Floaters, flashes, & retinal tears

Seeing things? Usually, it's just the harmless 'stuff' of age-related eye changes, but occasionally it's a sign of something more serious.
Floaters, flashes, & retinal tears
By Harvard Medical International
Thu 08 May 2008 04:00 AM

Seeing things? Usually, it's just the harmless 'stuff' of age-related eye changes, but occasionally it's a sign of something more serious.

Like the rest of the body, the eyes change as we grow older. Some changes set the stage for serious eye problems, such as macular degeneration and glaucoma. But others are more annoyances than medical problems.

Floaters and flashes are usually harmless, but occasionally, they indicate something more serious.

For example, almost everyone over the age of 50 develops some degree of presbyopia - difficulty focusing on near objects. A pair of reading glasses is the usual remedy.

Many older people also notice visual phenomena called floaters - shapes like dots, clouds, threads, or cobwebs - drifting across their line of vision. Occasional flashes of light are also common.

Floaters and flashes are usually harmless, but occasionally, they indicate a retinal tear - or worse, a retinal detachment, which can lead to vision loss. Treatment of a retinal tear can help prevent retinal detachment, so it's important to know when to see an ophthalmologist and what to expect.

Physiology

An egg white-like substance called vitreous humor or fluid (or simply the vitreous) fills about 80% of the eyeball - a space called the vitreous cavity - and helps to maintain its round shape. Floaters are tiny clusters of cells, flecks of protein, or bits of gel lodged in the vitreous.

What you actually see is the shadow these little clumps cast on the retina, the light-sensitive tissue at the back of the eye that captures images and sends them to the brain via the optic nerve.

Floaters move as your eyes move and seem to dart away when you try to look at them. Most tend to settle below the line of sight, although they don't go away completely. They're usually most noticeable when you're looking at something uniformly bright, like the sky or a white background.

The vitreous is a gel made mostly of water held together by an arrangement of collagen fibers and hyaluronic acid molecules. Some floaters are remnants of embryonic vitreous, but most arise from normal changes that occur with aging. Over time, the vitreous shrinks, tugging on the retina and stimulating photoreceptors that cause flashes.

The pulling may also cause tiny amounts of bleeding, which appear as floaters. Sometimes the vitreous becomes separated from the retina, an event called posterior vitreous detachment (PVD). A PVD can trigger a new onset of floaters and sometimes flashes in the peripheral vision.

PVDs are uncommon before the age of 50 but occur in more than 60% of people over the age of 70. They are also more common in people who are nearsighted (myopic) or who have had cataract surgery, an eye or head injury, or inflammation within the eye. Vitreous detachments usually take a week or more to develop.

Usually they do not threaten vision, but in 15% of cases, they lead to a retinal tear, which in turn may cause a retinal detachment; so if you suddenly see flashes and notice a new onset of floaters, see your ophthalmologist for a thorough eye examination.

Even if he or she finds no problems, your eyes should be re-examined in four to six weeks and earlier, if symptoms increase.

Contact your ophthalmologist immediately if you notice any of these warning symptoms of a retinal detachment:

• flashing lights

• sudden onset of new floaters

• gradual shading of vision from one side (like a curtain being drawn)

• rapid decline in sharp, central vision. This occurs when the macula - the area of the retina responsible for central vision - detaches.

Treating a retinal tear

When the vitreous pulls with enough force to cause a tear in the retina, vitreous fluid can then leak through the hole, detaching the retina from the underlying tissue that nourishes it.

A retinal detachment is quite serious, so it's important to recognize the symptoms.

Retinal tears don't always cause symptoms, and fortunately, those that don't are less likely to lead to retinal detachment. But when they do (as they may with PVDs), early treatment is important to prevent the development of a full-blown retinal detachment.

Studies suggest that such detachments occur in 30% to 55% of people who have a symptomatic tear and that preventive treatment reduces the risk to 1% to 12%.

An ophthalmologist will check for retinal tears by dilating the pupil and examining the internal surfaces of your eye with an indirect ophthalmoscope (a lighted device that is mounted on special headgear).

