||caring for your
What Is "20/20" Vision?
Firstly, what do you think of when I say normal vision? If you're
like most people the first thing that comes to your mind is 20/20
eyesight. But what does 20/20 eyesight really mean?
In 1862, a man named Snellen devised a testing system to
determine people's eyesight. He asked people to stand at 20 feet and
through experimentation discovered the smallest sized letter that
most people with good eyesight could see. He called this a size 20
letter and the vision was recorded as 20/20. At the time it was
thought that this was all you needed in the way of vision. Actually
it was a great breakthrough at the time. Now, over 130 years later,
we have made quantum leaps in our knowledge of the human visual
system. Yet, if you walk into many schools and pediatrician's
offices and even some eye doctor's offices the old 20/20 standard is
still the only way that vision is tested.
20/20 eyesight tells us how well we can see to drive or to see a
blackboard. It tells us if we can see a newspaper or a computer
screen. But there are many things 20/20 eyesight will never tell us.
It will never tell us if you or your child:
- sees clearly all day long
- can focus back and forth to the blackboard and book
- sees single rather than double
- can read without getting a headache
- can follow words on a page without losing his place
- can read without wanting to fall asleep
- has healthy eyes
Remember the vision chart that hangs in every eye specialist's
examining room? The one with a big "E" at the top? That's the basis
for measuring 20/20 vision. You are usually asked to identify the
letters at a distance of 20 feet. Then you'll be asked to read lines
on the chart with one eye and then the other. If you have 20/20
vision, you see at 20 feet what a person with normal vision would
see at 20 feet. If you have 20/40 vision, you see at 20 feet what a
person with 20/20 vision would see at 40 feet. And, if you're one of
the lucky ones (e.g., 20/15), you can see at 20 feet what others
would have to move closer (at 15 feet) to see.
Understanding Your Prescription
the refractive power of your eye. Your doctor uses this measure to
identify the amount of refractive error in your eyes. Diopter values
range from -14 to +14, depending on how significant the error is. A
negative diopter value indicates myopia and a positive diopter value
signifies hyperopia. And the larger the diopter value,
whether it's a positive number or a negative number, the greater the
refractive error. Someone with 20/20 vision will likely have
something close to zero diopters. If you've ever received a
prescription for glasses, it most likely included diopter readings
for each of your eyes. In the end, the most important thing to know
is that diopters are a precise way of measuring how much vision
correction you need, whether it's through laser eye surgery or
glasses and contact lenses.
More About Your Eyes
Over half the
population in the United States has common vision problems.
Generally, people with vision problems are nearsighted, farsighted,
and/or have an astigmatism.
There's another common condition
called presbyopia, a condition that many people develop as they age.
Presbyopia causes everything a person sees
to be a bit fuzzy, which is why many of us require reading glasses.
Unfortunately, there's no surgical remedy for presbyopia, so for
now, we will probably continue to need those reading
Until recently, most people addressed
nearsightedness, farsightedness and astigmatism by wearing glasses
or contact lenses. But today, people are finding an alternative to
glasses or contact lenses.
Everywhere, more and more people -
perhaps you - are considering a procedure known as laser eye surgery
or LASIK, Laser In-situ Keratomileusis, which means reshaping
your cornea, from within, using a
Laser vision correction uses quick bursts of excimer laser beams to reshape the cornea,
helping to eliminate the corneal errors or aberrations that change
our ability to focus as clearly as we should. When errors are
eliminated or reduced, images will focus more directly on your
retina - the back of the eye - where they should.
best way to understand vision problems - and how reshaping the
cornea can help correct them - is to start with learning some basics
about the human eye.
What you've always heard
is true: the human eye really does work like a camera. In normal
vision, light rays coming through the cornea and lens converge and focus perfectly and,
finally, focus directly onto the retina, at the back of the eye. The
retina sends the "signals" to our brain, which registers
"Poor vision" or vision
problems are primarily caused by refractive errors. These "errors"
occur when the cornea is shaped in such a way that the images we see
do not focus directly on the retina.
Poor vision caused by
refractive errors was treated with glasses, contact lenses, or
various refractive correction procedures.
Common Vision Problems
You see close
objects more clearly than those at a distance. When you're
nearsighted or myopic, images in the distance will seem blurry. Your
eyes may be longer than normal or the cornea may be too curved, so
images focus in front of the retina. People who are nearsighted see
near objects more clearly than distant ones. The nearsighted eye is
longer than normal so light rays converge and focus before they
reach the back of the eye.
who are farsighted see distant objects more clearly; however, all
objects may be blurred. The farsighted eye is shorter than normal
and light rays do not have enough space to converge and focus. When
you are farsighted or hyperopic, images that are near (the words on
a page, for example) appear to be more blurry than images in the
distance. Your eyes may be too short, or your cornea too flat, so
images focus behind the retina.
Astigmatism is the
inablility to focus clearly at any distance because of an irregular
or misshapen cornea. Light rays focus at various points within the
eye causing distorted vision. Astigmatism is often combined with
nearsightedness and farsightedness. This happens because the front
part of your eye (corneal is slightly irregular in shape.
Astigmatism, another cause of poor vision, occurs when the eye is
"football" shaped. Here, images focus on more than one point in
front of, or behind the retina. The result is that all images,
whether near or far, may be blurry. In mixed astigmatism, symptoms
of myopia or hyperopia are combined, resulting in the overall
inability to see images clearly.
Presbyopia is a
normal, age-related change that occurs as we approach our
mid-forties. The lens of the eye becomes less elastic and loses its
ability to change focus, making it difficult to see up-close. As
eyes age, they will experience presbyopia. A natural part of aging
begins to blur your reading and near vision by about age 40-45 and
gradually worsens. Presbyopia, a physiological weakening of vision
due to natural aging, cannot be corrected by LASIK. As mentioned
previously, there are currently no approved surgical procedures that
correct this condition.
Now that you know the basics about
your eyes, and poor vision, you're better equipped to address your
eye problem(s). Come in and we'll see how else we can help in
correcting or treating your vision problems. This site is dedicated
to assist you in informing you on
* A note on astigmatism:
You may have heard
or been told that astigmatism cannot be treated. Today, with the
right technology, it can. The FDA has approved select lasers to correct a
broad range of conditions. In some instances, that range includes
astigmatism associated with either myopia or hyperopia.