The eyelids act to protect the anterior surface of the globe from local injury. Additionally, thmaintenance by distributing the protective and optically important tear film over the cornea during blinking, and they aid in tear flow by their pumping action oney aid in regulation of light reaching the eye, they aid in tear film the conjunctival sac and lacrimal sac.
The upper eyelid extends superiorly to the eyebrow, which separates it from the forehead. The lower lid extends below the inferior orbital rim to join the cheek, forming folds where the loose connective tissue of the eyelid is juxtaposed with the denser tissue of the cheek.
The upper eyelid skin crease (superior v sulcus) is approximately 8-11 mm superior to the eyelid margin and is formed by the attachment of the superficial insertion of levator aponeurotic fibers (8-9 mm in men and 9-11 mm in women).
The inferior eyelid fold (inferior palpebral sulcus), which is seen more frequently in children, runs from 3 mm inferior to the medial lower lid margin to 5 mm inferior to the lateral lid margin.
The nasojugal fold runs inferiorly and laterally from the inner canthal region along the depression of separation of the orbicularis oculi and the levator labii superioris, forming the tear trough. The malar fold runs inferiorly and medially from the outer canthus toward the inferior aspect of the nasojugal fold.
The open eye presents the palpebral fissure, a fusiform space between the lid margins that is 28-30 mm in length and about 9 mm in maximal height. The natural curvature of the upper lid is a function of the static shape of the tarsus combined with adaptation of the lid to the curvature of the globe. In the normal adult fissure, the highest point of the upper lid is just nasal to the center of the pupil, while the lowest point of the lower lid is just temporal to the center of the pupil. In adults, the upper lid margin rests 1.5 mm below the limbus. The lower eyelid margin rests at the level of the lower limbus. The lateral canthal angle is 2 mm higher than the medial canthal angle in Europeans; it is 3 mm higher in Asians. The distance from the medial canthus to the midline of the nose is approximately 15 mm.
The palpebral fissure presents the lateral canthus (an angle of 30-40° approximately 5 mm from the lateral orbital rim); the medial canthus (forming the medial angle of the fissure, with the upper border passing inferomedially and the lower border horizontally); and the lacrimal papillae, which rest on the free lid margin, with the punctum lacrimale serving as an opening to the canaliculus.
Overview of Structure
Structures that must be considered in a description of lid anatomy are skin and subcutaneous tissue, orbicularis oculi muscle, submuscular areolar tissue, the fibrous layer consisting of the tarsi and the orbital septum, lid retractors of the upper and lower eyelids, retroseptal fat pads, and conjunctiva.
Skin and Subcutaneous Tissue
The skin of the eyelids is the thinnest of the body (<1 mm). The nasal portion of the eyelid skin has finer hairs and more sebaceous glands than the temporal aspect, making this skin smoother and oilier. The transition from this thin eyelid skin to the thicker skin of the eyebrow (approximately 10 mm below the lower eyebrow hairs) and the cheek skin (below the nasojugal and malar folds) is clinically evident. These boundaries should be considered in reconstructive eyelid surgery. The subcutaneous tissue consists of loose connective tissue.
Fat is very sparse in preseptal and preorbital skin and is absent from pretarsal skin. Subcutaneous tissue is absent over the medial and lateral palpebral ligaments, where the skin adheres to the underlying fibrous tissue. Dermatochalasis, blepharochalasis, and epicanthic folds all are conditions that primarily involve the skin and subcutaneous tissue of the eyelids.
Orbicularis Oculi Muscle
The orbicularis oculi muscle is one of the superficial muscles of facial expression. Invested by the superficial musculoaponeurotic system (SMAS), muscle contracture is translated into movement of the overlying tissues by the fibrous septa extending from the SMAS into the dermis.
The muscle may be arbitrarily divided into the:
- □ Orbital part
- □ Palpebral parts— The latter being divided further into
- Palpebral parts
- Pretarsal portions
The palpebral portion is used in blinking and voluntary winking.
The orbital portion is used in forced closure.
Facial nerve innervation is from the temporal branches and from zygomatic branches of the facial nerve. The nerves are orientated horizontally and innervate the muscle from the undersurface.
