Thyroid associated ophthalmopathy (TAO) is a chronic, multisystemic disease of the orbit caused by an autoimmune response and is closely related to hyperthyroidism. Among adult orbital diseases, thyroid associated ophthalmopathy is the first in prevalence, accounting for approximately 20%, both nationally and internationally. It is currently believed that thyroid-related ophthalmopathy is an organ-specific autoimmune disease characterized by lymphocytic infiltration with mucopolysaccharide and collagen deposition due to autoimmune reactions affecting the periorbital and retrobulbar tissues, with edema, protrusion of the eye, and diplopia as the main clinical manifestations. Early thyroid-related ophthalmopathy may manifest as ocular congestion, conjunctival edema, eyelid recession, and upper lid retardation, followed by ocular protrusion, ocular motility disorders, strabismus, diplopia, and hypermetropia. The diagnosis can be clarified by clinical symptoms + signs, laboratory tests, and relevant imaging. The main pathological change is extraocular muscle hypertrophy. 1. The main clinical manifestations of thyroid-related ophthalmopathy Eyelid signs. Eyelid changes are one of the most important signs of thyroid-related ophthalmopathy. The main signs include eyelid recession, delayed fall of the upper eyelid, and eyelid swelling. Eyelid recession mostly occurs in the upper eyelid, but in a few patients it can occur in both upper and lower eyelids, either in one eye or both eyes. In normal adults, the upper lid margin is positioned between the pupillary margin and the upper corneal margin, about 1 to 2 mm from the lower corneal margin, and the lower lid margin is located just above the lower corneal margin. When the upper lid margin is at or above the corneal margin and the lower lid margin is 1 to 2 mm below the lower corneal margin, the diagnosis of upper or lower lid recession is made. Soft tissue involvement of the eye. Due to infiltration of inflammatory cells in the orbit, patients may present with eyelid and conjunctival congestion and edema, and swelling of the lacrimal gland and soft tissues of the orbit. Soft tissue involvement of the eye is most pronounced in the acute phase. Soft tissue inflammatory changes are of great value in assessing the degree of activity of thyroid-related ophthalmopathy. Extraocular muscle hypertrophy. It is the second most common clinical manifestation after the eyelid sign and soft tissue changes. Hypertrophy or fibrosis of the extraocular muscles may present with ocular symptoms such as ocular motility disorders and diplopia. The first muscle to be involved is often the inferior rectus muscle, which has limited upward eye movement, followed by the internal rectus muscle, followed by the superior rectus muscle, and the external rectus muscle is the least involved. Multiple muscles may be involved at the same time. Protrusion of the eye. Ocular protrusion is defined as a protrusion of the eyeball that is 2 mm above the upper limit of normal or a difference of 2 mm or more between the two eyes. The incidence of ocular protrusion in patients with thyroid-related ophthalmopathy is approximately 40 to 70%. In patients with thyroid-related ophthalmopathy, bilateral proptosis is relatively symmetrical, with 58% of patients having a bilateral proptosis difference of less than 5 mm, 89% of patients having a difference of less than 7 mm, and generally not exceeding 10 mm. If this difference is exceeded, it suggests the possibility of an intraorbital tumor. Because of the discrepancy between different observers and a single observer observing the same patient’s ocular prominence, caution should be exercised in drawing conclusions when the ocular prominence is less than 2 mm change. In terms of the natural progression of thyroid-related eye disease, ocular protrusion is the most persistent change and is difficult to regress once present. Exposure keratoconjunctivitis. Protruding eyes and receding, lagging eyelids can cause difficulty in lid closure, leading to exposure keratitis, corneal ulcers, and punctate lesions of the cornea are seen in most patients with thyroid-related eye disease. Severe corneal lesions such as corneal ulcers and perforations are less common. Clinical examination by slit lamp combined with fluorescein staining is helpful in assessing the patient’s corneal condition. Compressive optic neuropathy. Compressive optic neuropathy is considered to be a serious complication of thyroid-related eye disease. Its incidence can reach about 10%. The main causes: hypertrophy of multiple extraocular muscles and increased volume of orbital connective tissue, resulting in filling of the orbital apex, leading to increased pressure as a result. Patients usually have a slow loss of vision and often complain of pressure and constant distension behind the eye. CT or MRI examinations can clearly show orbital apical crowding, protrusion of the eye, extraocular muscle hypertrophy, dilated supraocular veins, and anterior displacement of the lacrimal gland, suggesting the possibility of optic neuropathy. 2.Surgical treatment of thyroid-related eye disease For patients with a clear diagnosis of thyroid-related eye disease, the treatment mainly includes hormone, radiotherapy and surgery. Glucocorticoid drugs not only inhibit autoimmunity and non-specific anti-inflammatory effects. For active thyroid-related ophthalmopathy, they can significantly improve clinical signs. Therefore, it is often used as the drug of choice for active thyroid-related eye disease. The main mechanism of local orbital radiotherapy is its non-specific anti-inflammatory effect and the high sensitivity of lymphocytes to radiation. Low doses can suppress lymphocytes and alter the ratio of helper T cells/suppressor T cells (Th/1rs), and also reduce GAG secretion by orbital fibroblasts. Their proliferation is inhibited. When the lesion is fibrotic, it is insensitive to radiation, so this method is only effective in patients with early and active thyroid-related ophthalmopathy. Therefore, the general principles of treatment for thyroid-related eye disease are as follows: for mild thyroid-related eye disease, local protective therapy is given; for severe thyroid-related eye disease, the degree of activity needs to be determined first, and treatment such as glucocorticoids and/or radiation therapy should be given if the disease is active, or surgery should be considered if the disease is quiescent. The primary goal of surgery for thyroid-related ophthalmopathy is to maintain the function of the optic nerve and to protect the cornea from exposure. The secondary goal is to maintain monocular vision in both eyes and to restore aesthetics. Hormonal medications and radiation therapy are effective in the acute phase of thyroid-related ophthalmopathy to improve soft tissue inflammation and control disease progression, but are not effective in the advanced stages of the disease when there are fibrotic lesions of the extraocular and levator muscles causing optic neuropathy, strabismus, eyelid retraction, and corneal exposure. Therefore patients will eventually require surgical treatment to address the above problems. Patients with thyroid-related eye disease usually require more than one type of surgical treatment. However, the timing of surgery is very closely related to the patient’s prognosis. Considering the impact of complications arising after surgery: (1) Orbital decompression should be done first to relieve the symptoms of optic nerve compression. The relative position of the orbit to the eye will change after decompression, and the upper lid may be more receding. The eye may have a tendency to slant inward and downward, especially if the double wall decompression involves the inner wall and the fundus of the eye. Orbital decompression is also required first in cases of severe facial deformity. (2) The need for strabismus surgery should be decided prior to eyelid surgery. Otherwise the position of the upper and lower lids will be affected after vertical muscle surgery. (3) Various surgeries on the eyelids. These include upper eyelid lengthening, lower eyelid lift, lid margin suturing, and blepharoplasty. Obviously exposed keratitis is an indication for surgery of the eyelid. The inflammatory or acute phase of thyroid-related eye disease usually lasts about 12 months or longer, during which time the patient’s condition may recur or worsen several times, so the patient’s condition should be stable for at least 6 months, regardless of the procedure chosen. However, emergency surgical treatment such as orbital decompression or eyelid suturing should also be considered when the disease flares up in a way that seriously threatens the patient’s vision or other conditions. In addition, due to the complexity and long-term nature of thyroid-related eye disease, patients must be informed before surgery that a single surgery may not achieve the desired results and should be prepared for multiple surgeries.