There are two main types of contacts lenses - termed soft and hard rigid contact
lenses. Which is best contact lenses for you will depend on how wear time and for
what purposes. Contact lenses can reduce oxygen levels to the cornea and this amount
will vary according to material and type of contact lens
Hard Rigid Gas Permeable contact lenses
The rigid gas permeable contact lenses are made of harder material and so they do
not bend - hence rigid in shape and look bit like a tiny dome or cap. The contact
lenses are sometimes referred to as hard lenses or RGP lenses.
The rigid gas permeable lenses allow more oxygen to flow through than some soft lenses.
They are smaller than soft lenses and so don’t cover the entire cornea like soft
lenses. This allows more oxygen direct to cornea.
RGP lenses move more on blinking which allows fresh tears to pass under the contact
lenses instead of accumulating under.
The downside is hard contact lenses are initially not as comfortable as soft lenses
and so tend to take longer to adapt. The amount of wear time in one session for
hard lenses needs to built up slowly but comfort does improves with time.
The hard contact lenses are very useful in correcting astigmatism and especially
of irregular type like keratoconus and may be the only option for some people.
Soft contact lenses
The soft contact lenses are water filled plastic lenses that are bit larger than
rigid lenses. They are flexible and can bend. The soft material tends to be more
comfortable and easier to get used to.
There are many types of soft lenses with different water content and different oxygen
levels. The modern silicone hydrogel soft contact lensesallow moreoxygen through
than conventional material and can be used for extended wear.
How often contact lenses are worn or replaced.
Rigid gas lenses tend to be replaced after longer intervals than soft lenses.
These soft contact lenses are thrown away after one use. Daily disposables are convenient
esp for those who do not want the fuss of having to clean and disinfect. There is
less risk of infections as a result
Monthly contact lenses
These contact lenses are replaced monthly. This gives a fresh start each month with
new lenses. Otherwise deposits from the eye accumulate on the contacts lenses such
as protein that can encourage bacteria to grow or reduce clarity.
Contact lenses that last for six months or year may need cleaning with protein tablets
or more stronger disinfecting solutions like hydrogen peroxide.
Extended wear contact lenses.
These are worn and left in overnight and are termed extended wear contact lenses.
They are made of modern material called silicone hydrogel lenses. This provides
much more oxygen to the eye than conventional soft lenses and so have been approved
to leave in eye over night.
Do not attempt to do this with other contact lenses - as it can cause lot of pain
afterwards as well as compromising the cornea of the eye. Over wear can cause lack
of oxygen to the eye.
The extended wear contact lenses have been designed to leave in and so saves the
hassle of having to take insert or remove lenses.
However there is still the risk of eye infections - and build up of materials from
the eye. So some extended wear are designed to be replaced at regular intervals
as recommended by your eye care professional. This is very important to prevent
serious eye infections.