| Amblyopia (am-blee-oh'-pee-ah) |
Decreased vision in an eye that is not correctable with optical
devices and that exists without detectable disease or physical
abnormality to the eye or visual pathway. Often associated with
strabismus. Commonly referred to as "lazy eye." |
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| Aspheric |
A type of bifocal lens in which the lens power changes gradually,
from the center to the edge of the lens |
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| Astigmatic Keratotomy (AK) |
is a surgical procedure performed to correct
astigmatism. To correct astigmatism, the number, angle, and
distribution of the incisions will vary from patient to patient,
depending upon the degree and axis (location) of the astigmatism. |
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| Astigmatism |
Astigmatism is characterized by an irregularly shaped cornea
that causes light images to focus on two separate points in the
eye, creating a distorted image. Symptoms range from visual discomfort
in mild cases, to severe blurring and distortion similar to a
reflection in a fun-house mirror. |
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| Automated Lamellar Keratectomy (ALK) |
is a relatively new procedure performed for extremely nearsighted
patients. In this procedure, a flap of corneal surface tissue is
folded back, a layer of the central corneal tissue is removed, and
the surface flap is replaced.
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| Bifocal/multifocal contact lenses |
Contact lenses with two or more viewing zones, with part of the
lens designed for seeing distant objects and another part for seeing
near objects.
Click here for a detailed description of the different
types of bifocal contact lenses.
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| Bifocal glasses |
Spectacles with two viewing zones, one on top and one on the bottom
for seeing both near and far objects. Traditional bifocal glasses are
generally recognized by a well-defined visible line separating the
two viewing zones. Invented in 1784 by Benjamin Franklin.
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| Cataract |
A clouding of the crystalline lens within the eye, causing reduced
visual acuity. Cataracts can be surgically removed and replaced
with an intraocular lens implant, restoring vision.
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| Color blindness |
A nonspecific term for congenital or acquired impairment of color
discrimination. Technically it is an incorrect term, as most individuals
who are color "blind" see colors; they just have difficulty
distinguishing certain colors from others. A more precise term is
"color vision deficiency." It seems that more males are affected,
with 7% of males showing this deficiency, and only about 0.5% of
females. Color vision deficiency is not a disease or degenerative
condition, though occasionally an acquired color vision deficiency
may be a symptom of other health problems.
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| Contact lens |
A thin plastic lens designed to fit over the cornea, usually for
the correction of refractive error.
Click here for more information on the
TYPES and BENEFITS on contact lenses.
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| Cornea |
The transparent surface that covers the pupil and iris (like a
watch crystal), and provides most of the eye's optical power.
Contact lenses are worn over the corneal surface.
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| Crystalline lens |
The natural lens of the eye, a transparent structure suspended
behind the iris. Focuses light rays on the retina and changes
shape to change the focus of the eye for different distances
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| Daily wear contact lenses |
Contact lenses designed to be worn only during waking hours;
removed, disinfected and stored for the next day's use
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| Deposits |
Accumulations of substances, usually tear film components
(protein), onto the contact lens surface and/or in the lens
material. Types include protein, mucus, lipid, inorganic and
soilant. See solution.
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| Depth perception |
The ability to judge the relative distance of objects and the
spatial relationship of objects at different distances.
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| Disinfecting solution |
An agent that kills surface bacteria and microorganisms on
contact lenses
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| Disposable contact lenses |
Defined by the U.S. Food and Drug Administration as a contact
lens that is used one time and discarded. These can be either
worn for a single day or, if they are also "extended wear" lenses,
up to seven days, depending on wear schedule prescribed by the
eyecare professional. Any lens that is intended to be removed
from the eye, cleaned, rinsed, disinfected, and reinserted does
not qualify for inclusion in this category under the FDA definition.
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| Emmetropia |
The condition generally known as "normal vision" where light rays
from distant objects are focused on the retina so that vision is
sharp and clear (20/20)
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| Extended wear contact lenses |
Contact lenses designed to be worn round-the-clock for intervals
of one to seven days.
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| Farsightedness |
See Hyperopia
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| Glaucoma |
A condition in which the pressure inside the eye is elevated
to a point that can damage the optic nerve and cause a loss of
peripheral vision, or blindness. Read more.
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| Frequent & planned replacement contact lenses |
General term used to refer to contact lens regimens in which lenses
are replaced on a planned schedule, most often every two weeks,
monthly or quarterly.
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| Hyperopia (farsightedness) |
Hyperopia (farsightedness)
Hyperopia occurs when the eyeball is too short from front to
back, or the eye's focusing mechanism is too weak, causing light
rays to be focused behind, rather than on the retina. People with
hyperopia have difficulty seeing objects close up.
