount of vision restored and preserved with all procedures
is greater if the macula is still attached. Even if the prognosis
is poor, however, treatment is usually still advisable.
If a tear is in progress, the injury can usually
be treated with laser therapy (light energy) or cryotherapy (intense
cold). Both treatments seal the retina to the wall of the eye,
repairing the tear and preventing detachment. If a tear or two
adjacent tears have already occurred and there are signs of early
detachment, pneumatic retinopexy (pneumopexy) may be performed.
The procedure involves injecting a gas bubble into the eye and
positioning it over the tear to block fluid entry and permit
the fluid beneath the retina to be absorbed by the body. In 70%
to 80% of cases, this procedure relieves symptoms and prevents
If tears are more numerous or the retina has already
detached, either or both of the following surgical procedures
may be performed. In the scleral buckling procedure, the tear
is treated with cryotherapy. Then a soft silicone band is stitched
to the sclera (the thick, protective sheathing that encircles
the eye). The band pushes the sclera back toward the retina.
The other procedure is vitrectomy, in which the vitreous fluid
is removed to stop it from pulling on the retina. The vitreous
is then replaced with air or gas to discourage the movement of
fluid and promote its reabsorption. Over time, the air or gas
is replaced by the body's own fluids.
Scleral buckling is usually tried first, largely
because up to 80% of patients who never had cataracts develop
them after vitrectomy, generally within six months of the operation.
Buckling is also usually the first choice for people who have
had a cataract removed, since the new surgery mainly takes place
on the outside of the eye and affords less risk of infection.
Vitrectomy is more effective in more complicated cases, such
as when the tears are located far back in the eye. Afterward,
medication can be prescribed to ease any pain. For the first
few days following surgery, physical activity is usually restricted,
although reading, writing, and watching television are generally
possible soon after surgery. Improvement of vision in the affected
eye may take weeks to months, depending on individual circumstances.
The success rate is high for both types of surgery. "Although
it may take more than one procedure, in 95% of cases, the retina
can be reattached. Fifty percent of the time, eyesight will be
restored to better than 20/50 vision," says Peter Gehlbach,
M.D., Ph.D., Assistant Professor of Ophthalmology at Johns Hopkins
School of Medicine. A great advantage of scleral buckling, vitrectomy,
and pneumatic retinopexy is that if one technique fails, another
can be undertaken immediately or in a matter of days. In some
cases, scleral buckling and vitrectomy are performed at the same
Johns Hopkins Medical Letter: Health After 50, October