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| GAS
PERMEABLE (GP) LENSES |
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These
are today’s most state-of-the-art “hard”
contact lenses.
Hard lenses were made of a material known
as PMMA, and before 1971, when soft lenses
were introduced, just about all contact lenses
were PMMA.
PMMA lenses were difficult to get used to
and hence uncomfortable to wear. They also
did not allow oxygen to pass through them
and hence caused long term complications. |
What makes GPs different?
Introduced in the mid 1980s, they are actually
a newer technology than soft lenses.
They incorporate silicone, which makes them
more flexible then PMMA whilst also being
more oxygen permeable. This results in greater
comfort and better eye health.
GPs can also provide better vision, more durability,
and increased deposit resistance than soft
lenses. They are also easier to clean, are
longer lasting and less expensive in the long
term than soft lenses.
The need to adapt.
Soft lenses are more instantly comfortable
to wear and so this is why GPs are not everybody’s
first choice lens.
Advantages of GPs
Crisper vision than soft lenses due to increased
stiffness of material (it retains its shape
well when you blink).
Extremely durable (though they can break!!!)
Low deposit adhesion- GP material does not
contain water as soft contact lenses do, hence
deposits (protein and lipids) from your tears
do not bind to the lens material.
GPs are available as Toric, Bifocal and Multifocal
options.
Disadvantages of GPs
They take a lot longer to adapt to (compared
with soft lenses).
Unlike soft lenses, to achieve maximum comfort
with GPs, you have to wear them every day.
Spectacle blur
this is when lenses are removed, vision is
a little blurry (temporarily) even while
wearing glasses. This can necessitate full
time GP wear. Not suitable for many sports
due to their rigid nature.
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