Contact lenses are thin, curved plastic disks designed to cover the cornea; the clear front covering of the eye. Contact lenses provide a safe and effective way to correct vision when used with care and proper supervision. They can offer a good alternative to eyeglasses depending on your eyes and lifestyle.
History of the Contact lens
Leonardo da Vinci had proposed the idea of applying a corrective lens directly to the surface of the eye as early as 1508 and similar concepts surfaced from René Descartes in 1636 but it was not until 1887 that the German physiologist Adolf Eugen Fick constructed the first successful contact lens.
Daily-wear soft lenses are the most comfortable and your eyes will adjust to wearing them in less time than hard contact lenses. These soft lenses may be worn during vigorous physical activity and playing any sport with less likelihood that the lenses will slip out of place. Daily-wear lenses must be removed, cleaned and stored every day.
Disposable Contact Lenses are lenses designed to be replaced on a regular basis usually daily, bi-weekly or monthly. The more often a lens is replaced the less likely the lens will become deposited with proteins and oils. Many problems that contact lens wearers experienced in the past when lenses were replaced on an annual or two yearly bases are seldom seen nowadays. Disposable contact lenses are therefore a healthier alternative. Daily disposable contact lenses are a great option for people who only want to wear their contact lenses a few times a week for example for sport or for going out at night. They also remove the need for cleaning, since they are inserted in the morning (before the start of your day / play sport / work) and then thrown away at the end of the day offering exceptional convenience and good value for money. Lenses, which are replaced on a two-weekly or monthly basis, are good value if you want to wear lenses every day. 
Leave-in (extended wear) contact lenses are designed to be worn continuously for 30 days and nights and then replaced with a new contact lens. They offer the ultimate in convenience since they usually don't need removing or manual cleaning. Other advantages include being able to see without struggling to find your glasses if you get up in the night, or not having to worry about removing lenses with dirty hands. If you go camping or for any outdoor sport or short holiday you won't need to remember to carry bottles of solution around with you. 
Rigid gas Permeable contact lenses are usually used for correction of moderate levels of astigmatism. They provide excellent clarity of vision especially in cases where the astigmatism is irregular (such as with keratoconus). Rigid Gas permeable contact lenses offer excellent long-term corneal health since they allow almost as much oxygen to pass through to the cornea as without a lens on the eye. They require a longer period of adaptation than soft lenses. Many of the problems associated with reduced oxygen flow through old-style "hard lenses" are seldom seen nowadays due to the development in these various modern gas permeable lenses.
Colored contact lenses come in three kinds: visibility tints, enhancement tints and opaque color tints. Many of these colored contact lenses are available in Plano form, as well as in designs for people who have astigmatism, need bifocal contacts or want a disposable contact lens. A visibility tint is usually a light blue or green tint added to a lens, just to help you see it better during insertion and removal, or if you drop it. Since it's a very light tint, it does not affect your eye color An enhancement tint is a solid but translucent (see-through) tint that is a little darker than a visibility tint. An enhancement tint does change your eye color. As the name implies, it's meant to enhance the existing color of your eyes. These types of tints are usually best for people who have light colored eyes and want to make their eye color more intense. Color tints are deeper, opaque tints that can change your eye color completely. Usually they are made of patterns of solid colors. If you have dark eyes, you'll need this type of color contact lens to change your eye color. Color contacts come in a wide variety of colors, including hazel, green, blue, violet, amethyst and gray. The companies that make colored contact lenses have gone all out to mimic the natural look of the colored portion of the eye, called the iris Since this area is made up of colorful shapes and lines, some color contacts feature a series of tiny colored dots on the lens to make them look more natural on the eye. But the center of the lens, the part that lies over your pupil is clear so you can see.
