In order to understand how<unk>  occurs, we must understand of how the eye can maintain proper fixation with non aligned visual axis.<unk>  is actually the misalignment of the visual axis of both eyes. In other words, one or both eyes are not properly fixated to an object of interest. However, we must know that the eyes have a fusional vergence system which corrects this misalignment.
Heterophoria
Orthophoria
Esophoria
Exophoria
Polycoria
Musical anhedonia
Sexual anhedonia
Astigmatism 