lacrimal system

The lacrimal system

Dr. Samten Dorji

Outline

• Introduction

• Embryology

• Osteology

• Secretory system

• Excretory system

• Physiology of lacrimal pump

Introduction

Introduction • Tear formation and transport

• Secretory system

• Excretory system

Embryology

Lacrimal drainage system embryology. A. At 5.5 weeks' gestation, an ectodermal invagination forms between the lateral nasal process and maxillary process, which becomes pinched off from the surface. B. At 6 weeks' gestation, a solid cord of ectoderm is located between the primitive medial canthus and nose. C. At 12 weeks' gestation, proliferation of the cord occurs laterally toward the eyelid and inferiorly toward the inferior turbinate. The isolated cavities shown appear at 3 to 4 months. D. At 7 months, canalization is nearly complete, with only the puncta and valve of hasner remaining imperforate.

• Punctal membranes open at full term• The membrane of Hasner remains

imperforate in up to 70% newborns. This usually opens within the first month but may remain imperforate for a longer time, resulting in epiphora and/or mucopurulent discharge.

Congenital nasolacrimal duct obstruction

Lacrimal duct anlage

Congenital atresia of punctum

Absence of valves

Anomalies of canaliculi

Osteology

• The lacrimal sac fossa is a depression in inferior medial orbital rim

• Bordered by anterior lacrimal crest(maxillary bone) and posterior lacrimal crest(lacrimal bone).

Osteology

Frontoethmoidal suture

16mm high*4-9mm wide*2mm deep

• marks the roof of ethmoid sinus

• Bony dissection superior to it

may expose dura.

The secretory system

1. Lacrimal gland

2. Accessory glands

Lacrimal gland

orbital lobe (black arrow) and the palpebral lobe (white arrow) separated

by the lateral horn of the levator aponeurosis (pointer).

The orbital part

• Almond shape• 65% to 75% of gland• 20 mm long × 5 mm thick × 12

mm wide

The sharp anterior border of the left lacrimal gland (black arrow) rests behind the orbital septum (pointer)

The temporal portion of the central preaponeurotic fat pad (pointer) rests near the anterior border of the orbital portion of the lacrimal gland

The palpebral part

• 25% to 35% of the gland• extends anteriorly beyond the orbital

margin to lie in the lateral portion of the superior fornix

Secretory ducts

• 12 ducts(2-5 orbital and 6-8 palpebral)• 0.66 mm in diameter and 2.31 mm in length• Exit at conjunctival fornix 4 or 5 mm above the upper border of the

tarsus

Secretory ducts (arrow 1) of the right lacrimal gland (arrow 2) are seen passing to the palpebral conjunctiva (arrow 3).

Accessory glands

• exocrine glands of Wolfring and Krause

Blood supply and drainage

• Lacrimal branch of the ophthalmic artery

• Lacrimal vein

• Preauricular lymphnodes

Nerve supply

• lacrimal nerve (sensory)

• The facial nerve (parasympathetic)

• The sympathetic nervous system

Histology

Lobe

Lobules

Acinar unit Ductal system• central lumen,• a continuous inner layer

of columnar secretory epithelial cells

• myoepithelial (basket) cells

• central lumen,• luminal cell layer• basal cell layer.

1. Intralobular ducts2. Interlobular ducts3. main excretory

ducts

Lacrimal gland architectureThe acinar unit is composed of a central lumen, a continuous inner epithelial layer of secretory cells, and an interrupted outer layer of myoepithelial cells.

A larger interlobular duct is seen (middle right). A smaller intralobular duct is

seen among the acini.

Excretory system

Punctum

• Surrounded by lacrimal papilla

• average diameter of 0.2 to 0.3 mm

• nasal aspect of the eyelid margin

• Upper punctum opens inferoposteriorly and lower opens superoposteriorly

Canaliculi

• First vertical and then horizontal

• Vertical=2mm, horizontal 8mm• Angle has 1mm dilatation

called ampulla• traverse the lacrimal fascia

individually before they join to form the common canaliculus

• Stratified squamous epithelium supported by elastic tissue

Lacrimal sac

• lies within the bony lacrimal sac fossa

• The layer of periorbita that covers the lacrimal fossa is termed the lacrimal fascia

• 12 mm in height, 4 to 6 mm in depth, and 2 mm wide.