Origin and Insertion
The orbital portion extends in a wide circular fashion around the orbit, interdigitating with other muscles of facial expression. It has a curved origin from the medial orbital margin, being attached to the superomedial orbital margin, maxillary process of the frontal bone, medial palpebral ligament, frontal process of the maxilla, and inferomedial orbital margin. Fibers from this medial origin sweep around the orbital margin in a horseshoe fashion. The muscle fibers extend superiorly to intermix with the frontalis muscle and corrugator supercilii muscle, laterally to cover the anterior temporalis fascia, and inferiorly to cover the origins of the lip elevators.
The preseptal orbicularis muscles overlie the orbital septum and take origin medially from a superficial and deep head associated with the medial palpebral ligament. The fibers from the upper and lower lid join laterally to form the lateral palpebral raphe, which is attached to the overlying skin.
The pretarsal portion lies anterior to the tarsus, with a superficial and deep head of origin intimately associated with the medial palpebral ligament. Fibers run horizontally and laterally to run deep to the lateral palpebral raphe to insert in the lateral orbital tubercle through the intermediary of the lateral canthal tendon (LCT).
Submuscular Areolar Tissue
Submuscular areolar tissue consists of variable loose connective tissue below the orbicularis oculi muscle. The lid may be split into anterior and posterior portions through this potential plane, which is reached by division at the gray line of the lid margin. In the upper lid, this plane is traversed by fibers of the levator aponeurosis, some of which pass through the orbicularis to attach to the skin to form the lid crease. In the lower eyelid, this plane is traversed by fibers of the orbitomalar ligament.
Superior continuance in this submuscular plane arrives at the retro-orbicularis oculi fat (ROOF), which is best developed in the eyebrow region. Additionally, the suborbicularis oculi fat (SOOF) is found in the lower lid in a continuance of this plane.
The tarsal plates are composed of dense fibrous tissue and are responsible for the structural integrity of the lids.
Each tarsus is approximately 29 mm long and 1 mm thick. The crescentic superior tarsus is 10 mm in vertical height centrally, narrowing medially and laterally. The lower border of the superior tarsus forms the posterior lid margin. The rectangular inferior tarsus is 3.5-5 mm high at the eyelid center. The posterior surfaces of the tarsi adhere to conjunctivae.
Each tarsus encloses about 25 sebaceous meibomian glands that span the vertical height of the tarsus. Their ducts open at the lid margin posterior to the gray line and just anterior to the mucocutaneous junction. The medial and lateral ends of the tarsi are attached to the orbital rims by the medial and lateral palpebral ligaments.
Medial Palpebral Ligament
The medial palpebral ligament (medial canthal tendon [MCT]) is a fibrous band stabilizing the medial tarsi and is intricately related with the orbicularis oculi muscle and the lacrimal system.
The superficial head of the pretarsal orbicularis muscle lies anterior to the canaliculi and forms the anterior limb of the MCT. This head is primarily horizontal but also has a superior supporting extension inserting onto the frontal bone.
The deep head of the pretarsal orbicularis muscle (also constituting the Horner's muscle) inserts into the posterior lacrimal crest and onto the fascia of the lacrimal sac.
The upper and lower lid preseptal orbicularis have a superficial head that inserts into and augments the MCT and deep heads that insert into the lacrimal sac fascia.
The lacrimal sac, encased in fascia, is related anteriorly, laterally, and posteriorly to constituents of the MCT and medially to the bony fossa of the lacrimal sac.
Lateral Palpebral Ligament
The lateral palpebral ligament (lateral canthal tendon [LCT]) is formed by dense fibrous tissue arising from the tarsi and passes laterally deep to the septum orbitale to insert into the lateral orbital tubercle 1.5 mm posterior to the lateral orbital rim.
The tendon is approximately 10.5 mm in length and 6.5 mm in width, and the midpoint of the LCT inserts 10 mm inferior to the frontozygomatic suture.
A small pocket of fat (Eisler pocket) lies between the septum and the LCT. The LCT is also attached to the lateral orbital rim more superficially, through the orbital septum. Superiorly, the LCT is contiguous with the lateral horn of the levator aponeurosis, while the inferior edge is well defined and arcs inferiorly to its insertion.
