Anatomy & Physiology
Emmetropia & Ametropia

Simple Myopic Astigmatism One point comes to focus on the retina and one point comes to focus in front of the retina.	Simple Hyperopic Astigmatism One point comes to focus on the retina and one point comes to focus behind the retina.
Compound Myopic Astigmatism Both points of light come to focus in front of the retina.	Compound Hyperopic Astigmatism Both points of light come to focus behind the retina.
Mixed Astigmatism One point of light comes to focus in front of the retina, while the other comes to focus behind the retina.