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Contact lenses are easy and comfortable enough
to get fitted over the eye to replace the traditional spectacles by
providing superb peripheral vision without sacrificing on the part of
the appearance or outlook. There are various types of contact lenses
available in the market. You should select that lens which would suit
your requirements like profession, type of vision disorder and alike.
Out of the many types, contact lens can be hard or soft.
Soft lenses
Soft lenses are generally manufactured from
a plastic hydrogel polymer called hydroxyethylmethacrylate which
constitutes of 38 % to 70 % water. They are made of soft plastic and are
water absobing in nature which sits on the surface of the cornea. Some
soft lenses also provide ultraviolet protection. These lenses are more
comfortable to wear than the hard lenses as they are able to hold more
water. The main advantage of soft lenses is that, they are usually
disposable which means they can be thrown away after sometime, depending
upon the type of lens prescribed. This provides an opportunity to the
users to have a new pair of fresh lenses thus reducing the chances of
infection and giving enough comfort to the user. The size of the soft
lenses is somewhere between 13 and 14.50 mm with the center thickness of
100 um. These lenses allow the oxygen to reach the cornea. Apart from
the various benefits, it also has some disadvantages as they easily
absorb pollutants like soap or lotion from your hands resulting in
irritation in your eyes. They can also rip or tear easily as they are
more fragile than the hard lenses.
Hard lenses
Hard
contact lenses are generally manufactured from a rigid material called
polymethylmethacrylate. In order to increase the oxygen permeability,
this material can be combined with other plastics. The hard lenses
mainly come under the sizes of 8 to 18 mm with the center thickness of
100 um. These lenses are very durable but they don't allow oxygen to
reach the cornea, directly. Oxygen dissolved in the tear indirectly
reaches the cornea because of eye movement due to blinking of the eye.
Inspite of their durability and lower cost, these are the least
comfortable lenses and are used by very few people. But, they maintain
their shape better as compared to soft lenses. The reason behind its
least use is the number of adverse conditions associated with it like
risk of corneal ulcers, undesirable reshaping of the cornea, often
difficult to wear in case of non-habituality.
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