The appearance of crossed eyes is that the two eyes are inwardly oriented, which is the direction of the root of the nose, just like the eyes of a chicken. The internal strabismus is congenital and has been present since birth. It is usually accompanied by hyperopia, which may cause abnormal corrective vision and abnormal stereoscopic vision due to the skewed eye position. If you have crossed eyes since birth, early surgery is recommended in order to effectively improve your naked eye vision and stereo visual function. If the correction is late, the stereo vision will be greatly affected even after the correction of the strabismus, or crossed eyes.