The difference in height between the two eyes is usually due to several reasons: 1. due to monocular ptosis, as the eyelids of one eye cannot be elevated to normal height, thus making both eyes appear not to be at the same level, but without affecting visual function. 2. due to vertical strabismus, as the superior rectus, inferior rectus, superior oblique, and inferior oblique muscles, which control the vertical movement of the eye 3. Thyroid-related ophthalmopathy, which is caused by the protrusion of the orbital soft tissues, and the enlarged and impaired function of the extraocular muscles, causing the two eyes to not be at the same level, resulting in different heights.