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Glossary
Add Powers
In multifocal lenses, the part of the lens that corrects for near
vision.
Astigmatism
A common disorder in which one or more of the eye's refractive
surfaces (i.e., cornea, lens) is not symmetrical. Astigmatism
causes a perceived image to become distorted or blurred.
Autorefractor
A computerized screening device designed to detect abnormalities
of vision (e.g. nearsightedness, farsightedness, astigmatism).
Axis
In correcting for astigmatism, the cylinder power determines how
much correction and the axis determines where the correction goes.
Base Curve
The front curve on a lens.
Biomicroscope
Known as a slit lamp, this device is used to closely examine
external parts of the eye to detect degenerative changes in the
cornea and is also useful in routine contact lens evaluation.
Bridge
The area of the frame-front that rests on the wearer's nose.
Computer Vision Syndrome
CVS is caused by our eyes and brain reacting differently to
characters on the screen than they do to printed characters. If
you spend more than two hours each day in front of a computer
screen, you likely experience some symptoms of computer vision
syndrome or CVS. Including: headaches, loss of focus,
burning/tired eyes, double vision, blurred vision and neck and
shoulder pain.
Cataract
A condition characterized by clouding in the natural lens of the
eye. The cause is usually unknown but can result from exposure to
ultraviolet light, injury, heredity, disease and advancing age.
Some medical treatments include surgical replacement of the
natural lens with an artificial lens. Cataracts are usually
treated on an outpatient basis.
Computerized Visual Fields Test
This test is used to detect deficiencies in central or peripheral
vision.
Cornea
The clear outer covering of the eye. Known as the window of the
eye, it plays an important role in focusing images.
Cylinder Power
In correcting for astigmatism, the cylinder power determines how
much correction and the axis determines where the correction goes.
Demo Lenses
Plastic lenses inserted into frames for display purposes only.
Depth Perception
The appearance of depth is created when both eyes focus on the
same plane simultaneously.
Diabetic Retinopathy
Anyone with diabetes is at risk to develop diabetic retinopathy.
High blood sugar associated with diabetes can damage blood vessels
in the retina causing deposits to form blind spots and floaters in
your field of vision. Early symptoms of Diabetic Retinopathy
include double vision and difficulty reading or doing close work.
Eyewire
The section of the frame enclosing each lens.
Farsightedness
Also know as hyperopia, is the opposite of myopia. Distant objects
are clear and close up objects appear blurry. This condition is
the result of an eye that is too short, or a cornea that lacks the
necessary refractive power to focus on the retina.
Fitting Triangle
The three contact points on a person’s head wearing glasses:
right ear, left ear and nose.
Frame Width
The size of the frames from left side to right side. Frame
width should equal the width of the wearer's head.
Glaucoma
An eye disease characterized by an increase in pressure inside
the eye capable of causing damage to the optic nerve. Left
untreated, this condition can lead to blindness. Glaucoma is
usually treated with eye drops and medications. Severe cases may
require surgical correction.
Hyperopia
Farsightedness.
Keratometer
An instrument used to measure the curvature of the cornea.
This measurement enables the doctor to accurately fit contact
lenses.
Lens Blank
An unfinished lens that is ground to fit a customer's
prescription.
Lensometer
An instrument used to measure the power of an individual's
current prescription eyeglasses.
Multifocal Lens
A lens with more than one optical center (e.g., a bifocal with
two, a trifocal with three, a progressive with many).
Myopia
Nearsightedness.
Nearsightedness
Also known as myopia, causes poor distance vision. If your eye
is too long, or if your cornea has too much focusing power, images
focus in front of the retina.
O.D.
Doctor of Optometry, or Optometrist.
Ophthalmologist
A doctor specializing in the eye who is trained to examine,
diagnose, treat and manage diseases of the visual system,
including all types of surgical procedures. Requires completion of
a four-year undergraduate program, four years of medical school
and a minimum of three years in ophthalmology training.
Ophthalmoloscope
This hand-held, lighted instrument helps detect a wide range
of systemic and vision problems by giving the doctor a close-up
view of the retina and other important parts of the eye.
Optical Center
The spot on the eyeglass lens where light passes through
without bending (refracting). This point is normally placed in
front of the pupil.
Optician
A professional trained to fit and adjust eyewear based on the
specifications provided by an optometrist or ophthalmologist.
Training requirements vary by state.
Optometrist
A primary health care professional that can diagnose, manage
and treat conditions and diseases of the human eye and visual
system, as required by state law.
Peripheral Vision
The area of vision lying just outside the line of sight to
either side of the face. For activities such as driving and
sports, it is important not to obstruct peripheral vision.
Phoroptor
Instrument used by the doctor to determine the final lens
prescription and alignment of the eye.
Photo Refractive Keratotomy (PRK surgery)
A non-invasive, laser surgical procedure reshaping the cornea,
which is the major refractive surface of the eye, to correct a
refractive error. The only approved process right now is for
nearsightedness (myopia).
Polarized Lenses
Tinted lenses specifically designed to reduce glare. Those who
work or drive in bright conditions and those who play snow or
water sports would benefit from polarized lenses.
Polycarbonate
A synthetic, light material used to create impact-resistant
lenses.
Presbyopia
A condition given where the crystalline lenses in the eye lose
elasticity and do not change shape as easily as they should.
Presbyopia causes people to have increased difficulty with near
vision and reading, and is corrected with multifocals.
Prescribed Prism
An effect produced by de-centering a lens so that the optical
center is not in front of the wearer's pupils. Less than five
percent of all eyeglass wearers receive this prescription.
Progressives
Multifocal lenses with no telltale lines.
Pupil
In the eye, a round hole formed by the iris that regulates
what light passes into the eye. Light must pass through the pupil
to get to the retina.
Pupillary Distance
The distance, in millimeters, from one pupil center to the
other. PD measurement is used to ensure proper lens placement.
Pupilometer
A machine that measures the precise pupillary distance.
Refractions
Eye examinations conducted to determine appropriate eyewear
prescriptions.
Refractive Index (RI)
The ability of the lens to bend light. Materials that bend the
most light have the highest refractive index.
Retina
Part of the eye that picks up images and transmits them to the
brain through the optic nerve.
Segment
Segments of the eyeglass lenses that are used for near vision
bifocals. The surrounding larger portion of the lens is used for
distance vision.
Seg Height
The distance from the lowest portion of the eyewire to the top
horizontal line of the Segment.
Sphere Power
Sphere Power is the first number in a prescription for
corrective lenses that indicates the type and amount of
correction.
Tonometry
Computerized measure of internal eye pressure-glaucoma
screening. A tonometer detects glaucoma by measuring the internal
pressure of the eye with a puff of air.
Transition Zone
The area of progressive eyeglass lenses where the distance
vision curve gradually changes into the near-vision curve.
Trifocals
Eyeglass lenses having three areas of viewing, each with its
own focal power. Usually, the upper portion is for distance
viewing, the lower for near and the middle for the distance in
between.
UV Protection
The degree to which a lens or its coating protects the eye
from the sun's harmful rays.
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