It is mainly divided in two groups: Phoria (Hidden Squint) A binocular vision problem. This is a tendency for one eye to move horizontally or vertically away from the point of focus. Phoria can cause discomfort and headaches associated with the use of the eyes at distances, close up, or both. Some patients with phorias will see double when they get tired. Phoria can be detected with a cover test. Tropia( Manifest squint) is defines as manifest squint which is obvious all the time. An eye may turn in (convergent squint) or out (divergent squint) or one eye can be higher or lower than the other (vertical squint). A squint might be in one eye or swap between the eyes.