Strabismus is a misalignment of the eyes; it is a condition in which the eyes do not fixate as a pair, but one eye deviates inward, giving them a "crossed" look. One of the eyes may be turned in or out, or even up or down. Normally, the two eyes are designed to work together as a team, especially to improve depth perception and increase peripheral vision. This eye teamwork is significantly impaired by the misalignment of strabismus.
Exotropia: eye turns out away from the nose
Esotropia: eye turns in toward the nose
Hypertropia: Eye turns up
Hypotropia: Eye turns down