Contacts are basically very small eyeglasses made from a plastic material as oppose to glass. Contacts change the direction of rays of light to focus that light properly onto your retina and the nerves within it. There are contacts that correct both nearsightedness and farsightedness. If a person is nearsighted, the focus point of light rays is in front of your retina. If you are nearsighted, the light rays are not able to form a focus point before reaching the retina. Contacts fix both of these issues. Contact lens powers are calculated and expressed in diopters. Nearsighted lenses begin with a negative sign while farsighted lenses begin with a positive sign. The reason that contacts are so much thinner than eyeglasses is that they are a different distance from your eye. Contact lenses rest directly on our cornea so we can see everything without the feeling of looking into a lens. Eyeglasses are a bit further away from your eye and therefore need to be thicker to have a larger optic zone; you can only see through those lenses, most people with glasses have poor peripheral vision. You can think of this concept as if you were in your house loping out a window. If you are very close to the window you have a larger range of what you can see. If you were on the other side of the room you would only be able to see a much smaller percentage of what is outside. Eyeglasses are also thicker so that they do not break upon impact. Contacts don’t really fall off like glasses may. People should use contacts because they seem to be more convenient than glasses. Glasses can break pretty easily and also change a person’s appearance quite dramatically. I would recommend to anybody who needs to where glasses that they should at least try to wear contacts.
Sources:
http://www.allaboutvision.com/contacts/faq/how-contacts-work.htm
http://health.howstuffworks.com/wellness/cosmetic-treatments/contact-lens.htm