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 can be easily misdiagnosed as congenital ptosis. Treatment and Prevention of Bilateral Bell Phenomenon Asymmetry: The vertical strabismus is greater in the first eye position in monocular double supination palsy and may be accompanied by overfunctioning of the antagonist muscle in the ipsilateral eye and the spouse muscle in the contralateral eye, so surgery should focus on reducing the antagonist and/or spouse muscles to correct the vertical strabismus. If the affected eye is a gaze eye, according to Hering’s rule, the upward slope of the healthy eye is obvious, so we can consider weakening the upward and downward slope muscles of the healthy eye, which can take care of the frontal and lower gaze field without double vision. The following surgical design is used according to the above principles and vertical obliquity. 1. For vertical obliquity less than 30△, posterior migration of the lower rectus muscle of the affected eye; for 30△ to 50△, posterior migration of the lower rectus muscle of the affected eye and the upper rectus muscle of the healthy eye or lower rectus muscle amputation; for more than 50△, in addition to posterior migration of the lower rectus muscle of the affected eye and the upper rectus muscle of the healthy eye or lower oblique muscle amputation, the tendon of the upper oblique muscle of the affected eye should be amputated at the same time, which is the preferred method for the first operation. In case of combined horizontal obliquity, only one external rectus muscle posterior migration is done, which avoids ischemic lesions in the anterior segment of the eye due to simultaneous surgery of more than 2 rectus muscles in the same eye. For those who still have vertical obliquity after the first surgery and after 6 months of observation, the upper rectus muscle of the affected eye is removed or the lower oblique muscle of the healthy eye is excised for the second time; if the affected eye has already had 2 rectus muscles done and still has external obliquity, then the outer rectus muscle of the healthy eye is posteriorly migrated and the inner rectus muscle is excised. For pseudo ptosis, after correction of the vertical slope, the affected eye turns into a gazing eye and the ptosis disappears, so it is not necessary to consider surgery; for mixed ptosis, only the levator muscle folding is performed; for true severe ptosis, Bell’s phenomenon improves after correction of the eye position, and for cosmetic reasons, shortening of the levator muscle or frontalis flap suspension is feasible, but the amount of surgery should not cause exposure However, the amount of surgery should not cause exposure.