An internal strabismus is when the patient’s eye position is skewed inward. External strabismus means that the patient’s eye position is skewed inward. The pupil in the middle of the eye of a patient with esotropia is close to the center and looks like two chickens fighting, so it is also called cock-eye. There are two types of strabismus: congenital strabismus and acquired strabismus. In congenital esotropia, the angle of deviation is usually very large. Acquired esotropia is divided into accommodation and non-accommodation. Patients with accommodative esotropia usually have moderate to high hyperopia. External strabismus is divided into intermittent and constant external strabismus, among others. Patients with intermittent esotropia maintain a normal eye position most of the time. The only time they show an exotropic eye position is when they are in the sun or when they are tired and distracted. However, with age, intermittent exotropia may progress to constant exotropia.