Optical anomaly of the eye

Optical anomaly of the eye:
1 / Myopia: myopia is a very frequent optical defect, characterized by the impossibility of clearly seeing distant objects, the image of objects "far from" is formed in front of the retinal plane, myopia is therefore an Vergence of the eye, the most frequent cause of which is the lengthening of the eye, it is said that the myopic has an eye "too long".
2 / Hyperopia: hyperopia is characterized by the fact that the images form behind the retina even for the infinite, which obliges the hypermetropic to be constantly accompanied at the price of an additional fatigue, the eye of the hypermetropic Is "too short".

3 / Astigmatism: these do not clearly see certain vertical, horizontal or oblique lines of this figure; These subjects are astigmatized. This anomaly is due to defects in refraction of the cornea, the sphericity of which is imperfect.

4 / Presbyopia: the minimum distance of distinct vision increases with age because the maximum vergence of the eye decreases; The aging results in a loss of elasticity of the crystal that can no longer ensure accommodation for nearby objects.