Conventional Hard Contact Lenses
Contact lenses provide option of not wearing spectacles, and are worn for problems in eyes and eyesight, like nearsightedness, farsightedness, presbyopia, astigmatism, etc. They may be worn after a cataract surgery. They are placed directly on the eye. They float on above the cornea on a film of tears.
Hard contact lenses are two types basically, but overall we take only one as Hard Contact Lenses, while the other are considered a separate category altogether. Conventional hard contacts are made of Polymethyl Methacrylate and are also known as PMMA lenses. While rigid-gas permeable lenses are more comfortable of the two, they aren't exactly called as hard lenses, the name being used only for PMMA.
These are suitable in only a few conditions. They are much more difficult to wear and carry. They need to be handled with care as they can slide out of their place at a pressure lower than in other kinds of lenses. It usually takes longer to get used to them then soft contacts.
Hard Contact lenses or the PMMA are made of polymethyl methacrylate, and carry two huge drawbacks. One is that it is very difficult to get used to wearing them. Because they're so hard, it is very difficult to wear them regularly, and to get used to wearing them.
Second problem is that they don't allow oxygen to reach the eyes. It therefore causes the vision to blur, the cornea to swell a bit. The condition is called scratched cornea. Scratched cornea is a very painful condition, and requires the user to stop using the lenses for some time, until the problem diffuses a bit.
Certain precautions must be taken when using contacts, especially hard contacts. Regular and thorough cleaning is a must. Proper storing is also as important. Also, one must not use home-made saline solutions, but only commercially prepared sterile solutions to clean and store them. In case of any eye trouble, like unexplained eye discomfort, redness, swelling, watering eyes, or vision change, it's imperative one rushes to the doctor immediately to avoid any major trouble.
Hard Contact Lenses are now a history. They were used before 1971, when all contacts were made of PMMA. Now, we have better alternatives in the form of Soft Contacts, and RGPs.
