Anatomy of Eyelid Made Easy

Eyelids are mobile tissue curtains placed in front of eyeballs. They act as shutters protecting the eye. Lets us discuss in detail the gross anatomy and layers of eyelids in detail.

GROSS ANATOMY OF EYELIDS

WHAT IS THE NORMAL LID POSITION ?

In primary gaze position , the upper lid covers upper 1/6th of the cornea
The Lower lid however, just touches the inferior LIMBUS

WHAT ARE CANTHUS OF EYELIDS?

The upper and lower eyelid meet at the corners. These junctions are known as the canthus. Each eye has two canthi, one lateral canthus and one medial canthus .

LATERAL/ OUTER CANTHUS :

It is situated 5-7 mm from lateral orbital margin .
Lies in contact with the eyeball
Configuration of lateral canthus : Forms an angle of 60 degrees( wide open eyes );
30-40 degrees ( normal open eyes )

MEDIAL /INNER CANTHUS :

Has a rounded configuration
Separated from the globe by tear lake
CARUNCLE: medial rounded and fleshy structure at the medial canthus is known as the caruncle
PLICA SEMILUNARIS : Semicircular pink arc like structure lateral to the caruncle is known as the plica semilunaris

ANATOMY OF EYELID MARGIN ?

LACRIMAL PAPILLA : Each eyelid margin, upper and lower has a mound like structure called as the lacrimal papilla
LACRIMAL PUNCTA : On the lacrimal papilla we have an opening known as the lacrimal puncta
The lacrimal puncta divides the eyelid margin into two parts :-
PARS CILIARIS / CILIARY PART : This consists of the eyelid portion lateral to the lacrimal puncta. It consists of the meibomian gland orifices and the eyelashes .
PARS LACRIMALIS LACRIMAL PART: this consists of the eyelid portion medial to the lacrimal puncta. It is devoid of any structures
ANTERIOR BORDER of the eyelid is rounded
POSTERIOR BORDER of the eyelid is Sharper
GREY LINE : marked in the picture below, divides the eyelid vertically into an anterior lamina and a posterior lamina . We shall be discussing what is anterior and posterior lamina in detail when we talk about the layers of eyelids. But now lets continue with the gross anatomy of eyelids .

WHAT IS PALPEBRAL FISSURE ?

Elliptical space between the upper and the lower eyelid margins
Measurements in adult : 28-30 mm horizontally; 9-11 mm vertically

MONGOLOID SLANT

Elevation of lateral canthus more than 2 mm above the medial canthus
Pseudo A pattern strabismus
Seen in downs syndrome
Noonan syndrome

ANTI-MONGOLOID SLANT

Lateral canthus lower than the medial canthus
Pseudo V pattern strabismus
Seen in Treacher Collin syndrome
Coffin Lowry syndrome
Zygomatic maxillary complex fracture (tripod fracture )

LID CREASE AND FOLDS

We have one superior eyelid fold/crease and two inferior lid creases.

SUPERIOR EYELID FOLD :It is situated 4 mm above the edge of the eyelid. It is formed by fibrous slips from tendon of levator, that passes through the orbicularis muscle fibers to insert into skin
INFERIOR LID FOLDs : These are less prominent. these are formed by the fibrous slips that arise from fascia surrounding the inferior rectus muscle and are inserted into skin

NASOJUGAL FOLD /SULCUS ( medially)
MALAR FOLD /SULCUS ( laterally)

WHAT GLANDS OPEN AT EYELID MARGIN?

Here we shall discuss about the gland of Zeiss and the gland of Moll.

GLANDS OF ZEISS

MODIFIED SEBACEOUS GLANDS located on the margin of the eyelid.
Consists of few lobules ( usually UNILOBULAR) in contrast to normal sebaceous glands that have 10-15 lobules.
They produce sebum that keep eyelashes from becoming dry and brittle

GLANDS OF MOLL

Modified apocrine sweat glands
Lie in between cilia at the anterior lid margin.
Unbranched spiral shape
NOTE : Eccrine sweat glands are distributed throughout eyelid skin and are not confined to the lid margin, in contrast to glands of Moll

CLINICAL NUGGET

CYST OF ZEISS :Small, non-translucent cyst on the anterior lid margin arising from obstructed sebaceous glands associated with the eyelash follicle.

