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Vision

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Is It a Floater—or 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 ocular phenomenon.

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).

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.

Treatment Options

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 new ones.

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 time.

 

From The Johns Hopkins Medical Letter: Health After 50, October 2001.

 

 

 

 


 


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2005
WHITE PAPERS
Vision

The vision White Paper from The Johns Hopkins White Papers series is an annual, in-depth report written by Hopkins physicians.


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Johns Hopkins Medical Letter: Health After 50
Keep abreast of the latest medical news with the nation's leading health newsletter for people over 50.

 

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