The term strabismus is used to describe the condition in which the eyes do not move together in a coordinated fashion. This is usually because one of the eyes' muscles are weak. Cross-eye (a.k.a. esotropia), the condition where one eye looks straight ahead while the other moves towards the nose, is just one particular form of strabismus. Other forms include exotropia, hypertropia, and hypotropia. With exotropia (a.k.a. wall-eye), one eye wanders outwards to the side of the head. People with hypertropia have one eye turned upwards. Hypotropic people have one eye that turns downward.
If this condition is not treated, strabismus may also lead to amblyopia, or "lazy eye", another condition in which the child loses some or all vision from the weak eye.