Eyeglasses and Contact Lenses

Eyeglasses are corrective lenses mounted in frames that help those with vision problems see clearly. The lenses are shaped in order to bend light rays so that they will focus at the back of the eyes, the retina. Some people who can see distant objects clearly, but to some near objects look blurry suffer from hyperopia or farsightedness. As explained by Franciscus Donders, a Dutch physiologist, the cause of farsightedness is that the eyeball is too shallow and that the image actually focuses beyond the eye. To correct hyperopia, convex corrective lenses are used to make the light rays converge or come together on the retina. Some people suffer from myopia or nearsightedness, in which the image is focused in front of the retina so that only near objects can be seen clearly. Concave lenses can be worn to diverge the light rays and permit light from far away objects to focus directly on the retina. A condition called presbyopia occurs when the lens of the eye loses its elasticity and it can no longer change shape. The condition is usually associated with age and becomes evident after 40. Presbyopia causes people to be somewhat farsighted. Sometimes this is corrected by wearing bifocals, or eyeglasses that have a second lens below the top lens. A person with presbyopia can look through the bottom lens while reading and use the top lens for distant objects.You can conveniently purchase various glasses to rectify your eyesight on Glassesshop.
As you can see on Glassesshop, nowadays there are many kinds of glasses in the market. Today eyeglasses come in a wide array of styles and designs. Frames are generally made of metal or plastic, and lenses are made of glass or plastic. Polycarbonate is a type of very hard plastic used for lenses. Robust and lightweight, it is scratch-resistant and provides 100% protection from ultraviolet radiation that can contribute to cataract formation. Along with lightweight frames, such lenses are commonly used in sports glasses and childrens' glasses.
Eyewear has been revolutionized with the invention of the contact lens, corrective lenses without the frames, which put a tiny corrective lens directly onthe cornea of the eye. However the idea dates back to Leonardo da Vinci whodescribed a way of correcting vision using a water-filled tube, and to a number of scientists who experimented with layers of gelatin to correct vision during the seventeenth and eighteenth centuries. Contact lenses were first madein Europe near the turn of the twentieth century using glass. In 1936 IG Farben, a German company, made the first contact lens from Plexiglas--still usedtoday for "hard" contact lenses. An American inventor named Tuohy began useof a lens that covers only the cornea and in 1964 a Czech named Wichterle made the first flexible or "soft" lens. Today there is an array of hard and softlenses, extended wear lenses, tinted lenses, lenses that can correct astigmatism, and lenses to correct color blindness. Also you can find of sorts with excellent quality contact lenses on Glassesshop.