Because the underlying problem can cause a tear in the other eye as well, she or he will want to examine both eyes. Retinal tears can be repaired in the office with one of the following techniques:

Laser photocoagulation. In this procedure, the ophthalmologist numbs the eye with topical anesthesia (usually anesthetic eye drops) and uses pinpoints of laser light to create tiny burns around any small holes or tears in the retina.

Treatment of a retinal tear can help prevent retinal detachment.

The resulting scar tissue forms a barrier, welding the retina to the back wall of the eye so that it's less likely to become detached. Patients can return to normal activities in about four days.

Cryopexy. This is a freezing treatment, which works, like laser photocoagulation, as spot welding for the eye and is also performed under topical anesthesia. The procedure creates an adhesion that reduces the likelihood a tear will turn into a detachment. Cryopexy can be employed when the tear would be difficult or impossible to reach with a laser.

Fixing a tear in one area doesn't prevent tears from forming in another part of the retina. If you have been treated for a retinal tear with laser or cryopexy, you'll need to have your eyes examined at regular intervals during the year following the initial procedure.

Some retinal tears don't need immediate treatment - watchful waiting may be the preferred strategy - but only a clinician can make that determination.

A retinal detachment (as opposed to a retinal tear) usually calls for surgery to reposition the retina against the back wall of the eye.

Surgery for a retinal detachment

Occasionally, the vitreous gel (the egg white-like substance that fills most of the eyeball) pulls on the retina with enough force to tear it.

This separation of the retina from the back of the eye allows fluid from inside the eye to enter through this tear and detach the retina from the choroid (the nutrient-rich layer underlying the retina). If this rupture is caught and treated early, a retinal detachment may be prevented.

If not treated, the retinal detachment may continue until the retina is nearly totally detached from the back of the eye and maintains a connection only at the optic nerve in the back of the eye and the ciliary body (a ring of tissue that encircles the lens) in the front of the eye.

An ophthalmologist can repair tears that have not yet caused detachment by making tiny burns around the tear with a laser (laser photocoagulation) or applying a freezing probe (cryopexy) to the area, causing scar tissue to form and permanently sealing the tear. Both procedures are performed on an outpatient basis with a local anesthetic.

If the retina has already started to pull away from the choroid and the gap has filled with fluid, the situation may call for a different approach. Surgical options for repairing a retinal detachment include the following procedures:

Scleral buckling. This procedure is usually done in a hospital with general or local anesthesia and may involve an overnight stay. After repairing the tear with a laser or freezing technique, the surgeon wraps a small silicone strip around the outside of the eye (the sclera) to indent it slightly, like cinching a belt, so that the wall of the eye makes contact with the retina.

The silicone buckle is sutured around the circumference of the eyeball and is usually left in place permanently.

Gas bubble. Also called pneumatic retinopexy, this procedure may also be combined with laser photocoagulation or cryopexy.

The doctor injects a gas bubble into the vitreous cavity to push the retina back into place against the inside wall of the eye, block the passage of fluid, and promote adhesion.

The head must be positioned to keep the bubble over the area of the tear (for example, the patient may need to keep his or her head tilted down or to one side or another) for as long as it takes for the retina to reattach - sometimes up to a month or more.

If a gas bubble is placed in your eye, avoid flying or traveling to high altitudes until the doctor says the bubble is gone; a rapid rise in altitude could lead to an increase in the size of the bubble and a dangerous increase in eye pressure.

Vitrectomy. Some complicated cases may require removal of the vitreous humor, a process called vitrectomy.

In this delicate procedure, which is usually performed in the operating room of a hospital or medical center, the surgeon uses microsurgery to aspirate the gel from the eye and saline solution or another substance is inserted as a permanent substitute.

Sometimes a gas bubble is also placed in the vitreous cavity. The eye is covered with a patch until the next day. Patients can usually return to work in two weeks.

This article is provided courtesy of Harvard Medical International. © 2008 President and Fellows of Harvard College.

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