1. Structural and functional features The eyelid is a curtain-like structure, divided into two parts: the upper and lower lids. The upper lid is wider than the lower lid. The eyelid covers the orbital outlet and the anterior part of the eyeball, and its main function is to protect the eyeball. The eyelid skin is thin and elastic to accommodate eyelid movement. The orbicularis oculi and levator aponeurosis muscles work organically to keep the eyelid close to the surface of the eye, yet open and close freely. The reflexive closing action of the eyelid protects the eye from bright light and foreign objects. Frequent transient movements of the eyelid remove dust or microorganisms from the surface of the eye and spread tears evenly over the corneal surface, forming a tear film and preventing corneal dryness. The eyelashes grow before the lid margin to remove dust and diminish the stimulation of intense light. 2. Types of eyelid disease The eyelids occupy a major position on the face, and diseases of the eyelids often affect appearance. The skin of the eyelids is part of the skin of the entire body, so all skin lesions can occur on the eyelids, such as contact dermatitis, viral blepharitis, squamous cell carcinoma, and basal cell carcinoma. Many eyelid disorders occur in association with malfunction of the eyelid opening and closing functions or eye position relationships, such as entropion, ectropion, and ptosis. The diagnosis of many eyelid disorders can be made by visual observation alone. Even if the tumor is examined pathologically, it is relatively easy to obtain material. 3. Precautions in the treatment of eyelid disease It is important to maintain the integrity of the eyelid and its normal relationship to the eyeball and to maintain the function of the eyelid. For example, when dealing with ocular trauma, the eyelid should be sutured in layers according to its anatomy, and the skin should not be removed during debridement. Plastic surgery should be performed when removing a tumor. Because the shape of the eyelid is so important to a person’s appearance, cosmetic considerations should be taken into account when performing eyelid surgery and trauma management. The veins of the eyelid communicate with each other and the face without venous valves, and septic infections of the eyelid can easily reflux through these veins into the cavernous sinus. Therefore, when dealing with eyelid inflammation, it is important not to squeeze the affected area arbitrarily to avoid spreading the inflammation. Common disorders of the eyelid include inflammation, abnormal position and function, congenital anomalies, and tumors.