Glossary of Terms
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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."
Aspheric A type of bifocal lens in which the lens power changes
gradually, from the center to the edge of the lens
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
Daily wear contact lenses Contact lenses designed to be worn only
during waking hours; removed, disinfected and stored for the next
day's use
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.
Depth perception The ability to judge the relative distance of objects
and the spatial relationship of objects at different distances.
Disinfecting solution An agent that kills surface bacteria and microorganisms
on contact lenses
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.
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)
Extended wear contact lenses Contact lenses designed to be worn
round-the-clock for intervals of one to seven days.
Farsightedness See Hyperopia
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.
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.
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.
Intraocular lens (IOL) Plastic lens implanted in place of the crystalline
lens (either behind cornea or behind the iris) during cataract surgery
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
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.
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.
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.
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.
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.
Oxygen permeability The amount of oxygen diffusing through a given
amount of lens material in a given amount of time, under specified
testing conditions
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.
PRK see Photorefractive Keratotomy below
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).
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.
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.
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.
Saline solution A sterile salt solution used in cleaning, rinsing,
and sometimes storing of contact lenses
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.
Strabismus The inability of one eye to obtain binocular vision with
the fellow eye; usually due to imbalance of the muscles of the eyeball
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.
Tonometry A standard eye test that determines the fluid pressure
inside the eye. Elevated pressure is a possible sign of glaucoma.
Toric lenses Contact lenses designed to correct astigmatism by bearing
two different optical powers at right angles to each other
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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