Myopia is a vision condition in which people can see close objects clearly, but objects farther away appear blurry.
The main causes of myopia are three:
- the eyeball is too long;
- the cornea or the crystalline lens have too much curvature;
- the altered refractive power of the crystalline lens.
Myopia is measured in diopters.
Moreover, there are different degrees of myopia: mild myopia (within 4 diopters), medium myopia (up to 8 diopters) and high myopia. Finally, there is a further distinction: physiologic myopia and pathological myopia.
Physiologic myopia, the most common type, is a simple physical mismatch between the length of the eyeball and the focusing power of the lens.
Pathological myopia is a type of myopia where the eyeball continues to grow, becoming longer than it should be, leading to degenerative alterations. This form of myopia usually begins during adolescence and it has been described also as progressive or malignant myopia.