lenses make contact with the eye. Glasses do not do this.
Contacts float on a thin layer of liquid. There are three types
of lenses the corneal , scleral, and the
haptic. The scleral contact goes over the whole front
The corneal contact goes on the cornea which is in front of the iris(the color part of the eye). Corneal contacts are small and light. Corneal contact lenses are the most popular contact. These contacts do not restrict your vision. They move with the eye.
Haptic lenses are thick and are held in place by the eyelids. These lenses are worn by people in sporting events because they do not pop out as easily. Also people who have diseased or damaged eyes wear the haptic contacts. The haptic lens can be shaped to fit any eye(you could have scars or anything else and they would be able to fit your eye).
Most people that wear contact lenses wear them for cosmetic reasons. Some types of vision corrections are best done with contact lenses. Like Anisometropia is where the refracting(bending of the light by the lens or cornea) is different in each eye. Those people have to have a concave and a convex lens. If these people wear glasses they can not just move their eyes, but have to move their whole head to look in a different direction. If they don't them might see double images, but if they wear contacts they do not have to worry about that problem. Keratoconus is a disease that makes the conical shape of the cornea. Lenses can let these people have normal lives. This is what contacts do.