Myopia or short sightedness is a type of refractive error in which parallel light rays coming from an object are focused in front of retina when accomodation is at rest. Retina is nervous coat of eyeball. When image is formed on retina by light rays focused on it,retina conveys signal to brain via optic nerve and we can see image.

Actually function of normal eye is much complecated and i told u very short story. So,in myopia, either there is increase in antero-posterior length of eyeball or increased curvature of lens,cornea or both..also, there may be lens of eye placed anteriorly or increased refractive index of lens. Here,Refractive index may be explaind as ability of focusing light rays by lens.

Main symptom of myopia is poor vision for distance. Child shuts his eyes half, to have clear vision. Treatment is mainly in the form of prescribed glasses. Concave lens of appropriate power is used. You can understand here that concave lens is used to correct this refractive error,to counteract or cancel increased refractive index of lens of eye. And image is now formed on retina.

But how many of us like to use spects everywhere. Its cosmatic blemish is always there with them. Contact lens can be used on other hand... As glasses cause minification of lens and can produce diplopia i.e. two images of single object seen by patient. Thick glass's edge also causes chromatic(colour)and spherical abberations {aberration is lapses from perfection},

and most important drawback of glasses is LIMITED FIELD OF VISION. Contact lenses hav overcome all these faults and provide wider and better field of vision. There are also no aberrations by contact lenses as by glasses...one can also go for surgery...(bt..i do hate to have done surgery on me.) Just you take care of contact lenses and they will take care of your eyes...