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Accessory Visual Structures

Organa oculi accessoria

For medical students2 min readUpdated 2026-10-10

The accessory structures of the eye comprise a complex of anatomical formations that protect the eyeball from trauma, drying, and foreign particles. The primary components of this complex are the eyelids, conjunctiva, and lacrimal apparatus, which together provide mechanical protection and continuous moisturization.

EyelidsMusculocutaneous folds acting as a mechanical barrier.
ConjunctivaMucous membrane forming the fornices and conjunctival sac.
Lacrimal ApparatusSystem responsible for tear production and drainage into the nasal cavity.

Anatomy of the Eyelids (*Palpebrae*)

The eyelids are movable musculocutaneous folds whose primary function is to protect the eye from external influences. Anatomically, an eyelid has a distinct layered structure composed of tissues of varying density and functional purpose.

Eyelid Layers (from superficial to deep):

Within the thickness of the tarsal plates lies a complex of glands whose secretions contribute to eye protection. These include tarsal glands (Meibomian glands — glandulae tarsales), as well as ciliary glands (glandulae ciliares) and sebaceous glands (glandulae sebaceae).

Conjunctiva (*Tunica conjunctiva*)

The conjunctiva is a continuous mucous membrane that lines the inner surface of the protective structures and reflects onto the eyeball itself.

Topographically, it is divided into two main parts:

  1. Palpebral conjunctiva (conjunctiva palpebrarum) — covers the posterior surface of the eyelids, firmly adhering to the tarsus.
  2. Bulbar conjunctiva (conjunctiva bulbi) — reflects onto the anterior regions of the eyeball.

At the sites where the mucous membrane transitions from the eyelids to the eyeball, deep folds form — the superior and inferior conjunctival fornices (fornices conjunctivae superior et inferior). Together, this system forms a closed space when the eyelids are closed, known as the conjunctival sac (saccus conjunctivalis). Additionally, intrinsic conjunctival glands (glandulae conjunctivales) are located within the thickness of the mucous membrane, providing supplementary moisturization of the surface.

Lacrimal Apparatus (*Apparatus lacrimalis*)

The lacrimal apparatus is functionally and anatomically divided into two major groups of structures: tear-producing (secretory) and tear-drainage pathways.

Tear-Producing Structures The primary secretory organ is the lacrimal gland (glandula lacrimalis). It is located in the superolateral part of the orbit and anatomically divided into two parts: the larger orbital part (pars orbitalis) and the smaller palpebral part (pars palpebralis).

Tear-Drainage Pathways Produced tears initially enter the conjunctival sac, bathing the anterior surface of the eye. The fluid then accumulates at the medial angle of the eye in the lacrimal lake (lacus lacrimalis).

The subsequent pathway of tear drainage is strictly sequential:

Mnemonic

The tear drainage pathway can be easily remembered by the sequence: "Puncta — Canaliculus — Sac — Duct".

Frequently asked questions

Which muscles provide closure and opening of the eyelids?

Eyelid closure and opening are associated with the orbicularis oculi and the levator palpebrae superioris.

  • Orbicularis oculi muscle (m. orbicularis oculi) — circular fibers are present in both eyelids; the muscle consists of orbital, palpebral, and lacrimal parts.
  • Levator palpebrae superioris muscle — in the upper eyelid, some of its fibers are vertically oriented; it elevates the upper eyelid.
Which nerves innervate the lacrimal gland?

The lacrimal gland is innervated by sensory, parasympathetic, and sympathetic nerve fibers.

  • Lacrimal nerve (n. lacrimalis) — a branch of the ophthalmic nerve, provides sensory innervation.
  • Nasociliary nerve (n. nasociliaris) — also gives off a branch to the lacrimal gland.
  • Facial nerve (CN VII) — contains parasympathetic fibers originating from the lacrimal nucleus (nucleus lacrimalis).
  • Sympathetic fibers — derive from the superior and middle cervical ganglia of the sympathetic trunk.
Where does the nasolacrimal duct open into the nasal cavity?

The nasolacrimal duct opens into the inferior nasal meatus of the nasal cavity.

  • Inferior nasal meatus (meatus nasi inferior) — located between the inferior nasal concha and the floor of the nasal cavity.

Tears from the lacrimal sac travel via the nasolacrimal duct (ductus nasolacrimalis) into this meatus, from which they may exit externally through the nostrils.

Which arteries supply blood to the lacrimal gland?

Blood supply to the lacrimal gland is related to the lacrimal artery and its connection with the middle meningeal artery.

  • Lacrimal artery (a. lacrimalis) — a branch of the ophthalmic artery (a. ophthalmica), directed toward the lacrimal gland and eyelids.
  • Middle meningeal artery (a. meningea media) — gives off an anastomotic branch to the lacrimal artery (r. anastomoticus cum a. lacrimali).
What layers make up the eyelid?

The eyelid consists of skin, loose subcutaneous tissue, the orbicularis oculi muscle, the tarsal plate, and the mucous membrane (palpebral conjunctiva).

What glands are located within the tarsal plates of the eyelids?

The tarsal plates contain the tarsal (Meibomian) glands, as well as ciliary and sebaceous glands.

What does the conjunctiva form when transitioning from the eyelids to the eyeball?

Upon transition, the conjunctiva forms the superior and inferior fornices, collectively creating the conjunctival sac.

What is the sequence of the tear drainage pathways?

From the lacrimal lake, tears pass into the lacrimal puncta, then into the lacrimal canaliculi, into the lacrimal sac, and finally drain through the nasolacrimal duct.

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