The reason of eye defects are varied from different eye defects. For example, If you suffered from Hypermetropia, some people also called it long-sightedness. And it can happen when the lens is unable to thicken sufficiently. Besides, myopia is also a common eye defects for most of people. And most people called it nearsightedness, is a condition in which the light rays are focused in front of the retinal surface. The lens of the eyes can focus close objects, but can't focus distance objects. And these eye defects can be corrected by eyeglasses.