Are
contacts lenses hard to take care of?
Up until the late 1970s, contact lenses were made
from two materials. Hard contact lenses were made of polymethymethacrylate
(PMMA), while the soft contact lenses were made of a hydrated
polymer, hydroxyethylmethacrylate (HEMA), which contained 37.8%
water by weight. These lenses provided clear vision and comfort,
but there was a problem. These lenses did not allow oxygen to
reach the cornea. Because of this, the cornea could change,
adversely, in some contact lens wearers.
PMMA is now obsolete, and is replaced with rigid plastics,
mostly hydrophobic materials with high oxygen permeability.
These lenses are called Rigid Gas Permeable (RGP) lenses.
For the manufacture of soft lenses, HEMA is being replaced
by polymers which contain as much as 80% water. These soft
lenses, often called hydrogels because of the amount of water
have high oxygen transfer while retaining shape despite high
water content. These new materials used in the manufacture
of contact lenses as well as thinner lenses and greater oxygen
transfer has reduced corneal issues, but there are still other
possible complications.
The new materials have also been instrumental in the creation
of disposable contact lenses in a variety of types. Disposable
contact lenses come in monthly, bi-monthly, weekly, and even
daily disposable types. The thinner materials make wearing
these contact lenses more comfortable, and the cost of contact
lenses has been reduced. This allows for close to maintenance
free contact lens wear.
|
|
