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Info:
Lenses
for correcting or improving vision:
There are two types of lenses prescribed for correcting or improving
vision. These include:
·
eyeglasses (Also called spectacles.)
Eyeglasses, the most common form of eyewear used to correct
or improve many types of vision problems, are a frame that holds
two pieces of glass or plastic, which have been ground into
lenses to correct refractive errors. Refractive errors can include
nearsightedness or myopia (difficulty seeing far away), farsightedness
or hyperopia (difficulty seeing close up), and astigmatism (blurring
due to an irregularly shaped cornea). Eyeglasses perform this
function by adding or subtracting focusing power to the eye's
cornea and lens.
·
contact lenses
Contact lenses are worn directly on the cornea of the eye. Like
eyeglasses, contact lenses help to correct refractive
errors and perform this function by adding or subtracting focusing
power to the eye's cornea and lens.
How to read an eyeglass prescription:
The lens power of eyeglasses is measured in diopters. This measurement
reflects the amount of power necessary to focus images directly
on to the retina. When looking at an eyeglass prescription,
you will see the following abbreviations:
O.D. - Oculus dextrus simply refers to the right eye (sometimes
the abbreviation RE is used).
O.S. - Oculus sinister refers to the left eye (sometimes the
abbreviation LE is used).
In
addition, the eyeglass prescription may also contain the following
measurements:
· sphere - this number measurement reflects the
extent of the nearsightedness or farsightedness.
·
cylinder - this number measurement refers to the amount
of astigmatism (an irregularly shaped cornea which causes blurring)
in the eye.
·
axis - this number measurement describes the direction
of the astigmatism in degrees. Bifocal is additional power in
the lens and has an additional measurement listed on the prescription
as "add," to indicate the strength of the lens.
What are the different types of eyeglass lenses?
The type of lenses used in eyeglasses depends on the type of
vision problem, and may include:
· concave lenses - are thinnest in the center.
Used to correct nearsightedness (myopia), the numerical prescription
in diopters is always marked with a minus (-) symbol.
·
convex lenses - are thickest in the center, like a magnifying
glass. Used to correct farsightedness (hyperopia), the numerical
prescription in diopters is always marked with a plus (+) symbol.
·
cylindrical lenses - curve more in one direction than in
the other and are often used to correct astigmatism.
Facts about contact lenses:
Many people wear contact lenses, half of whom wear daily wear
soft lenses. Currently, there are five types of contact lenses
in use, including the following:
· the original "hard" lens
· the rigid, gas-permeable lens
· other rigid lenses
· the soft, water-absorbing lens
· other flexible, non-water absorbing lenses
Reading a contact lens prescription:
The prescription for contact lenses includes more information
than what is available on the prescription for eyeglasses. Special
measurements are taken of the curvature of the eye. In addition
your optician will determine if the eyes are too dry for contact
lenses, and if there are any corneal problems that may prevent
a person from wearing contact lenses. Trial lenses are usually
tested on the eyes for a period of time to ensure proper fit.
The contact lens prescription usually includes the following
information:
· contact lens power (measured in diopters, like eyeglasses)
· contact lens base curve
· diameter of the lens
Eye care specialists are required to give you a copy of your
contact lens specifications.
You can find out more here at
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