Strabismus is a phenomenon in which the visual axis of both eyes cannot look at the same target at the same time, and only one eye looks at the target while the other eye’s visual axis deviates to the side of the target. There are many kinds of strabismus, the most common one is the inward strabismus, which is called internal strabismus, commonly known as “opposite eye” and “crossed eyes”. The most common type of strabismus is inward strabismus, which is known as “crossed eyes” and “crossed eyes”, and outward strabismus, which is known as exotropia. Of course, strabismus does not only refer to cases where the relative position of the two eyes is obviously deformed, but also includes cases where the obliquity is so small that it is not easily detectable on the surface, but the visual function of both eyes is not normal. Therefore, the concept of strabismus should be understood as an abnormality in both the relative position of the two eyes and the visual function of both eyes. There is no organic lesion in the eye, but the distance visual acuity is less than 0.9 and the corrected visual acuity is not normal due to functional factors; or there are organic changes and refractive abnormalities, but the visual acuity is low and uncorrectable which is not compatible with its lesion is called amblyopia. Amblyopia is divided into mild amblyopia (visual acuity 0.8-0.6), moderate amblyopia (visual acuity 0.5-0.2), and severe amblyopia (visual acuity less than or equal to 0.1) by degree. Amblyopia can occur during visual development, mostly starting at the age of 1 to 2 years. The earlier the onset of amblyopia, the more severe it is.