CYST OF MOLL( APOCRINE HYDROCYSTOMA) :Small retention cyst of the lid margin apocrine glands. It appears as a round, non-tender, translucent fluid-filled lesion on the anterior lid margin

LAYERS OF EYELIDS

From outside to inwards the eyelid consists of the following layers :-

Skin
Subcutaneous areolar tissue
Striated muscle layer
Submuscular areolar tissue
Fibrous layer ( tarsal plate and orbital septum)
Non striated muscle fibers
Conjunctiva

CUTANEOUS LAYER : SKIN OF EYELID

The skin of eyelid is the thinnest in the body ,and it has the thinnest subcutaneous fat.
It is loosely adherent to underlying orbicularis muscle and is mobile

CLINICAL NUGGET :

In old age the skin becomes redundant and is an excellent source of skin grafting in eyelid reconstruction
This redundancy of eyelid skin allows Primary closure of large eyelid defects upto 30 %.

SUBCUTNOEUS AREOLAR TISSUE

Present just below the skin of the eyelid
This layer is devoid of any fat
Consists of only the areolar tissue

STRIATED MUSCLE LAYER OF THE EYELID

Below the subcutaneous layer, the eyelid has the striated muscle layer. Here, two striated /voluntary muscles are situated , namely the ORBICULARIS MUSCLE and the LEVATOR PALPEBRAE SUPERIORIS MUSCLE.

ORBICULARIS MUSCLE

The orbicularis muscle has fibres oriented in a circular fashion around the eye and the orbit. It has two parts:-

ORBITAL PART : Part of orbicularis situated in front of the orbital rims is called the orbital part. It is attached medially to the anterior limb of medial canthal tendon. Laterally, it is attached to the lateral palpebral raphe.
It is responsible for forceful closure of eyelids
It also pulls the eyebrow downwards
PALPEBRAL PART : Part of the orbicularis fibres which are present in the eyelid are called the palpebral part of orbicularis .It is responsible for gentle closure of eyelids during blinking, sleeping. The palpebral part of orbicularis can again be divided into two parts: –

Preseptal fibers of orbicularis: Portion of the palpebral orbicularis in front of the orbital septum. It divides medially into a deep head and a superficial head. Laterally it attaches to the Whitnall lateral orbital tubercle.
Pretarsal Fibers of orbicularis: Portion of the palpebral orbicularis in front of the tarsal plate. It also divides medially into a deep and a superficial head.

What are JONES Muscle, HORNER Muscle and RIOLAN Muscle?

JONES MUSCLE

The deeper origin of the pre-septal fibres of orbicularis arises from the posterior lacrimal crest and the fascia surrounding the lacrimal sac. This deep head of the pre-septal orbicularis is known as the Jones muscle.
The superficial head of pre-septal orbicluaris attaches to the anterior limb of medial canthal ligament.

HORNER’S MUSCLE :

The deep head of pretarsal orbicularis is called the Tensor Tarsi muscle of Horner/ Horner muscle. It attaches behind the posterior lacrimal crest and to the medial canthal tendon.
The superficial head of pretarsal orbicularis attaches to the anterior lacrimal crest.

RIOLAN MUSCLE

The marginal portion of the palpebral orbicularis i.e. adjacent to the eyelid margin is known as the muscle of Riolan.
It forms the grey line of the eyelid margin.

CLINICAL NUGGET
Contraction of the Horner muscle pulls the lateral wall of the upper half of the lacrimal sac, causing it to expand and create a negative pressure.
It also compresses the canaliculi and pulls them posterior and medially.
This is known as lacrimal pump which empties the content of canaliculi into the expanded sac. To understand about lacrimal pump, check out the video on lacrimal pump, or the post on lacrimal pump.

