At present very few individuals wear hard contact lenses because of the availability of improved types of contact lenses that are convenient to use. Hard plastic material is used in making hard contact lenses and is available as either non-gas permeable or gas permeable. They are capable of providing clear vision and are known for their durability.
Hard contact lenses can last for a great duration of time which can range from 5 to 10 years but users find them difficult to adjust. Although users face difficulty in placing them in the eyes and encounter problems while removing them as well, hard lenses are known to rectify the majority of vision problems. Non-gas permeable lenses do not permit oxygen to travel to the cornea. These types of lenses cannot be worn for long since major harm can happen to the eye if no oxygen moves to the cornea. Gas permeable lenses make available similar benefits but also offers increased wearing time and enhanced comfort due to the fact that oxygen can move easily through them.
Hard contact lenses are made from a tough material known as polymethylmethacrylate. PMMA is a durable, transparent material that was the plastic originally utilized in the development of contact lenses. In contemporary hard lenses, PMMA is frequently used in combination with other plastics to enhance the oxygen permeability of lenses. These are referred to as rigid gas permeable (RGP) lenses. A plastic hydrogel polymer, hydroxyethylmethacrylate (HEMA) which has high water content is used for making soft lenses.
There are only a limited number of individuals who use the old type of hard contact lenses because of the fact that improved versions of the lenses are readily available to the users at present. The old kind of hard contact lenses which were manufactured from a hard plastic material known as Polymethylmethacrylate or “PMMA” were characterized by admirable durability and vision rectification, but had two main disadvantages.
Two major drawbacks
- First, users found it difficult to adapt to wearing the lenses as they did not provide a great deal of comfort.
- Second, they did not permit oxygen to get in touch with the cornea without difficulty and hence resulted in its swelling thereby clouding one’s vision.
Occasionally the swelling could give rise to serious problems and resulted in a “scratched cornea” which was exceedingly agonizing and compelled one to stop wearing lenses for sometime. However due to its robust nature the cornea generally healed within a short period of time.
Even when the hard lenses were worn without much trouble, hard contact lenses was responsible for molding or altering the shape of the cornea making it tough if not unfeasible to put on glasses after taking off the hard contact lenses. Due to this reason hard contact lenses were substituted by gas permeable contact lenses, which although hard in nature permitted oxygen to move to the cornea, reducing the chances of change in the cornea’s shape and making it possible for individuals to wear glasses after their removal.