The lower eyelid is a bilamellar structure composed of skin, muscle, tarsus and conjunctiva. This article details the anatomy, blood supply and lacrimal system.
Summary Card
Overview
A bilamellar structure of skin, muscle, tarsus and conjunctiva.
Anterior Lamella
Composed of skin and orbicularis oculi. The muscle has 3 components: pretarsal, preseptal and orbital.
Posterior Lamella
Composed of the tarsal plate and palpebral conjunctiva. Tarsal plate is a support structure that contains meibomian glands.
Middle Lamella
A descriptive term to describe the orbital septum, 3 fat pads and capsulopalpebral fascia. It helps contain the orbital contents.
Blood Supply
Supplied by branches of the internal and external carotid arteries that communicate through marginal and peripheral arcades.
Lacrimal System
A secetory and drainage system that produces a trilaminar substance that travels from the punctum to the inferior meatus of the nose.
Flashcards
Evidence-based flashcards to improve your active recall.
Overview of Lower Eyelid
The lower eyelid is a bilammellar structure consisting of skin, muscle, tarsus and conjunctiva.
The lower eyelid anatomy can be remembered with the “Rule of 2’s” mnemonic.
- 2 Eyelids: Upper Eyelid and Lower Eyelid
- 2 Lamellae: Anterior (Outer) and Posterior (Inner) Lamellae
- 2 structures in each lamella: Skin & Orbicularis, Tarsus & Conjunctiva.
Anterior Lamella Anatomy
Key Point
The anterior lamella is composed of the skin and orbicularis oculi. The muscle has 3 components: pretarsal, preseptal and orbital.
The Anterior Lamella is composed of Skin and Orbicularis Oculi muscle.
Skin
- Thinnest on the human body
- Loosely adherent to underlying orbicularis oculi muscle
Orbicularis Oculi
The orbicularis oculi are organised concentrically around the palpebral fissure into 3 regions: pre-septal, pre-tarsal and orbital. It is innervated primarily by the zygomatic branch of the facial nerve.
- Pre-Tarsal: covers tarsal plate, helps with involuntary blinking & tear flow.
- Pre-septal: covers the orbital septum, helps with blinking
- Orbital: the outermost part and helps with voluntary eye closure.
These sections of the orbicularis oculi can be seen in the image below.
The preseptal and pretarsal components of the orbicularis oculi form the superficial and deep parts of the medial canthal tendon:
- Superficial part: merges with the tarsal plates to insert into the anterior lacrimal crest.
- Deep part: inserts into the posterior lacrimal crest, posterior to the lacrimal sac.
Posterior Lamella Anatomy
Key Point
The posterior lamella is composed of the tarsal plate and palpebral conjunctiva. The tarsal plate is a support structure that contains meibomian glands.
The posterior lamella is composed of tarsal plate and conjunctiva.
Lower Tarsal Plate
The tarsal plate is a structural support sheet to the lids
- Dimensions: ~25mm long, 1 mm thick and 5mm tall.
- Contents: meibomian glands just posterior to the grey line.
- Lateral border: anchored lateral orbit periosteum via lateral canthal tendon.
- Inferior border: capsulopalpebral fascia
The tarsal plate can be visualised in the image below.
Palpebral Conjunctiva
The palpebral conjunctiva is a mucosal layer adjacent to the eyelids. It lines the inner surface of the eyelid, whilst the bulbar portion of the conjunctiva lines the sclera (the white of the eye).
The two sections of the conjunctiva can be visualised in the image below.
Middle Lamella Anatomy
Key Point
The "middle lamellar" is more of a descriptive term to describe the location of the orbital septum, 3 fat pads and capsulopalpebral fascia. It helps contain the orbital contents.
The "middle lamella" can be used to help describe the contents between the anterior and posterior lamellae. It technically doesn't form the "bilamellar structure" of the eye. It contains the orbital septum, fat pads and capsulopalpebral fascia.
Orbital Septum
The anterior and posterior lamellae are separated by the orbital septum (and preaponeurotic fat). It is a fibrous membrane of connective tissue that separates orbital contents from periorbital soft tissues.
- Origin: periosteum of the orbital rim as thickening called the arcus marginalis
- Insertion: tarsus via levator aponeurosis or directly (in some Asian patients).
Fat Pads
In the lower eyelid, there are 3 pre-aponeurotic (post-septal) fat pads: nasal, central and lateral. Important points include
- Location: between the orbital septum and levator aponeurosis.
- Divisions: nasal, central and lateral separated by fibrous septa.
- Inferior oblique muscle lies between the nasal and central fat pads.
These fats pads of the lower eyelid are visualised in the image below.
Capsulopalpebral Fascia
The capsulopalpebral fascia is a fibroelastic tissue with components of smooth muscle fibres. It is the lower eyelid equivalent of the levator aponeurosis found in the upper eyelid.
- Origin: anterior to Lockwood ligament (equivalent to Whitnall's ligament)
- Insertion: inferior tarsus.
- Action: lower eyelid retraction
Lower Eyelid Blood Supply
Key Point
The lower eyelid is supplied by branches of the internal and external carotid arteries that communicate through marginal and peripheral arcades.
The lower eyelid is supplied primarily by branches of the facial artery. There is a significant number of communications that results in marginal and peripheral arcades that travel in the infratarsal space along the lower tarsal border.
Branches of the internal carotid artery include:
- Medial Canthus: facial artery and angular artery
- Lateral Canthus: superficial temporal artery
- Lower eyelid: infraorbital artery
Branches of the external carotid artery include:
- Ophthalmic Artery: travels laterally on the anterior tarsus as the marginal arcades to give of superior and inferior marginal arteries.
- Lacrimal Artery: travels medially to anastomose with the marginal arcades and provides a lateral palpebral artery to each lid.
These lower eyelid arteries are visualised below.
Canthal Tendons
Key Point
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Lacrimal System
Key Point
A secetory and drainage system that produces a trilaminar substance that travels from the punctum to the inferior meatus of the nose.
The eyelid lacrimal system is involved in both secretion and drainage that enables lid lubrication with a trilaminar tear film, osmosis regulation and antimicrobial effects.
Secretion
Secretion is a trilaminar substance, which means it has 3 layers produced from 3 different anatomical regions.
- Inner (pre-corneal): mucinous produced by mucin-secreting goblet cells
- Middle: aqueous produced by accessory lacrimal glands
- Outer: oily/fat from the meibomian, Zeis and Moll glands.
The lacrimal gland is a reflex secretor that produces a fluid similar to the middle layer.
Drainage
The lacrimal system is a well-designed "pump" that begins in the puncum and ends at the inferior meatus of the nose.
- Punctum drains into the canaliculi at the apices of the lacrimal papillae
- Canaliculi form the ampulla at the vertical and horizontal junction
- Horizontal canaliculi form the common canaliculus
- Common canaliculus drains into the lacrimal sac (surrounded by orbicularis)
- Lacrimal sac drains into the nasolacrimal duct
- Nasolacrimal duct finishes in the inferior meatus of the nose.
This lacrimal duct drainage system is visualised in the image below.
Flashcards
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