The orbital septum is a connective tissue structure that attaches peripherally at the periosteum of the orbital margin (the arcus marginalis); it centrally fuses with the lid retractor structures near the lid margins, thus acting as a diaphragm reported to retain orbital contents.
A septal extension, from the line of fusion of the orbital septum to the levator aponeurosis, extending caudally to cover the tarsal plate up to the ciliary margin. The septal extension acts as an adjunct to the levator aponeurosis; recognition of this structure is important to avoid relapse or complications in ptosis repair and blepharoplasty.
Levator Palpebra Superioris
The levator palpebra superioris (LPS) arises at the orbital apex from the undersurface of the lesser wing of the sphenoid bone. The levator muscle and superior rectus muscle share a developmental origin and are connected by fibrous attachments.
The LPS proceeds anteriorly for 40 mm and ends in an aponeurosis approximately 10 mm behind the orbital septum. The levator complex changes direction from a horizontal to a more vertical direction at the superior transverse ligament (Whitnall's ligament).
The superior transverse ligament lies near the junction of the muscular and aponeurotic levator and represents an orbital fascial condensation spanning the anterosuperior orbit between the trochlea and the lacrimal gland fascia. Variations in thickness and adherence to the levator complex are evident. Thin fascial attachments lie between the superior transverse ligament and superior orbital rim.
The levator aponeurosis spreads laterally and medially to form lateral and medial horns.
The medial horn attaches to the posterior lacrimal crest.
The lateral horn divides the lacrimal gland into orbital and palpebral lobes before attaching to the lateral retinaculum at the lateral orbital tubercle.
The aponeurosis fuses with the orbital septum prior to reaching the level of the superior tarsal plate border. At the inferior edge of this fusion, some aponeurotic fibers descend to insert into the lower third of the anterior surface of the tarsal plate.
An anterior extension from this fusion inserts into the pretarsal orbicularis oculi muscle and overlying skin, forming the upper lid skin crease.
The levator palpebra superioris is innervated by the superior branch of the oculomotor nerve, entering the muscle from its inferior surface in its posterior third.
Elevation of the lid.
Müller's muscle is smooth muscle innervated by the sympathetic nervous system.
Fibers originate from the undersurface of the levator in the region of the aponeurotic muscle junction, travel inferiorly between the levator aponeurosis and conjunctiva.
Insert into the superior margin of the tarsus. The peripheral vascular arcade of the upper eyelid lies adherent to the lower border of the anterior surface of the Müller's muscle, just above the upper border of the tarsus, and is apparent during blepharoptosis surgery as a plane of dissection is created between the levator aponeurosis and Müller's muscle.
The action is to widen the palpebral fissure with increased sympathetic tone. About 2 mm of ptosis is observed in Horner's syndrome.
Lower Lid Retractors
The lower eyelid retractor is a fascial extension from the terminal muscle fibers and tendon of the inferior rectus muscle, originating as the capsulopalpebral head.
As it passes anteriorly from its origin, it splits to envelop the inferior oblique muscle and reunites as the inferior transverse ligament (Lockwood's ligament). From there, the fascial tissue passes anterosuperiorly as the capsulopalpebral fascia.
The bulk of the capsulopalpebral fascia inserts on the inferior border of the inferior tarsus. Fibers also pass forward to unite with the Tenon capsule and to the inferior fornix conjunctiva, through orbital fat to the orbital septum, and forward to the subcutaneous tissues forming the lower eyelid crease. The orbital septum fuses with the capsulopalpebral fascia approximately 5 mm below the inferior tarsal border.
The inferior tarsal muscle (Müller's muscle) lies just posterior to the fascia and is intimate with its structure.
In the Asian lower lid, the line of fusion of the orbital septum to the capsulopalpebral fascia is often higher, or indistinct, with anterior and superior orbital fat projection, and overriding of the preseptal orbicularis oculi over the pretarsal orbicularis.
Upper eyelid preaponeurotic fat is found immediately posterior to the orbital septum and anterior to the levator aponeurosis. A central fat pad and a medial fat pad are described in the upper lid, while the lacrimal gland occupies the lateral compartment. The medial fat pad usually is pale yellow or white and lies anterior to the levator aponeurosis extending superomedial to the medial horn of the levator.
