There is a vast selection of contact
lenses available. Contact lenses can be broken down
into several main categories based on what they're made
of, how often you need to replace them and whether you
can sleep in them.
Contact lenses are made of many different types of plastic,
but they are divided into two main groups: soft or rigid
gas permeable (RGP lenses, now called GP lenses). Soft
contacts contain from 25% to 79% water, are easy to
adapt to and are quite comfortable. Rigid gas permeable
contact lenses take longer to adapt to, but are more
durable and more resistant to deposit buildup. They
tend to be less expensive over the life of the lens
(but the upfront cost is higher) and can offer some
people crisper vision than they would have with soft
contacts.
The replacement schedule of a contact
lens refers to how long you can safely wear it before
you need to throw it away. With GP lenses, you generally
replace them every couple of years, because they are
made of a very durable material (though a prescription
change would of course necessitate new lenses).
