A Química das Coisas - Lentes de Contacto


Uploaded by quimicadascoisas on 12.03.2012

Transcript:
THE CHEMISTRY OF THINGS
Today's episode literally shows us the chemistry
hidden right before our eyes.
We will talk about contact lenses!
The first contact lenses were these uncomfortable slices of glass
that covered much of the eye,
and could only be used for a few hours.
Then we have lenses made of synthetic polymers, or plastic.
Later, poly-methyl methacrylate lenses,
which is to say "acrylic", became popular.
They were smaller, adapted to the cornea,
but still very stiff, uncomfortable and unstable,
which made it a common sight to see users
looking for them on all fours on the floor.
These problems were solved through a chemical modification:
the poly-methyl methacrylate
was replaced by poly-hidroxyethil methacrylate,
a very big word that means an equally strong and clear acrylic polymer
but which is much more malleable.
But the main problem of contact lenses was still not solved:
they were impermeable to oxygen.
The cornea has no blood vessels,
and therefore it is not blood that supplies nutrients and oxygen to its cells.
Nutrients are transported by the lacrimal fluid and the vitreous humor of the eye,
while oxygen reaches the cells of the cornea directly through contact with the air.
Because they were totally impermeable to oxygen,
acrylic lenses could only be used for a few hours.
More recently, chemical laboratories have developed a solution to this problem:
the hydrogel, a gelatinous material composed of a network of insoluble polymers
containing large amounts of water.
This highly hydrated material is very comfortable for the eyes
and above all, is permeable to oxygen in the air.
As a result, current hydrogel contact lenses can be used for long periods…
with chemistry right in front of your eyes!
To know more about the chemistry of contact lenses,
visit our website quimicadascoisas.org
or look for us on Facebook.