Types of Contact Lenses
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Contact lens terminology can be confusing. We have listed the most
common terms to help you understand the terminology that will be
brought up with your eye care provider. Contact Lenses Direct starts
with a general description of the various types of lenses and contact
lens modalities.
Corneal Contact Lenses
As their name implies, these are small contact lenses that fit
on the cornea and the cornea only. The contact lens does not extend
beyond the limbus, which is the juncture of the cornea and the sclera,
the white part of the eye. Rigid gas permeable lenses (RGP) are
considered corneal in nature. Soft contact lenses are not generally
referred to as corneal lenses since they cover the cornea and go
on to cover approximately 1.0 to 1.5 mm of the conjunctiva around
the limbus.
Scleral Contact Lenses
Large rigid-plastic lenses that fit the entire anterior surface
of the eye. These lenses have a corneal portion and a scleral. They
are not very common but are making a come back in the specialty
lens market.
Hydrogel Contact Lenses
Also known as Soft Contact Lenses. These contact lenses have a
water content ranging from 29% to 81% water by weight. The contact
lens material fits over the cornea and beyond the limbus. Soft contact
lenses were introduced to the North American market in the early
seventies. Soft contact lenses tend to be more comfortable than
rigid lenses because of the larger size causing less irritation
on the corneal nerves. Soft contact lenses are produced in a variety
of materials by different manufacturers. Soft lenses are available
in a clear, visibility tints and cosmetic tints that can enhance
or change the color of your eyes. Soft contact lens designs are
available to correct astigmatism and presbyopia. Soft contact lenses
dominate the market as the cost of materials continues to fall.
"Hard" Contact Lenses
Made of PMMA (Polymethelymethacyralate) these contact lenses were
referred to as hard lenses. These contact lenses do not allow oxygen
through the material whereas rigid gas perms do allow oxygen to
pass through to the cornea. As such, the term "hard contact
lenses" is reserved for this material. Most eye care providers
have switched their patients from hard contact lenses to RGP contact
lenses for the oxygenation of the cornea.
RGP Contact Lenses
These contact lenses are made out of material that allows oxygen
to pass through the structure and oxygenate the cornea. They are
classified as a corneal contact lenses due to fitting only on the
cornea. Lenses are available in different degree of gas permeability.
RGP contact lenses are used to correct nearsightness,farsightedness,
astigmatism, presbyopia and keratoconus. Available in an assortment
of visibility tints.
Daily Wear (DW)
Refers to contact lenses that are approved by the FDA to be worn
only during the day. The "daily wear" DW schedule for
most people ranges from 8 to 14 hours per day. The wearing schedule
applies for both RGP and hydrogel soft contact lenses. They should
NOT be worn overnight.
Extended Wear (EW)
Refers to a wearing schedule for contact lenses that are worn
during the day as well as overnight. Under the USA FDA guidelines,
extended wear contact lenses should not be worn continuously for
more six nights before being removed and left off the eye for one
full day. Extended wear also applies to wearing schedules for both
RGPs.
Flexible Wear (FW)
Refers to a wearing schedule for contact lenses that may be worn
either for daily wear or overnight wear. Flexible wear lenses are
available in both soft and RGP contact lens forms.
Flexible wear contact lenses--refers to lenses that are approved
by the USA FDA for overnight wear, yet eye care providers may decide
to dispense the lenses mostly for daily wear with occasional overnight
wear not to extend beyond 6 nights.
One Day Disposable Contact Lenses
These contact lenses are the fastest growing segment in contact
lens wear. The contact lens is disposed of after one wear . These
contact lenses are deemed the ultimate in lens systems due to the
extreme low complication rate. No solutions are involved. Examples
of such lenses are Ciba's Focus Dailies, Soflens One Day, and Johnson
and Johnson's One Day.
Frequent Replacement System
These contact lenses are generally Daily Wear contact lenses or
Extended Wear contact lenses that are replaced after a specific
wearing period such as, monthly or every 3 months etc. Examples
of these lenses are Focus Monthly, and Bausch & Lomb Optima
FW
These contact lenses are available in color to enhance and even
change a brown eyes blue or what ever color your heart desires.
Contact Lens Care System
A system of contact lens care solutions consisting of all components
necessary for maintaining contact lenses in wearable state. Usually
includes cleaning solution, rinsing solution, storage or disinfecting
solution and protein remover.
Bifocal Contact Lenses
Hydrogel and RGP contact lenses designed especially to correct
presbyopia. Monovision is not a type of a contact lens, rather it
is a method to correct presbyopia.
Astigmatic or Toric Contact Lenses
Hydrogel and RGP contact lenses that are used to correct astigmatism.
Therapeutic Contact Lenses
Contact lenses used to protect the cornea or aid in the corneal
healing process.
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