Emmetropia
When light from the infinite (six meters) enters the visual optical system and focusing on the retina.
Ametropia
When light enters the optical system and is located in one or several different points on the retina. In ametropia are four optical states:
1. Myopia: When the light coming from infinity is focused at a point before the retina.
2. Hyperopia: When light from infinity is focused on one point after the retina.
It is worth noting that the hyperopia facultative and this can be compensated by accommodation, therefore the person reported in good vision.
3. Astigmatism: When the light coming from infinity is located at two different points within the eye’s optical system.
4. Presbyopia: A condition where the visual optical system loses the ability to zoom in the light on the retina. It is a process given by the depletion of physiological eye starting about forty years old, and stabilized to sixty.