Nasolacrimal duct

• Inferiorly directed continuation of the nasolacrimal sac

• 3 to 4 mm in diameter in adults and 2 mm in infants

• 12.5 mm in vertical length and usually terminates as a 5-mm extension into the inferior nasal meatus

Valves

• The mucosal lining of the nasolacrimal duct contain crypts and folds that usually disappear by adulthood.

• .The most significant fold is the one situated at the meatal opening of the nasolacrimal duct called the valve of Hasner.

• 30% of full-term neonates, there persists a delicate membrane that, within 6 months after birth, usually undergoes spontaneous perforation.

• Massage or lacrimal probing may be necessary to permit patency

Diagram of the valves and sinuses of the nasolacrimal passages. 1 = Maier's sinus 2 = Rosenmüller's valve3 = Arlt's sinus 4 = Kraus's or Béraud's valve5 = spiral valve of Hyrtl6 = Taillefer's valve7 = Hasner's valve

Prevents sudden blast of air from entering the lacrimal sac

Vascular supply • The ophthalmic artery terminates as

the dorsal nasal artery, from which emanates the superior medial palpebral branches that supply the lacrimal sac.

• The angular artery perforates the superior orbital septum above the medial canthal tendon to send branches to the lacrimal sac as well as to the duct.

• The infraorbital artery sends branches to the lower lid that eventually pierce the lateral margin of the upper nasolacrimal canal to supply the sac as well as the duct.

Venous drainage• Superior aspect- see picture• Inferior aspect-sphenophenopalatine

veins into the pterygoid plexus and the internal maxillary vein

• The angular vein and artery are important surgical landmarks in dacryocystorhinostomy surgery.

Lymphatic drainage

• Sac- submaxillary nodes• Lower aspect of nasolacrimal duct- deep

cervical nodes

Nerve supply

Sensory nerve supply•sac-infratrochlear nerve•The lower portion of the nasolacrimal duct receives sensation from the anterior superior alveolar branch of the maxillary division of the fifth cranial nerve

Histology

• mucous membrane continuously from the conjunctiva at the lacrimal puncta, to the nasal mucosa at the valve of Hasner beneath the inferior turbinate

• Lacrimal puncta and canaliculi-nonkeratinizing stratified squamous epithelium

• Nasolacrimal sac- columnar epithelium

Physiology of lacrimal pump

• Action of orbicularis oculi

Pump mechanism

• (1) the superficial and deep heads of the pretarsal orbicularis muscle;

• (2) the deep heads of the preseptal orbicularis muscle; and

• (3) the lacrimal fascia.

Passive phase

• Eyelids open

• The superficial and deep heads of the pretarsal orbicularis muscle relax

• Canaliculus elongate and the puncta opens to lie in contact with the lacrimal lake.

• Aided by capillary attraction, tears collect within the ampulla and canaliculus.

Passive phase

• The deep head of the preseptal orbicularis muscle relaxes

• lacrimal sac collapse.

• The positive pressure assisted by gravity forces fluid within the sac to move into the nasolacrimal duct.

• The valve of Rosenmüller prevents retrograde flow of fluid from the lacrimal sac into the canaliculus.

Active phase

• eyelid closure

• Contraction of the superficial and deep head of the pretarsal orbicularis

• The canaliculi shorten and the puncta close.

Active phase

• contraction of the deep heads of the preseptal orbicularis muscle

• Fluid within the canaliculi is drawn into the lacrimal sac by the negative pressure in sac.

• As the lids reopen and the passive phase returns

• The lacrimal fascia and sac resume their relaxed, closed position.

• The puncta reopen and the canaliculi elongate, permitting the drainage system to accept fluid once again.

Outline

• Introduction

• Embryology

• Osteology

• Secretory system

• Excretory system

• Physiology of lacrimal pump

Thank you

References

• Duane’s Clinical ophthalmology Chapter 21Orbital Anatomy and Its Clinical ApplicationsDeborah D. Sherman, Cat N. Burkat and Bradley N. Lemke

• American academy of ophthalmology• Medscape• internet