Cryptotropia, or occult strabismus, is a type of strabismus. The muscle imbalance between the two eyes has a tendency to deviate, but in normal times, there is coordination between the eye muscles to obtain the fusion of objects in both eyes, so that the appearance does not show a strabismus state, which is called occluded strabismus. When the right alternate right and left eyes are covered, and the eye that is immediately removed from the cover is found to have movement or deviation, it proves that the child has occlusion. Since children with occluded strabismus have good fusion and can still maintain monocularity in both eyes, the strabismus is not apparent on the outside. Occult strabismus and dominant strabismus are convertible, and occult strabismus can develop into intermittent strabismus and gradually become constant strabismus or dominant strabismus. The discovery of occult strabismus and intermittent strabismus has positive significance for the early detection and treatment of strabismic amblyopia.