Reading Glasses, as Inevitable as Death and Taxes. Or Are They?
By ABIGAIL ZUGER
he quick fix of laser surgery may be
freeing more and more people from eyeglasses and contact lenses, but no matter
how successful the surgery, their liberation
is only temporary.
Sooner or later the need
for reading glasses descends on all adults --
and from those devices there is still no quick
escape.
Human bodies age at enormously different rates with one single exception: the fine-focus mechanism of the human eye. The
lens of the eye and the muscle that surrounds it tick away the passage of time like
tiny atomic clocks, slowly deteriorating
with a precision so immutable that ophthalmologists say they can accurately estimate
patients' ages to within a few years by
measuring their ability to focus close up.
The loss of close-up focus is known as
presbyopia, from the Greek for "elderly
vision," but the process actually begins in
very young adulthood.
Children with normal
vision can generally focus on objects an inch
or so from their eyes, but they lose that
ability as teenagers, and by the age of 50 or
so, when the eyes can focus no closer than a
yard or two away, almost all adults in the
world need glasses to read newspapers or
thread needles.
Those who claim they do not, researchers
say, are simply unusually skilled at "blur
interpretation," fooled by good guesswork
into thinking they are exceptions to a universal biological rule.
Presbyopia is thought to represent not so
much a sign of approaching decrepitude as
a leftover feature of primate life, when
scanning for food or predators on the horizon was a more important survival task for
adults than was any close-up work.
Remarkably, though, for such a longstanding and uniform feature of human
biology, scientists are still not sure exactly
what causes presbyopia or what might reverse it.
And for the last five years, they have been
arguing heatedly over the risks and the
merits of an experimental surgical procedure, scleral expansion surgery, that, despite a host of scientific objections, appears
to fix it.
"It's extremely difficult to study the internal structures of the eye," said Dr. Adrian Glasser, an expert in the physiology of
the eye at the University of Houston College
of Optometry in Texas.
"It's such a finely
regulated organ that many of the technologies that have been available to study it
have in one way or other disrupted the very
thing we're trying to study."
Dissections of human specimens have
provided only partial snapshots of the focusing process, while animal research is of
limited help because few animals focus the
way humans do.
The lens of the eye is suspended in the
eyeball right behind the iris, connected by a
halo of fibers to a ring of circular muscle.
The lens, the fibers and the muscle itself all
show changes with the passing years, but
exactly which of these changes drives the
loss of focusing ability is disputed.
The lens is the best-studied part of the
system. A protein-filled disk, it derives from
the same type of cells as do the skin and the
hair and, like them, continues to grow
throughout life. Unlike other continuously
growing structures, though, the lens cannot
shed its older cells, or blindness would result. Instead, it slowly gets bigger and
thicker, bulging forward into the fluid-filled
space that separates it from the iris.
According to the principles of optics, the
bulging curvature should make the lens
focus better and better with advancing
years.
The fact that exactly the opposite
occurs means that other powerful factors
are operating too, and the clue to presbyopia
lies with them.
Many scientists think that the most important factors are the age-related changes
that take place within the lens proteins,
making the lens harder and less elastic with
the years.
"The proteins in the lens of an adult are
decades old," said Dr. Jane F. Koretz, a
professor of biophysics at Rensselaer Polytechnic Institute in Troy, N.Y.
"They are
even older than we are, because the first
ones were laid down before we were born.
In
no other part of the body is that the case.
Everything else gets replaced."
The protein molecules in the aging lens
slowly change in ways that make them bend
light less, Dr. Koretz said.
Thus, although it
is more spherical, an elderly lens is less and
less able to focus the light from nearby
objects.
Age-related changes also take place in the
muscles surrounding the lens. Most scientists agree that these muscles do not become weak with age -- it would make no
sense for one isolated muscle in the body to
slowly give out while all the others continue
to work perfectly well.
A recent study using
high-resolution magnetic resonance to photograph the eye muscles confirmed that the
muscles still contracted powerfully in older
people who could not focus up close.
But the geometry of the fibers connecting
the muscle to the lens shifts as the lens
grows with age, and the fibers themselves
appear to harden and become less elastic, a
process that also interferes with the ability
to focus.
Exercises purporting to "strengthen" the
lens muscles are purposeless, Dr. Koretz
said, since the muscles are already strong:
it is their position and fibrous attachments
that may hamper their ability to move.
If not exercise, then, can any measures
help the owner of two aging eyes elude
reading glasses?
Some people find that a satisfactory solution is the creation of "monovision," in
which one eye is manipulated to focus well
at reading distances (usually with a contact
lens or an intraocular lens placed after
cataract surgery), while the other focuses
for distance.
People instinctively grow to
favor one eye or the other for different
tasks.
But while some people are delighted
with this solution, Dr. Koretz said, others
are plagued by dizziness or nausea, or miss
the depth of vision they once had.
Finding a better fix for presbyopia is
rapidly becoming the Holy Grail of experimental ophthalmology, especially as researchers and entrepreneurs begin to calculate the profits that might accrue from
curing an annoyance affecting every single
adult in the population.
But the basic disagreements as to why the
process occurs have meant that viable solutions are slow to emerge, and are extremely
controversial when they do.
Among the most disputed to date is scleral expansion surgery, a procedure devised
by Dr. Ronald Schachar, a Texas ophthalmologist and physicist, in the early 1990's.
A maverick who has argued that much of
what scientists think they know about the
focusing mechanism of the eye is actually
untrue, Dr. Schachar holds that presbyopia
develops only because, as the lens of the eye
swells with age, the muscles and fibers
surrounding it grow lax, and the system can
no longer work effectively.
By stretching the system out again, Dr.
Schachar says, presbyopia can be easily and
permanently reversed.
He claims to restore
tension to the muscle and fibers by surgically implanting four small curved pieces of
plastic in the white of the eye a few millimeters from the iris, which, he says, re-establish an effective working distance between
the lens muscles and the lens.
His technique has evoked howls of protest
from physiologists who point out that it
ignores decades of solid experimental evidence implicating age-related changes within the lens itself as key causes of presbyopia.
"The scientific community never took
scleral expansion surgery seriously," Dr.
Glasser said.
But a few hundred patients who have
volunteered for the surgery over the last
decade in Mexico, Canada and Europe have
stymied the procedure's critics with reports
that the surgery does indeed seem to restore
their ability to see up close.
In March, the Food and Drug Administration approved preliminary trials of the operation at six sites in the United States, including the New York Eye and Ear Infirmary in
Manhattan, where Dr. Barrie D. Soloway,
co-medical director for vision correction,
will head the studies. Dr. Stephan D. Plager,
60, an ophthalmologist in Santa Cruz, Calif.,
is also among the investigators who are to
take part in the evaluation of surgical expansion surgery.
In early May, Dr. Plager
himself became a patient, undergoing the
procedure in both eyes.
Two days later, he said, he was performing cataract surgery in his office, and 10
days later, vision still a little blurry but
"getting clearer every day," he cheerfully
read passages from his local newspaper to a
reporter over the telephone.
"I can't tell you how excited I am," he
said.
"I haven't seen this well since I was
35."
Familiar with all the reasons that his
surgery should not work, Dr. Plager said
only that while the theory behind the procedure might be flawed, the end result was
hard to ignore.
"The proof that it works will ultimately be
in the scientific studies," he said, "but the
proof as far as I'm concerned is already on
the table.
I'm not so courageous -- I'm more
of a pragmatist than courageous.
I just
wanted to get rid of the glasses."
