The distance between the upper and lower eyelid margins is called the palpebral fissure, which is about 9 mm in Westerners and 7-8 mm in Easterners.When the upper eyelid margin falls below 2 mm below the upper corneal margin for any reason, so that the upper lid covers part or all of the pupil and causes visual impairment, it is called Ptosis (upper eyelid ptosis).
Etiology: The main muscle that lifts the upper lid is the levator palpebrae, with the frontalis and Müller muscles acting as synergists. The levator aponeurosis is innervated by the ophthalmic nerve, and the Müller muscle is innervated by the sympathetic nerve. Various degrees of ptosis can result from the loss of function of the levator and Müller muscles for various reasons. Patients with ptosis tend to contract the frontalis muscle excessively or look up to get rid of the visual impairment. Ptosis not only affects appearance and appearance, but also visual function such as visual field and vision development.
Classification: There are several ways to classify ptosis. It is classified as mild, moderate, or severe based on the height of the lid margin or the degree to which the pupil is obscured. When the frontalis muscle is removed, the upper lid margin is located at the superior pupil margin for mild; at the superior pupil margin and obscuring 1/2 of the pupil for moderate; and obscuring more than 1/2 of the pupil for severe. The etiologic classification is more helpful in the overall understanding, diagnosis and treatment of the disease. The following is a comprehensive classification of the room.
I. Congenital Ptosis
The most common type of ptosis is due to hypoplasia of the levator muscle or a disorder of the nerves (peripheral and central) that innervate it. There are four clinical types of ptosis, depending on whether the ptosis is associated with abnormalities of the eye or other areas.
1. Simple ptosis, which is the most common type, is caused by the developmental abnormality of the levator muscle, resulting in diminished function or loss of function, and is not associated with extraocular muscle dysfunction or other abnormalities.
2. Ptosis with extraocular muscle paralysis is reported in 12% of congenital ptosis and is associated with paralysis of the superior rectus or inferior oblique muscles in addition to ptosis, resulting in limited upturn of the eye. This is usually due to a central neurodevelopmental disorder.
3. Ptosis syndrome, which is characterized by ptosis, small lid fissures, inverted medial canthus, and widened medial canthus, is called small lid fissure syndrome, also known as komoto syndrome, and is sometimes associated with small eyeballs, lid defects, and polydactyly or syndactyly.
4. Synergistic ptosis, mandibular-transient syndrome (Macus-Gunn syndrome), manifests as ptosis on one side at rest, and when chewing, opening the mouth, or moving the jaw to the opposite side, the ptotic upper lid suddenly lifts to normal, or even beyond the normal eyelid height on the opposite side. This is a specific type of congenital ptosis, which may be caused by an abnormal connection between the extra-parietal nerve portion of the trigeminal nucleus and the nucleus accumbens region of the levator muscle, or by an abnormal connection of the motor branch occurring between the trigeminal nerve and the motoneurotic nerve. The condition has a tendency to heal on its own, and some patients return to normal ptosis after developmental maturity.
Acquired ptosis
1. Ptosis with oculocutaneous nerve paralysis occurs when there is damage to the peripheral or central part of the oculocutaneous nerve, sometimes accompanied by paralysis of the extraocular muscles and changes in the pupil. The cause can be tumor, trauma, inflammation, or vascular disease.
2. Sympathetic ptosis is a type of ptosis that occurs when the sympathetic nerve is paralyzed and causes dysfunction of the Müller muscle, such as sunken eyeballs on the side of the lesion, reduced pupil size, smaller lid fissures, and the same let’s-get-it-done ridge (2).
3. Myogenic ptosis, the most common type of ptosis is myasthenia gravis. The earliest symptom in patients with generalized myasthenia gravis is ptosis, with the typical “morning lightness and evening heaviness” phenomenon, and a positive neostigmine test can help in the differential diagnosis. In addition, chronic progressive extraocular muscle paralysis, progressive myotonic dystrophy, and myotonic syndrome are all associated with myogenic ptosis.
4. Tenosynovial ptosis is caused by damage to the levator aponeurosis due to various causes. It is also the more common type of ptosis. It is classified as traumatic, age-related, medical and atrophic.
5. Mechanical ptosis is caused by lesions of the eyelid itself, such as tumors, inflammation, scarring, and tissue proliferation that increase the weight of the eyelid itself, resulting in ptosis.
III. Pseudopelvic ptosis
The appearance shows a drooping upper eyelid, but objective examination reveals that the levator muscle strength is normal, the upper eyelid margin is in a normal position, or the lid margin is in a lower than normal position due to a lack of eyelid support, and the levator muscle strength is basically normal. The main causes of pseudopalpebral ptosis are as follows.
1. Upper lid skin laxity. In elderly people, the upper lid skin laxity covers part or all of the pupil, obscuring the visual field and affecting the visual field in severe cases, but after lifting the upper lid skin the lid margin position is seen to be normal and the function of the levator muscle is checked normally. The symptoms can be improved by surgically removing the loose skin.
2. Lack of support of the upper lid, small eyeballs, sunken eyeballs, and atrophy of the eyeballs can cause the eyelid to lose support, resulting in lid collapse and lower than normal lid margin position.
3. Protective pseudophakic ptosis, which can occur as a result of corneal inflammation, changes in luminosity, reflexive half-closed eyes, or half-closed eyes in wind and dust blowing.
4. In patients with abnormal eye position and superior obliquity, the upward turning pupil is excessively obscured by the eyelid and mistaken for the presence of ptosis; clinical differentiation should be noted against the function of the levator muscle in normal eyes.
Pathogenesis: In terms of the mechanism of ptosis, there are four main types: neurogenic, myogenic, tenosynovial, and mechanical. Neurogenic ptosis mainly refers to ptosis caused by dysfunction of the motoneurotic and sympathetic nerves that innervate the levator and Müller muscles, including motoneurotic nerve palsy, oculomotor palsy, mandibular-transient syndrome, and Horner’s syndrome. Myogenic ptosis mainly refers to hypoplasia of the levator muscle alone or with hypotony of the extraocular muscles and includes congenital ptosis, microphthalmos syndrome, and myasthenia gravis. Tendonoplegia refers to ptosis caused by lesions of the levator aponeurosis, including age-related ptosis and lid laxity. Mechanical ptosis refers to ptosis caused by eyelid tumors or scarring.