Eyelid & Orbital Trauma - Anatomy

Our eyes are probably {the} most important vital structures we have in our body. They discovered on {the} surface by a thin layer of skin and soft tissue called {the} eyelids. The eyelids serve multiple purposes including protecting {the} eyeball from injury, controlling {the} amount of light that enters {the} eye and also constantly lubricating {the} eyeball with tears secreted by {the} lacrimal gland during blinking. All these functions together help maintain {the} structural integrity of {the} eyeball and protect them from external influences.

From an anatomical point of view, {the} eyelid consists primarily of skin, underlying soft tissue also called a subcutaneous tissue and a thin layer of muscle called {the} orbicularis oculi. Under this muscle are other issues that divide {the} area into different planes. These are called septum and include {the} fibrous orbital septum and tarsi. In addition to this, in order for {the} eyelids to open are lid retractors that help assist blinking. Finally, there also exists a small amount of fat tissue as well. The eyeball is covered by a thin layer of tissue called {the} conjunctiva.

Anatomy of {the} eyelid

The description above only offers a superficial overview of {the} anatomy of {the} eyelid. If one were to look at {the} eyelid in a more detailed manner, a sagittal section taken across {the} eyelid will offer a clear view of {the} various structures that form it. Of course, it must be borne in mind that {the} structures that are visualised depend on {the} plane at which {the} sections are taken.

As mentioned above, {the} tissues can be divided into planes by structures called {the} septum. The orbital septum differentiates {the} orbital tissue from {the} lid. Behind {the} septum are a number of different other structures, a knowledge of which is essential if surgery is to be performed. In particular, it is essential to identify {the} anterior and posterior lamellae. In essence, {the} anterior lamella consists of {the} skin and {the} orbicularis oculi muscle while {the} posterior lamella consists of {the} conjunctiva and {the} tarsus.

Let's take a look at {the} structures of {the} eyelid in a bit more detail.

Layers & Components of {the} Eyelid

Skin

• thinnest in body, no subcutanous fat
• upper lid crease (fold) = levator . attachment to pretarsal orbicularis and skin; located at level of sup border of tarsus
• upper puntca is more medial
• mucocutaneous border is post to meibomian gland level
• gray line = muscle of Riolan (superficial orbicularis)
• Zeis, sebaceous glands (holocrine) with cilia
• Moll glands (only apocrine gland on lid) with skin
• 100 lashes on upper lid, 50 on lower

Blood supply

• extensive anastamosis between supraorbital, lacrimal branches of ophthalmic a. (from internal carotid) and angular and temporal a. (from ext carotid)
• venous drainage: pretarsal, poatarsal
• NO lymphatics for {the} orbit except in conjunctiva
• eyelid medial lymphatics drain to submandibular nodes and laterally to preauricular nodes

Subcutaneous tissue

• no fat, loose connective tissue holds fluid in preseptal > pretarsal area b/c less firmly attached

Orbicularis Muscle

• main protractor
  
  • supplied by Cranial Nerve VII, narrows PF, helps lacrimal pumporbital
  • voluntary sphincter (wink, blepharospasm)
  • origin at medial canthal tendon and corrugator supercilius muscle
  • palpebral (pretarsal & preseptal)
  • reflex blink and involuntary
  • pretarsal origin at post lacrimal crest (most important to keep lid apposed to globe to let punctum lie in tear lake ) & ant limb of med canthal tendon; deep head of pretarsal m. (Horner’s tensor tarsi) encircles canaliculi to facilitate tear drainage
  • upper & lower segments of pretarsal orb m. fuse to become lateral canthal tendon
  • pretarsal muscle firmly adherent
  • pretarsal muscle of Riolan = gray line = superficial orbicularis

• Septum
  
  • extension of periosteum
  • in non-Asians, upper lid septum fuses w/levator aponeurosis. 2-5 mm above sup tarsal border; in lower lid it fuses w/capsulopalpebral fascia at or just below inf tarsal border
  • passes medially in front of trochlea
  • barrier to hemorrhage and infection between lid and orbit
  • orb fat can herniate through septum into lids causing bags
  • central orb fat pad lies behind septum, in front of levator aponeurosis.

• Tarus
  
  • dense connective tissue, attach med & lat to periosteum
  • 1 x 29 x 11 mm upper lids, 4 mm vertical height in lower lids
  • meibomian glands are modified holocrine glands
  • in upper lid marginal arcade lies 2 mm sup to lid margin, ant to tarsus
  • peripheral art arcade is sup to tarsus, between levator aponeurosis, Muller’s

• Conjunctiva
  
  • mucin is produced from goblet cells
  • aqueous is produced from glands of l Krause & Wolfring

• Eyelid Retractors (muscle)
  
  • Upper lid
    • Levator Palpebrae Superioris
      • starts just above annulus of Zinn, then 40 mm of muscle, then 14-20 mm of aponeurosis.
      • becomes vertical near Whitnall's (superotransverse) ligament (near transition m. to aponeurosis.) which is a fulcrum for vertical lid retraction (lower lid analog is Lockwood’s ligament)
      • Whitnall's ligament is condensation of tissue around SR and LPS, helps suspend tissue
      • levator aponeurosis: attaches to lower 1/2 of ant tarsus; lat horn of aponeurosis divides lacrimal gland into orb and palpebral lobes, attaches to lat orb tubercle; medial horn attaches to post lacrimal crest
      • lid crease is formed by attachment of ant portion of aponeurosis w/ septum between {the} pretarsal orbicular m.’s: here {the} pretarsal tissues are in close apposition to underlying tarsus
    • Superior Tarsal Muscle of Muller
      • posterior to LPS
      • sympathetically innervated; use neo drops to test function in Ptosis w/u: normal = 2 mm lift
      • origin from under LPS, attaches to upper tarsus, firm attachment to conj
• Lower Eyelids
• Inferior Tarsal muscle

• • • Capsulopalpebral Fascia
      • lower lid analog to levator aponeurosis
      • originates from attachments to Inferior rectus ; therefore do vertical m. surgery before lid surgery
      • inserts onto lower tarsal border
      • inferior tarsal m. is analog to Muller’s, runs post to Capsulopalpebral Fascia