A-exotropia: also known as exotropia A sign, exotropia Aphenomenon, A-exotropia, divergent strabismus A syndrome, i.e., the degree of exotropia becomes smaller when looking straight up, or even disappears, while the degree of exotropia increases when looking straight down. In this case, the exotropia becomes smaller or even disappears when looking directly above, while the exotropia increases when looking directly below. There is no change in the degree of exotropia when looking far and near, and the superior oblique muscle is often overactive, and the eyeball is sunken in the internal eye position. Patients may have an inward jaw movement, a small solid field of vision in both eyes, and often a terror-like appearance. There are many reasons for the formation of A-V sign, including factors of the extraocular muscles themselves, anatomical factors, innervation factors and genetic factors. The development of A-V sign is mainly due to the imbalance of abduction and fusion function. When there is insufficient pooling ability and low fusion ability, it cannot counteract the excessive abduction ability and makes the eye position have a tendency to deviate outward.