Asymmetry of Bell’s phenomenon in both eyes is one of the symptoms of monocular double supination palsy. Monocular double supination palsy is characterized by asymmetric Bell phenomenon in both eyes, which is often poor or absent in the affected eye. There are congenital and acquired forms of the disease, and the true etiology is not well understood. The pathological changes are mainly located in the anterior horn of the spinal cord, where the motor cells are significantly reduced and degenerated, with residual nerve cells showing consolidation and nucleolysis, thinning of the axons of the anterior spinal cord roots, and swelling of the peripheral cells of the axons. Brainstem motor nerve nucleus degeneration, with facial nerve, vagus nerve, and hypoglossal nerve are more common. The examination items include the following: 1. Eye position: the affected eye is downgradient in the first eye position, the downgradient is large, often combined with exotropia, the downgradient is usually greater than 30△, and the exotropia is mostly within 20△. 2. Eye movement: When the affected eye is in the first eye position and the eyes are moving in the same direction, the upward rotation movement of the superior rectus and inferior oblique muscles are obviously restricted. The examination of the same vision machine mainly shows that the left upper and right upper position of the healthy eye is higher than the affected eye. The lower rectus muscle of the affected eye is not mechanically restricted by the pull test, and the upper rectus and lower oblique muscles of the affected eye are partially or completely incompetent by the active contraction test. 3. Ptosis: The affected eye is often associated with true, pseudo, or mixed ptosis. If the ptosis of the affected eye disappears when the affected eye is covered and the lid fissure is larger than the affected eye, this is considered pseudo- ptosis; if the ptosis of the affected eye improves when the affected eye is looked at, but still does not reach the normal height of the lid fissure and is smaller than the affected eye, this is considered mixed ptosis; if the ptosis of the affected eye does not improve, this is true ptosis. According to Hering’s rule, the nerve impulses from the brain are determined by the need to gaze at the eye. In monocular double supination paralysis, the normal nerve impulses from the brain are appropriate for the healthy eye, but for the double supination paralysis in the affected eye, the impulses are insufficient to cause normal contraction and backward rotation, and there are few nerve impulses to the levator muscle at the same time, so when the healthy eye is gazing, ptosis ensues in the affected eye. When the paralyzed eye is covered, the brain must strengthen the nerve impulses to the supraspinatus in order to maintain the gaze of the paralyzed eye, and the nerve impulses to the levator muscle are also strengthened, so the ptosis disappears, which is called pseudo- ptosis. 4. Visual acuity: Because of the downward slant of the affected eye and the combination of exotropia and ptosis, amblyopia often occurs in the healthy eye, and about 50% of cases are accompanied by amblyopia in the affected eye. 5. Bell’s phenomenon: Bell’s phenomenon is asymmetrical in both eyes and tends to be worse or disappear in the affected eye. 6. Lower lid changes: Due to the retraction of the inferior rectus muscle, which is transmitted to the lower lid through the fascial ligaments, the affected eye often shows creasing or deepening of the skin at the lower lid margin when gazing downward; or recession of the lower lid. Double superior rotator muscle palsy in one eye is less common clinically and is not difficult to diagnose based on its clinical features and the necessary tests, such as the emmetropic machine and retraction test.