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, which is mostly pseudo or mixed and easily misdiagnosed as congenital ptosis. Asymmetry of the bell phenomenon in both eyes should be diagnosed differently from the following diseases: 1. Supraoptic rectus muscle palsy alone: This is characterized by upward strabismus in the affected eye and downward strabismus in the affected eye when the affected eye is gazing. The eye movement can be seen as insufficient rotation of the affected eye to the outside, which can be followed by overfunctioning of the contralateral eye mate muscle (inferior oblique muscle) or the direct antagonist muscle (inferior rectus muscle) of the ipsilateral eye, and unrestricted rotation of the inside and top. The only thing seen on the synoptic examination is that the external superior orientation of the affected eye is significantly lower than that of the healthy eye. Ptosis may be combined with ptosis, but is mostly true. 2. Inferior oblique muscle palsy alone: The eye position is low, the eye is restricted to turn inward, the superior oblique muscle is too strong, and the Bielschowsky head tilt test is positive, i.e., the eye is more oblique when the head is tilted to the healthy side. External upward rotation is normal and is not accompanied by ptosis. 3. Inferior oblique muscle and inferior rectus muscle adhesion syndrome: The eye position is low and the eye is restricted in internal upward, external upward and downward rotation. There is significant resistance to the inferior rectus muscle on the pull test. It is not associated with ptosis. 4. Congenital ptosis: Congenital ptosis is classified as mild, moderate or severe depending on the degree. Except for severe ptosis, which can cause amblyopia, amblyopia rarely occurs in congenital ptosis without strabismus, high refractive error, or refractive error. In addition, in congenital ptosis, the levator muscle is weak and does not disappear when the gaze is changed. 5. Orbital floor fracture: In cases with embedded extraocular muscles and surrounding tissues, vertical diplopia, limited upward and downward eye rotation, and limited upward and downward eye rotation on the pull test can be seen.