Ptosis, also known as ptosis, is the partial or complete loss of function of the muscles that lift the upper eyelid so that the upper eyelid cannot be partially or completely lifted, covering more than 2 mm of the upper corneal edge when the eyes are looking straight ahead. The muscles that lift the upper eyelid are the levator muscle, which is innervated by the motoneurone nerve, and the Müler’s muscle, which is innervated by the cervical sympathetic nerve, and when both of these muscles are incomplete or lost, ptosis occurs. To overcome the visual impairment, patients often have to tighten the frontalis muscle, wrinkle the forehead and shrug the eyebrows to raise the upper eyelid, or in severe cases, they must tilt their head or even use their fingers to stroke the upper eyelid in order to see. Ptosis can be classified as congenital or acquired according to its cause. 1. Congenital ptosis is caused by a defective levator muscle or an underdeveloped nucleus accumbens. It is present from birth, is mostly bilateral, and often has a genetic component. If the ptosis is due to a defective levator muscle, it is usually a simple ptosis, while if it is due to a nerve nucleus hypoplasia, it is often combined with other ocular abnormalities such as canthus, microphthalmia, and strabismus. 2. Acquired ptosis can be divided into the following categories according to its cause: (1) Actinic nerve palsy ptosis: This is caused by damage to the nerve or nucleus accumbens and is usually unilateral, often accompanied by ocular motility disorders and sometimes diplopia. (2) Sympathetic nerve palsy ptosis: This is a partial symptom of sympathetic nerve palsy and is most often seen in patients with neck surgery, trauma, and thyroid. It manifests as mild ptosis, slightly elevated lower lid position forming a small lid fissure, posterior sunken eyes, and narrow pupils, constituting Hner’s syndrome. (3) Myogenic ptosis:Commonly associated with myasthenia gravis and progressive extraocular muscle palsy, ptosis due to myasthenia gravis is worse with fatigue, lighter in the morning and worse in the evening with fatigue, and symptoms improve significantly with neostigmine injection. (4) Mechanical ptosis:This is due to lesions of the eyelid itself, such as tumors, amyloidosis, severe trachoma, inflammatory edema, trauma, and tissue proliferation (elephantiasis). In addition to the direct destruction of the levator muscle, the lesion causes hypertrophy of the eyelid, resulting in mechanical ptosis. There is another type of ptosis of unknown origin, geriatric myopathic ptosis, which is due to primary muscle atrophy and is bilateral and is more common in older women. Treatment for ptosis should be administered differently depending on the cause. For congenital ptosis, surgical correction is effective, whereas for acquired ptosis, treatment should be tailored to the different causes. In cases such as myotonic dystrophy, total eye muscle paralysis, or diplopia after lid lift, surgical correction is not indicated. Severe myasthenia gravis should generally not be surgically corrected, but if it is confined to the eyelid and medication is unsatisfactory or unacceptable then surgical correction may be considered. The timing of surgery for congenital ptosis has been considered by most people in the past only in terms of the impact on visual function, but in fact it should be determined in terms of both necessity and feasibility. Necessity refers to the fact that if surgery is not performed in a timely manner, it will affect the child’s normal visual development. Feasibility refers to the fact that the degree of ptosis is already fixed and the correction will not change due to the child’s growth and development. Generally, surgery is appropriate when the child is 2 to 4 years old. In children with congenital ptosis, if the ptosis is monocular, it is more fixed after one year of age and begins to form an internal image of itself around the age of 3. If the ptosis is not treated in a timely manner, it can easily affect the child’s normal psychological development. In children with severe ptosis, if surgery is delayed, compensatory phenomena such as forehead frowning, eyebrow raising, jaw elongation, and head tilting back can develop. In monocular cases, the development of visual function in the affected eye is affected and in a few cases amblyopia develops. However, in cases of paralytic ptosis, surgery should not be performed immediately if there is a combination of other extraocular muscle paralysis and diplopia after lid lifting, as this may cause more hindrance to the patient’s life and work after surgery than is warranted. In the case of a trauma-induced ptosis, it is important to repair the severed end of the muscle in time for the surgical revision of the trauma, otherwise surgery should be performed after the local reaction has subsided, usually about 3 months after the injury when the scar is stable.