LEVATOR PALPEBRAE SUPERIORIS MUSCLE (LPS)

Levator palpebrae Superioris is the primary retractor of the Upper Lid
ORIGIN: It originates from the lesser wing of sphenoid
INSERTION : Levator aponeurosis divided into Anterior and posterior portion.
Anterior Fibres go towards the pretarsal orbicularis and some fibers insert into the skin forming the skin crease
Posterior Fibers insert into the anterior surface of tarsus.

SUBMUSCULAR AREOLAR TISSUE LAYER

Loose connective tissue present between the orbicularis muscle and the fibrous layer .
Consists of The Nerves and the vessels of the eyelid.
This layer Splits the eyelid into two parts ANTERIOR LAMINA and a POSTERIOR LAMINA
Corresponds to the GREY line on the margin

CLINICAL NUGGET

This layer of submuscular areolar tissue communicates superiorly with the Subaponeurotic layer of the scalp ( dangerous area of scalp)
Therefore there is a potential communication for pus and blood between the two spaces.

FIBROUS LAYER ( TARSUS and ORBITAL SEPTUM )

The Fibrous layer is situated below the submuscular areolar tissue
It forms the framework of the eyelids
It consists of the central thick part ( tarsus) and the peripheral thinner part ( septum orbitale)
It also consists of the medial and lateral palpebral ligaments which anchors the lids to the orbit .

TARSAL PLATE /TARSUS

Tarsal plate is a dense fibrous tissue plate acting as a skeleton of the eyelid giving it shape and firmness.
Height of the tarsus is about 10-11mm and that of Lower tarsus is 4–5 mm.
It consists of the tarsal glands ( MEIBOMIAN glands ) embedded in it.
Meibomian glands are modified sebaceous glands found in the tarsal plates.
They empty through a single row of 20–30 orifices on each lid.
Gland consists of a central duct with multiple acini, the cells of which synthesize lipids (meibum) that form the outer layer of the tear film.

ATTACHMENTS OF TARSUS

SUPERIOR TARSAL BORDER : orbital septum + muller’s muscle
INFERIOR TARSAL BORDER : Orbital septum , Capsulo-palpebral fascia , Inferior palpebral muscle
LPS aponeurosis attached 3-4 mm below the upper tarsus border on anterior surface
LATERAL ends of tarsi attached to Whitnall tubercle by lateral palpebral ligament
MEDIAL ends attached to anterior lacrimal crest and frontal process of maxilla by medial palpebral ligament.
To understand the attachments of tarsus visually, you can watch our video on anatomy of eyelid.

ORBITAL SEPTUM

The orbital septum is a thin floating membrane of connective tissue.

Centrally /inferiorly it is continuous with convex border of the tarsi of each lid.
Peripherally it is attached to the orbital margin at a thickening of the orbital rim known as ARCUS MARGINALIS.

LAYER OF NON -STRIATED MUSCLE

This layer is situtaed below the orbital septum.
It consists of the smooth muscle fibres.
They are responsible for retraction of the eyelids
The smooth muscle fibres present in this layer in upper lid and lower lid are known as the superior palpebral muscle and inferior palpebral muscle respectively.
SUPERIOR PALPEBRAL MUSCLE( Mullers muscle ) : It arises from the striated fibres of the Levator palpebrae superioris and gets inserted into the tarsal plate( look at the image above)
INFERIOR PALPEBRAL MUSCLE : It arises from expansion of the inferior rectus in lower lid and is inserted into the lower tarsus. To know more about this muscle watch our video on anatomy of eyelid .
Both the above non striated/involuntary /smooth muscles are supplied by the sympathetic nerve supply.

CLINICAL NUGGET :

Sympathetic nerve irritation leads to retraction of the lids, due to irritation of the Muller’s muscle.
Disruption of sympathetic nerve supply to these retractors leads to ptosis seen in HORNERS SYNDROME (video on channel )

CONJUNCTIVA :INNERMOST LAYER OF EYELID

Posterior and innermost layer of the eyelid.
It is formed by the palpebral conjunctiva.
it exxtends from mucocutaneous junction at lid margin to the conjunctival fornix.
The palpebral conjunctiva here is firmly attached to the tarsal plate and mullers muscle .

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