The common symptom of diplopia is that both eyes see one object but perceive it as two images. The specific symptoms are as follows: 1. Ipsilateral diplopia: when the external rotation muscle group is paralyzed, the image seen by the left eye is on the left side and the image seen by the right eye is on the right side; 2. Crossed diplopia: when the internal rotation muscle group is paralyzed, the image seen by the left eye is on the right side and the image seen by the right eye is on the left side; 3. Common diplopia: the distance between diplopia images does not change in all directions, often as an unconscious manifestation; 4. The distance between the compound images changes when looking in all directions, which is common in non-common strabismus; 5. Crossed diplopia is common in rectus muscle palsy; 7. Rotational diplopia: due to the tilt of the upper and lower ends of the pseudophakic or imaginary image, the upper end is tilted mainly, and the tilt to the nasal side is internal rotation and to the temporal side is external rotation.