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
with high oxygen permeability
have been approved
(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.
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.
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
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
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 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.)
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
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
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
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.