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Hard Vs. Soft Contact Lenses- What?s The Difference? |
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The history of contact lenses dates back to the 1500’s
where it is reported that Leonardo Da Vinci made the first reference of
a device to correct corneal defects by a contact device. It wasn’t until
1888 in Germany when the first glass-blown scleral contacts were made by
August Muller that the birth of the contact lens was fully realized.
Contacts were made of glass until the 1930’s with the invention of
polymethyl methacrylate, commonly known as Plexiglas or PMMA.
A smaller version of contacts was first introduced in the 1950’s.
These contacts covered only the cornea instead of the whole visible part
of the eye, as was the case of the older version of contacts. These
contacts were made from PMMA, and gained in popularity throughout the
1960’s. The major disadvantage to these lenses is that they did not
allow for oxygen to pass through them to the eye. This led to potential
problems with the health of the eye.
To overcome this obstacle, a
range of new rigid materials were developed between the 1970’s and
1990’s that allowed for oxygen to pass through to the eye. These contact
lenses came to be known as Rigid Gas Permeable (RGP). All of the lenses
created to this time were considered hard, but the RGP lenses offered
more comfort to the wearer and better health for the eye.
For
contact lens wearers who have astigmatism or distorted corneal shapes,
RGP have some unique qualities that are of a great benefit. RGP lenses
can provide the distorted cornea shape with a new refracting surface,
thus greatly improving vision. This is done in part by trapping the
eye’s own tears underneath the surface of the lens. Tears have a
refractive index very similar to that of the cornea, thus the contact
lens creates a sort of “new” cornea through which the wearer experiences
better vision.
Hard contact lenses last for a couple of years
before they need to be replaced. As long as they are properly
maintained, they should last at least 2 years. These types of lenses do
require a few days for the eye to completely adjust to the feel of the
material. The wearer usually has them in for about two hours the first
day, four the next, and gradually moves towards being able to wear them
all day. Once the eye adjusts, wearing these types of contact lenses is
easy and comfortable. Some contact lens wearers prefer the hard lenses
to the soft because they easily go on the eye and do not require placing
one’s fingers on the eye to remove them.
Soft contact
lenses are a fairly recent development in the field of eye care.
Hydrogel lenses were invented by Otto Wichterle and were first used in
some countries in the 1960’s, but did not receive the Food and Drug
Administration’s approval until 1971 under the name of Soflens. Soft
contact lenses are of almost immediate comfort to the wearer, thus they
became more popular and were prescribed more often than hard lenses. The
materials used in soft lenses were modified many times over the next 25
years to increase the amount of oxygen allowed through to the eye.
Wearers
of soft contact lenses need to take extra care with the lenses. They are
easily torn and the maintenance of them is more involved than with hard
lenses, which is one of the reasons why disposable contact lenses have
become available. The wearer throws the pair of lenses away at the end
of the day and starts with a fresh pair in the morning. This is
convenient as the wearer does not have to worry too much about tearing
the lens, but if that does happen, a new pair of lenses can be opened.
Silicone
hydrogels were the next major breakthrough in contact lens technology.
These lenses, introduced in 1999, were originally designed for extended
wear. Silicone has a material with high oxygen permeability and these
lenses combined the benefits of silicone with the comfort of the
hydrogel. Recently, the silicone hydrogels are being used for daily wear
lenses as well as the extended wear.
For some clinical purposes,
a variety of hybrid contact lenses are being used. These lenses are
often referred to as piggybacking and entail the use of a hard contact
lens over a soft lens. This is done for several reasons; among them are
increased optical strength and optimal comfort.
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