Contrast eye is also known as “crossed eyes”, a medical term for internal strabismus, which is a condition in which the two eyeballs converge and tilt inward, giving the appearance of having more white eyes on the temporal side. It can occur in people of all ages and can be congenital or secondary. Adjusted internal strabismus is often combined with refractive abnormalities, mainly manifested by the uncorrected refractive error, both eyes from the appearance of the internal strabismus, but with the appropriate refractive correction glasses, from the appearance of the eye position is significantly better than before, that is, can be completely or partially corrected by the use of glasses method of internal strabismus. Non-modulated strabismus is a type of strabismus that does not have a modulating factor, but can be combined with an abnormal refractive state, but cannot be corrected with refractive correction glasses. There are four types of strabismus: basic strabismus, actinic deprivation strabismus, periodic strabismus, and acute common strabismus. In addition, there is a physiological condition in which some children have congenital developmental problems that result in the formation of an internal canthus.