Blind World


When Shadows Float Before Your Eyes.





January 25, 2005.
By JONATHAN KOLATCH.




My introduction to floaters came on a sunny September afternoon in the orchard. I was high on a ladder picking Jonagold apples when I felt a pop in my left eye, followed by blurriness. I thought that maybe a branch had slapped across my glasses, dirtying the lens, and I went inside to clean it. But the blurriness - a sort of floating haze - persisted overnight.



After hearing the symptoms, my ophthalmologist, Dr. William Kirber, diagnosed a posterior vitreous detachment, one of several causes of floaters, sensations that many people describe as specks, bugs or cobwebs floating in their fields of vision. In 85 percent of cases, the floaters caused by posterior detachment are mere annoyances, but when they occur suddenly, immediate medical examination is essential.


The most common type of floater is caused by aging. Sitting directly between the lens and the retina is a cavity known as the vitreous or vitreous humor. Its outer boundary is defined by a crust like the skin of Jell-O. The function of the vitreous, which makes up four-fifths of the volume of the eye, is to give it its shape, to be a shock absorber in younger eyes and, some argue, to nourish the inner eye.


The vitreous cavity is filled with a clear, sticky gel that is 99 percent water. The balance consists of strands of a protein called collagen and acidic molecules. With aging, the molecules break down, releasing water that gathers in pockets. At the same time, strands of collagen, normally translucent, bunch into larger opaque fibrils or wispy sheaths.


It is these clumps of protein and water, of varying shape, meandering unpredictably within the vitreous cavity, that are the source of most floaters. As light passes through the vitreous, floaters cast annoying shadows on the retina, the eye's movie screen. Most adults experience this type of floater at some time.


Much less common is a second type, floaters caused by specks or globs of blood, the result of bleeding brought on by rips in the retina or as a complication of diabetes.


In each case, the brain almost always gets used to the floaters or they migrate out of view. The third kind of floater, however, caused by a posterior vitreous detachment, is far more likely to impair vision.


In posterior vitreous detachment, as the fluid from the degenerating vitreous gel moves between the skin of the vitreous and the retina, the vitreous separates from the retina, usually near the optic nerve. As the vitreous tears from the retina, a fragment of tissue remains attached to the receding vitreous.


Because the tissue is tethered to the vitreous, this fragment, known as Weiss's ring, sometimes remains in the central field of vision. Under the ophthalmologist's slit lamp, Weiss's ring resembles a blob of oil floating on water under a lattice of blood vessels. How disabling this vitreous detachment is depends on how far the vitreous peels from the retina.


Posterior vitreous detachments occur in fewer than 10 percent of people under 50, but in 60 percent of people over 70. In 10 to 15 percent of detachments, as the vitreous separates, it tears the retina, requiring immediate treatment, either with a laser or through surgery.


The question is, When are floaters alarming and when are they benign?


"Almost everyone has floaters," Dr. Jim Garrity, a Mayo Clinic ophthalmologist, stresses in a periodic lecture he offers for general practitioners. "It is the sudden onset of the tiny ones accompanied by flashes of light that you have to be concerned about."


Many ophthalmologists underrate floaters because they cannot be visualized precisely and because the potential complications from removing the vitreous, the only sure remedy, heavily outweigh the benefits, some experts say.


Dr. William Schiff, a retinal surgeon at Columbia and the lead author of a 2000 article in the journal Retina on vitreous removal to relieve disabling floaters, has called the surgery "eminently doable but universally discouraged." Surgical complications include the almost certain development of cataracts, bleeding and retinal detachment as the vitreous is peeled from the retina.


Still, in rare instances surgery is necessary.


Dr. Stanley Chang, chairman of ophthalmology at Columbia, says that in many cases eye doctors do not appreciate the effect floaters have on patients' lives.


In screening patients for surgery, Dr. Chang evaluates the floaters' impact on reading speed, the ability to read signs and newsprint, the ability to play sports and driving ease. He says he follows patients for a year to see if the surgery, which he performs only once every year or two, is really needed.


Dr. Chang sometimes refers patients to an article written by a retinal surgeon, Dr. Travis A. Meredith, about his own trials with floaters. "When patients say that their floaters are driving them crazy," Dr. Meredith confesses, "it is not such an exaggeration as I had imagined."


Although most ophthalmologists agree that floaters are almost always best left alone, they rank high on the list of patient complaints, and many eye surgeons offer a less drastic procedure, laser surgery, to break up the clumps. But a recent study found that in no cases were patients' symptoms completely alleviated by laser surgery. Dr. Chang and Dr. Schiff note that floater fragments that result from laser treatment are often no improvement over the floaters themselves.


It is not practical to relieve floaters by mechanically sucking out the vitreous contents, filtering it and returning it or a substitute fluid to the cavity, Dr. Chang explained. The obstacle, he said, is that vitreous gel appears to block oxygen from reaching the lens. Any disturbance of the vitreous is likely to bring on cataracts.


Thus, for the time being, the best candidates for surgery to relieve floaters are those who have already had cataracts removed.


A promising drug, just arriving on the market, may point the way to eventually treating disabling floaters more effectively. Vitrase, by ISTA Pharmaceuticals, is a natural enzyme made from ram testes that the company claims can induce the vitreous to separate from the retina, removing the floaters from the visual field.


At higher doses, Vitrase is said to liquefy the vitreous contents, making it possible to readily suck out the fluid. Dr. Chang's reservation about the drug is that, in addition to loosening vitreous material, excess dosing may also dissolve weak spots in the retina. If the dosing problem with Vitrase is resolved and a way is found to prevent vitreous intervention from inducing cataracts, disabling floaters may become a thing of the past.


In the meantime, Dr. Chang counsels people who suffer from floaters to alert their eye doctors to their problems before being fitted with corrective lenses. Especially with high prescriptions, floaters can obstruct parts of letters on the eye chart, making it harder to measure vision.




End of article.



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