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| Intraocular lens (IOL) |
Plastic lens implanted in place of the crystalline lens (either
behind cornea or behind the iris) during cataract surgery
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| Iris |
The round, pigmented membrane surrounding the pupil of the eye,
having muscles that adjust the size of the pupil to regulate the
amount of light entering the eye
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| LASIK |
Common abbreviation for laser-assisted in situ keratomileusis. LASIK
is a kind of laser eye surgery designed to improve focus by altering
the shape of the cornea. To perform the procedure, a qualified
ophthalmologist uses a microkeratome to cut a circular "protective"
flap to expose the inner layers of the cornea, which are reshaped
with the laser. This procedure has been dubbed "flap-and-zap". To
complete the procedure, the ophthalmologist then repositions the flap.
This last step is important, for if done incorrectly, it can lead to
scarring and optical distortion.
Click here for a more detailed discussion of laser surgeries.
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| Myopia (nearsightedness) |
Myopia is a condition which occurs when the eyeball is too long,
or the eye's focusing mechanism is too powerful (cornea and lens),
and light rays are focused in front of the retina. People with this
condition can see clearly up close but not at a distance.
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| Ophthalmologist (MD) |
Medical doctors (MD or osteopath) uniquely trained to diagnose and
treat all disorders of the eye. An ophthalmologist is trained in all
aspects of eyecare--medical, surgical and optical.
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| Optician |
A paramedical professional who manufactures and dispenses eyeglasses
and helps in the selection of frames. The optician may also dispense
and/or fit contact lenses, depending on individual states' licensing
practices.
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| Optometrist (OD) |
State-licensed health care professionals who diagnose and treat eye
health and vision problems. An OD can prescribe glasses, contact
lenses, engage in low vision rehabilitation and vision therapy,
have the authority to prescribe ophthalmic
medications and perform certain surgical procedures. Optometrists
hold the doctor of optometry (OD) degree.
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| Oxygen permeability |
The amount of oxygen diffusing through a given amount of lens
material in a given amount of time, under specified testing conditions
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| Presbyopia |
This is a condition that occurs as the eye's lens grows older
and begins to lose some of the elasticity needed to switch
focus between viewing near and far objects. Also known as
"aging eye," presbyopia actually starts at about age 10, although
most people do not begin to experience the effects of presbyopia
until their forties. As the eye's lens continues to lose its elasticity,
the eye takes longer to adjust between objects such as the road and
the speedometer. For more on presbyopia,
click here.
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| PRK |
see Photorefractive Keratotomy below
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| Photorefractive Keratotomy (PRK) |
Using an excimer laser with power controlled by computer, PRK
is designed to change the shape of the cornea to reduce vision
problems. The laser vaporizes microscopic slivers from the outer
layer of the cornea to flatten it. The flattening of the cornea
is intended to correct myopia (nearsightedness) and astigmatism
(uneven curvature of the cornea that distorts vision).
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| Radial Keratotomy (RK) |
Once the most common type of refractive surgery, RK is now
considered the riskiest of all corrective eye surgeries. During
RK surgery, a number of spoke-like incisions are made on the
surface of the eye with a small diamond-tipped blade to flatten
the cornea so light rays focus directly on the retina. The procedure
is designed to correct or reduce nearsightedness.
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| Retina |
The thin nerve tissue in the back of the eye. It receives an
image from the lens, and transforms this image into electrical
impulses that are carried by the optic nerve to the brain for
interpretation.
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| Rigid gas permeable lenses, or RGPs |
(also known as oxygen permeable lenses)
RGPs consist of a durable plastic that transmits oxygen. Because they
don't contain water, RGPs resist deposits and are not prone to
harboring bacteria.
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| Saline solution |
A sterile salt solution used in cleaning, rinsing, and sometimes
storing of contact lenses
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| Snellen Chart |
A standardized test chart introduced in 1862 by Dutch ophthalmologist
Hermann Snellen to measure visual acuity. Visual acuity is expressed
as a fraction (e.g. 20/20) in which the numerator denotes the testing
distance and the denominator indicates the distance at which a person
with normal eyesight can read the letters on the chart. For example,
if the smallest letters that the person being tested can see are on
the "20/40" line, it means a person with normal eyesight can see these
same letters at a testing distance of 40 feet.
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| Strabismus |
The inability of one eye to obtain binocular vision with the fellow
eye; usually due to imbalance of the muscles of the eyeball
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| Therapeutic contact lenses |
Contact lenses designed to aid in protecting and helping a sick
eye to heal. These unique lenses are frequently combined with
precise medication delivery schedules to heal the eye.
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| Tonometry |
A standard eye test that determines the fluid pressure inside the
eye. Elevated pressure is a possible sign of
glaucoma.
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| Toric lenses |
Contact lenses designed to correct astigmatism by bearing two
different optical powers at right angles to each other
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| Visual acuity |
Expressed as a fraction (e.g. 20/20) in which the numerator
denotes the testing distance and the denominator indicates the
distance at which a person with normal eyesight can resolve the
letters on the chart
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