Inside the Eye
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Five options for laser eye surgery
Only a few years ago, having imperfect vision simply meant that you
went to the eye doctor, got fitted for glasses or contact lenses, and
went on your merry way. But now, there's an array of laser surgeries
to choose from, each with a slightly different procedure to accommodate
particular vision problems.
In general, laser eye surgery modifies the cornea, the clear covering
of the front of the eye that bends (or refracts) light rays as they enter
the eye. For clear vision, the cornea must have the correct shape to
focus light rays precisely on the retina at the back of the eye. If the
cornea is too steep, too flat, or irregular in shape, the image focuses
either in front of or behind the retina hence, blurry vision.
Eyeglasses or contact lenses can compensate for this problem by increasing
or reducing the angle of light as it enters the eye.
In 2000 the U.S. Food and Drug Administration approved a procedure,
laser thermal keratoplasty (LTK), and it approved another in April 2002
called conductive keratoplasty (CK), which is specifically used to correct
farsightedness. The most common procedures are photorefractive keratectomy
(PRK) and Laser-Assisted In Situ Keratomileusis (LASIK). As time and
experience advances, these techniques become ever more precise and predictable.
The following chart will help you sort out this alphabet soup of laser
||How It Works
| Laser Thermal Keratoplasty (LTK)
|| Farsightedness (Distant objects are clear,
but the eye can't focus properly on close ones.)
|| Steepens the slope of the cornea, so light
can focus on the retina.
|| A laser reshapes the cornea without touching
the eye's surface by gently heating the collagen at the periphery
of the cornea.LTK takes only a few minutes.
|| Most people feel very little discomfort
during the surgery. LTK is best suited for people over 40 who require
only reading glasses and whose prescription has changed very little
over the last six months. How long the correction lasts depends
largely on the amount of correction needed and the patient's age.
| Conductive Keratoplasty (CK)
|| Age-related farsightedness (As we age,
the lens of the eye becomes less flexible, making it difficult
to focus on close objects.)
|| Like LTK, CK steepens the cornea's slope.
|| CK typically lasts less than a minute.
Short bursts of radio waves shrink the cornea's collagen fibers
to reshape it.
|| While this technique appears to be generally
effective, it can take a few months before the full benefits are
| Nearsightedness (Close objects are clear,
but the eyeball is too long or the cornea curves too steeply to
sharply focus on distant objects.)Astigmatism (The cornea is irregularly
shaped, and vision may be blurry at all distances.)
|| Flattens (or reduces the curvature of)
|| A laser removes a thin layer from the center
of the cornea by vaporizing corneal tissue in very precise amounts.
|| This procedure takes only a few minutes
and is usually performed with local anesthetic eye drops. Most
people can return to their normal routines in a day or two.
| Laser-Assisted In Situ Keratomileusis (LASIK)
|| Severe nearsightedness, farsightedness,
|| Combines surgery and laser to reshape the
|| The surgeon cuts a flap in the cornea using
a knife, and then reshapes the cornea's middle layer with a laser.
The flap heals over that layer.
|| While a more complex surgery than PRK,
LASIK requires less recovery time. Many patients can see well enough
to drive home after surgery. Candidates for LASIK should be at
least 18 years old and have stable vision and no abnormalities
of the cornea or external eye.
| Radial keratotomy (RK)
|| Moderate or mild nearsightedness
|| Reduces the curvature of the cornea.
|| The doctor makes small, radial incisions
in the periphery of the cornea to flatten it.
|| The incisions can weaken eye structure.
No other procedures to improve vision can be done after RK. Candidates
should be at least 18, with stable vision and no corneal or external
June 2002 Update
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New Drugs Have Had Impact on Glaucoma
Glaucoma strikes nearly 4 million people in the United
States, and is a major cause of blindness. It is characterized by excessive
fluid pressure in the eye, which can damage the optic nerve. The good
news is that when caught and treated early, vision can usually be spared.
Glaucoma can be treated either with medications or with surgery. Until
recently, physicians primarily treated glaucoma with topical ß blockers,
which reduced the amount of fluid, called aqueous humor, produced
in the eye. When drugs were not effective, a surgical procedure would
be used to improve drainage of the fluid. Over the past five years, however,
three new classes of glaucoma medications have come into use: prostaglandin
analogues (latanoprost), which remove aqueous humor through the uveal
tissues; topical carbonic anhydrase inhibitors (dorzolamide), which reduce
the amount of aqueous humor produced in the eye; and α-2 agonists
(brimonidine), which decrease production of aqueous humor and increase
Investigators in Scotland set out to determine the impact that these
new classes of drugs have had on the treatment of glaucoma. They reviewed
a national registry that recorded the prescription and surgery statistics
for Scotland from 1989 through 1999. The researchers found that the number
of surgical procedures performed per 1,000 glaucoma patients increased
between the years 1989 and 1994, then decreased by 45.9% from 1994 through
1999. During the same period (19941999), the number of medications
prescribed per 1,000 glaucoma patients increased by 24.9%, mostly due
to a rise in the prescription of the new drug classes.
Although the new drugs have altered the medical and surgical treatment
of glaucoma, the researchers note that it is still too early to tell
whether the new medications will prevent the need for surgery, or only
March 2002 Update
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New Treatment for "Wet" Age-Related
The U.S. Food and Drug Administration (FDA) has recently
approved verteporfin (Visudyne) for the treatment of age-related macular
degeneration. Verteporfin is used to treat the "wet" (or "classic")
form of this disease in which well-defined blood vessels proliferate
beneath the retina. These vessels leak blood and fluid, which causes
scarring and loss of vision in the center of the eye. Peripheral vision
remains unimpaired. Affected individuals experience a sudden worsening
and distortion of their central vision and may become legally blind within
a few weeks or months of the time symptoms first appear. Only 10% of
age-related macular degeneration cases are of this type.
The new treatment is applied in two stages. First, verteporfin, a photosensitive
dye, is injected intravenously into the bloodstream over a 10-minute
period. The dye is picked up by the abnormal blood vessels behind the
retina. The physician then directs a "cold" laser into the
eye. This activitates the dye and triggers clotting and constriction
of the abnormal blood vessels without damaging the retina. In many people,
the effects of this therapy last only a few months, but the procedure
can be repeated every three months if necessary.
In a recent clinical trial comparing treatment with verteporfin to treatment
with a sugar-water solution (placebo) and the same phototherapy, the
patients treated with verteporfin had significantly better outcomes than
those treated with placebo. At the 12-month follow-up visit, 61% of the
verteporfin group had lost fewer than three lines of vision compared
with 46% of the placebo group. The benefit was even greater for those
with the purely
"classic" form of the disease 77% of the verteporfin
group versus 27% of the placebo group. No benefit was seen in members
of the verteporfin group who did not have primarily "classic"
Side effects of verteporfin treatment include headache, visual disturbances,
injection site reactions, and infusion-related low back pain. A small
percentage of patients (1%4%) experienced severe vision loss within
a week after treatment, but this loss of vision was not always permanent.
Patients who undergo this therapy must avoid exposing their eyes and
skin to direct sunlight or bright light indoors for five days so as not
to activate any traces of verteporfin still in the bloodstream.
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