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.
