Asymmetry of Bell’s phenomenon in both eyes is one of the symptoms of monocular double supination palsy. Monocular double elevator paralysis is characterized by asymmetry of Bell’s phenomenon in both eyes, which is often poor or absent in the affected eye. Double elevator paralysis refers to the simultaneous paralysis of the superior rectus and inferior oblique muscles in one eye. The clinical presentation is a downward strabismus in the affected eye, mostly combined with horizontal strabismus and ptosis. This ptosis is mostly pseudo or mixed and is easily misdiagnosed as congenital ptosis. The diagnosis of asymmetrical binocular bells: 1. Eye position In the first eye position, the affected eye is downslanted, with a large downslope, often combined with exotropia, and the downslope is usually greater than 30△, while the exotropia is mostly within 20△. 2.Ocular movement The upward rotation of the superior rectus and inferior oblique muscles is obviously limited when the affected eye is in the first eye position and the eyes are moving in the same direction. 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 on the pull test, and the upper rectus and lower oblique muscles of the affected eye are partially or completely incompetent on the active contraction test. 3. Ptosis The affected eye often has true, pseudo or mixed ptosis. If the ptosis of the affected eye disappears when the affected eye is covered and gazed upon, the lid fissure of the affected eye is larger than that of the affected eye, which is considered pseudo- ptosis; if the ptosis of the affected eye improves when the affected eye is gazed upon, but still does not reach the normal height of the lid fissure and is smaller than that of the affected eye, which is considered mixed ptosis; if the ptosis of the affected eye does not improve, which is considered 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. Because of the downward slant of the affected eye and the combination of exotropia and ptosis, amblyopia often occurs in the healthy eye and is associated with amblyopia in the affected eye in about 50% of cases. Bell’s phenomenon is asymmetrical in both eyes, and is often worse or absent in the affected eye. 6. Lower lid changes Due to the retraction of the inferior rectus muscle, which travels through the fascial ligaments to the lower lid, 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 the traction test.