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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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