20/20 Vision
A fraction
commonly used to indicate normal vision. A bottom number larger than twenty
indicates diminished vision. For example, a person with 20/400 vision can just
make out an object that is twenty feet away that a person with "normal" vision
could see from 400 feet.
Anti-Reflection
Coating
This type of lens coating provides
exceptional clarity and improves
the performance of your lenses.
These advanced coatings are
easy to clean and improve the
outward appearance of your
eyewear by reducing reflections.
More importantly they improve
the visual performance of your
spectacle lenses by increasing
the amount of light that passes
through the lenses. They
minimize abberation and
annoying surface reflections.
Astigmatism
If the shape of the cornea is perfectly
spherical there is no astigmatism. However, most corneas are not spherical but
rather like the back side of a spoon. If you look at a spoon, you see that the
shape across the spoon is more curved than the shape along the spoon. The
greater the difference between the two curves the more astigmatism. The amount
of astigmatism is measured during an eye examination. Astigmatism can be
corrected with Laser Vision Correction techniques.
Automated Lamellar Keratoplasty (ALK)
A surgical
procedure utilizing a microkeratome to remove a thin section of
corneal tissue. This procedure was used to correct large amounts of myopia and mild to moderate
amounts of hyperopia. This procedure has been replaced by the significantly
more accurate Laser Vision Correction techniques.
Automated Lensometer
The Automated Lensometer measures the power of your existing eyewear allowing the doctors and staff to compare your new prescription to the previous one.
Autorefractor
The autorefractor uses infrared light to measure you vision. This data acts as a second opinion increasing the accuracy of your new eyewear prescription
Cataract
The lens is a clear structure in the eye that slowly grows and opacifies or gets cloudy as we age. When this cloudiness begins to affect vision we call that a cataract.
Cornea
A clear structure that forms a dome over the
iris (colored part of the eye). It is responsible for two thirds
of the focusing power
of the eye, and is the site of most refractive procedures.
Corneal Topography
A test that provides a surface shape map of the front of the eye. Results from this test are useful when fitting contact lenses or considering refractive surgery. This test can also help to detect corneal diseases such as keratoconus.
CV 5000
The CV5000 is an electronic refracting system for determining the focussing power of the eye. It interfaces with the auto-lensometer and auto-refractor. This provides a starting point for the doctor to determine your eyeglass prescription. One of the advantages of this new system is that it allows the patient to see both choices at once. No more one or two.
Diopter
A unit of focusing power of a lens. A two diopter
lens is twice as strong as a one diopter lens. While a 1 diopter lens will
focus light at one meter (39.3inches) a two diopter lens will focus light at
half a meter (19.7 inches). This is because the two diopter lens will bend
or focus a
beam of light more than a one diopter lens.
Excimer Laser
An argon-fluoride laser that emits
ultra-violet light at a wave length of 193 nm. This "cool" laser uses
ultra-violet light to alter the front surface of the eye by breaking intra
molecular bonds in collagen molecules. This laser was originally developed for
use in the microprocessor industry and later found its application in vision
correction.
Focusing Power of the Eye
As light enters our eye, it
must be brought to a focus on the retina in order to perceive a clear image.
About two thirds of the focusing power of the eye comes from the cornea, the
rest comes from the lens inside the eye. As the light enters the eye it is
focused a fixed amount by the cornea. As the light passes through the pupil, the
lens then adjusts the focus a variable amount with the exact amount of focusing
power applied dependent on the distance of the object being viewed. Objects at
near like a book or knitting require more power than distance objects like
movies or traffic signs. Laser Vision Correction adjusts the power of the eye
by changing the focusing power of the cornea.
Glaucoma
Glaucoma is a disease that damages the optic nerve. The damage is thought to occur when pressure in the eye squeezes the nerve fibers as they enter the eye causing an interruption of the flow of nutrients through the nerve fiber. This disease is typically painless and causes a gradual loss of vision. Patients are usually not aware of this vision loss until the disease is quite advanced. Glaucoma is controlled, not cured, with eyedrops and or surgery. Early detection is key.
Hyperopia
Hyperopia or farsightedness is a condition where the eye is too
weak. This occurs when the axial length of the eye is too
short for the focusing system of the eye. Far sighted
individuals see more easily at distance than they do at near.
The natural lens is normally at rest when a person looks at a
distance object, however in a younger hyperopic patient they may
focus this lens to see clearly in the distance. At near the
hyperopic patient must exert additional effort in order to see
objects clearly.
Iris
This structure gives the eye its color. The iris
has a function similar to the iris of a camera. It is capable of adjusting the
size of its opening (the pupil) to allow for varying brightness levels.
