Do you ever wonder what kind of plastic is inside the contact lens? Well, maybe you can get a better understanding by telling you the history of contact lens.
The first contact lens is form from heavy blown glass and at a diameter of 18-21mm at the year of 1888. This remained as the only form of contact lens until 1930s when polymethyl methacrylate (PMMA) was introduced and be modified into plastic lens at 1936. This kind of lens is a combination of plastic and glass.
PMMA is actually a polymer of C5H8O2. It is a clear polymer and thus widely use in optical applications. It is also use in making windows as it is more transparent than a glass especially when comes to making a thick window. Thus, PMMA is now widely use to make windows, aquarium and even the clear barrier at the ice rinks also made from PMMA!!
But there is an disadvantage of using PMMA, that is no oxygen can pass through the lenses which will cause a number of side effects. Thus, from 1970s to 1990s, oxygen permeable materials were introduced. These ploymer is called rigid gas permeable (RGP). In 1999, silicone hydrogel was first introduced. This is a highly oxygen permeable lens and later be used to make for daily wear lens and overnight wear lens.
Later, second generation of silicone hydrogel was produced which is a slightly modified molecule. In this second generation of silicone hydrogel, a polar group called Tanaka monomer is added without changing the structure. Example of second generation silicone hydrogel are galyfilcon A which may found in Acuvue Advance, Vistakon and senofilcon A which may found in Acuvue Oasys, Vistakon. Both these polymers are added Tanaka monomer. For Vistakon, they even improved the silicone hydrogel by adding in other molecule to become the internal wetting agent.
Sooner, third generation of silicone hydrogel is launch in the market. Comfilcon A which may found in Biofinity, CooperVision, is the first polymer of third generation of silicone hydrogel. This third generation polymer is made of two siloxy macromers where when they combine can give a very high oxygen permeability. Another type of third generation silicone hydrogel is Enfilcon A where you can find in Avaira and CooperVision. It is natural wetting agent in lens where it contains 46% of water.There are many types of contact lens in the market. One of the latest type is the lens that allow wearers to be continuous wearing the lens for 30 consecutive days. This is very convenient for wearers that are lazy to deal with contact lens daily. The reasons behind that allows the contact lens to be allocate on our cornea for long time is because it is able to increase the rate of uptake of water and thus the rate of oxygen intake as well as removal of carbon dioxide. This kind of lens has an oxygen permeability up to 6 times higher than the normal contact lens!!
Other than this, there are some other types of contact lens that are made to treat other problems rather than shortsighted only. These include contact lens for
1) longsighted (hyperopia)
2) astigmatism
3) presbyopia
*The picture shown is a cornea contact lens inspector*
Longsighted or hyperopia people can have a better vision at a longer distance. They can be treated with a "plus" prescription available at a wide range of contact lens.While for astigmatism, people tends to have problems in focusing their view as the image is focused on two separate points in the eye. People with this problems thus have to specially make their "toric" contact lens with different curvatures at the front and back as their lens will have to correct the irregular shaped cornea, so that light passed through can fall at only one point. Since they are more difficult to fit and manufacture, thus the price of this contact lens will be slightly more expensive. There are also monthly disposal contact lens for this.
For presbyopia, it is also called "ageing eye". As what it is called, it normally happens when someone is ageing. It happens that they are losing the ability to shift focus between far and near object. Thus, to treat people with this problems, special correctable bifocal contact lens is needed. They are specially made according to the person's special combination of distance and near vision.
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