| MadSci Network: Chemistry |
Contact lenses are mostly soft type these days and they are made from plastics, they will actually dry up and become quite hard, but when hydrated and wet they are floppy and soft. They are pourous enough that the liquid they take up will hopefully also take up some oxygen to deliver to your cornea (the clear part of your eye). The cells, corneal epithelial cells, that cover your cornea do not have a blood supply and must obtain the oxygen they need from the tear layer over your eyeball. There are lenses that some people wear for many days and then dispose of. Some of these lenses are coated with various materials to try to decrease how fast protein sticks and builds up on the lens. Regular plastic soft contacts must be cleaned daily. You can see more of soft contacts at :cibavisions web site
Rigid gas permeable lenses are aslo available which are also plastic, but more stiff than regular soft lenses: they allow better access of oxygen to the cornea. No lenses exist that let the normal level of oxygen reach the cornea, so contacts always creat a stress on the corneal epithelium.
The chemical name of the a plastic used in some soft lenses is poly (2- hydroxyethyl methacrylate-co-ethylene dimethacrylate co-methacrylic acid-g- povidone). Basically, these are all derivatives of the acrylic-type of plastic polymers. Acrylics are used in super glues, floor waxes and plastics that are clear, etc. The cibavision web site has more information on lenses like this You can also try going to yahoo.com, and searching for "contact lenses".
Ken Mitton, PhD.
Research Fellow
Ophthalmology and Visual Sciences
University of Michigan - Kellogg Eye Center
ken@mitton.com
kpmitton@umich.edu
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