Polymer Tutorial
Contact Basics	Eye Tutorial	Contact History

Why learn about polymers?

Contact lenses have only become popular since the mid 20th century. Their increasing popularity has come about because of the great ease with which they can be mass produced and the wonderful variety of polymers with completely different structure and functions. Polymers are used for many things, but in order to understand completely the great variety of contact lenses it is very important to have a basic understanding of what polymers are.

What are polymers?

Polymer comes from the Greek polumeres, which means `having many parts'. Polymers are large molecules consisting of repeated chemical units (`mers') joined together, usually in a line, like beads on a string. Most polymers are based on a backbone chain of carbon atoms. The most simply polymer is shown in the picture below. This polymer is called polyethylene. It is a normal constituent of malleable plastics like garbage bags. (See sources)

How are polymers made?

Smaller molecules (mers) which form the base sequence of the polymer chain are reacted together to make the long chains. Polyethylene is made from a particular molecule called ethylene. The reaction is shown here.

Other molecules can be polymerized, forming longs chains that will have different qualities. The qualities that the chains show is dependent on the structure of the functional groups. Here are some other examples of polymers, their uses compared to their structure.:

Polystyrene - styrofoam cups and foam packing
Polyvinyl chloride (PVC) - piping, more durable and long lasting
Polymethyl methacrylate (Hard Contact Lens) - clearer and more durable replacement for glass

How does this relate to contact lenses?

Because the number of molecules that can be polymerized are infinite, the number of possible qualities that they can have are equally infinite. In the mid 20th century it was the advent of a hydrophilic polymer that revolutionized the contact lenses industry. This hydrophilic polymer absorbed water; the water made the contact more comfortable to wear. Water contains oxygen which allow the eye to "breath" and thus tolerate the contact lenses for extended periods of time. This new lenses was also very malleable and could now be fit to the cornea to correct vision more easily.

Since the invention of the hydrophilic contact increasing types of lenses have come on the market. One revolutionary example is the disposable lenses that can be made for only a few dollars; this gives convenience to those who put lots of stress on contact lenses. Another great example is the extended-wear contact, that can be worn for weeks at a time without ever removing them. This is made possible by a polymer that is about 100 times more permeable to oxygen. There are many qualities that are being researched to obtain better and cheaper contact lenses. The following list has some examples.

• Transparency - if you can't see through the lens it's no good
• Water absorbency - for comfort
• Protein resistance - protein from the eye will grow and collect. This will ruin increase the possibility of infection and blur the vision.
• Oxygen permeability - the eye needs a certain amount of oxygen just like the rest of the body. Because there are no blood vessel in the seeing part of the eye (you can't see through blood) the body relies on oxygen from the air to breath. If the eye is not supplied with this oxygen it will become irritated and, in extreme cases, grow blood vessels into the eye and block vision.
• For more information on qualities of contact lenses see CIBA Vision's excellent site on the subject.

Please see our list of sources for more information.