Correction of myopia
Schematic depiction of the human eye with its anterior (left) and posterior (right) eye chamber, in front of the lens and seperated by the iris. On the right: The exit of the optic nerve. Myopia (shortsightedness) can have two reasons, the first is a too long eyeball (axial myopia), the second is too much refractive power (refractive myopia). The result is, in both cases, that the seen picture isn't depicted sharply on the retina, but in front of it, and as blurred circles on the retina. This can be corrected by concave glasses.