Intacs or Intra Corneal Ring Segments (ICRS)
This device is the key element of an Intacs procedure. In this procedure the surgeon creates a two semi
circular channels in the cornea at about 70 percent of the corneal
depth. The surgeon then inserts a semicircular piece of
plastic that flattens the front surface of the cornea by expanding
the periphery of the cornea. This procedure is currently
limited to lower nearsighted prescriptions and is not appropriate
for patients with significant astigmatism. This technique is finding
a new use for patients with keratoconus. In these relatively
rare cases the need for a corneal transplant can sometimes be
delayed with this device sometimes indefinitely.
Laser Assisted In-Situ Keratomileusis (LASIK)
An
advanced laser procedure, this procedure involves making a thin flap on the surface of the
cornea. This flap is then lifted like a submarine hatch, and the exposed
surface is reshaped using the excimer laser. After altering the corneal
curvature, the flap is replaced and adheres without stitches.
This procedure can be used to flatten or steepen the cornea and
allows the correction of myopia, hyperopia, and astigmatism.
Lens
A transparent structure that focuses light rays
which pass through it. There are two structures of the eye that focus light.
The first is the cornea or front surface of the eye that provides about 65% of
the focusing power of the eye. The human lens is located behind the iris and
provides the remaining power for the eye. In younger patients (below about 45)
the lens is able to adjust its power allowing the eye to change its
focal
length from distance to near. As we age the lens becomes
increasingly stiff and looses its ability to adjust from distance
to near.
Macular Degeneration
The center of the retina is called the fovea or macula. This is area of the retina where light falls from an object that you are looking at. When this part of the retina begins to fail, called Age Related Macular Degeneration or ARMD, central vision is disturbed. This can have a devastating effect on every day activities such as reading.
Myopia
More commonly known as nearsightedness, is a
condition of excess focusing power causing light rays to focus in front of the
retina. The excess power can be measured during an eye examination
and is stated in
negative (minus) diopters. Myopia causes blurred distance vision.
Phakic Intraocular Lens
This new technology involves the surgical placement of a small
lens in front of the natural lens of the eye. This
replacement lens is capable of correcting large amounts of
nearsightedness and farsightedness. Early generations of this
product are not capable of correcting astigmatism. This lens
does not affect the ability of the eye to focus at near.
Photo Refractive Keratectomy (PRK)
A surgical procedure
utilizing an excimer laser to reshape the central cornea to a flatter shape for
people who are nearsighted and a more curved surface for people who are
farsighted. PRK techniques can also be used to correct astigmatism.
The PRK procedure does not involve making a flap.
Presbyopia
Is part of the normal process of aging.
People over the age of forty to forty-five begin to lose the flexibility of the
natural lens of the eye. This loss of flexibility limits the ability of the eye
to change its point of focus from distance to near. Everyone experiences
presbyopia, sooner or later. Because of this normal process, people begin to
wear bifocals or other reading correction in their forties. Even those who
never needed glasses require reading glasses. People who have had their vision
returned to normal through refractive surgery will need reading
correction like other people with normal vision. This usually occurs between
the ages of forty and fifty. The excimer laser does not change the ability of
the natural lens to change its focus for better or for worse.
Pupil
The pupil appears as a small black dot in the center of the
iris (the colored part of the eye). The pupil changes its diameter in response
to changes in ambient lighting. Operating much like the aperture of a camera,
the pupil varies the amount of light reaching the retina and the depth of focus
of the eye.
Radial Keratotomy (RK)
A surgical procedure which alters the shape of the cornea by placing microscopically thin
relaxing incisions in the peripheral cornea. This causes the central portion of
the cornea to flatten reducing the power of the eye and correcting myopia. This
technique has been replaced by newer Laser Vision Correction techniques.
Refractive Errors
When the eye does not provide the
correct amount of power for its size, more specifically the axial length, a
refractive error results. When the eye provides too much power, the person is
nearsighted or myopic. When the eye does not provide enough power, then the
person is farsighted or hyperopic. If you are still confused it may help you to
know that the eye requires more power to see things at near so an eye with too
much power (nearsighted) would see things better at near, while an eye with too
little power (farsighted) would see better at far. People who
are nearsighted (eye is too strong) have spectacle lens prescriptions that start
with a minus (-) sign. Their glasses subtract power from the optical
system of the eye. For farsighted or hyperopic patients, the opposite is
true. Their prescriptions start with a plus (+) sign because they must add
power to an eye that is optically weak.
Refractive Surgery
Any procedure which alters the
focusing power of the eye in order to permanently decrease or eliminate
refractive errors.
Retina
The retina lines the inside back surface of the eye.
You could think of this as a piece of cellophane lining the inside a hollow
racquetball. This remarkable tissue converts light energy into nervous impulses and sends
them to the part of the brain which is responsible for turning these
electrical impulses into
images.