How are contact lenses made?
The principle of using
lenses directly on the surface of the eye
has been around for many years, but the use
of contact lenses has only become popular in
about the last 40 years. The reason for this
is that manufacturing contact lenses was
traditionally very difficult. However,
breakthroughs in materials and manufacturing
over the past 70 years have made contact
lenses more available, to the point that, in
the present, they easily rival traditional
eyeglasses in terms of the number of
wearers.
The first contact lenses,
produced in the late nineteenth century,
were made of glass and were blown by skilled
glassblowers. However, because they
restricted oxygen flow to the eye they
tended to be uncomfortable, and the vision
corrective properties were difficult to
standardize.
The discovery of a useful
plastic material called polymethylmethacrylate in 1934 meant that
lenses could be cast molded, which is a
process that involved using the eye as a
cast while moldable plastic was placed on
it. The resulting mold was used to make
lenses – but these were still impermeable
and thus uncomfortable.
Today, most contact lenses
are created using a process known as spin
casting. The material used to make the
lenses is placed in a mold, and is then spun
around at high speed. This process spreads
the material evenly over the surface of the
lens. The materials used vary from
fluorosilicone acrylate material for rigid
gas permeable lenses to materials such as
Bausch & Lomb's polymacon for soft contact
lenses, but all of these now have excellent
oxygen permeability for greater comfort and
eye health.
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