Eyelid
Overview
The eyelid (palpebra) is a thin fold structure composed of skin, muscle, and conjunctiva that covers the front of the eyeball. It protects the eyeball from external stimuli, distributes tears evenly, and keeps the cornea moist. It is divided into the upper eyelid (superior palpebra) and lower eyelid (inferior palpebra), and through blinking it removes foreign substances and rebuilds the ocular surface. Abnormalities in eyelid shape and function go beyond simple cosmetic issues and can lead to serious complications such as vision loss, dry eye syndrome, and corneal damage, giving them important clinical significance in ophthalmology.
Main Content
Anatomical Structure
The eyelid is composed of five layers: skin, subcutaneous tissue, muscle layer, tarsus (tarsal plate), and conjunctiva. The skin is one of the thinnest areas of the body. The orbicularis oculi muscle closes the eye, while the levator palpebrae superioris and Müller muscle open it. Within the tarsus, numerous meibomian glands secrete the lipid component of the tear film and prevent tear evaporation. The upper eyelid has 100–150 eyelashes, and the lower eyelid has 50–80; the glands of Zeis and glands of Moll at the eyelid margin are involved in lubricating the eyelashes. The eyelids are rich in blood vessels and lymphatic vessels, so they swell easily during inflammation and bleed readily.
Function
Its most basic function is protection of the eyeball. Blinking occurs about 15–20 times per minute and redistributes the tear film over the corneal surface. Tears consist of a three-layer structure—lipid layer, aqueous layer, and mucous layer—and the lipid layer secreted by the eyelid's meibomian glands suppresses evaporation on the outermost side. The eyelids also block light, contributing to the regulation of sleep and wakefulness, and play an important role in facial expression and nonverbal communication. When a foreign substance approaches, the corneal reflex causes reflexive closing to protect the eyeball.
Major Diseases
Representative eyelid diseases include hordeolum (stye), chalazion, blepharitis, entropion (inward turning of the eyelashes), ectropion, ptosis (drooping eyelid), blepharospasm (eyelid spasm), and eyelid tumors. A hordeolum is an acute inflammation of the eyelid glands caused by staphylococcal infection, while a chalazion is a chronic granulomatous inflammation. Ptosis is divided into congenital and acquired; acquired ptosis can be caused by age-related laxity of the levator aponeurosis or by neurological causes such as myasthenia gravis, Horner syndrome, and third cranial nerve palsy. Eyelid tumors are mostly benign, but malignant tumors such as basal cell carcinoma, squamous cell carcinoma, and melanoma can also occur, requiring biopsy.
Diagnosis and Treatment
Diagnosis of eyelid disease is made through visual acuity testing, slit-lamp microscopy, measurement of eyelid position (palpebral fissure, MRD1/MRD2), and tear film break-up time (BUT) measurement. Hordeolum is treated with warm compresses and antibiotic ointment, while chalazion is treated with steroid injections or incision and drainage. For ptosis, if it is severe or obstructs the visual field, surgical correction such as levator resection or Müller muscle resection is considered. Entropion can cause the eyelashes to irritate the cornea and lead to ulcers, so electrolysis, cryotherapy, or surgical correction is required. Eyelid surgery often combines functional and cosmetic purposes, making sufficient consultation with the patient important.
Recent Trends
In 2024–2025, digital technologies are being actively introduced into the diagnosis and treatment of eyelid diseases. Research using AI-based facial image analysis to automatically screen for ptosis and entropion is active, and self-analysis of eyelid photographs using smartphone apps has entered the commercialization stage. As interest in dry eye syndrome and meibomian gland dysfunction (MGD) grows, eyelid thermal compression devices and intense pulsed light (IPL) equipment are being widely used. For dry eye treatments, prescription use of cyclosporine, lifitegrast, and others is expanding, and new therapies that induce meibomian gland regeneration are in clinical trials. Cosmetic double eyelid and under-eye fat repositioning surgeries increasingly pursue natural results, and fast-recovery non-incisional and buried suture methods are preferred. Functional blepharoplasty to correct age-related ptosis and eyelid drooping is also increasing in demand along with the aging population. In addition, a multidisciplinary approach with collaboration among ophthalmology, dermatology, and plastic surgery is becoming standard, and the importance of patient education to prevent postoperative dryness and corneal complications is emphasized.
Related Topics
- [[Dry eye syndrome]]
- [[Ptosis]]
- [[Meibomian gland]]
- [[Ophthalmology]]
- [[Cornea]]
- [[Tears]]
- [[Blepharitis]]
- [[Double eyelid surgery]]