A person who is myopia has trouble seeing targets in the distance, but he or she can see close targets well. Nearsightedness is also called “myopia”.

In some cases, myopia is a heritable condition due to an unusually long eye, as measured from front to back. As there’s a longer distance between the cornea (the clear “window” that crosses the front of the eye) and the retina (the light-sensitive bed at the back of the eye), images tend to focalise ahead of the retina, instead of than on the retina itself.

In other cases, myopia is the final result of a mismatch between the length of the eye and the power of the eye’s lens to focus an image in the correct location. Once Again, this results in a state where images to focus ahead of the retina, resulting in nearsightedness.

So, if you are nearsighted, you have to have on spectacles so that correct your visual flaw. The rationale of the lens arrangement within the spectacles is to modify the focal length of the light rays reflected from the target visual object, so that it focuses precisely on the retina. That way you will make out a sharply focussed object in the distance. So your spectacles have to have a lens that counters any blemish in your own cornea/lens focussing system.