The central fat pad is yellow and broad. A portion of the lateral end of this pad surrounds the medial aspect of the lacrimal gland. The lacrimal gland has a pinkish lobulated firm structure in contrast to the yellow soft intraorbital fat. The lacrimal gland's anterior border is normally just behind the orbital margin, but involutional changes may lead to prolapse anteroinferiorly, which is prominent on external lid examination.
Three retroseptal fat pads are associated with the lower eyelid. The medial and central fat pads are separated by the inferior oblique. However, an isthmus of fat generally lies anterior to the muscle belly. The inferior oblique muscle takes a bony origin from a shallow depression on the anteromedial orbital floor, directly posterior to the orbital margin and lateral to the nasolacrimal canal.
The conjunctiva is a smooth translucent mucous membrane. Palpebral conjunctiva lines the posterior surface of the lids as tarsal conjunctiva (from the mucocutaneous junction of the lid margin to the tarsal plate border) and continues as orbital palpebral conjunctiva into the fornix.
The tarsal conjunctiva is adherent to the tarsus, while a submucosal lamina propria underlies the orbital palpebral conjunctiva and allows dissection from the vascular Müller's muscle. At the depths of the fornices, conjunctiva reflects anteriorly onto the globe as bulbar conjunctiva.
Sensory innervation of the eyelids is subserved by terminal branches of the ophthalmic (CN V1) and maxillary (CN V2) divisions of the trigeminal nerve (CN V).
Branches of the facial nerve innervate the muscles of facial expression.
The frontal and zygomatic branches of CN VII innervate the orbicularis oculi muscle; the frontal branch of CN VII innervates the forehead muscles.
The orbicularis oculi is innervated by multiple motor branches from the branches of CN VII; in the lower eyelid, they enter the inferior edge of the orbicularis oculi, with branches both lateral and medial to the lateral limbus, and there is no single dominant branch for the supply.
The levator palpebra superioris is innervated by the superior branch of the oculomotor nerve, entering the muscle from its inferior surface in its posterior third.
Müller's muscle (and the inferior tarsal muscle) requires sympathetic innervation. Postganglionic sympathetic fibers arise from the superior cervical ganglion and travel superiorly in the neck as a plexus with the internal carotid artery. The fibers take an intracranial course to the cavernous sinus, where the fibers travel through the superior orbital fissure into the orbit via CN branches.
Both the internal and external carotid arteries contribute to lid arterial supply.
The internal carotid arterial supply is from the terminal branches of the ophthalmic artery medially (giving supraorbital, supratrochlear, and dorsal nasal branches) and the lacrimal artery laterally.
In the medial upper eyelid, two medial palpebral arteries arise from the ophthalmic artery as the superior and inferior marginal vessels and pass laterally—one to supply the upper lid and one to supply the lower lid. The inferior marginal vessel is actually a branch of the superior marginal vessel and passes deep to the MCT and canaliculi for about 10 mm before passing into the lower eyelid proper. These marginal vessels pass horizontally as marginal arcades.
The marginal arcades lie on the anterior tarsal surface approximately 4 mm and 2 mm from the upper and lower eyelid margin, respectively. In the upper lid, a peripheral arcade arises from the marginal arcade and lies on the anterior surface of the Müller's muscle, just above the superior tarsal border, where it is susceptible to injury during blepharoptosis surgery. In the lower lid, no (or only a rudimentary) peripheral arcade exists.
Laterally, the lacrimal artery pierces the orbital septum to give two lateral palpebral arteries. They pass medially, one to the upper eyelid and one to the lower eyelid, and anastomose with the marginal arcades.
The external carotid artery contributes via branches of the facial artery, the superficial temporal artery, and the infraorbital artery. The facial artery gives the angular artery, which passes to the medial canthal region, anastomosing with the dorsal nasal artery. The superficial temporal artery supplies eyelid anastomoses via the transverse facial and zygomatic branches. The infraorbital artery exits the infraorbital foramen as a terminal branch of the maxillary artery, anastomosing with vessels of the lower eyelid.
The eyelids and conjunctiva have a rich lymphatic drainage. The drainage of most of the upper lid and the lateral half of the lower lid is to the preauricular lymph nodes. The medial portion of the upper lid and the medial half of the lower lid drain into the submandibular nodes by vessels that follow the angular and facial vessels.