Structure of the eyelid margins
The eyelids follow the contour of the anterior segment of the eye and are covered by thin, mobile skin. They close at the free margin, forming the palpebral fissure (rima palpebrarum). At the angles of the palpebral fissure, the eyelid margins are anchored to the bones by the medial and lateral palpebral ligaments.
Two margins of the eyelid are distinguished:
- Anterior margin (limbus palpebralis anterior). Eyelashes grow here, and sebaceous glands open into their bases.
- Posterior margin (limbus palpebralis posterior). This margin features the openings of the meibomian (sebaceous) glands embedded within the tarsal plate.
The lateral 2/3 of the eyelid margins are covered with eyelashes, while the medial third is devoid of them. This lashless part bounds the lacrimal lake (lacus lacrimalis). Inside the lake lies the lacrimal caruncle (caruncula lacrimalis), and externally it is bounded by the lacrimal fold of the conjunctiva (plica lacrimalis).
Layer-by-layer topography of the eyelids
Viewing the eyelid from superficial to deep, four main layers can be identified:
- Skin and subcutaneous tissue. The tissue is very loose, which predisposes it to easy edema. Vascular anastomoses between the vessels of the face, eye, and temporal region pass through it.
- Muscular layer (orbicularis oculi muscle, m. orbicularis oculi). Consists of three parts: orbital (extends beyond the eyelids), palpebral (attaches to the palpebral ligaments), and lacrimal (surrounds the lacrimal sac and acts as a pump during blinking).
- Fibrous skeleton. Composed of the dense tarsus of the eyelid and the orbital septum (septum orbitale), which attaches to the bony margin of the orbit and the tarsus. At the angles, the septum thickens into the palpebral ligaments.
- Conjunctiva (tunica conjunctiva). The mucous membrane lining the posterior surface of the eyelids and reflecting onto the eyeball. The transition zones are called the superior and inferior fornices.
Lacrimal gland and drainage pathways
The lacrimal gland (glandula lacrimalis) is located in the superior-lateral angle of the orbit. The tendon of the levator palpebrae superioris muscle divides it into two parts: a large orbital part (in the lacrimal fossa) and a small palpebral part (near the lateral margin of the superior fornix). Tears are secreted through 15 excretory ducts into the lateral part of the superior conjunctival fornix.
Lacrimal drainage pathways begin in the medial angle of the eye:
- Lacrimal puncta (punctum lacrimale). Located on the lacrimal papillae of the upper and lower eyelids, submerged in the lacrimal lake.
- Lacrimal canaliculi (cannaliculi lacrimales). Run from the puncta first vertically, then horizontally, merging together or opening separately.
- Lacrimal sac (saccus lacrimalis). Lies in the lacrimal fossa of the same name. Encircled by the lacrimal part of the orbicularis oculi muscle.
- Nasolacrimal duct (ductus nasolacrimalis). Projected along the nasolabial fold (from the inner canthus of the eye to the nasal ala) and drains tears into the inferior nasal meatus.
Briefly: answers to topical questions
Specifically, from which arterial бассейны (pools) is the blood supply to the eyelids derived?
- Ophthalmic artery (a. ophthalmica) — the main artery of the internal carotid artery system, giving rise to branches that supply blood to the eyelids and form arterial arches on the anterior surface of the tarsi (arcus palpebralis superior and arcus palpebralis inferior).
- Lacrimal artery (a. lacrimalis) — a branch of the ophthalmic artery participating in the blood supply to the lacrimal gland and eyelids, giving off lateral palpebral arteries (aa. palpebrales laterales).
- Medial palpebral arteries (aa. palpebrales mediales) — branches of the ophthalmic artery running along the eyelid margins and forming the superior and inferior palpebral arterial arches.
Which nerves provide sensory and motor innervation to the eyelids?
- Ophthalmic nerve (n. ophthalmicus, V1) — provides sensory innervation to the upper eyelid via its branches; sources indicate that V1 innervates the skin of the upper eyelid, while the frontal nerve innervates the upper eyelid.
- Maxillary nerve (n. maxillaris, V2) — provides sensory innervation to the lower eyelid; sources indicate that V2 innervates the skin of the lower eyelid.
- Facial nerve (n. facialis, cranial nerve VII) — provides motor innervation to the facial muscles; muscles of the eyelid region include the orbicularis oculi muscle (m. orbicularis oculi).
Which nerve provides secretory parasympathetic innervation to the lacrimal gland?
- Greater petrosal nerve (n. petrosus major) — a nerve from the intermediate and facial nerve system, whose preganglionic fibers run to the pterygopalatine ganglion (ganglion pterygopalatinum).
- Pterygopalatine ganglion (ganglion pterygopalatinum) — an autonomic ganglion where preganglionic parasympathetic fibers synapse, from which postganglionic fibers travel as part of the zygomatic nerve (n. zygomaticus) and the maxillary nerve to the lacrimal gland.
What is the topographical-anatomical difference between a stye (hordeolum) and a chalazion?
| Pathology / structure | What is explicitly stated in the sources | Topographical location |
|---|---|---|
| Hordeolum (Stye) (cholasion — as stated in the source) | Purulent inflammation of the sebaceous glands at the base of the eyelashes | Anterior margin of the eyelids (limbus palpebralis anterior), where the eyelashes are located |
| Meibomian glands | Sebaceous glands embedded within the substance of the eyelid tarsi | Their openings are visible at the posterior margin of the eyelids (limbus palpebralis posterior); the glands themselves are located within the substance of the eyelid tarsi (tarsus palpebrae) |
A topographical-anatomical description of chalazion as a separate pathology is not provided in the cited sources.
Where does venous drainage from the eyelid tissues occur?
- Facial vein (v. facialis) — the main superficial collector receiving venous blood from the eyelids via the superior and inferior palpebral veins (vv. palpebrales superiores et inferiores).
- Superficial temporal vein (v. temporalis superficialis) — a venous vessel of the temporal region, which also receives drainage from the eyelid tissues.
- Ophthalmic veins (vv. ophthalmicae) — deep veins providing blood drainage from the eyelids and anastomosing with the superficial venous system.
Class and exam questions
Where does the nasolacrimal canal open?
The nasolacrimal duct opens into the inferior nasal meatus of the nasal cavity.
Which muscle is responsible for the outflow of tears from the lacrimal sac?
Drainage is driven by the lacrimal part of the orbicularis oculi muscle (pars lacrimalis m. orbicularis oculi), which exerts a pumping action on the lacrimal sac upon contraction.
What divides the orbital and palpebral parts of the lacrimal gland?
They are separated by the tendon of the levator palpebrae superioris muscle (m. levator palpebrae superioris).
Where are the excretory ducts of the meibomian glands located?
Their openings are located at the posterior margin of the eyelid (limbus palpebralis posterior).
What else to study on this topic
- Vascular anastomoses of the eyeball, face, and temporal region within the eyelid subcutaneous tissue
- Orbital septum (septum orbitale) and its role in the spread of infections
- Topography of the branches of the trigeminal nerve in the orbital and facial regions (according to Sisher and Tandler)
- Conjunctival fornices and the technique for everting the upper eyelid
- Innervation and blood supply of the lacrimal gland
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