Classic contact lens types: hydrogel silicone hydrogel hybrid (RGP - Rigid Gas
Permeable part in the middle of the lens, edges are out of soft materials) Since
1999, some types of silicone hydrogel contact lenses with high oxygen
permeability have been approved for extended wear (to be worn overnight, or for
longer than one day). Nowadays, extended wear is not often recommended, as
prolonged wear presents a higher risk of eye infections and other health
complications.
Advantages
The advantages of soft contact lenses include
comfort of wear, easy application and low cost. Silicone hydrogel contact lenses
have a high oxygen permeability, which ensures sufficient oxygen flow to the
cornea. On the other hand they have worse wettability, increased stiffness and a
propensity for harboring lipid deposits when compared to hydrogel lenses.
Disadvantages
Soft contact lenses are made of a more fragile material,
which makes them more difficult to care for. They must be cleaned or changed
regularly in order to prevent lipids, proteins and other deposits from forming
on the tear film. Complications can occur due to insufficient lens care,
incorrect selection of lenses, or by wearing the lenses longer than prescribed.
Neglecting the lens care can lead to conjunctivitis and corneal
neovascularization.
Replacement schedule
Each type of contact lens is
designed to follow a specific replacement schedule, ie. how often the lenses
must be disposed of and replaced.
Daily wear routine
The lenses should
be worn for no more than 16 hours a day (for some brands, this time should be
limited to 10 hours because of their lower oxygen permeability). The daily wear
routine starts in the morning when the lens is inserted into the eye. At night,
the lenses should be removed and placed in a lens case with contact lens
solution where they will be disinfected overnight.
Extended wear
Extended wear is possible with several types of
daily
contact lenses that have high oxygen permeability. Contact lenses with
extended wear can be worn overnight, but for a maximum of 6 days continously.
This type of wear shortens the total lifetime of the lenses. (Eg. Monthly lenses
will be viable for three weeks instead of four.)
Continuous wear
Contact lenses for continuous wear can be worn without removing for the duration
of the time for which they are prescribed. For example, monthly lenses can be
worn for 30 days, 24/7. This type of wear should only be prescribed by an eye
specialist, because it is not suitable for every eye.
Lifetime of soft
contact lenses
Daily contact lenses - inserted in the morning; thrown out
at the end of the day Bi-weekly and
monthly
contact lenses - removed each night to be disinfected with contact lens
solution Quarterly or Yearly contact lenses – not often used now due to the
lower prices of the types above.
Durability of contact lenses
Contact
lenses gradually accumulate lipid, protein, and calcium deposits in which
microorganisms can grow. Therefore, it is necessary to properly clean the lenses
with a suitable solution. This helps to remove impurities and properly disinfect
the lenses.
Summary
Soft contact lenses have one disadvantage - they
are more prone to accumulation of impurities. Therefore, they must be changed
regularly to avoid possible eye infections. The advantage of these lenses is
that they have high oxygen permeability, so they can be worn for a longer time.
Some can even be worn continuously.